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• Published: 12 September 2019

The effects of plant-based diets on the body and the brain: a systematic review

• Evelyn Medawar   ORCID: orcid.org/0000-0001-5011-8275 1 , 2 , 3 ,
• Sebastian Huhn 4 ,
• Arno Villringer 1 , 2 , 3 &
• A. Veronica Witte 1  

Translational Psychiatry volume  9 , Article number:  226 ( 2019 ) Cite this article

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• Human behaviour
• Molecular neuroscience
• Psychiatric disorders

Western societies notice an increasing interest in plant-based eating patterns such as vegetarian and vegan, yet potential effects on the body and brain are a matter of debate. Therefore, we systematically reviewed existing human interventional studies on putative effects of a plant-based diet on the metabolism and cognition, and what is known about the underlying mechanisms. Using the search terms “plant-based OR vegan OR vegetarian AND diet AND intervention” in PubMed filtered for clinical trials in humans retrieved 205 studies out of which 27, plus an additional search extending the selection to another five studies, were eligible for inclusion based on three independent ratings. We found robust evidence for short- to moderate-term beneficial effects of plant-based diets versus conventional diets (duration ≤ 24 months) on weight status, energy metabolism and systemic inflammation in healthy participants, obese and type-2 diabetes patients. Initial experimental studies proposed novel microbiome-related pathways, by which plant-based diets modulate the gut microbiome towards a favorable diversity of bacteria species, yet a functional “bottom up” signaling of plant-based diet-induced microbial changes remains highly speculative. In addition, little is known, based on interventional studies about cognitive effects linked to plant-based diets. Thus, a causal impact of plant-based diets on cognitive functions, mental and neurological health and respective underlying mechanisms has yet to be demonstrated. In sum, the increasing interest for plant-based diets raises the opportunity for developing novel preventive and therapeutic strategies against obesity, eating disorders and related comorbidities. Still, putative effects of plant-based diets on brain health and cognitive functions as well as the underlying mechanisms remain largely unexplored and new studies need to address these questions.

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Introduction

Western societies notice an increasing interest in plant-based eating patterns such as avoiding meat or fish or fully excluding animal products (vegetarian or vegan, see Fig.  1 ). In 2015, around 0.4−3.4% US adults, 1−2% British adults, and 5−10% of German adults were reported to eat largely plant-based diets 1 , 2 , 3 , 4 , due to various reasons (reviewed in ref. 5 ). Likewise, the number of scientific publications on PubMed (Fig.  2 ) and the public popularity as depicted by Google Trends (Fig.  3 ) underscore the increased interest in plant-based diets. This increasing awareness calls for a better scientific understanding of how plant-based diets affect human health, in particular with regard to potentially relevant effects on mental health and cognitive functions.

From left to right: including all food items (omnivore), including all except for meat (pesco-vegetarian) or meat and fish (ovo-lacto-vegetarian) to including only plant-based items (vegan)

Frequency of publications on PubMed including the search terms “vegan” (in light green), vegetarian (in orange) and plant-based (dark green)—accessed on 19 April 2019

Note indicates technical improvements implemented by Google Trends. Data source: Google Trends . Search performed on 18 April 2019

A potential effect of plant-based diets on mortality rate remains controversial: large epidemiological studies like the Adventist studies ( n  = 22,000−96,000) show a link between plant-based diets, lower all-cause mortality and cardiovascular diseases 6 , 7 , while other studies like the EPIC-Oxford study and the “45 and Up Study” ( n  = 64,000−267,000) show none 8 , 9 . Yet, many, but not all, epidemiological and interventional human studies in the last decades have suggested that plant-based diets exert beneficial health effects with regard to obesity-related metabolic dysfunction, type 2 diabetes mellitus (T2DM) and chronic low-grade inflammation (e.g. refs. 6 , 7 , 10 , 11 , for reviews, see refs. 12 , 13 , 14 , 15 , 16 , 17 , 18 ). However, while a putative link between such metabolic alterations and brain health through pathways which might include diet-related neurotransmitter precursors, inflammatory pathways and the gut microbiome 19 becomes increasingly recognized, the notion that plant-based diets exert influence on mental health and cognitive functions appears less documented and controversial 20 , 21 , 22 , 23 , 24 . We therefore systematically reviewed the current evidence based on available controlled interventional trials, regarded as the gold standard to assess causality, on potential effects of plant-based diets on (a) metabolic factors including the microbiome and (b) neurological or psychiatric health and brain functions. In addition, we aimed to evaluate potential underlying mechanisms and related implications for cognition.

We performed a systematic PubMed search with the following search terms “plant-based OR vegan OR vegetarian AND diet AND intervention” with the filter “clinical trial” and “humans”, preregistered at PROSPERO (CRD42018111856; https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=111856 ) (Suppl. Fig.  1 ). PubMed was used as search engine because it was esteemed to yield the majority of relevant human clinical trials from a medical perspective. Exclusion criteria were insufficient design quality (such as lack of a control group), interventions without a plant-based or vegetarian or vegan diet condition, intervention with multiple factors (such as exercise and diet), and the exclusive report of main outcomes of no interest, such as dietary compliance, nutrient intake (such as vitamins or fiber intake), or nonmetabolic (i.e., not concerning glucose metabolism, lipid profile, gastrointestinal hormones or inflammatory markers) or non-neurological/psychiatric disease outcomes (e.g. cancer, caries).

Studies were independently rated for eligibility into the systematic review by three authors based on reading the abstract and, if needed, methods or other parts of the publication. If opinions differed, a consensus was reached through discussion of the individual study. This yielded 27 eligible out of 205 publications; see Table  1 for details. To increase the search radius for studies dealing with microbial and neurological/psychiatric outcomes, we deleted the search term “intervention”, which increased the number of studies by around one third, and checked for studies with “microbiome/microbiota”, “mental”, “cognitive/cognition” or “psychological/psychology” in the resulting records. Through this, we retrieved another five studies included in Table  1 . Further related studies were reviewed based on additional nonsystematic literature search.

Section I: Effects of plant-based diets on body and brain outcomes

Results based on interventional studies on metabolism, microbiota and brain function.

Overall, the vast majority of studies included in this systematic review reported a short-term beneficial effect of plant-based dietary interventions (study duration 3−24 months) on weight status, glucose, insulin and/or plasma lipids and inflammatory markers, whereas studies investigating whether plant-based diets affect microbial or neurological/psychiatric disease status and other brain functions were scarce and rather inconclusive (Table  1 ).

More specifically, 19 out of 32 studies dealing with T2DM and/or obese subjects and seven out of 32 dealing with healthy subjects observed a more pronounced weight loss and metabolic improvements, such as lowering of glycated hemoglobin (HbA1c)—a long-term marker for glucose levels—decreased serum levels of low-density (LDL) and high-density lipoproteins (HDL) and total cholesterol (TC), after a plant-based diet compared to an omnivore diet. This is largely in line with recent meta-analyses indicating beneficial metabolic changes after a plant-based diet 25 , 26 , 27 .

For example, Lee et al. found a significantly larger reduction of HbA1c and lower waist circumference after vegan compared to conventional dieting 28 . Jenkins et al. found a disease-attenuating effect in hyperlipidemic patients after 6 months adopting a low-carbohydrate plant-based diet compared to a high-carbohydrate lacto-ovo-vegetarian diet 29 , 30 . However, lower energy intake in the vegan dieters might have contributed to these effects. Yet, while a plant-based diet per se might lead to lower caloric intake, other studies observed nonsignificant trends toward higher effect sizes on metabolic parameters after a vegan diet, even when caloric intake was comparable: two studies in T2DM patients 31 , 32 compared calorie-unrestricted vegan or vegetarian to calorie-restricted conventional diets over periods of 6 months and 1.5 years, respectively, in moderate sample sizes ( n  ~ 75−99) with similar caloric intake achieved in both diet groups. Both studies indicated stronger effects of plant-based diets on disease status, such as reduced medication, improved weight status and increased glucose/insulin sensitivity, proposing a diabetes-preventive potential of plant-based diets. Further, a five-arm study comparing four types of plant-based diets (vegan, vegetarian, pesco-vegetarian, semi-vegetarian) to an omnivore diet (total n  = 63) in obese participants found the most pronounced effect on weight loss for a vegan diet (−7.5 ± 4.5% of total body weight) 33 . Here, inflammation markers conceptualized as the dietary inflammatory index were also found to be lower in vegan, vegetarian and pesco-vegetarian compared to semi-vegetarian overweight to obese dieters 33 .

Intriguingly, these results 28 , 29 , 30 , 31 , 32 , 33 cohesively suggest that although caloric intake was similar across groups, participants who had followed a vegan diet showed higher weight loss and improved metabolic status.

As a limitation, all of the reviewed intervention studies were carried out in moderate sample sizes and over a period of less than 2 years, disregarding that long-term success of dietary interventions stabilizes after 2−5 years only 34 . Future studies with larger sample sizes and tight control of dietary intake need to confirm these results.

Through our systematic review we retrieved only one study that added the gut microbiome as novel outcome for clinical trials investigating the effects of animal-based diets compared to plant-based diets. While the sample size was relatively low ( n  = 10, cross-over within subject design), it showed that changing animal- to plant based diet changed gut microbial activity towards a trade-off between carbohydrate and protein fermentation processes within only 5 days 35 . This is in line with another controlled-feeding study where microbial composition changes already occurred 24 h after changing diet (not exclusively plant-based) 36 . However, future studies incorporating larger sample sizes and a uniform analysis approach of microbial features need to further confirm the hypothesis that a plant-based diet ameliorates microbial diversity and health-related bacteria species.

Considering neurological or psychiatric diseases and brain functions, the systematic review yielded in six clinical trials of diverse clinical groups, i.e. migraine, multiple sclerosis, fibromyalgia and rheumatoid arthritis. Here, mild to moderate improvement, e.g. measured by antibody levels, symptom improvement or pain frequency, was reported in five out of six studies, sometimes accompanied by weight loss 37 , 38 , 39 , 40 (Table  1 ). However, given the pilot character of these studies, indicated by small sample sizes ( n  = 32−66), lack of randomization 37 , or that the plant-based diet was additionally free of gluten 40 , the evidence is largely anecdotal. One study in moderately obese women showed no effects on psychological outcomes 41 , two studies with obese and nonobese healthy adults indicated improvements in anxiety, stress and depressive symptom scores 23 , 24 . Taken together, the current evidence based on interventional trials regarding improvements of cognitive and emotional markers and in disease treatment for central nervous system disorders such as multiple sclerosis or fibromyalgia remains considerably fragmentary for plant-based diets.

Among observational studies, a recent large cross-sectional study showed a higher occurrence of depressive symptoms for vegetarian dieters compared to nonvegetarians 20 . Conversely, another observational study with a sample of about 80% women found a beneficial association between a vegan diet and mood disturbance 24 .

Overall, the relationship between mental health (i.e. depression) and restrictive eating patterns has been the focus of recent research 20 , 21 , 22 , 24 , 42 ; however, causal relationships remain uninvestigated due to the observational design.

Underlying mechanisms linking macronutrient intake to metabolic processes

On the one hand, nutrient sources as well as their intake ratios considerably differ between plant-based and omnivore diets (Suppl. Table  1 ), and on the other hand, dietary micro- and macromolecules as well as their metabolic substrates affect a diversity of physiological functions, pointing to complex interdependencies. Thus, it seems difficult to nail down the proposed beneficial effects of a plant-based diet on metabolic status to one specific component or characteristic, and it seems unlikely that the usually low amount of calories in plant-based diets could explain all observed effects. Rather, plant-based diets might act through multiple pathways, including better glycemic control 43 , lower inflammatory activity 44 and altered neurotransmitter metabolism via dietary intake 45 or intestinal activity 46 (Fig.  4 ).

BMI body-mass-index, HbA1c hemoglobin A1c, LDL-cholesterol low-density lipoprotein cholesterol, Trp tryptophan, Tyr tyrosine. Images from commons.wikimedia.org , “Brain human sagittal section” by Lynch 2006 and “Complete GI tract” by Häggström 2008, “Anatomy Figure Vector Clipart” by http://moziru.com

On the macronutrient level, plant-based diets feature different types of fatty acids (mono- and poly-unsaturated versus saturated and trans) and sugars (complex and unrefined versus simple and refined), which might both be important players for mediating beneficial health effects 18 . On the micronutrient level, the EPIC-Oxford study provided the largest sample of vegan dieters worldwide ( n (vegan) = 2396, n (total) = 65,429) and showed on the one hand lower intake of saturated fatty acids (SFA), retinol, vitamin B12 and D, calcium, zinc and protein, and on the other hand higher intake of fiber, magnesium, iron, folic acid, vitamin B1, C and E in vegan compared to omnivore dieters 47 . Other studies confirmed the variance of nutrient intake across dietary groups, i.e. omnivores, vegetarians and vegans, showing the occurrence of critical nutrients for each group 48 , 49 . Not only the amount of SFA but also its source and profile might be important factors regulating metabolic control (reviewed in ref. 14 ), for example through contributing to systemic hyperlipidemia and subsequent cardiovascular risk. Recently, it has been shown in a 4-week intervention trial that short-term dietary changes favoring a diet high in animal-based protein may lead to an increased risk for cardiovascular derangements mediated by higher levels of trimethylamine N-oxide (TMAO), which is a metabolite of gut bacteria-driven metabolic pathways 50 .

Secondly, high fiber intake from legumes, grains, vegetables and fruits is a prominent feature of plant-based diets (Table  1 ), which could induce beneficial metabolic processes like upregulated carbohydrate fermentation and downregulated protein fermentation 35 , improved gut hormonal-driven appetite regulation 51 , 52 , 53 , 54 , 55 , and might prevent chronic diseases such as obesity and T2DM by slowing down digestion and improving lipid control 56 . A comprehensive review including evidence from 185 prospective studies and 58 clinical trials concluded that risk reduction for a myriad of diseases (incl. CVD, T2DM, stroke incidence) was greatest for daily fiber intake between 25 and 29 g 57 . Precise evidence for underlying mechanisms is missing; however, more recently it has been suggested that high fiber intake induces changes on the microbial level leading to lower long-term weight gain 58 , a mechanism discussed below.

The reason for lower systemic inflammation in plant-based dieters could be due to the abundance of antiinflammatory molecule intake and/or avoidance of proinflammatory animal-derived molecules. Assessing systemic inflammation is particularly relevant for medical conditions such as obesity, where it has been proposed to increase the risk for cardiovascular disease 59 , 60 . In addition, higher C-reactive protein (CRP) and interleukin-6 (IL-6) levels have been linked with measures of brain microstructure, such as microstructural integrity and white matter lesions 61 , 62 , 63 and higher risk of dementia 64 , and recent studies point out that a diet-related low inflammatory index might also directly affect healthy brain ageing 65 , 66 .

Interventional studies that focus on plant- versus meat-based proteins or micronutrients and potential effects on the body and brain are lacking. A meta-analysis including seven RCTs and one cross-sectional studies on physical performance and dietary habits concluded that a vegetarian diet did not adversely influence physical performance compared to an omnivore diet 67 . An epidemiological study by Song et al. 11 estimated that statistically replacing 3% of animal protein, especially from red meat or eggs, with plant protein would significantly improve mortality rates. This beneficial effect might however not be explained by the protein source itself, but possibly by detrimental components found in meat (e.g. heme-iron or nitrosamines, antibiotics, see below).

Some studies further hypothesized that health benefits observed in a plant-based diet stem from higher levels of fruits and vegetables providing phytochemicals or vitamin C that might boost immune function and eventually prevent certain types of cancer 68 , 69 , 70 . A meta-analysis on the effect of phytochemical intake concluded a beneficial effect on CVD, cancer, overweight, body composition, glucose tolerance, digestion and mental health 71 . Looking further on the impact of micronutrients and single dietary compounds, there is room for speculation that molecules, that are commonly avoided in plant-based diets, might affect metabolic status and overall health, such as opioid-peptides derived from casein 72 , pre- and probiotics 73 , 74 , carry-over antibiotics found in animal products 75 , 76 or food-related carcinogenic toxins, such as dioxin found in eggs or nitrosamines found in red and processed meat 77 , 78 . Although conclusive evidence is missing, these findings propose indirect beneficial effects on health deriving from plant-based compared to animal-based foods, with a potential role for nonprotein substances in mediating those effects 18 . While data regarding chemical contaminant levels (such as crop pesticides, herbicides or heavy metals) in different food items are fragmentary only, certain potentially harmful compounds may be more (or less) frequently consumed in plant-based diets compared to more animal-based diets 79 . Whether these differences lead to systematic health effects need to be explored.

Taken together, the reviewed studies indicating effects of plant-based diets through macro- and micronutrient intake reveal both the potential of single ingredients or food groups (low SFA, high fiber) and the immense complexity of diet-related mechanisms for metabolic health. As proposed by several authors, benefits on health related to diet can probably not be viewed in isolation for the intake (or nonintake) of specific foods, but rather by additive or even synergistic effects between them (reviewed in refs. 12 , 80 ). Even if it remains a challenging task to design long-term RCTs that control macro- and micronutrient levels across dietary intervention groups, technological advancements such as more fine-tuned diagnostic measurements and automated self-monitoring tools, e.g. automatic food recognition systems 81 and urine-related measures of dietary intake 82 , could help to push the field forward.

Nutrients of particular interest in plant-based diets

As described above, plant-based diets have been shown to convey nutritional benefits 48 , 49 , in particular increased fiber, beta carotene, vitamin K and C, folate, magnesium, and potassium intake and an improved dietary health index 83 . However, a major criticism of plant-based diets is the risk of nutrient deficiencies for specific micronutrients, especially vitamin B12, a mainly animal-derived nutrient, which is missing entirely in vegan diets unless supplemented or provided in B12-fortified products, and which seems detrimental for neurological and cognitive health when intake is low. In the EPIC-Oxford study about 50% of the vegan dieters showed serum levels indicating vitamin B12 deficiency 84 . Along other risk factors such as age 85 , diet, and plant-based diets in particular, seem to be the main risk factor for vitamin B12 deficiency (reviewed in ref. 86 ), and therefore supplementing vitamin B12 for these risk groups is highly recommended 87 . Vitamin B12 is a crucial component involved in early brain development, in maintaining normal central nervous system function 88 and suggested to be neuroprotective, particularly for memory performance and hippocampal microstructure 89 . One hypothesis is that high levels of homocysteine, that is associated with vitamin B12 deficiency, might be harmful to the body. Vitamin B12 is the essential cofactor required for the conversion of homocysteine into nonharmful components and serves as a cofactor in different enzymatic reactions. A person suffering from vitamin B12 insufficiency accumulates homocysteine, lastly promoting the formation of plaques in arteries and thereby increasing atherothrombotic risk 90 , possibly facilitating symptoms in patients of Alzheimer’s disease 91 . A meta-analysis found that vitamin B12 deficiency was associated with stroke, Alzheimer’s disease, vascular dementia, Parkinson’s disease and in even lower concentrations with cognitive impairment 92 , supporting the claim of its high potential for disease prevention when avoided or treated 93 . Further investigations and longitudinal studies are needed, possibly measuring holotranscobalamin (the active form of vitamin B12) as a more specific and sensitive marker for vitamin B12 status 94 , to examine in how far nonsupplementing vegan dieters could be at risk for cardiovascular and cognitive impairment.

Similar health dangers can stem from iron deficiency, another commonly assumed risk for plant-based dieters and other risk groups such as young women. A meta-analysis on 24 studies proposes that although serum ferritin levels were lower in vegetarians on average, it is recommended to sustain an optimal ferritin level (neither too low nor too high), calling for well-monitored supplementation strategies 95 . Iron deficiency is not only dependent on iron intake as such but also on complimentary dietary factors influencing its bioavailability (discussed in ref. 95 ). The picture remains complex: on the one hand iron deficiency may lead to detrimental health effects, such as impairments in early brain development and cognitive functions in adults and in children carried by iron-deficient mothers 96 and a possible role for iron overload in the brain on cognitive impairment on the other hand 97 . One study showed that attention, memory and learning were impaired in iron-deficient compared to iron-sufficient women, which could be restored after a 4-month oral iron supplementation ( n  = 118) 98 . Iron deficiency-related impairments could be attributed to anemia as an underlying cause, possibly leading to fatigue, or an undersupply of blood to the brain or alterations in neurobiological and neuronal systems 99 provoking impaired cognitive functioning.

This leads to the general recommendation to monitor health status by frequent blood tests, to consult a dietician to live healthily on a plant-based diet and to consider supplements to avoid nutrient deficiencies or nutrient-overdose-related toxicity. All in all, organizations such as the Academy of Nutrition and Dietetics 100 and the German Nutrition Society do not judge iron as a major risk factor for plant-based dieters 101 .

Section II: Effects of diet on the gut microbiome

The link between diet and microbial diversity.

Another putative mechanistic pathway of how plant-based diets can affect health may involve the gut microbiome which has increasingly received scientific and popular interest, lastly not only through initiatives such as the Human Microbiome Project 102 . A common measure for characterizing the gut community is enterotyping, which is a way to stratify individuals according to their gut bacterial diversity, by calculating the ratio between bacterial genera, such as Prevotella and Bacteroides 103 . While interventional controlled trials are still scarce, this ratio has been shown to be conclusive for differentiating plant-based from animal-based microbial profiles 36 . Specifically, in a sample of 98 individuals, Wu et al. 36 found that a diet high in protein and animal fats was related to more Bacteroides, whereas a diet high in carbohydrates, representing a plant-based one, was associated with more Prevotella. Moreover, the authors showed that a change in diet to high-fat/low-fiber or to low-fat/high-fiber in ten individuals elicited a change in gut microbial enterotype with a time delay of 24 h only and remained stable over 10 days, however not being able to switch completely to another enterotype 36 . Another strictly controlled 30-day cross-over interventional study showed that a change in diet to either an exclusively animal-based or plant-based diet promoted gut microbiota diversity and genetic expression to change within 5 days 35 . Particularly, in response to adopting an animal-based diet, microbial diversity increased rapidly, even overshadowing individual microbial gene expression. Beyond large shifts in overall diet, already modest dietary modifications such as the daily consumption of 43 g of walnuts, were able to promote probiotic- and butyric acid-producing bacterial species in two RCTs, after 3 and 8 weeks respectively 104 , 105 , highlighting the high adaptability of the gut microbiome to dietary components. The Prevotella to Bacteroides ratio (P/B) has been shown to be involved in the success of dietary interventions targeting weight loss, with larger weight loss in high P/B compared to low P/B in a 6-month whole-grain diet compared to a conventional diet 106 . Only recently, other microbial communities, such as the salivary microbiome, have been shown to be different between omnivores and vegan dieters 107 , opening new avenues for research on adaptable mechanisms related to dietary intake.

A continuum in microbial diversity dependent on diet

Plant-based diets are supposed to be linked to a specific microbial profile, with a vegan profile being most different from an omnivore, but not always different from a vegetarian profile (reviewed in ref. 15 ). Some specifically vegan gut microbial characteristics have also been found in a small sample of six obese subjects after 1 month following a vegetarian diet, namely less pathobionts, more protective bacterial species improving lipid metabolism and a reduced level of intestinal inflammation 108 . Investigating long-term dietary patterns a study found a dose-dependent effect for altered gut microbiota in vegetarians and vegans compared to omnivores depending on the quantity of animal products 109 . The authors showed that gut microbial profiles of plant-based diets feature the same total number but lower counts of Bacteroides, Bifidobacterium, E. coli and Enterobacteriaceae compared to omnivores, with the biggest difference to vegans. Still today it remains unclear, what this shift in bacterial composition means in functional terms, prompting the field to develop more functional analyses.

In a 30-day intervention study, David et al. found that fermentation processes linked to fat and carbohydrate decomposition were related to the abundance of certain microbial species 35 . They found a strong correlation between fiber intake and Prevotella abundance in the microbial gut. More recently, Prevotella has been associated with plant-based diets 110 that are comparable to low-fat/high-fiber diets 111 and might be linked to the increased synthesis of short-chain fatty acids (SCFA) 112 . SCFAs are discussed as putative signaling molecules between the gut microbiome and the receptors, i.e. free fatty acid receptor 2 (FFA2) 51 , found in host cells across different tissues 113 and could therefore be one potential mechanism of microbiome−host communication.

The underlying mechanisms of nutrient decomposition by Prevotella and whether abundant Prevotella populations in the gut are beneficial for overall health remain unknown. Yet it seems possible that an increased fiber intake and therefore higher Prevotella abundance such as associated with plant-based diets is beneficial for regulating glycemic control and keeping inflammatory processes within normal levels, possibly due to reduced appetite and lower energy intake mediated by a higher fiber content 114 . Moreover, it has been brought forward that the microbiome might influence bodily homeostatic control, suggesting a role for the gut microbiota in whole-body control mechanisms on the systemic level. Novel strategies aim to develop gut-microbiota-based therapies to improve bodily states, e.g. glycemic control 115 , based on inducing microbial changes and thereby eliciting higher-level changes in homeostasis. While highly speculative, such strategies could in theory also exert changes on the brain level, which will be discussed next in the light of a bi-directional feedback between the gut and the brain.

Effects on cognition and behavior linking diet and cognition via the microbiome−gut−brain axis

While the number of interventional studies focusing on cognitive and mental health outcomes after adopting plant-based diets overall is very limited (see Section I above), one underlying mechanism of how plant-based diets may affect mood could involve signaling pathways on the microbiome−gut−brain axis 116 , 117 , 118 , 119 . A recent 4-week intervention RCT showed that probiotic administration compared to placebo and no intervention modulated brain activity during emotional decision-making and emotional recognition tasks 117 . In chronic depression it has been proposed that immunoglobulin A and M antibodies are synthesized by the host in response to gut commensals and are linked to depressive symptoms 120 . Whether the identified gram-negative bacteria might also play a role in plant-based diets remains to be explored. A meta-analysis on five studies concluded that probiotics may mediate an alleviating effect on depression symptomatic 121 —however, sample sizes remained rather small ( n  < 100) and no long-term effects were tested (up to 8 weeks).

Currently, several studies aim to identify microbial profiles in relation to disease and how microbial data can be used on a multimodal way to improve functional resolution, e.g. characterizing microbial profiles of individuals suffering from type-1 diabetes 122 . Yet, evidence for specific effects of diet on cognitive functions and behavior through changes in the microbiome remains scarce. A recent study indicated the possibility that our food choices determine the quantity and quality of neurotransmitter-precursor levels that we ingest, which in turn might influence behavior, as shown by lower fairness during a money-redistribution task, called the ultimatum game, after a high-carbohydrate/protein ratio breakfast than after a low-ratio breakfast 123 . Strang et al. found that precursor forms of serotonin and dopamine, measured in blood serum, predicted behavior in this task, and precursor concentrations were dependent on the nutrient profile of the consumed meal before the task. Also on a cross-sectional level tryptophan metabolites from fecal samples have been associated with amygdala-reward network functional connectivity 124 . On top of the dietary composition per se, the microbiota largely contributes to neurotransmitter precursor concentrations; thus, in addition to measuring neurotransmitter precursors in the serum, metabolomics on fecal samples would be helpful to further understand the functional role of the gut microbiota in neurotransmitter biosynthesis and regulation 125 .

Indicating the relevance of gut microbiota for cognition, a first human study assessing cognitive tests and brain imaging could distinguish obese from nonobese individuals using a microbial profile 126 . The authors found a specific microbiotic profile, particularly defined by Actinobacteria phylum abundance, that was associated with microstructural properties in the hypothalamus and in the caudate nucleus. Further, a preclinical study tested whether probiotics could enhance cognitive function in healthy subjects, showing small effects on improved memory performance and reduced stress levels 127 .

A recent study could show that microbial composition influences cerebral amyloidogenesis in a mouse model for Alzheimer’s disease 128 . Health status of the donor mouse seemingly mattered: fecal transplants from transgenic mice had a larger impact on amyloid beta proliferation in the brain compared to wild-type feces. Translational interpretations to humans should be done with caution if at all—yet the results remain elucidative for showing a link between the gut microbiome and brain metabolism.

The evidence for effects of strictly plant-based diets on cognition is very limited. For other plant-based diets such as the Mediterranean diet or DASH diet, there are more available studies that indicate protective effects on cardiovascular and brain health in the aging population (reviewed in refs. 129 , 130 ). Several attempts have been made to clarify potential underlying mechanisms, for example using supplementary plant polyphenols, fish/fish-oil consumption or whole dietary pattern change in RCTs 131 , 132 , 133 , 134 , 135 , 136 , 137 , yet results are not always equivocal and large-scale intervention studies have yet to be completed.

The overall findings of this paragraph add to the evidence that microbial diversity may be associated with brain health, although underlying mechanisms and candidate signaling molecules remain unknown.

Based on this systematic review of randomized clinical trials, there is an overall robust support for beneficial effects of a plant-based diet on metabolic measures in health and disease. However, the evidence for cognitive and mental effects of a plant-based diet is still inconclusive. Also, it is not clear whether putative effects are due to the diet per se, certain nutrients of the diet (or the avoidance of certain animal-based nutrients) or other factors associated with vegetarian/vegan diets. Evolving concepts argue that emotional distress and mental illnesses are linked to the role of microbiota in neurological function and can be potentially treated via microbial intervention strategies 19 . Moreover, it has been claimed that certain diseases, such as obesity, are caused by a specific microbial composition 138 , and that a balanced gut microbiome is related to healthy ageing 111 . In this light, it seems possible that a plant-based diet is able to influence brain function by still unclear underlying mechanisms of an altered microbial status and systemic metabolic alterations. However, to our knowledge there are no studies linking plant-based diets and cognitive abilities on a neural level, which are urgently needed, due to the hidden potential as a dietary therapeutic tool. Also, further studies are needed to disentangle motivational beliefs on a psychological level that lead to a change in diet from causal effects on the body and the brain mediated e.g., by metabolic alterations or a change in the gut microbiome.

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Acknowledgements

This work was supported by a scholarship (E.M.) by the German Federal Environmental Foundation and by the grants of the German Research Foundation contract grant number CRC 1052 “Obesity mechanisms” Project A1 (AV) and WI 3342/3-1 (A.V.W.).

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Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

Evelyn Medawar, Arno Villringer & A. Veronica Witte

Berlin School of Mind and Brain, Humboldt-Universität zu Berlin, Berlin, Germany

Evelyn Medawar & Arno Villringer

Charité—Universitätsmedizin Berlin, Humboldt-Universität zu Berlin, Berlin, Germany

Helmholtz Centre for Environmental Research GmbH—UFZ, Leipzig, Germany

Sebastian Huhn

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E.M., A.V. and A.V.W. designed research; E.M. conducted research; E.M., S.H. and A.V.W. analyzed data; E.M. and A.V.W. wrote the paper; E.M., A.V. and A.V.W. had primary responsibility for final content. All authors read and approved the final manuscript.

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The 16 Best Research Paper Topics About Vegetarianism

Writing a research paper about vegetarianism can be interesting if you come up with an original topic and find various materials to support your thesis idea. There are several things that you should keep in mind.

Firstly, remember that vegetarianism is a lifestyle that is becoming popular all over the planet. The subject itself has many interesting aspects that you can focus on in your study. Secondly, keep in mind that there are different points of view about this alternative way of life, so you should choose the one that you support. Thirdly, make sure to find some statistics and new facts about your chosen topic, so your research paper will attract readers.

No matter what your research subject is, the easiest way to select a topic for your research paper is to find a list of the best ideas, read them, and get inspired. Your instructor might provide such a list for you. You can also search on the Internet or brainstorm with your friends. To get started, study the following list of 16 sample topics:

• Vegetarianism as a modern lifestyle in Western countries.
• The main differences between a conventional and vegetarian diet.
• The key benefits of switching diets.
• The main reasons why people want to become vegans.
• The key similarities and differences between vegan and vegetarian diets.
• The ethical issues involved in becoming a vegetarian.
• Medical conditions that require changing one’s diet.
• A collection of the scientifically proven benefits of vegetarianism.
• Myths and facts about being a vegetarian.
• The reasons why a vegetarian diet is considered healthy.
• How can a vegetarian lifestyle affect the environment in the long run?
• What are the common health effects of a vegetarian diet?
• Why do committed environmentalists support vegetarian diets?
• What products are an essential part of a vegetarian diet?
• What celebrities are vegetarians or vegans and why did they choose such a lifestyle?
• What factors should people consider before they decide to become vegetarians?

The study subject is controversial, so it’s a good idea to decide whether or not you support vegetarianism before you start to work on your assignment. For example, you can provide points of view from experts in the field in order to strengthen your argument. This will help you build a strong argument and select the right materials in order to prove that your position is correct.

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A List Of Interesting Vegetarian Research Paper Topics For College

Many people today choose to lead a healthy lifestyle. Switching to a vegetarian diet is one of the changes that quite a few of them make in order to improve their overall wellbeing. Therefore, this particular subject is a good topic for a research paper.

If you can’t come up with any interesting topics for a vegetarianism essay, take a look at the following prompts:

• 1. Reasons for becoming a vegetarian.

Identify different reasons that make people choose this particular diet. Be sure to mention fighters for animal rights and those who suffer from various digestive disorders that prevent people from eating meat.

• 2. Living a vegetarian.

What are the pros and cons of being a vegetarian? What kind of changes in your everyday life do you need to make in order to accommodate this change of diet? What difficulties will you encounter while eating out? Explore every little detail that will explain how your life in general will change when you become a vegetarian.

• 3. How to become a vegetarian.

To quit eating meat isn’t easy. Offer some viable methods that will help people make this change of diet more painless and smooth.

• 4. Different kinds of vegetarians.

There are plenty of types of vegetarians today. List them and explain the peculiarities of each. Which do you consider to be the best and the worst? Why?

• 5. Animals must have rights.

This paper should be focused on vegetarianism from the position of animals instead of exploring this diet from a human’s point of view. Explain why animals must have rights and how slaughtering them for food reflects on people.

• 6. History of vegetarianism.

What cultures accepted vegetarianism as their main diet? Look up some historic facts about this particular diet and describe its position in societies from different ages.

• 7. Health considerations of vegetarian diet.

Is vegetarian diet really good for you? What are the risks? What steps does one need to take in order to ensure that your body gets proper nutrition even without meat?

• 8. Perks of a vegetarian diet.

What are the best things about this diet? Don’t forget to mention its effect on maintaining healthy weight.

• 9. Vegetarian extremism.

Some types of vegetarian diets are really outlandish. Explain what they are and what kind of effect they can have on people.

• 10. Anorexia and vegetarianism.

Can switching to a vegetarian diet help people with anorexia? How will this disorder affect a person’s wish to become a vegetarian?

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The long-term health of vegetarians and vegans

Affiliation.

• 1 Cancer Epidemiology Unit, Nuffield Department of Population Health,University of Oxford,Richard Doll Building,Old Road Campus,Roosevelt Drive,Oxford OX3 7LF,UK.
• PMID: 26707634
• DOI: 10.1017/S0029665115004334

Vegetarians, who do not eat any meat, poultry or fish, constitute a significant minority of the world's population. Lacto-ovo-vegetarians consume dairy products and/or eggs, whereas vegans do not eat any foods derived wholly or partly from animals. Concerns over the health, environmental and economic consequences of a diet rich in meat and other animal products have focussed attention on those who exclude some or all of these foods from their diet. There has been extensive research into the nutritional adequacy of vegetarian diets, but less is known about the long-term health of vegetarians and vegans. We summarise the main findings from large cross-sectional and prospective cohort studies in western countries with a high proportion of vegetarian participants. Vegetarians have a lower prevalence of overweight and obesity and a lower risk of IHD compared with non-vegetarians from a similar background, whereas the data are equivocal for stroke. For cancer, there is some evidence that the risk for all cancer sites combined is slightly lower in vegetarians than in non-vegetarians, but findings for individual cancer sites are inconclusive. Vegetarians have also been found to have lower risks for diabetes, diverticular disease and eye cataract. Overall mortality is similar for vegetarians and comparable non-vegetarians, but vegetarian groups compare favourably with the general population. The long-term health of vegetarians appears to be generally good, and for some diseases and medical conditions it may be better than that of comparable omnivores. Much more research is needed, particularly on the long-term health of vegans.

Keywords: AHS-2 Adventist Health Study-2; EPIC-Oxford; European Prospective Investigation into Cancer and Nutrition-Oxford; Morbidity; Mortality; Vegan; Vegetarian.

Publication types

• Research Support, Non-U.S. Gov't
• Body Mass Index
• Cardiovascular Diseases / epidemiology
• Cardiovascular Diseases / prevention & control
• Diabetes Mellitus, Type 2 / epidemiology
• Diabetes Mellitus, Type 2 / prevention & control
• Diet, Vegan*
• Diet, Vegetarian*
• Health Status*
• Neoplasms / epidemiology
• Neoplasms / prevention & control
• Obesity / epidemiology
• Obesity / prevention & control
• Risk Factors
• Weight Gain

Grants and funding

• 16491/CRUK_/Cancer Research UK/United Kingdom
• MR/M012190/1/MRC_/Medical Research Council/United Kingdom

Benefits of Vegetarianism Research Paper

Introduction.

Food is an integral part of the human experience and human beings must eat in order to survive. Human beings are omnivores by nature, which means that they can consume both meat and vegetables. However, there exists a subgroup that abstains from eating animal or fish flesh.

This people are called vegetarians and their practice is called vegetarianism. Key, Gwyneth and Appleby (1999) elaborate that the vegetarian diet is based on cereals, pulses, fruits and vegetables. Vegetarianism has become more mainstream in recent decades with more people taking up this dietary practice. The prominence of vegetarianism is mostly attributed to the many benefits obtained from this practice. This paper will set out to discuss the most significant benefits of vegetarianism.

Benefits of Vegetarianism

A vegetarian diet can help in the prevention of chronic diseases such as diabetes, heart disease, and obesity. While family history is a risk factor in some diseases such as diabetes, heart disease and some cancers, dietary patterns can also increase or decrease a person’s risk of developing these conditions.

Research by Hart (2009) found out that people who ate meat were 29& more likely to develop type 2 diabetes compared to those who ate no meat. A vegetarian diet rich in fruits and vegetables can be effective in the prevention and management of cardiac disease. Research indicates that the risk of death from heart disease was 24% lower in vegetarians compared with non-vegetarians (Hart, 2009). This is because vegetarian diets have lower cholesterol levels than non-vegetarian diets.

The vegetarian diet also offers some levels of cancer prevention with research indicating that vegetarians have lower cancer rates than the general population. Cancer is one of the leading causes of death worldwide and in spite of enormous research efforts and many treatment options, there is still no guaranteed cure for the disease.

anou and Svenson (2011) assert that in spite of the prevalence of cancer in the past decades, it is still a largely preventable disease since 90% of the risks are rooted in the environment and lifestyle choices of an individual. Research indicates that “70% of cases of colorectal and prostate cancer, 50% of cases for breast, endometrial, pancreatic, and gallbladder cancers” may be linked to the dietary habits of an individual (Lanou & Svenson, 2011, p.1).

Dietary patterns are therefore important modulators of cancer risk in an individual. A non-vegetarian diet is made up of high levels of meat intake and studies have linked meat to a variety of cancers. The vegetarian diet greatly reduced risk of cancer since the diet is rich in whole plant foods and low on fats and sugars. This is an important point considering the fact that there is a correlation between higher levels of body fatness and increased risk of cancers.

Vegetarianism helps individuals to avoid the public health threats posed by meat consumption. A common habit in livestock factory farming is the indiscriminate feeding of antibiotics to farm animals. The rationale behind this mass feeding of antibiotics is to prevent diseases and promote growth.

However, this practice raises negative health risks in human beings who consume the meat. Henning (2011) confirms that the meat product sold to consumers is laced with residues from the antibiotics that are routinely fed to livestock. McCarthy (2010) warns, “Every inappropriate use of antibiotics in agriculture is potentially signing a death warrant for a future patient” (p.13).

This concern is echoed by Henning (2011) who asserts that the mass production and overconsumption of meat now represent the single greatest threats to public health. Meat consumption is responsible for the increase in “antibiotic-resistant human bacterial illnesses”. Since the vegetarian diet is free from meat, the individual is free from the risk of antibiotic resistance that meat consumers face.

A vegetarian diet promotes mental health in the individual. Research indicates that a people on a meat-free diet experience a calmer disposition and are less vulnerable to anger. Vegetarian diets are associated with feelings of serenity, reduced aggression, increased compassion for others, and a sense of mental stability.

Kaza (2005) suggests that these states of mind may come from the reduced intake of toxic hormones and pesticides from animal products and eliminating the intake of animal adrenaline that is released at death and persists even in processed meat. Vegetarianism therefore increases mental health and enhances mental clarity in the individual. He/she is therefore able to be more productive in life because of the mental benefits accrued form the vegetarian diet.

A vegetarian diet will help to offset the environmentally destructive nature of intensive livestock production. Livestock production has many deleterious impacts on the ecosystem’s health with cattle ranching contributing to soil erosion, degradation of stream habitat, deforestation, and desertification.

Henning (2011) asserts that cattle ranching is the primary reason for reforestation in the Amazon with the rising demand of beef being deemed as the single greatest contributor to deforestation worldwide.

Henning (2011) marks out the livestock sector as the single greatest source of freshwater use and pollution in the US with these animals producing ten times more waste than the human population.

However, unlike human waste that is cleaned through waste treatment facilities, livestock effluent is allowed to leak into aquifers and waterways every day. A vegetarian diet would greatly mitigate these negative implications of livestock production on freshwater resources.

Meat consumption contributes to climate change, which has been acknowledged to be a global environmental problem. Specifically, meat production leads to an increase in greenhouse gas emissions. As the enormous quantities of manure produced by cattle decay, they produce methane, which is a greenhouse gas.

For this reason, Harrison (2007) observes that eating meat comes at a cost to the environment with the average meat consumer increasing his/her carbon footprint significantly. Global warming will negatively affect the food resources of the world since it will turn previously arable land useless for agricultural purposes. Adopting a vegetarian diet will mitigate this harmful emission and prevent the climatic changes.

Vegetarianism is necessary to ensure the food security of the world. While the world’s supply of food is today adequate to feed the entire human population, there is increased concern over the ability of the world to feed itself in future. The increasing human population is already putting pressure on the food supply.

The meat intensive diet is especially to blame for the additional pressure on the world’s fragile food resources. Henning (2011) records that the world has experienced a four-fold increase in meat production since 1960. As it currently stands, large tracts of land are dedicated to cattle grazing.

Farm animals consume the greatest share of cereal productions therefore requiring increased cereal production, which puts a strain on the land resources. In contrast to this, a vegetarian diet would only require 25% of the energy used to sustain a red-meat rich diet (Brown, 2010). Vegetarianism therefore reduces the pressure on land and water resources therefore guaranteeing sustainability.

Vegetarianism will help avoid the unnecessary suffering that animals are subjected to through factory farming. Over nine billion animals live in factory farms in the US each year to provide for the demand for meant in the country. The conditions under which these animals live are generally miserable with animals being confined in small cages or overcrowded pens to maximize profits.

Nobis (2002) reveals that the animals are kept on a constant regimen of antibiotics to ward off death and disease. All this suffering by the animals is unjustified since humans do not need to eat meat and other animal products in order to survive. Vegetarianism will remove the need for animal products and this degrading factory farming will not be necessary.

Vegetarianism is more economical than a meat-based diet. To begin with, the cost of maintaining a vegetarian diet is cheaper than maintaining meat-based diet. Henning (2011) declares that the seemingly low costs of meat are the result of agricultural subsidies by the government to meat producers. The taxpayer eventually pays for these subsidies therefore increasing the financial burden for the taxpaying citizen.

The meat-based diet is associated with a number of health issues and the person engaging in this diet will therefore spend significant amount of money on health care costs. In addition to this, the person will suffer from negative economic effects in terms of lost jobs and revenue due to the deleterious effects of meat eating upon health. Practicing vegetarianism will ensure that a person does not suffer from the negative economic effects that a meat-based diet is bound to result in.

There has been a changing attitude towards vegetarianism in America in the last five decades with more people adopting vegetarian diets. People are discovering that it is possible to thrive on a non-meat based diet and that eating meat is nutritionally unnecessary. This combined with the knowledge that meat-eating costs more to the global supply of food than it provides is making people reconsider their eating habits.

Even so, vegetarianism has not been able to effectively challenge the primacy of meat in many American homes and many people still hold the view that meat and vegetables complement each other. However, as the many advantages of a vegetarian diet become known to the general population, it can be expected that the segment of the general public practicing vegetarianism will increase significantly.

This paper set out to give a detailed discussion of the benefits of vegetarianism. It began by defining vegetarianism as the practice of not eating animal flesh. The paper has documented the health benefits of a vegetarian diet. It has shown the strong correlation between meat-based diets and health problems and highlighted the fact that vegetarians are less prone to these health problems and tend to outlive meat-eaters.

The paper has also discussed the significant negative environmental impacts that a meat-based diet causes. It has also highlighted that the meat-based diet consumes too many resources and is therefore unsustainable. Considering the numerous health benefits accrued through vegetarianism and the harms that a meat consuming diet brings to the environment, all humans ought to practice vegetarianism.

Brown, L. (2010). How to feed 8 billion people. The Futurist , 44 (1), 28-33.

Harrison, C. (2007). Vegetarian with benefits. Proquest . Web.

Hart, J. (2009). The Health Benefits of a Vegetarian Diet. Alternative and Complementary Therapies , 15(2), 64-68.

Henning, B. (2011). Standing in Livestock’s ‘Long Shadow’ The Ethics of Eating Meat on a Small Planet. Ethics & The Environment , 16(2), 1085-6633.

Kaza, S. (2005). Western Buddhist motivations for vegetarianism. Worldviews, 9 (3), 385-411.

Key, T.J. Gwyneth, K.D. & Appleby, P.N. (1999). Health benefits of a vegetarian diet. Proceedings of the Nutrition Society , 58 (2), 271 275.

Lanou, J.A. & Svenson, B. (2011). Reduced cancer risk in vegetarians: an analysis of recent reports. Cancer Management and Research , 3 (1), 1–8.

McCarthy, K. (2010). Plant-Based Diets: A solution to our public health crisis . Washington: World Progressive Foundation.

Nobis, N. (2002). Vegetarianism and Virtue: Does Consequentialism Demand Too Little? Social Theory and Practice , 28 (1), 135-155.

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Articles on Vegetarianism

Displaying 1 - 20 of 105 articles.

Climate labels similar to cigarette packet warnings could cut meat consumption – new research

Jack Hughes , Durham University ; Mario Weick , Durham University , and Milica Vasiljevic , Durham University

Vegan diet has just 30% of the environmental impact of a high-meat diet, major study finds

Michael Clark , University of Oxford and Keren Papier , University of Oxford

Are vegan pet diets as unhealthy as they’re claimed to be? Here’s what the evidence says

Alexandra Whittaker , University of Adelaide ; Adriana Domínguez-Oliva , Universidad Autónoma Metropolitana (México) , and Daniel Mota-Rojas

Egg shortage: a nutritionist on the best egg alternatives

Hazel Flight , Edge Hill University

My kid has gone vegetarian. What do I need to know (especially if they’re a picky eater)?

Evangeline Mantzioris , University of South Australia

Vegetarians more likely to be depressed than meat-eaters – possible reasons

Chris Bryant , University of Bath

Vegetarian diets may be better for the planet – but the Mediterranean diet is the one omnivores will actually adopt

Nicole Allenden , University of New England ; Amy Lykins , University of New England , and Annette Cowie

Vegan and vegetarian diets may lack certain nutrients – here’s how to get more of them

Martin Warren , Quadram Institute ; Kourosh Ahmadi , University of Surrey ; Liangzi Zhang , Quadram Institute , and Maria Traka , Quadram Institute

Why Seventh-day Adventists are so often vegan or vegetarian

Tamas Lestar , University of Winchester

The meat paradox: how your brain wrestles with the ethics of eating animals

Sarah Gradidge , Anglia Ruskin University and Magdalena Zawisza , Anglia Ruskin University

‘Sallets’ – how to eat healthily the 1600s way

Catie Gill , Loughborough University and Sara Read , Loughborough University

Diners more likely to choose a vegetarian option when 75% of the menu is meat-free – new research

Beth Parkin , University of Westminster

Individual dietary choices can add – or take away – minutes, hours and years of life

Olivier Jolliet , University of Michigan and Katerina S. Stylianou , University of Michigan

Does a plant-based diet really help beat  COVID-19 ?

Duane Mellor , Aston University

Anti-nutrients – they’re part of a normal diet and not as scary as they sound

Jill Joyce , Oklahoma State University

Diet resolutions: 6 things to know about eating less meat and more plant-based  foods

Mariana Lamas , Northern Alberta Institute of Technology

Singapore approves cell-cultured chicken bites – who will be the first to try them?

Vegetarian and vegan diet: five things for over-65s to consider when switching to a plant-based  diet

Taibat (Tai) Ibitoye , University of Reading

My talk with Jane Goodall: vegetarianism, animal welfare and the power of children’s advocacy

Clive Phillips , The University of Queensland

Looking forward to a future without factory farming

Kendra Coulter , Brock University

Related Topics

• Animal welfare
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Top contributors

Director, Agri-Food Analytics Lab, Professor in Food Distribution and Policy, Dalhousie University

Associate Professor in Sociology, University of East Anglia

Lecturer in Social Psychology, Lancaster University

Lecturer in Criminology, The Open University

Senior research associate, University of Technology Sydney

Senior Lecturer in Science Communication, The University of Western Australia

Honorary Research Associate, Department of Psychology, University of Bath

Professor of History and Philosophy, and Deputy Dean Research (Faculty of Arts), University of Adelaide

NHMRC Emerging Leadership Fellow and Senior Research Fellow at the Institute for Physical Activity and Nutrition, Deakin University

PhD Candidate, Biological and Experimental Psychology, Queen Mary University of London

Senior Visiting Fellow, School of Medical Sciences, UNSW Sydney

Adjunct Senior Research Fellow, University of South Australia

Medical Doctor and Clinical Senior Fellow, The University of Melbourne

Professor, Melbourne School of Psychological Sciences, The University of Melbourne

Program Director of Nutrition and Food Sciences, Accredited Practising Dietitian, University of South Australia

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Home — Essay Samples — Life — Vegetarianism — Research Paper on Vegetarian Diet for Adults

Research Paper on Vegetarian Diet for Adults

• Categories: Adult Diet Vegetarianism

About this sample

Words: 1470 |

Published: Dec 3, 2020

Words: 1470 | Pages: 3 | 8 min read

Table of contents

Introduction, nutrition needs.

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• Here, S., 1, H., Women, H., Men, H., Phlebotomy, T., & Tests, L. et al. (2019). Heme Iron vs Non-Heme Iron in Foods. retrieved from: https://hemochromatosishelp.com/heme-iron-vs-non-heme-iron/
• Iyer, S. (2019). The Pros And Cons Of Going Vegan. retrieved from: https://www.self.com/story/vegan-diet-pros-cons
• Vegetarian, Vegan and Meals Without Meat. (2019). retrieved from: https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/nutrition-basics/vegetarian-vegan-and-meals-without-meat
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• What is the body mass index (BMI)? (2019), National Health Service of United Kingdom. retrieved from: https://www.nhs.uk/common-health-questions/lifestyle/what-is-the-body-mass-index-bmi/
• Stiftung, H. B. (2014). Meat atlas : facts and figures about the animals we eat (1 st ed.). Berlin: Heinrich Böll
• Foundation & Friend of the Earth Europe. Elmadfa, I. (2005). Diet diversification and health promotion. Vienna: Basel: S.
• Karger AG. Ion, R.A. (2007). Reasons why people turn to vegetarian diet. Institute of Agricultural Economics, 54, 353-358, Retrived from https://ageconsearch.umn.edu/record/245701

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Sat / act prep online guides and tips, 113 great research paper topics.

General Education

One of the hardest parts of writing a research paper can be just finding a good topic to write about. Fortunately we've done the hard work for you and have compiled a list of 113 interesting research paper topics. They've been organized into ten categories and cover a wide range of subjects so you can easily find the best topic for you.

In addition to the list of good research topics, we've included advice on what makes a good research paper topic and how you can use your topic to start writing a great paper.

What Makes a Good Research Paper Topic?

Not all research paper topics are created equal, and you want to make sure you choose a great topic before you start writing. Below are the three most important factors to consider to make sure you choose the best research paper topics.

#1: It's Something You're Interested In

A paper is always easier to write if you're interested in the topic, and you'll be more motivated to do in-depth research and write a paper that really covers the entire subject. Even if a certain research paper topic is getting a lot of buzz right now or other people seem interested in writing about it, don't feel tempted to make it your topic unless you genuinely have some sort of interest in it as well.

#2: There's Enough Information to Write a Paper

Even if you come up with the absolute best research paper topic and you're so excited to write about it, you won't be able to produce a good paper if there isn't enough research about the topic. This can happen for very specific or specialized topics, as well as topics that are too new to have enough research done on them at the moment. Easy research paper topics will always be topics with enough information to write a full-length paper.

Trying to write a research paper on a topic that doesn't have much research on it is incredibly hard, so before you decide on a topic, do a bit of preliminary searching and make sure you'll have all the information you need to write your paper.

#3: It Fits Your Teacher's Guidelines

Don't get so carried away looking at lists of research paper topics that you forget any requirements or restrictions your teacher may have put on research topic ideas. If you're writing a research paper on a health-related topic, deciding to write about the impact of rap on the music scene probably won't be allowed, but there may be some sort of leeway. For example, if you're really interested in current events but your teacher wants you to write a research paper on a history topic, you may be able to choose a topic that fits both categories, like exploring the relationship between the US and North Korea. No matter what, always get your research paper topic approved by your teacher first before you begin writing.

113 Good Research Paper Topics

Below are 113 good research topics to help you get you started on your paper. We've organized them into ten categories to make it easier to find the type of research paper topics you're looking for.

Arts/Culture

• Discuss the main differences in art from the Italian Renaissance and the Northern Renaissance .
• Analyze the impact a famous artist had on the world.
• How is sexism portrayed in different types of media (music, film, video games, etc.)? Has the amount/type of sexism changed over the years?
• How has the music of slaves brought over from Africa shaped modern American music?
• How has rap music evolved in the past decade?
• How has the portrayal of minorities in the media changed?

Current Events

• What have been the impacts of China's one child policy?
• How have the goals of feminists changed over the decades?
• How has the Trump presidency changed international relations?
• Analyze the history of the relationship between the United States and North Korea.
• What factors contributed to the current decline in the rate of unemployment?
• What have been the impacts of states which have increased their minimum wage?
• How do US immigration laws compare to immigration laws of other countries?
• How have the US's immigration laws changed in the past few years/decades?
• How has the Black Lives Matter movement affected discussions and view about racism in the US?
• What impact has the Affordable Care Act had on healthcare in the US?
• What factors contributed to the UK deciding to leave the EU (Brexit)?
• What factors contributed to China becoming an economic power?
• Discuss the history of Bitcoin or other cryptocurrencies  (some of which tokenize the S&P 500 Index on the blockchain) .
• Do students in schools that eliminate grades do better in college and their careers?
• Do students from wealthier backgrounds score higher on standardized tests?
• Do students who receive free meals at school get higher grades compared to when they weren't receiving a free meal?
• Do students who attend charter schools score higher on standardized tests than students in public schools?
• Do students learn better in same-sex classrooms?
• How does giving each student access to an iPad or laptop affect their studies?
• What are the benefits and drawbacks of the Montessori Method ?
• Do children who attend preschool do better in school later on?
• What was the impact of the No Child Left Behind act?
• How does the US education system compare to education systems in other countries?
• What impact does mandatory physical education classes have on students' health?
• Which methods are most effective at reducing bullying in schools?
• Do homeschoolers who attend college do as well as students who attended traditional schools?
• Does offering tenure increase or decrease quality of teaching?
• How does college debt affect future life choices of students?
• Should graduate students be able to form unions?

• What are different ways to lower gun-related deaths in the US?
• How and why have divorce rates changed over time?
• Is affirmative action still necessary in education and/or the workplace?
• Should physician-assisted suicide be legal?
• How has stem cell research impacted the medical field?
• How can human trafficking be reduced in the United States/world?
• Should people be able to donate organs in exchange for money?
• Which types of juvenile punishment have proven most effective at preventing future crimes?
• Has the increase in US airport security made passengers safer?
• Analyze the immigration policies of certain countries and how they are similar and different from one another.
• Several states have legalized recreational marijuana. What positive and negative impacts have they experienced as a result?
• Do tariffs increase the number of domestic jobs?
• Which prison reforms have proven most effective?
• Should governments be able to censor certain information on the internet?
• Which methods/programs have been most effective at reducing teen pregnancy?
• What are the benefits and drawbacks of the Keto diet?
• How effective are different exercise regimes for losing weight and maintaining weight loss?
• How do the healthcare plans of various countries differ from each other?
• What are the most effective ways to treat depression ?
• What are the pros and cons of genetically modified foods?
• Which methods are most effective for improving memory?
• What can be done to lower healthcare costs in the US?
• What factors contributed to the current opioid crisis?
• Analyze the history and impact of the HIV/AIDS epidemic .
• Are low-carbohydrate or low-fat diets more effective for weight loss?
• How much exercise should the average adult be getting each week?
• Which methods are most effective to get parents to vaccinate their children?
• What are the pros and cons of clean needle programs?
• How does stress affect the body?
• Discuss the history of the conflict between Israel and the Palestinians.
• What were the causes and effects of the Salem Witch Trials?
• Who was responsible for the Iran-Contra situation?
• How has New Orleans and the government's response to natural disasters changed since Hurricane Katrina?
• What events led to the fall of the Roman Empire?
• What were the impacts of British rule in India ?
• Was the atomic bombing of Hiroshima and Nagasaki necessary?
• What were the successes and failures of the women's suffrage movement in the United States?
• What were the causes of the Civil War?
• How did Abraham Lincoln's assassination impact the country and reconstruction after the Civil War?
• Which factors contributed to the colonies winning the American Revolution?
• What caused Hitler's rise to power?
• Discuss how a specific invention impacted history.
• What led to Cleopatra's fall as ruler of Egypt?
• How has Japan changed and evolved over the centuries?
• What were the causes of the Rwandan genocide ?

• Why did Martin Luther decide to split with the Catholic Church?
• Analyze the history and impact of a well-known cult (Jonestown, Manson family, etc.)
• How did the sexual abuse scandal impact how people view the Catholic Church?
• How has the Catholic church's power changed over the past decades/centuries?
• What are the causes behind the rise in atheism/ agnosticism in the United States?
• What were the influences in Siddhartha's life resulted in him becoming the Buddha?
• How has media portrayal of Islam/Muslims changed since September 11th?

Science/Environment

• How has the earth's climate changed in the past few decades?
• How has the use and elimination of DDT affected bird populations in the US?
• Analyze how the number and severity of natural disasters have increased in the past few decades.
• Analyze deforestation rates in a certain area or globally over a period of time.
• How have past oil spills changed regulations and cleanup methods?
• How has the Flint water crisis changed water regulation safety?
• What are the pros and cons of fracking?
• What impact has the Paris Climate Agreement had so far?
• What have NASA's biggest successes and failures been?
• How can we improve access to clean water around the world?
• Does ecotourism actually have a positive impact on the environment?
• Should the US rely on nuclear energy more?
• What can be done to save amphibian species currently at risk of extinction?
• What impact has climate change had on coral reefs?
• How are black holes created?
• Are teens who spend more time on social media more likely to suffer anxiety and/or depression?
• How will the loss of net neutrality affect internet users?
• Analyze the history and progress of self-driving vehicles.
• How has the use of drones changed surveillance and warfare methods?
• Has social media made people more or less connected?
• What progress has currently been made with artificial intelligence ?
• Do smartphones increase or decrease workplace productivity?
• What are the most effective ways to use technology in the classroom?
• How is Google search affecting our intelligence?
• When is the best age for a child to begin owning a smartphone?
• Has frequent texting reduced teen literacy rates?

How to Write a Great Research Paper

Even great research paper topics won't give you a great research paper if you don't hone your topic before and during the writing process. Follow these three tips to turn good research paper topics into great papers.

#1: Figure Out Your Thesis Early

Before you start writing a single word of your paper, you first need to know what your thesis will be. Your thesis is a statement that explains what you intend to prove/show in your paper. Every sentence in your research paper will relate back to your thesis, so you don't want to start writing without it!

As some examples, if you're writing a research paper on if students learn better in same-sex classrooms, your thesis might be "Research has shown that elementary-age students in same-sex classrooms score higher on standardized tests and report feeling more comfortable in the classroom."

If you're writing a paper on the causes of the Civil War, your thesis might be "While the dispute between the North and South over slavery is the most well-known cause of the Civil War, other key causes include differences in the economies of the North and South, states' rights, and territorial expansion."

#2: Back Every Statement Up With Research

Remember, this is a research paper you're writing, so you'll need to use lots of research to make your points. Every statement you give must be backed up with research, properly cited the way your teacher requested. You're allowed to include opinions of your own, but they must also be supported by the research you give.

#3: Do Your Research Before You Begin Writing

You don't want to start writing your research paper and then learn that there isn't enough research to back up the points you're making, or, even worse, that the research contradicts the points you're trying to make!

Get most of your research on your good research topics done before you begin writing. Then use the research you've collected to create a rough outline of what your paper will cover and the key points you're going to make. This will help keep your paper clear and organized, and it'll ensure you have enough research to produce a strong paper.

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About 1 in 4 u.s. teachers say their school went into a gun-related lockdown in the last school year.

Twenty-five years after the mass shooting at Columbine High School in Colorado , a majority of public K-12 teachers (59%) say they are at least somewhat worried about the possibility of a shooting ever happening at their school. This includes 18% who say they’re extremely or very worried, according to a new Pew Research Center survey.

Pew Research Center conducted this analysis to better understand public K-12 teachers’ views on school shootings, how prepared they feel for a potential active shooter, and how they feel about policies that could help prevent future shootings.

To do this, we surveyed 2,531 U.S. public K-12 teachers from Oct. 17 to Nov. 14, 2023. The teachers are members of RAND’s American Teacher Panel, a nationally representative panel of public school K-12 teachers recruited through MDR Education. Survey data is weighted to state and national teacher characteristics to account for differences in sampling and response to ensure they are representative of the target population.

We also used data from our 2022 survey of U.S. parents. For that project, we surveyed 3,757 U.S. parents with at least one child younger than 18 from Sept. 20 to Oct. 2, 2022. Find more details about the survey of parents here .

Here are the questions used for this analysis , along with responses, and the survey methodology .

Another 31% of teachers say they are not too worried about a shooting occurring at their school. Only 7% of teachers say they are not at all worried.

This survey comes at a time when school shootings are at a record high (82 in 2023) and gun safety continues to be a topic in 2024 election campaigns .

Teachers’ experiences with lockdowns

About a quarter of teachers (23%) say they experienced a lockdown in the 2022-23 school year because of a gun or suspicion of a gun at their school. Some 15% say this happened once during the year, and 8% say this happened more than once.

High school teachers are most likely to report experiencing these lockdowns: 34% say their school went on at least one gun-related lockdown in the last school year. This compares with 22% of middle school teachers and 16% of elementary school teachers.

Teachers in urban schools are also more likely to say that their school had a gun-related lockdown. About a third of these teachers (31%) say this, compared with 19% of teachers in suburban schools and 20% in rural schools.

Do teachers feel their school has prepared them for an active shooter?

About four-in-ten teachers (39%) say their school has done a fair or poor job providing them with the training and resources they need to deal with a potential active shooter.

A smaller share (30%) give their school an excellent or very good rating, and another 30% say their school has done a good job preparing them.

Teachers in urban schools are the least likely to say their school has done an excellent or very good job preparing them for a potential active shooter. About one-in-five (21%) say this, compared with 32% of teachers in suburban schools and 35% in rural schools.

Teachers who have police officers or armed security stationed in their school are more likely than those who don’t to say their school has done an excellent or very good job preparing them for a potential active shooter (36% vs. 22%).

Overall, 56% of teachers say they have police officers or armed security stationed at their school. Majorities in rural schools (64%) and suburban schools (56%) say this, compared with 48% in urban schools.

Only 3% of teachers say teachers and administrators at their school are allowed to carry guns in school. This is slightly more common in school districts where a majority of voters cast ballots for Donald Trump in 2020 than in school districts where a majority of voters cast ballots for Joe Biden (5% vs. 1%).

What strategies do teachers think could help prevent school shootings?

The survey also asked teachers how effective some measures would be at preventing school shootings.

Most teachers (69%) say improving mental health screening and treatment for children and adults would be extremely or very effective.

About half (49%) say having police officers or armed security in schools would be highly effective, while 33% say the same about metal detectors in schools.

Just 13% say allowing teachers and school administrators to carry guns in schools would be extremely or very effective at preventing school shootings. Seven-in-ten teachers say this would be not too or not at all effective.

How teachers’ views differ by party

Republican and Republican-leaning teachers are more likely than Democratic and Democratic-leaning teachers to say each of the following would be highly effective:

• Having police officers or armed security in schools (69% vs. 37%)
• Having metal detectors in schools (43% vs. 27%)
• Allowing teachers and school administrators to carry guns in schools (28% vs. 3%)

And while majorities in both parties say improving mental health screening and treatment would be highly effective at preventing school shootings, Democratic teachers are more likely than Republican teachers to say this (73% vs. 66%).

Parents’ views on school shootings and prevention strategies

In fall 2022, we asked parents a similar set of questions about school shootings.

Roughly a third of parents with K-12 students (32%) said they were extremely or very worried about a shooting ever happening at their child’s school. An additional 37% said they were somewhat worried.

As is the case among teachers, improving mental health screening and treatment was the only strategy most parents (63%) said would be extremely or very effective at preventing school shootings. And allowing teachers and school administrators to carry guns in schools was seen as the least effective – in fact, half of parents said this would be not too or not at all effective. This question was asked of all parents with a child younger than 18, regardless of whether they have a child in K-12 schools.

Like teachers, parents’ views on strategies for preventing school shootings differed by party. 

Note: Here are the questions used for this analysis , along with responses, and the survey methodology .

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About Pew Research Center Pew Research Center is a nonpartisan fact tank that informs the public about the issues, attitudes and trends shaping the world. It conducts public opinion polling, demographic research, media content analysis and other empirical social science research. Pew Research Center does not take policy positions. It is a subsidiary of The Pew Charitable Trusts .

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A new way to detect radiation involving cheap ceramics

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The radiation detectors used today for applications like inspecting cargo ships for smuggled nuclear materials are expensive and cannot operate in harsh environments, among other disadvantages. Now, in work funded largely by the U.S. Department of Homeland Security with early support from the U.S. Department of Energy, MIT engineers have demonstrated a fundamentally new way to detect radiation that could allow much cheaper detectors and a plethora of new applications.

They are working with Radiation Monitoring Devices , a company in Watertown, Massachusetts, to transfer the research as quickly as possible into detector products.

In a 2022 paper in Nature Materials , many of the same engineers reported for the first time how ultraviolet light can significantly improve the performance of fuel cells and other devices based on the movement of charged atoms, rather than those atoms’ constituent electrons.

In the current work, published recently in Advanced Materials , the team shows that the same concept can be extended to a new application: the detection of gamma rays emitted by the radioactive decay of nuclear materials.

“Our approach involves materials and mechanisms very different than those in presently used detectors, with potentially enormous benefits in terms of reduced cost, ability to operate under harsh conditions, and simplified processing,” says Harry L. Tuller, the R.P. Simmons Professor of Ceramics and Electronic Materials in MIT’s Department of Materials Science and Engineering (DMSE).

Tuller leads the work with key collaborators Jennifer L. M. Rupp, a former associate professor of materials science and engineering at MIT who is now a professor of electrochemical materials at Technical University Munich in Germany, and Ju Li, the Battelle Energy Alliance Professor in Nuclear Engineering and a professor of materials science and engineering. All are also affiliated with MIT’s Materials Research Laboratory

“After learning the Nature Materials work, I realized the same underlying principle should work for gamma-ray detection — in fact, may work even better than [UV] light because gamma rays are more penetrating — and proposed some experiments to Harry and Jennifer,” says Li.

Says Rupp, “Employing shorter-range gamma rays enable [us] to extend the opto-ionic to a radio-ionic effect by modulating ionic carriers and defects at material interfaces by photogenerated electronic ones.”

Other authors of the Advanced Materials paper are first author Thomas Defferriere, a DMSE postdoc, and Ahmed Sami Helal, a postdoc in MIT’s Department of Nuclear Science and Engineering.

Modifying barriers

Charge can be carried through a material in different ways. We are most familiar with the charge that is carried by the electrons that help make up an atom. Common applications include solar cells. But there are many devices — like fuel cells and lithium batteries — that depend on the motion of the charged atoms, or ions, themselves rather than just their electrons.

The materials behind applications based on the movement of ions, known as solid electrolytes, are ceramics. Ceramics, in turn, are composed of tiny crystallite grains that are compacted and fired at high temperatures to form a dense structure. The problem is that ions traveling through the material are often stymied at the boundaries between the grains.

In their 2022 paper, the MIT team showed that ultraviolet (UV) light shone on a solid electrolyte essentially causes electronic perturbations at the grain boundaries that ultimately lower the barrier that ions encounter at those boundaries. The result: “We were able to enhance the flow of the ions by a factor of three,” says Tuller, making for a much more efficient system.

Vast potential

At the time, the team was excited about the potential of applying what they’d found to different systems. In the 2022 work, the team used UV light, which is quickly absorbed very near the surface of a material. As a result, that specific technique is only effective in thin films of materials. (Fortunately, many applications of solid electrolytes involve thin films.)

Light can be thought of as particles — photons — with different wavelengths and energies. These range from very low-energy radio waves to the very high-energy gamma rays emitted by the radioactive decay of nuclear materials. Visible light — and UV light — are of intermediate energies, and fit between the two extremes.

The MIT technique reported in 2022 worked with UV light. Would it work with other wavelengths of light, potentially opening up new applications? Yes, the team found. In the current paper they show that gamma rays also modify the grain boundaries resulting in a faster flow of ions that, in turn, can be easily detected. And because the high-energy gamma rays penetrate much more deeply than UV light, “this extends the work to inexpensive bulk ceramics in addition to thin films,” says Tuller. It also allows a new application: an alternative approach to detecting nuclear materials.

Today’s state-of-the-art radiation detectors depend on a completely different mechanism than the one identified in the MIT work. They rely on signals derived from electrons and their counterparts, holes, rather than ions. But these electronic charge carriers must move comparatively great distances to the electrodes that “capture” them to create a signal. And along the way, they can be easily lost as they, for example, hit imperfections in a material. That’s why today’s detectors are made with extremely pure single crystals of material that allow an unimpeded path. They can be made with only certain materials and are difficult to process, making them expensive and hard to scale into large devices.

Using imperfections

In contrast, the new technique works because of the imperfections — grains — in the material. “The difference is that we rely on ionic currents being modulated at grain boundaries versus the state-of-the-art that relies on collecting electronic carriers from long distances,” Defferriere says.

Says Rupp, “It is remarkable that the bulk ‘grains’ of the ceramic materials tested revealed high stabilities of the chemistry and structure towards gamma rays, and solely the grain boundary regions reacted in charge redistribution of majority and minority carriers and defects.”

Comments Li, “This radiation-ionic effect is distinct from the conventional mechanisms for radiation detection where electrons or photons are collected. Here, the ionic current is being collected.”

Igor Lubomirsky, a professor in the Department of Materials and Interfaces at the Weizmann Institute of Science, Israel, who was not involved in the current work, says, “I found the approach followed by the MIT group in utilizing polycrystalline oxygen ion conductors very fruitful given the [materials’] promise for providing reliable operation under irradiation under the harsh conditions expected in nuclear reactors where such detectors often suffer from fatigue and aging. [They also] benefit from much-reduced fabrication costs.”

As a result, the MIT engineers are hopeful that their work could result in new, less expensive detectors. For example, they envision trucks loaded with cargo from container ships driving through a structure that has detectors on both sides as they leave a port. “Ideally, you’d have either an array of detectors or a very large detector, and that’s where [today’s detectors] really don’t scale very well,” Tuller says.

Another potential application involves accessing geothermal energy, or the extreme heat below our feet that is being explored as a carbon-free alternative to fossil fuels. Ceramic sensors at the ends of drill bits could detect pockets of heat — radiation — to drill toward. Ceramics can easily withstand extreme temperatures of more than 800 degrees Fahrenheit and the extreme pressures found deep below the Earth’s surface.

The team is excited about additional applications for their work. “This was a demonstration of principle with just one material,” says Tuller, “but there are thousands of other materials good at conducting ions.”

Concludes Defferriere: “It’s the start of a journey on the development of the technology, so there’s a lot to do and a lot to discover.”

This work is currently supported by the U.S. Department of Homeland Security, Countering Weapons of Mass Destruction Office. This support does not constitute an express or implied endorsement on the part of the government. It was also funded by the U.S. Defense Threat Reduction Agency.

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After being insulted, writing down your feelings on paper then getting rid of it reduces anger

A research group in Japan has discovered that writing down one's reaction to a negative incident on a piece of paper and then shredding it or throwing it away reduces feelings of anger.

"We expected that our method would suppress anger to some extent," lead researcher Nobuyuki Kawai said. "However, we were amazed that anger was eliminated almost entirely."

This research is important because controlling anger at home and in the workplace can reduce negative consequences in our jobs and personal lives. Unfortunately, many anger management techniques proposed by specialists lack empirical research support. They can also be difficult to recall when angry.

The results of this study, published in Scientific Reports , are the culmination of years of previous research on the association between the written word and anger reduction. It builds on work showing how interactions with physical objects can control a person's mood.

For their project, Kawai and his graduate student Yuta Kanaya, both at the Graduate School of Informatics, Nagoya University, asked participants to write brief opinions about important social problems, such as whether smoking in public should be outlawed. They then told them that a doctoral student at Nagoya University would evaluate their writing.

However, the doctoral students doing the evaluation were plants. Regardless of what the participants wrote, the evaluators scored them low on intelligence, interest, friendliness, logic, and rationality. To really drive home the point, the doctoral students also wrote the same insulting comment: "I cannot believe an educated person would think like this. I hope this person learns something while at the university."

After handing out these negative comments, the researchers asked the participants to write their thoughts on the feedback, focusing on what triggered their emotions. Finally, one group of participants was told to either dispose of the paper they wrote in a trash can or keep it in a file on their desk. A second group was told to destroy the document in a shredder or put it in a plastic box.

The students were then asked to rate their anger after the insult and after either disposing of or keeping the paper. As expected, all participants reported a higher level of anger after receiving insulting comments. However, the anger levels of the individuals who discarded their paper in the trash can or shredded it returned to their initial state after disposing of the paper. Meanwhile, the participants who held on to a hard copy of the insult experienced only a small decrease in their overall anger.

Kawai imagines using his research to help businesspeople who find themselves in stressful situations. "This technique could be applied in the moment by writing down the source of anger as if taking a memo and then throwing it away when one feels angry in a business situation," he explained.

Along with its practical benefits, this discovery may shed light on the origins of the Japanese cultural tradition known as hakidashisara ( hakidashi refers to the purging or spitting out of something, and sara refers to a dish or plate) at the Hiyoshi shrine in Kiyosu, Aichi Prefecture, just outside of Nagoya. Hakidashisara is an annual festival where people smash small discs representing things that make them angry. Their findings may explain the feeling of relief that participants report after leaving the festival.

• Anger Management
• Social Psychology
• Disorders and Syndromes
• Educational Psychology
• Consumer Behavior
• Anger management
• Social psychology
• Cognitive dissonance
• Self-awareness
• Obsessive-compulsive disorder
• Collaboration

Story Source:

Materials provided by Nagoya University . Note: Content may be edited for style and length.

Journal Reference :

• Yuta Kanaya, Nobuyuki Kawai. Anger is eliminated with the disposal of a paper written because of provocation . Scientific Reports , 2024; 14 (1) DOI: 10.1038/s41598-024-57916-z

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Vegan diet: nutritional components, implementation, and effects on adults’ health

Edyta Łuszczki.

1 Institute of Health Sciences, Medical College of Rzeszów University, Rzeszów, Poland

Faustina Boakye

Magdalena zielińska, katarzyna dereń, anna bartosiewicz, Łukasz oleksy.

2 Faculty of Health Sciences, Department of Physiotherapy, Jagiellonian University Medical College, Kraków, Poland

Artur Stolarczyk

3 Orthopedic and Rehabilitation Department, Medical University of Warsaw, Warsaw, Poland

Vegan diet has emerged as a popular dietary choice for people worldwide in recent times, due to concerns such as health issues, animal rights and welfare, and the sustainability of the environment. The purpose of this literature review was to explain how a vegan diet may affect the health of adults and to point out beneficial components found in it as well as any difficulties associated with its implementation. Evidence supports that a vegan diet can reduce the risk of chronic diseases, such as type 2 diabetes, hypertension, and certain types of cancer. A well-planned vegan diet must include adequate calories and nutrients, as well as the necessary supplements, such as vitamin B12, vitamin D and EPA/DHA. Given the current growing interest in plant-based diets among the general population, it is crucial to understand both the barriers, risks, and benefits of the vegan diet among physicians, policy makers, and the general population.

1. Introduction

1.1. topic overview.

Vegan diet has become a popular diet choice for people around the world, in recent times, due to concerns such as health issues, animal rights and welfare, and sustainability of the environment ( 1 ). A recent nutrition report from Germany stated that the number of vegetarians and vegan shaved doubled from pre-COVID (5%) to post-COVID (10%) ( 2 ). The prevalence of vegans in Europe has been estimated to be between 1 and 10% ( 3 ). Over the years, research has explored the nutritional benefits of a vegan diet and its potential effects on health and well-being. A well-planned vegan diet contains only plant-derived foods, such as fruits, vegetables, legumes, grains, seeds, and nuts ( 4 ). While these natural sources offer a myriad of essential nutrients, special attention must be paid to certain key components that may be more difficult to obtain solely from plant-based sources. To prevent deficiencies and ensure overall health and well-being, particular attention must be paid to nutrients such as protein, iron, calcium, vitamin B12, vitamin D, and omega-3 fatty acids with a very long chain in a vegan diet ( 5 ). As adults cultivate a vegan lifestyle, their dietary choices can substantially affect their health ( 6 ). Many studies have identified that a well-planned vegan diet can provide numerous health benefits. Evidence supports that a vegan diet may reduce the risk of chronic diseases, such as type 2 diabetes, hypertension, and certain types of cancer ( 5 ). Research conducted in Adventists has presented convincing evidence that adequately balanced vegan diets are nutritionally sufficient ( 7 ). On the contrary, inadequate intake of critical nutrients, such as vitamin B12 and iron, can lead to anemia and other health complications if not addressed or attended appropriately ( 8 ). The plant-based diet index has been developed to assess intakes of both plant and animal foods, considering the quality of plant foods: overall plant-based diet index (PDI), healthful plant-based diet index (hPDI), and unhealthful plant-based diet index (uPDI). All indices negatively weigh animal foods, but differently weigh plant foods depending on their nutritional quality ( 9 ). Previous studies have reported that hPDI was associated with a lower risk of cardiovascular disease or type 2 diabetes ( 10 , 11 ).

Central to the interest in the vegan diet lies its foundation in plant-based foods, which are abundant in a diverse array of bioactive components. These constituents contribute to the potential influence of the diet on health, especially in adults ( 12 ). Bioactive components are inherent compounds within plant foods, which extend their impact beyond basic nutrition ( 13 ). Functioning as key regulators, these bioactive components modulate physiological processes and are associated with a spectrum of positive health advantages, such as antioxidant, anti-inflammatory, and anticarcinogenic properties ( 13 ). Flavonoids have positive effects on cardiovascular health and anti-cancer properties. Carotenoids exert protective effects against several types of cancers, in addition to their benefits for vision and skin. Glucosinolates have protective roles against cancer and dementia ( 13 ).

Research has indicated that a well-planned vegan diet can confer improved health benefits while aligning with principles that favor ethical and environmental concerns ( 6 ). However, certain knowledge gaps must be explored. By extensively exploring the nutritional components of a vegan diet and their implications for well-being, individuals, especially adults, can make informed choices about adhering to a vegan lifestyle. This article analyses the essential aspects of a well-planned vegan diet, while concentrating on its nutritional components, health effects in adults, and specific nutrients that require careful consideration to ensure the maintenance of optimal health. Therefore, the purpose of this review of the literature was to explain how a vegan diet may affect the health of adults and to point out the beneficial components found in it, as well as any difficulties associated with its implementation.

2. Materials and methods

The article is of a narrative review nature. The main objective of this study was to review scientific publications in order to establish relationships arising from the adoption of a vegan diet among adults. Attention was focused on the beneficial components present in the vegan diet and their impact on health, the appearance of vitamin deficiencies, and the challenges associated with adhering to this type of diet.

The following source selection criteria were applied: studies related to the adoption of a vegan diet among individuals aged 40–85 years, encompassing randomized clinical trials, observational studies, meta-analyses, systematic reviews, as well as documents containing recommendations and guidelines.

General reviews, case studies, articles not published in the English language, and studies involving pregnant and breastfeeding women and athletes were excluded from the review.

The following databases were utilized: PubMed, Science Direct, Web of Science, Scopus, Google Scholar, CINAHL, Web of Knowledge, Medline, PsycINFO. The search process employed the following words, phrases, and sentences in accordance with the content and purpose of the study: “vegan diet,” “adults,” “bioactive compounds,” “health,” “plant sources,” “carotenoids,” “antioxidants.”

In total, 155 literature sources were collected.

3. An explanation of the vegan diet

It should be noted that the various types of diet that exist are identified and distinguished by the items that are included and excluded ( 12 ). According to Jakše et al., a vegan diet can be described as one excludes any foods derived from animals but is rich in foods from various plant-based dietary groups, such as fruits and vegetables, grains, legumes, nuts, etc. and the vegan diet is the most stringent version of a plant-based diet ( 4 ). Insights collected from previous research indicate that a carefully structured vegan diet can lead to notable health benefits, as the components of food typically contain essential components vital for well-being ( 4 ).

4. Substances/compounds present in vegan diet

4.1. dietary fiber.

Dietary fiber is an integral component of the vegan diet, offering multifaceted contributions to human health. Dietary fiber resists digestion within the gastrointestinal tract ( 12 ), providing a range of physiological benefits that encompasses the modulation of digestion, absorption of nutrients, and impact on gut microbiota ( 14 ). Depending on how well fibers dissolve in water, they can be classified as soluble or insoluble ( 15 ). Soluble fiber, found in foods like fruits, oats, and beans, dissolves in water to create viscous substances. This property contributes to slowing digestion and increasing satiety ( 16 ). On the other hand, insoluble fiber, prevalent in whole grains and vegetables, adds bulk to fecal matter, thereby facilitating regular bowel movements and preventing constipation ( 14 ). The mechanisms through which dietary fiber exerts its health effects are well-established. Soluble fiber forms a gel-like matrix within the digestive tract, delaying stomach emptying and retarding glucose absorption, thus supporting blood glucose regulation ( 17 ). Furthermore, dietary fiber has a positive influence on gut microbiota. The interaction between dietary fiber and gut microbiota involves a fermentation process. Bacterial fermentation of fibers, including resistant starch, some simple sugars, and polysaccharides, leads to the production of short-chain fatty acids (SCFAs) like acetate, propionate, and butyrate. These SCFAs play an essential regulatory role in lipid metabolism, cholesterol and glucose regulation, anti-inflammatory responses, immune functions, and the maintenance of the integrity of the gut barrier ( 18 , 19 ). These SCFAs create an environment conducive to the growth of beneficial bacteria such as Lactobacillus and Bifidobacteria . These bacteria thrive on SCFAs and utilize saccharide metabolism to compete effectively with harmful bacteria for resources ( 18 ). These microbial byproducts, along with other bioactive compounds formed through the fermentation or degradation processes driven by gut microbiota, not only provide vital sustenance for the growth of gut microbes but also exhibit the capacity to influence diverse pathways within the intestines, liver, and pancreas, thereby contributing to the overall enhancement of gut health ( 20 ).

SCFAs offer a broad spectrum of health-enhancing effects, acting as anti-inflammatory agents by regulating cytokine production and immune cell functions. In colon cancer cells, they demonstrate properties that counteract carcinogenesis by influencing acetylation and activating G protein-coupled receptors (GPCRs); they also share associations with microRNAs and Vascular Endothelial Growth Factor (VEGF) ( 19 ). In particular, SCFAs play a vital role in preserving the integrity of the intestinal barrier by coordinating the expression of tight junction proteins. Furthermore, they contribute to alleviating oxidative stress by regulating oxidoreductase activity, promoting nuclear factor erythroid 2-related factor 2 (Nrf2), and reducing reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels ( 19 ). Disruption in the equilibrium of the gut microbiota can result in impairment of the intestinal barrier, thereby increasing susceptibility to particular diseases ( 21 ). Simultaneously, microbial byproducts like short-chain fatty acids and other bioactive constituents, generated through the fermentation or breakdown processes facilitated by gut microbiota, serve as essential nourishment for the proliferation of gut microbes. Furthermore, these compounds have the potential to influence various pathways within the intestines, liver, and pancreas, ultimately contributing to improved intestinal health ( 22 ).

Based on findings from a study exploring the association of dietary type with fecal microbiota and short chain fatty acids in vegans and omnivores, it was observed that individuals following the vegan diet showed a distinctive composition of gut microbiota, characterised by increased amounts of Firmicutes and Bacteroidetes ( 23 ). In the study by Reiss et al., Firmicutes and Bacteroidetes were shown to make up about 95–97.7% of the total gut microbiota in vegans and omnivores, with Firmicutes contributing around 59% and Bacteroidetes contributing 39% to the total gut microbiota in vegan ( 23 ). Compared to omnivorous diets, vegan diets are generally richer in fiber and contain less saturated fat and protein. Long-term vegetable intake has been shown to correlate with gut microbiota diversity, and higher fiber intake increases the prevalence of microorganisms associated with a healthy gut ( 24 ).

Another study investigated the interaction between dietary fiber intake and microbial diversity within diverse diet patterns, including the vegan diet. Although there was no notable variation in microbial abundance between diets, the study found that people following a vegan diet exhibited reduced microbial diversity compared to those consuming a western diet. Subsequent analysis of beta diversity indicated discernible differences in the composition of gut microbiota, regardless of fiber intake levels. Notably, within the vegan group, both high and low fiber intake led to unique microbial compositions compared to the Western Diet. These findings underscore the collaborative impact of diet composition and fiber intake on the diversity of the gut microbiota, highlighting the need to consider both aspects in understanding interactions between diet and gut microbiota ( 25 ). The study emphasizes the importance of considering diet quality, aligning with a research that underscores the role of incorporating whole foods and dietary fiber to foster improved and holistic health results ( 8 ).

Consequently, this mechanism forms a protective barrier against the invasion and proliferation of pathogenic bacteria, contributing to the establishment of a healthier and more balanced gut microbial community ( 5 ). Insoluble fiber, due to its bulk-enhancing effect, accelerates intestinal transit and prevents constipation, functioning through the mechanical stimulation of regular bowel movements and the maintenance of gut motility ( 26 ). The role of dietary fiber in mitigating constipation has been established. A randomized controlled trial that administered a “vege powder” comprising whole grains, broccoli and chicory to constipated participants showed improved symptoms, including increased defecation frequency, softer stool, and reduced strain ( 14 ). Additionally, dietary fiber has demonstrated efficacy in enhancing insulin sensitivity and overall metabolic health. According to Barber et al., an observational study highlighted an association between increased dietary fiber ratio and a significant reduction in HbA1C, when compared to general carbohydrate intake ( 14 ). A double-blind, randomized, placebo-controlled trial suggested the potential for fiber as a complement to lifestyle and/or pharmaceutical interventions for managing type 2 diabetes including improved HbA1c ( 27 ). Dietary fiber offers an array of critical functions within the context of a vegan diet. Its contributions include weight management, lowered cholesterol levels, stabilized blood glucose levels, and improved digestive health ( 4 ). A randomized controlled trial comparing the effectiveness of different plant-based diets for weight loss investigated how various diets influenced weight loss and dietary behaviors, revealing significant insights. Diets did not emphasize caloric restriction. During 6 months, participants adhering to a vegan diet exhibited the most substantial weight loss (−7.5% ± 4.5%), surpassing the other diet groups. This weight loss trend was statistically significant at 2 months ( p < 0.01) and 6 months (p < 0.01). Notably, the vegan group showed significant increases in fiber intake compared to other groups at 2 months (p < 0.01), underscoring the potential impact of dietary fiber, particularly within vegan diets, on weight loss outcomes. These results underscore the importance of incorporating fiber-rich diet choices, such as those of a vegan diet, to promote successful weight management ( 28 ).

Furthermore, in a prospective study investigating the effects of changes in the diet pattern on diabetes risk, the exclusion of individuals with existing diabetes, elevated fasting blood glucose, a history of cancer, coronary heart disease, stroke, and alcohol / cigarettes led to a final analysis of 2,918 participants. Within this group, nonvegetarians demonstrated higher BMI, waist circumference, and fasting blood glucose levels. During a 5.2-year period, 183 participants developed diabetes. In particular, both people who consistently followed high-fiber diets and those who recently switched to such diets exhibited a remarkable 40–60% decrease in risk of diabetes compared to non-vegetarians. This protective effect of embracing a high fiber diet was particularly pronounced among those with healthier metabolic profiles. The robustness of these findings was consistently supported by sensitivity analyses. Taken together, the evidence from this study underscores the potential of adopting a high-fiber diet, whether through ongoing adherence or conversion, to significantly mitigate the risk of diabetes ( 29 ).

This makes a vegan diet particularly advantageous for adults who may be susceptible to various chronic diseases and disorders.

4.2. Bioactive components

Plants contain essential minerals necessary for a well-balanced human diet, along with other primary and secondary metabolites that affect both nutrition and health ( 12 ). Plant foods serve as abundant reservoirs of nutrients such as magnesium, calcium, potassium, minerals, and vitamins, and bioactive elements such as polyphenols, dietary fiber, and carotenoids. For antioxidants, their health benefits have been well established. Antioxidants are compounds in plants that counteract the harmful effects of oxidative stress, protecting cells from free radical damage. They can be obtained from the phenolic components of plants ( 12 ). The role of antioxidants in mitigating damage caused by free radicals has been extensively studied. The consumption of a large number of plant-based foods in the diet reveals this significant benefit ( 30 ). Consuming plant foods rich in antioxidants has been associated with reduced risk against various diseases such as cancer, cardiovascular disease, and type 2 diabetes ( 30 ). A study conducted by Miller et al. (2017) investigated a cohort of 135,335 younger and older adults from 18 different countries. The findings of this study indicated a significant link between a diet rich in fruits, vegetables, and legumes and a decreased susceptibility to cardiovascular-related mortality. The observation of this study implies that the phytochemicals in these plant-based foods could play a role in mitigating diabetes and decreasing susceptibility to cardiovascular diseases. These potential mechanisms include the regulation of α-glucosidase and lipase activities, the postprandial decrease in blood glucose levels, anti-inflammatory effects, enhancement of pancreatic function, and potential synergistic interactions with hypoglycemic medications ( 30 ). Vegan diets play a vital role in counteracting the detrimental effects of free radicals and ROS by harnessing robust antioxidant capacities. Abundant in antioxidants, the vegan diet effectively combats harm related to oxidative stress, promotes cellular health, and reduces susceptibility to chronic diseases ( 31 ). Antioxidants also regulate immune processes, reduce DNA damage, and reduce lipid peroxidation, all of which contribute to better health ( 13 ). By donating electrons, antioxidants disrupt the chain reaction of oxidation, effectively mitigating cellular damage ( 26 ). Within a vegan diet, a variety of diverse antioxidants, including vitamins C and E, polyphenols, and carotenoids, collaborate synergistically to counteract the formation of ROS arising from multiple origins such as metabolic processes, lifestyle activities, and environmental elements. This holistic defensive mechanism offers robust protection against the aforementioned diseases ( 26 ). In addition to scavenging free radicals, research has shown that antioxidants in fruits and vegetables are responsible for the expression of genes through transcription factors, cell signaling modulation, and enzyme activities. These antioxidant properties can be linked a reduction in oxidative stress, improved cell function, and a lower risk of chronic diseases ( 30 ). Carotenoids represent another group of bioactive compounds found in a vegan diet. Fruits and vegetables that are yellow or orange possess this bioactive compound ( 32 ).

Carotenoids are known for their diverse health-promoting characteristics, including anti-cancer, anti-inflammatory, anti-aging and anti-microbial traits ( 12 ). They eliminate free radicals by neutralising them and blocking lipid peroxidation, which is associated with cell damage ( 33 ). In particular, carotenoids serve as precursors to vitamin A, which is a crucial fat-soluble vitamin with various functions in maintaining health and immune function ( 34 ). Vitamin A is known to regulate the differentiation and proliferation of immune cells, thus affecting the immune response ( 33 ). Furthermore, it has been postulated that they can interact with nuclear receptors, such as retinoic acid receptors, influencing gene expression involved in inflammation and immune function. Through conversion to vitamin A, they are recognized for their pivotal role in the health and functionality of photoreceptor cells in the eyes, for good vision ( 33 ). In a study with 74 participants having type 2 diabetes, an 8-week fruit and vegetable (F&V) intervention significantly increased carotenoid levels, including α -carotene, β -cryptoxanthin, lutein, and zeaxanthin ( p < 0.05). These increases, ranging from ~8% to ~25%, were evident in both serum and HDL fractions. The results suggest that elevated F&V intake may enhance HDL’s antioxidant properties through an increase in carotenoid content ( 35 ). Polyphenols are another set of bioactive compounds present in plant foods. They are distinguished by the presence of various phenol groups in their chemical structures. These naturally occurring bioactive compounds are synthesized by plants as secondary metabolites. Polyphenols can be classified into four main classes, namely flavonoids, phenolic acids, lignans, and stilbenes, according to their structural characteristics ( 16 ). Numerous in vitro studies have highlighted the substantial antioxidant capacity of polyphenols, a result of their facilitation of ROS neutralization. This pronounced antioxidant potential, combined with its ability to support nitric oxide (NO) production, contributes to the protection of endothelial function of polyphenols. Furthermore, polyphenols contribute to improving cardiovascular health by inhibiting platelet aggregation, mitigating vascular inflammation, facilitating apoptosis, reducing LDL cholesterol oxidation, and improving lipid profiles ( 16 , 36 ). Investigating the effects of bioactive compounds, a study explored the potential cardiovascular benefits of olive oil polyphenols, yielding significant insights into LDL-related health outcomes. This 3-weeks randomized controlled trial in Men investigated the effects of olive oil polyphenols on health. The intervention led to reduced LDL concentrations, including apolipoprotein B-100 (apo B-100) levels a crucial component of LDL, which has a history of being associated with atherosclerosis and cardiovascular risk, making the reduction in apo B-100 levels a significant finding and total LDL particles, compared to low-polyphenol olive oil ( p = 0.004 and p = 0.013, respectively). Notably, the high-polyphenol olive oil intervention also lowered the number of small LDL particles ( p = 0.029) and increased LDL resistance against oxidation ( p = 0.038), suggesting potential cardiovascular benefits by improving LDL-related health outcomes ( 37 ).

Another study was conducted to compare polyphenol intakes according to different food patterns and food sources in the Adventist Health Study-2 cohort. Among the dietary groups examined, vegans emerged as having the most substantial polyphenol intake. This elevated intake among vegans was statistically significant ( p < 0.05). These observations emphasize the potential of a vegan dietary approach to offer increased polyphenol consumption, underscoring its relevance in the intake of bioactive compounds ( 38 ). Furthermore, exploring the effects of polyphenols, a study investigated the influence of strawberry and cranberry polyphenols (SCP) on parameters such as insulin sensitivity, glucose tolerance, insulin secretion, lipid profile, inflammation, and markers of oxidative stress in individuals with insulin resistance, overweight, or obesity. The trial included participants with similar baseline characteristics. In particular, the SCP group demonstrated a significant 14% increase in insulin sensitivity ( p = 0.05), while the control group showed a nonsignificant decrease of 7% ( p = 0.28). This improvement in insulin sensitivity within the SCP group was statistically significant in contrast to the control group ( p = 0.03). Although the responses to glucose, insulin, and free fatty acids aligned between the groups, the SCP beverages contributed to higher levels of specific phenolic metabolites in plasma. Of particular interest was the discovery of a significant negative correlation between plasma p-coumaric acid concentration and changes in the response to C-peptides during the oral glucose tolerance test (OGTT) ( p = 0.0046, r^2 = 0.34). This observation suggests a potential association between different phenolic metabolites arising from SCP consumption and the improvement of insulin sensitivity ( 39 ). Another study also highlighted the effects of polyphenols on health. The objective was to investigate the effects of polyphenols and omega-3 fatty acids (LCn3) on various health markers. To achieve this, participants were randomly assigned to one of four nutritional isoenergetic interventions for 8 weeks: a control diet low in LCn3s and polyphenols; a diet rich in LCn3s and low in polyphenols; a diet rich in polyphenols and low in LCn3s; or a diet rich in both LCn3s and polyphenols. Throughout the controlled diet interventions, the experimental groups showed significant variations in polyphenol and LCn3 content. The baseline characteristics were consistent among all groups. Fasting levels of lipids, cholesterol, and glucose did not show notable differences. Body weight remained steady throughout the intervention, with slight reductions in the high-LCn3 group. Waist circumference changes were insignificant. Polyphenols appeared to significantly lower fasting triglycerides and cholesterol in larger lipoprotein fractions, while omega-3 fatty acids (LCn3) did not produce significant effects. After meals, lipid and lipoprotein levels improved, mainly due to the impact of polyphenols on triglycerides. Furthermore, markers of oxidative stress, such as 8-isoprostane, decreased significantly in the high-polyphenol groups. Interestingly, the effects of diets naturally rich in polyphenols and/or marine LCn3s on urinary 8-isoprostane were correlated with changes in plasma lipoproteins, particularly in polyphenol-rich groups ( 39 , 40 ).

Polyphenols have the ability to modulate enzyme and anticancer activities and metal chelation, all of which contribute to their intrinsic characteristic of reducing the occurrence of chronic diseases ( 41 ). They prevent cytokines from binding to cancer cells and prevent oxidative stress, thus protecting against cancer ( 42 ). Certain types of polyphenols found in varieties such as green and black tea exhibit the ability to inhibit the growth of harmful bacteria such as Helicobacter pylori, Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, Salmonella typhimurium, and Pseudomonas aeruginosa ( 20 ).

Another substance, ferulic acid, is a phenolic acid of the polyphenol family, found more commonly in plant-based foods such as cereals, fruits, and vegetables. It has antioxidant qualities that can help prevent many chronic diseases ( 36 ). Anthocyanins have also been found to have great antioxidant properties. They support health by controlling metabolic syndromes and neurological diseases ( 12 ). Anthocyanins exhibit the ability to form complexes with metal ions, reducing the catalytic influence of active metal ions on the generation of free radicals. This interaction contributes to an elevated antioxidant effect. In addition, anthocyanins can form complexes with copper, effectively inhibiting the oxidation of LDL induced by copper or proxy radicals ( 41 ). Vitamin C (ascorbic acid) and vitamin E (tocopherols) represent two potent antioxidants obtained primarily through the consumption of fruits and vegetables ( 12 ). Vitamin C is recognized for its involvement in cellular signaling, programmed cell death (apoptosis), and the maintenance of cell growth. Vitamin C is also a premier water-soluble antioxidant – it also functions to recycle vitamin E (e.g., reduction to active form). Vitamin E, a fat-soluble micronutrient, is involved in DNA protection and has been suggested to play a pivotal role in mitigating the reactivity of redox-active metals, such as copper and iron. In addition, vitamin E contributes to protecting against lipid peroxidation, which exemplifies its multifaceted functions in maintaining cellular health ( 34 ).

5. The health benefits of a vegan diet

5.1. overweight and obesity prevention.

Numerous studies have shown how vegan diets affect body composition, particularly when it comes to losing weight ( 31 ). Vegan diets likely lead to weight loss because they are associated with a reduced calorie intake due to a lower fat content and a higher dietary fiber content. Calorie density is very important for reducing body weight. Consuming foods with lower calories is more advantageous for weight loss than reducing portion sizes ( 30 ). Foods of plant origin have a lower calorie density than foods of animal origin ( 43 ). Data from the Adventist Health Study (AHS) have shown that the body mass index (BMI) increases as the amount of animal foods in the diet increases ( 44 ). Furthermore, results from the European Prospective Investigation into Cancer and Nutrition – Oxford (EPIC-Oxford) study have shown that vegans gain significantly less weight as they age compared to omnivores ( 45 ). The European Prospective Investigation into Cancer and Nutrition-Physical Activity, Nutrition, Alcohol, Cessation of Smoking, Eating Out of Home and Obesity (EPIC-PANACEA) study, found a positive association between total meat consumption and weight gain, even after adjusting for energy intake: an increase in 250 g/day of meat led to a weight gain of 2 kg after 5 years (95% CI, 1.5–2.7 kg) ( 46 ). In a study that examined a cohort of 49,098 Taiwanese adults, the percentage of participants with a BMI ≥ 27 kg/m2 was significantly lower among those following a vegetarian diet (10.9%) as compared to those following a non-vegetarian diet (15.4%). Furthermore, this study also found that for each year on a vegan diet, the risk of obesity decreased by 7% ( 47 ).

Vegan diets have been shown to have the lowest calorie density and the least amount of cholesterol among various plant-based diets ( 41 ). According to a study conducted by Kahleova et al. overweight participants with a body mass index between 28 and 40 kg/m2 were randomly assigned to follow a low-fat vegan diet in a randomized clinical trial ( 48 ). According to the study findings, the overweight group assigned to a vegan diet experienced a considerable decrease in fat mass and visceral fat compared to the control group. Research has shown that a vegan diet can help adults lose weight by replacing high-calorie items with low-calorie alternatives and maintaining a balance between energy intake and energy expenditure ( 40 ). Based on available evidence, the vegan diet should be considered a viable option for patients who are interested in preventing overweight and obesity or losing weight. Researchers report that a vegan diet is generally associated with a healthy lifestyle that excludes smoking and includes regular physical activity. It is very likely that the health benefits from such nutritional behavior are the result of the combination of these factors, and not only the diet alone. Such a lifestyle provides many benefits and can prevent some chronic lifestyle-associated diseases, including obesity and cardiovascular diseases (CVD).

5.2. Cardiovascular diseases (CVD)

Cardiovascular disease is a major cause of mortality and is currently responsible for a third of all deaths worldwide ( 1 ). CVD is a collection of different conditions that are directly related to the health of the heart. These include arteriosclerosis, arterial stenosis, arterial thrombosis, coronary heart disease and high blood pressure ( 49 ). Plant-based diets reduce CVD risk factors, as confirmed by a meta-analysis and systematic review of prospective cohort studies by Quek et al. in which they show a beneficial effect of plant-based diets in terms of reducing cardiovascular mortality and CVD ( 50 ). However, specifically in the context of a vegan diet, the systematic review by Kaiser et al. evaluated the usefulness of vegan diets in the prevention of cardiovascular disease ( 51 ). The evidence among the Western populations studied weakly suggests an association between vegan diets and the risk of cardiovascular disease. The risk of total CVD, coronary heart disease, acute myocardial infarction, primary stroke, haemorrhagic stroke and ischaemic stroke was assessed. None of the trials found a significantly increased or decreased risk of any cardiovascular complication in people who followed a vegan diet. The authors noted that due to the limited number of high-quality studies, the overall evidence on the role of a vegan diet in the development or prevention of CVD is weak ( 51 ). In this year’s systematic review and meta-analysis of prospective cohort studies, Dybvik et al. observed an 18% reduction in the relative risk of ischaemic heart disease among vegans. No clear association was observed between vegan diets and CVD or stroke. The authors indicated that the number of studies was limited and the associations unclear and imprecise ( 52 ).

Benefits of vegan diets can include reduced inflammation, blood pressure, total cholesterol, serum glucose, improved endothelial function, reduced risk of blood clots, reduction in body weight, etc. ( 53 , 54 ). These beneficial cardiovascular health results can be attributed to a lower intake of dietary cholesterol, saturated fat, trans fatty acids, processed meat, and a higher and more regular intake of fibre, vegetable protein, beta-carotene, vitamin C, vitamin K, folic acid and magnesium and potassium ( 53 ). The study by Pickering et al. highlights the importance of potassium and magnesium for the health of the cardiovascular system ( 55 ). The main role of potassium in the prevention of cardiovascular disease is due to its influence on maintaining electrolyte balance, reducing blood pressure, and the risk of stroke through its beneficial effects on endothelial function and vascular homeostasis, while magnesium is involved in the regulation of blood pressure and metabolism. It is worth noting that the balance between potassium and sodium is of crucial importance for the health of the cardiovascular system ( 56 ).

In particular, the soluble fiber fraction, through its effects on lowering total cholesterol and low-density lipoprotein (LDL) levels, better glycaemic control, weight loss, and reduced inflammation, provides a number of health benefits in the context of CVD risk reduction ( 57 ). According to Pereira et al. an increase in soluble fiber intake of 10 g per day can reduce the risk of a coronary event by 14% and the risk of coronary death by 27% ( 58 ). Furthermore, the above fiber fraction may have an effect on the production of short-chain fatty acids (SCFAs) in the colon, which in turn may potentially have an effect on cholesterol synthesis ( 59 ). Nevertheless, it is worth noting that in the systematic review and meta-analysis by Wang et al. vegetarian diets were effective in lowering blood levels of total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and non-high-density lipoprotein cholesterol to a greater extent than control diets; however, it is unclear whether vegan diets have a similar effect ( 60 ). A vegan diet seems to exhibit greater efficacy in reducing overall and LDL cholesterol when compared to omnivorous control diets; nevertheless, its impact on HDL cholesterol and triglyceride levels remains inconclusive ( 61 ).

Vegan diets are also rich in polyphenols, which is relevant in relation to cardiovascular disease. The antioxidant capacity of polyphenolic compounds is known from in vitro studies, mainly through their role in the capture and neutralization of free oxygen and nitrogen species and protection against oxidative stress. This antioxidant capacity, possibly together with their ability to modulate nitric oxide (NO) production, enables polyphenolic compounds to contribute to the maintenance of vascular homeostasis. Through their role in inhibiting platelet aggregation, reducing vascular inflammation, modulating apoptotic processes, reducing LDL oxidation, and improving the lipid profile, polyphenols can also contribute to cardiovascular health ( 62 ).

The gut microbiome is another emerging pathway through which a healthy plant-based diet may influence the risk of CVD ( 63 ). Microorganisms in the gut metabolize a variety of dietary substrates, which can have an impact on cardiovascular health ( 64 ). The trimethylamine N-oxide (TMAO) pathway is an example. Choline and L-carnitine, compounds derived mainly from animal-based foods such as red meat, poultry, and fish, are broken down by microbes in the gut to produce trimethylamine (TMA), which is further broken down in the liver to form TMAO. Associated with an increased risk of cardiovascular events, TMAO is believed to affect heart health through cholesterol and sterol metabolism, inflammation, thrombotic, and atherosclerotic pathways ( 65 ). As a recent study did not find an association between TMAO and dietary factors, it is possible that the association of animal foods with heart disease risk through the TMAO pathway is modified by eating foods rich in TMAO precursors and by gut microbial composition ( 66 ). Certain phytochemicals (e.g., resveratrol) have been found to potentially inhibit TMAO production in animal model studies ( 67 ). Plant-based diets also differ from animal-based diets in several other microbiota-dependent metabolic pathways, including increased metabolism of dietary fiber and polyphenols, and decreased metabolism of bile acids and amino acids, which may mediate links to cardiovascular disease. To elucidate the likely complex pathways by which diet interacts with the intestinal microbial environment to influence cardiovascular health, larger studies with longer follow-up and repeated assessment of diet and microbiome are needed.

There are also limitations and risks associated with following a vegan diet for cardiovascular health, especially if the diet is poorly balanced, as vegans may have lower amounts of dietary nutrients such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), selenium, zinc, iodine, iron, calcium and vitamin B12, vitamin D, compared to non-vegans, which can lead to adverse cardiovascular effects ( 68 , 69 ). Van Winckel et al. stress that it is important to understand that both an unhealthy diet and a vegan diet can induce chronic inflammation, if the vegan diet contains insufficient amounts of nutrients and omega-3 fatty acids ( 70 ). One of the many issues in the context of vitamin B12 deficiency in a vegan diet is the risk of leading to hyperhomocysteinemia. As a result of reduced vascular elasticity and altered homeostasis, elevated levels of homocysteine induce vascular endothelial impairment. This is an important risk factor for CVD ( 44 ). It is also worth mentioning the problem of consuming large amounts of processed plant products in a vegan diet, meat substitutes and dairy substitutes, which can be high in sugars, salt, and trans fatty acids ( 71 , 72 ).

Most short-term studies on vegan diets do not provide accurate data on long-term effects on cardiovascular health, based mainly on changes in biomarkers. Following a vegan diet also brings about a number of health benefits in terms of cardiovascular disease, but is also associated with the risk of nutrient deficiencies. It seems that a well-balanced vegan diet, rich in high-quality plant-based foods such as whole grains, fruits, vegetables and nuts, based on unprocessed products, together with supplementation (for example, an algae-based DHA supplement in addition to regular consumption of sources of ALA and vitamin B12, vitamin D) may be considered a suitable route to the prevention of cardiovascular disease, but more research on this issue is needed ( 49 , 62 ). Although it requires more research and a personalized diet approach, a vegan diet may not only benefit heart health, but may also have the potential to regulate blood glucose levels and manage diabetes mellitus.

5.3. Diabetes mellitus

A chronic metabolic disorder called diabetes mellitus is characterised by persistently high blood glucose levels, insulin resistance, and insufficient amounts of insulin compared to physiological requirements. Due to the decreased sensitivity of the body to insulin hormone, which controls blood glucose levels, and the pancreas’ insufficient ability to produce enough insulin to compensate for this resistance, this syndrome develops ( 73 ).

The global diabetes prevalence in 20–79 year olds in 2021 was estimated to be 10.5% (536.6 million people), rising to 12.2% (783.2 million) in 2045. Just over half a billion people are living with diabetes worldwide which means that over 10.5% of the world’s adult population now have this condition ( 74 , 75 ).

Because a healthful, well-planned vegan diet may be inclusive of entirely whole plant foods such as fruits, vegetables, legumes, whole grains, nuts, and seeds, which are excellent sources of dietary fiber, it naturally contains a lot of fiber ( 1 ). Soluble dietary fiber can improve glycaemic control by delaying the process by which food leaves the stomach, resulting in slower glucose uptake and absorption ( 76 ). It is well established that a vegan diet can tackle important pathophysiological processes related to beta cell dysfunction and insulin resistance. A 16-week randomized controlled experiment with 75 overweight adults, half of whom followed a vegan diet, and the other half a control diet, illustrates this. The vegan group demonstrated a notable improvement in beta cell function and fasting insulin sensitivity compared to the control group. These two elements are recognized to be the main pathophysiological mechanisms driving type 2 diabetes ( 77 ). Another study has shown that fiber helps delay the absorption of glucose in the gastrointestinal tract, which causes blood glucose levels to gradually rise. This result may reduce the likelihood of insulin resistance and hyperglycemia ( 78 ). A study by Chester et al. showed that a low-fat vegan diet resulted in improved glycaemic control and decreased medication consumption in those with type 2 diabetes over the age of 50 years ( 79 ). According to the study, the weight loss effect of the vegan diet may account for a sizable amount of its effects on hemoglobin A1C levels, a measure of blood glucose control over time. A low-fat vegan diet was found to significantly improve glycaemic control in a 22-week randomized clinical trial ( 79 ), which included people with type 2 diabetes. In particular, the study found that the A1C readings in the vegan group dropped noticeably more than those of the other diet group. In a 12-week randomized clinical trial by Lee et al., participants diagnosed with type 2 diabetes were randomly assigned to follow a vegan diet or a conventional diet. Both diets led to lower HbA1c levels, but glycaemic control was better with the vegan diet (0.3–0.6% greater reduction) than with the conventional diet ( 80 ).

5.4. Cognitive function

Quercetin, which is only found in plant foods, may be responsible for the effects of a vegan diet on the reduction of anxiety and/or depressive symptoms ( 81 ). Quercetin can act as a natural antidepressant by inhibiting the activity of monoamine oxidase (MAO), an enzyme that breaks down mood-regulating neurotransmitters such as serotonin, dopamine, and norepinephrine ( 82 ), resulting in higher levels of these neurotransmitters in the brain ( 83 ). This impact might reduce the signs and symptoms of anxiety and despair.

Nutrition plays an increasingly important role in maintaining optimal brain function as people age ( 84 ). Studies have shown a protective effect of a vegan diet against Alzheimer’s ( 84 ). Alzheimer’s disease is a neurological disease that typically develops with increasing age and is known to be the leading cause of dementia worldwide ( 84 ). It is defined by a steady deterioration in cognitive abilities, including memory, reasoning, and behavior. The effects of diet and lifestyle choices, including a vegan diet, on Alzheimer’s disease have received much attention from researchers ( 85 ).

Part of the protective mechanisms of a vegan diet could be attributed to its beneficial effect on the reduction of inflammatory markers in dementia and Alzheimer’s disease. Meat-based dietary patterns appear to be positively correlated with biomarkers of low-grade inflammation, whereas vegetable- and fruit-based diets are inversely correlated ( 86 ). Studies providing data on biomarkers of inflammation in vegans, however, are few and inconsistent. Menzel et al. found no significant differences in any of the seven inflammatory biomarkers measured. Participants who followed a vegan diet for more than 4.8 years were more likely to have lower hsCRP levels compared to those who followed a vegan diet for less than 4.8 years ( 87 ). This may suggest that diet length may be an important factor in reducing systemic inflammation. Šebeková et al. also found that plasma CRP levels were not significantly different between vegans and omnivores ( 88 ). In the other hand, Franco de Moreaes et al. identified lower values of inflammatory markers, CRP and TNF-α/IL-10 ratio in strict vegetarians compared to vegetarians and omnivores ( 89 ). Lastly, a recent meta-analysis showed that vegans have lower CRP levels than omnivores ( 90 ).

With the popularity of veganism rising rapidly, there is an increased need for scientific study to determine how a vegan diet affects human health, particularly in relation to cognitive functioning. A low-risk lifestyle adjustment that can help maintain cognitive function and prevent cognitive ageing is to switch to a vegan diet ( 62 ). Further research is needed to prove that a vegan diet can help prevent or counteract inflammation and subsequently help reduce the risk of Alzheimer’s disease.

5.5. Bone wellness

Numerous health problems have been associated with adulthood and ageing, and the severity of these problems depends on various circumstances. A study by Rodrigues et al. found that ageing is related to a loss of bone mass, increasing the incidence of fractures with age ( 91 ). Osteoporosis is a degenerative skeletal condition that can increase the susceptibility of a person to fractures, especially in the hip, spine, and wrist ( 92 ). Key characteristics of osteoporosis include low bone mass and decreased bone mineral density. The health of an adult is greatly influenced by its diet, which is one of the key determinants. A vegan diet has some consequences, according to several studies conducted in the context of food. Bone health is one example. Bone health problems, which often develop with age, are substantially more common in women than in men ( 93 ). In general, high bone mineral density is preferred since it has a negative correlation with the risk of fragility fractures, especially in female adults. In other words, the lower the risk of fractures caused by decreased bone strength, the higher the concentration of bone mineral ( 94 ). Adopting a vegan diet can raise concerns about inadequate nutrient intake, which can eventually lead to lower bone mineral density (BMD) ( 95 ). Certain nutrients, such as vitamin B12, vitamin D, calcium, and omega-3 fatty acids, may be insufficient in a vegan diet. This is so because, as cited by Richter et al. and Menzel et al., these nutrients are commonly present in animal products ( 96 , 97 ). Vegans showed lower bone mineral density than omnivores in a variety of bone locations, including the hip, femoral neck, and lumbar spine, according to a cross-sectional study conducted by Menzel et al. ( 97 ), which included 36 vegans and 36 omnivores, as well as adults. Furthermore, compared to omnivores, vegans exhibited lower levels of calcium, vitamin D, and vitamin K. However, the bone turnover markers of the two groups did not show appreciable variations. The study findings indicated that vegans should consume enough calcium, vitamin D, and vitamin K to maintain strong bones because they may be more susceptible to osteoporosis and bone fractures. The study also emphasized how crucial nutrient balance is for vegan diets because vegans who consume an unbalanced diet run the risk of depleting many nutrients. Vitamin D, which is often obtained by exposure to sunlight but can also be found in foods such as fatty fish, egg yolks, and the liver, is crucial for the health of bones ( 98 ). The relevance of nutritional practices as a modifiable factor that affects bone mineral density has been acknowledged ( 99 ).

5.6. Muscle integrity

Sarcopenia and frailty syndrome are debilitating conditions primarily associated with aging-related changes in body composition, characterized by low muscle mass and strength. These conditions ultimately lead to an increased risk of adverse health outcomes such as disability, hospitalization, or death ( 6 , 100 ). It is estimated that sarcopenia affects 30% of individuals over 60 years old and 50% of those over 80 years old. Data analysis from 62 countries worldwide indicates a prevalence of frailty syndrome ranging from 12 to 24% of the population ( 101 ). This, in the face of an ever-increasing number of elderly people, is becoming a serious public health problem ( 77 , 78 ). A well-planned diet is essential for older people. Although the evidence base for the role of dietary protein in maintaining good muscle health in older age is strong, the importance of protein sources is an ongoing subject of research ( 101–104 ). With the increasing number of people adopting flexitarian, vegetarian, and vegan diets, scientists are highlighting the need to pay attention to the dietary habits of older people to prevent sarcopenia and frailty syndrome. The results of the study conducted by Sotos-Prieto et al. indicate that a healthful plant-based diet was associated with lower risk of frailty whereas an unhealthful plant-based diet was associated with higher risk ( 105 ). Adequate consumption of high-quality dietary protein combined with regular physical activity is crucial to the prevention of the aforementioned conditions among older people ( 106 ). Furthermore, increasing portion sizes could be helpful in improving the intake of protein and essential amino acids (EAAs) to address the challenge of the lower anabolic properties of plant-based foods and proteins. Essential amino acids are essential components found in dietary protein that play a crucial role in maintaining muscle growth and strength throughout an individual’s lifetime. Attention should be paid to the intake of branched chain amino acids (BCAAs), especially leucine, isoleucine, and valine ( 107 ). Ingestion of dietary protein induces hyperaminoacidemia, promoting muscle protein synthesis and inhibiting muscle protein breakdown through various pathways ( 108 ). However, scientific opinions on the use of a vegan diet among older individuals and its impact on the development of sarcopenia are highly divided. According to studies by Hengeveld et al. and Tieland et al., the lower quality of protein present in many vegan meals can be problematic, especially considering that a significant number of adults struggle to meet the recommended increase in dietary protein intake ( 109 , 110 ). According to Domić et al., older Spanish adults who consumed more animal protein than vegetable protein had a lower incidence of frailty. Additionally, researchers point out that several observational studies have shown a favorable correlation between animal-based protein and muscle mass and strength, indicating that a vegan diet might have negative effects on muscle mass and strength ( 6 ). The study conducted by Maroto-Rodriguez et al. provides intriguing results and a fresh perspective on the dietary habits of seniors. According to the researchers, diets with a high consumption of plant-derived foods and a lower consumption of animal-derived foods could potentially reduce the risk of frailty in elderly individuals. The study attributes positive health outcomes to the adoption of a plant-based diet, characterized by a significant intake of plant products and a lower intake of animal products. Unlike other vegetarian diets, a plant-based diet places emphasis on the quality of plant-based items. It associates the favorable impact of healthy plant-derived foods such as vegetables, fruits, whole grains, and nuts with improved health among individuals over 65, in contrast to unhealthy plant-derived products like refined grains, sugary beverages, and animal-based foods ( 111 ). The authors of the study suggest that the protective effect of a plant-based diet against frailty could be linked to the provision of essential nutrients. They highlight the antioxidant effects of vitamins C and E, carotenoids, and selenium derived from fruits and vegetables. These elements may protect against sarcopenia by reducing the exposure of muscle fibers to oxidative stress. However, biomarkers of selenium and zinc were lower in vegans, confirming that a sufficient supply of these trace elements is more difficult to achieve when following a plant-based diet ( 112 ). Additionally, the inclusion of legume and nuts protein might help prevent sarcopenia ( 111 , 113 ). The authors also point out the potential anti-inflammatory effects of fruits, olive oil, unsaturated fatty acids, nuts, or coffee, which may help mitigate the low-grade chronic inflammation associated with frailty ( 111 , 114 ). Similar results are presented by a Chinese study conducted among nearly 4,000 participants ( 115 ).

Researchers have shown that a vegan diet is linked to a reduced risk of frailty in men and older adults who lead a healthy lifestyle. More research is required to establish a vegan diet as a recommended dietary approach to prevent and minimize frailty among older adults. Furthermore, it should be considered to incorporate dietary interventions along with lifestyle changes to promote successful ageing, a factor that could also be significant for women ( 116 ).

Considering the substantial increase in the elderly population worldwide and the significance of the issue, future studies are needed to develop an optimal approach to nutrition and/or supplementation with isolated protein preparations for individuals who, for various reasons, choose to adhere to a vegan diet ( 117 ).

6. Nutritional factors to consider in a vegan diet

Some nutrients need to be taken special into account when following a vegan diet. According to a position document of the Academy of Nutrition and Dietetics (AND), a well-planned vegan diet is nutritious and can have health benefits for the prevention and treatment of various diseases. It also highlights the fact that a vegan diet should be carefully planned to ensure optimal nutritional intake. The article also highlights the particular nutrients in vegan diets that must be taken into account, such as protein, vitamin B12, vitamin D, calcium, iron, and omega-3 fatty acids ( 1 , 118 ).

6.1. Protein

Numerous research efforts have aimed to evaluate the capacity of a vegan diet regimen to meet the appropriate protein requirements. A significant proportion of these studies contend that mean protein intake, which represents approximately 13–14% of daily caloric intake, aligns favorably with the guidelines established by the American diet recommendations ( 119 ). According to a study conducted by Alles et al., 27% of individuals following a vegan diet do not reach a minimum protein intake of 10%, thus initiating enquiries into the sufficiency of protein provisioning within the vegan diet ( 3 ). Conversely, despite a lower average protein intake in vegan diet, all studies reported in the article of Neufingerl et al. protein intake within the level of the adequate macronutrient distribution range (ie 10% E). None of the 64 studies reported protein intake below the acceptable macronutrient distribution range (AMDR) for any dietary pattern ( 53 ). In Bakaloudi et al ’s review of 12,096 vegans, macronutrient intakes were largely adequate in vegans, with the exception of protein, where intakes were lower, slightly below the RNI ( 68 ). However, it should be noted that expert opinion is divided on the protein content of plant-based diets.

Therefore, it is essential for vegans to ensure that they get an adequate amount of proteins in their diet. Protein quality is influenced by the effectiveness of digestion and the presence of crucial amino acids. Another recommendation is to eat a variety of foods as amino acid limitation is not as serious ( 118 ). In particular, certain vegetable proteins, such as soy, exhibit enhanced digestibility, distinguishing them from the typical digestibility observed in many other plant-based foods. This concept is in alignment with the principles of the Digestible Indispensable Amino Acid Score (DIAAS), a widely used measure to assess protein quality ( 3 ). As Mariotti and Gardner highlighted, the distribution of amino acids in plant-based foods often displays a less optimal profile compared to animal-derived foods. However, it should be noted that even when adhering to a vegan diet characterised by limited diversity, achieving a considerable intake of total protein remains attainable. This can be accomplished by consuming significant amounts of plant protein foods, such as soybeans, tofu, legumes, nuts, seeds ( 120 ).

In the context of a vegan diet, the fulfilment of protein requirements is ensured through the complementary consumption of legumes and cereals, allowing individuals to obtain a comprehensive array of essential amino acids that are of paramount importance for human nutrition ( 14 ). This is especially noteworthy when considering that the Recommended Dietary Allowance (RDA) for protein intake is commonly set at 0.8 g/kg body weight ( 120 ). Advancements in modern food technology have played a crucial role in producing plant-based food products that mimic the attributes of animal-derived options. In particular, the use of soy and its derivatives has emerged as a significant strategy, allowing the achievement of satisfactory protein intake that could otherwise be difficult to achieve ( 15 ). Currently, vegans commonly include substantial amounts of legumes in their dietary patterns, a protein source that has gained attention as a potential preventive factor against ailments such as stomach, prostate, and colon cancer. Furthermore, the consumption of legumes demonstrates potential cardioprotective effects, evident through the reduction in serum lipids and lipoproteins circulating, including total cholesterol, low-density lipoprotein (LDL) and triglycerides ( 5 ).

6.2. Vitamin B12

Deficiencies in specific vitamins, particularly vitamin B12is significant concerns in the context of a vegan diet. Vitamin B12, a water-soluble nutrient found primarily in animal-derived foods, plays a vital role in hematopoiesis and nervous system function ( 5 , 14 ). However, due to the absence of animal products, getting sufficient vitamin B12 is a challenge for vegans, leading to potentially severe deficiencies. These deficiencies can be the result of impaired absorption or inadequate intake of this essential nutrient, contributing to conditions such as megaloblastic anemia and degenerative disorders ( 5 , 121 ). In particular, neurological symptoms of vitamin B12 deficiency include numbness and tingling of the hands and feet, decreased sensation, difficulty walking, loss of control of the bowel and bladder, memory loss, dementia, depression, general weakness, and even psychosis. Elevated rates of vitamin B12 deficiency, up to 80%, are observed in populations in Hong Kong and India, particularly among people following a vegan diet with limited inclusion of fortified foods or supplementation ( 5 ). As an exclusive animal-derived nutrient, vitamin B12 is absent in vegan diets, necessitating supplementation or fortified plant-based alternatives such as plant milk, cereals, and nutritional yeast ( 14 , 122 ). Although the established daily recommended dietary allowance for adults in the United States is 2.4 microgrammes of vitamin B12, research suggests that due to variations in the absorption and utilization of vitamin B12 from plant sources, vegans might require higher doses of this vitamin ( 123 ). Therefore, regular monitoring of vitamin B12 levels and adaptive supplementation strategies become imperative to maintain optimal health ( 4 ).

6.3. Vitamin D

Vitamin D, classified as a fat-soluble micronutrient, plays a central role in promoting calcium absorption and maintaining optimal bone health ( 124 ). Its synthesis takes place on the human skin when exposed to sunlight. However, various factors, such as geographic location and time of year, can influence the skin’s ability to produce sufficient vitamin D ( 4 , 5 ). According to research conducted by Melina et al., certain individuals following a vegan diet have been observed to experience a low vitamin D intake and exhibit lower serum 25-hydroxyvitamin D levels, especially during winter or in regions with higher latitudes ( 118 ). Furthermore, a study by Allès et al. indicated that vegans tend to consume less vitamin D relative to recommended dietary guidelines ( 3 ). The recommended daily intake of vitamin D varies, ranging from 600 IU/day to 800 IU/day ( 124 ) or approximately 5 μg to 15 μg ( 52 ). In particular, Menzel et al. underscore the critical nature of this nutrient, as its deficiency could lead to decreased bone mineral density, increased bone turnover, and an increased risk of premature bone ageing, thus increasing the susceptibility to fractures. This concern is particularly relevant for vegans, who, due to their exclusion of animal-derived foods, face an increased risk of inadequate vitamin D supply, which could lead to adverse effects on bone health ( 94 ). Sources of vitamin D include fortified breakfast cereals and non-dairy milk substitutes such as oat, almond and rice beverages. When exposure to the sun and fortified food intake are insufficient to meet dietary requirements, vitamin D supplementation is recommended for individuals of all ages ( 5 ).

6.4. Omega 3 fatty acids

Omega-3 fatty acids, with a particular focus on alpha-linolenic acid (ALA), play an important role in preventing atherosclerosis and improving lipid profiles through the reduction of inflammation and the mitigation of oxidative stress. ALA, which is an essential fatty acid, acts as a precursor for the synthesis of EPA and DHA ( 125 ), but only a small portion is converted to longer-chain fatty acids. Current research indicates that n-3 conversion from short chain to long chain in humans is very limited; ALA converts to EPA at a rate of 5–15%, and < 1% of ALA reliably converts to DHA. Individuals who follow a vegan diet and include no marine foods in their diet will consume ALA because of its wide distribution in plant-sourced foods ( 126 ). However, literature suggests there is individual variation in conversion rate of fatty acids, influenced by genetics and dietary habits, including the presence of other fatty acids in the diet. Vegan may be more efficient at n-3 conversion, but this has not been confirmed ( 127 ).

According to Menzel et al., the main sources of EPA and DHA, include oily fish, dairy and meat, therefore intake of EPA and DHA among vegans is lower compared to omnivores, due to the omission of these foods from their diet. Their study revealed reduced plasma levels of n-3 fatty acids in vegans ( 118 ). ALA sources, such as vegetable oils, cereals, nuts such as walnuts and chia seeds, as well as plant-derived oils such as rapeseed, linseed, canola, and hemp should be included in the well-balanced vegan diet ( 125 , 128 ). Optimizing the intake of omega-3 fatty acids is crucial for those following a vegan diet ( 7 ) as the Adequate Intake (AI) guidelines for n-3 fatty acids suggest a daily intake of 1.1 grams of alpha-linolenic acid for women and 1.6 grams for men ( 128 ). An abundance of foods fortified with EPA and/or DHA from either marine or algal sources are now available; called functional foods, examples include soy milks and juices, cooking oils, spreads, snack foods ( 126 ).

6.5. Calcium

Vegans generally demonstrate lower calcium intake compared to individuals who follow alternative diet patterns such as lacto-ovo-vegetarian diets ( 52 , 118 ). However, though various plant-based sources offer substantial calcium content, its absorption is negatively influenced by compounds such as oxalates, phytates, and fiber present in vegetables ( 5 ). To improve calcium intake, there are a number of interventions that can be implemented. These include promoting the consumption of foods naturally high in calcium, using food processing techniques that could improve calcium content or bioavailability, staple food fortification, and biofortification to produce higher calcium-containing crops ( 129 ). Noteworthy calcium-rich plant foods include green leafy vegetables, tofu, tahini, as well as fortified options such as cereals, soy, rice, and nut and fruit beverages. Optimal absorption is observed in low-oxalate vegetables, such as broccoli and kale ( 5 ). The WHO recommended dietary allowance for adults ranges from 1,000 to 1,200 mg ( 130 ), and meeting this requirement is feasible for vegans by consuming a variety of plant-based foods rich in calcium.

In a comparative study involving various dietary groups, including meat eaters, fish eaters, vegetarians, and vegans, a noticeable increase in fracture rates was observed among vegan participants. This trend appeared to be associated with a significantly lower average calcium intake within the vegan group ( 128 ). The study by Menzel et al. offers information on the impact of transitioning from an omnivorous diet to a vegan diet, revealing a reduction in calcium excretion indicative of dietary changes. The study effectively employed 24-h urine samples to accurately assess mineral statuses, unveiling a decrease in calcium excretion among vegans compared to omnivores. This variation in excretion is probably attributed to differences in dietary calcium intake, which is reflected in urinary calcium concentrations ( 94 ).

Among vegans, decreased plasma zinc levels can contribute to iron deficiency anemia ( 5 ). Poor zinc status is most commonly linked to innate immunity and reduced resistance to infections. Dimitra et al. conducted a systematic review that revealed that vegans have the lowest zinc intake compared to groups following various diet habits ( 52 ). Furthermore, a study carried out by Allès et al. showcased notable insufficiency of zinc among vegans ( 3 ). Zinc serves as a facilitator in iron metabolism and is less readily absorbed from plant-derived sources compared to animal products, which typically contribute about half of the zinc intake. Plant-based sources rich in zinc include wholemeal bread, peas, corn, nuts, carrots, whole grains, wheat germs, soybeans, cabbage, radish, watercress, and legumes ( 5 , 118 ). Vegans are advised to consume these foods in sufficient amounts to prevent zinc deficiency. Supplementation and the inclusion of fortified breakfast cereals and foods could be crucial for meeting the nutritional needs of individuals following a vegan diet ( 124 ). The WHO has established a classification for zinc bioavailability based on the phytic acid: zinc ratio. Ratios below 5 are designated as indicating “high” zinc availability, resulting in 50% absorption (High Bioavailability: Females: 3.0 mg, Males: 4.2 mg). Ratios spanning from 5 to 15 signify “moderate” bioavailability, yielding 30% absorption (Moderate Bioavailability: Females: 4.9 mg, Males: 7.0 mg). Ratios surpassing 15 indicate “low” zinc availability, leading to 15% absorption (Low Bioavailability: Females: 9.8 mg, Males: 14.0 mg). These categories align with recommended zinc intake levels for different gender groups, providing tailored guidance for optimal nutritional adequacy ( 52 , 131 ). Vegan dietary patterns are categorized as possessing a moderate degree of zinc availability, given that their predominant reliance is not on unrefined, unfermented, or ungerminated cereal grains, or high-extraction-rate flours ( 131 ).

Anemia resulting from iron deficiency is more prevalent among vegans than among omnivores ( 124 ). Despite vegans having the potential to achieve a daily iron intake similar to non-vegans, their blood iron and ferritin levels tend to be lower, partly due to the less effective absorption of non-haem iron found in plant-derived foods compared to haem iron from animal sources. This is supported by another study that found higher iron intake among vegans compared to other diets, especially in German vegan women, although the absorption levels did not correspond proportionally to the increased intake ( 5 , 48 ). Iron sources include legumes, beans, whole grains, whole cereals, dark-green leafy vegetables, fruits, seeds, and nuts ( 5 ). Enhanced absorption of non-haem iron is facilitated by ascorbic acid, minor alcohol intake, retinol, and carotenes ( 5 , 132 ). However, factors such as phytates, tannins/polyphenols, and soy protein inhibit absorption ( 133 ). Marrone et al. emphasized that menopausal women among vegans are particularly prone to iron deficiencies. The recommended dietary allowance of iron is established at 8 mg per day for men and 18 mg per day for women ( 130 ). There is an iron RDA specific for vegetarians/vegans in the U.S. due to lack of dietary haem iron: 32 milligrams per day for women and 14 milligrams per day for men ( 119 ). To combat iron deficiency, fortified foods such as salt, wheat flour, and rice can be incorporated into the diet ( 14 ).

Haem iron, which is mainly found in products of animal origin, is not available in a vegan diet. Therefore, people on a vegan diet are not at risk of an excess of this form of iron. Haem iron is a type of iron that is found in haem-containing proteins, such as haemoglobin in the red blood cells and myoglobin in the muscles. It is important to the body because it is necessary for the transport of oxygen from the lungs to tissues and for the storage and transport of oxygen in muscles ( 134 ). However, certain types of damage can occur if there is an excess of haem iron or if it is processed incorrectly. One of the main concerns regarding the harmful effects of haem iron is its role in oxidative stress. This is due to its ability to catalyse the formation of reactive oxygen species. Reactive molecules can cause damage to cells, proteins, lipids and nucleic acid (DNA), which can contribute to inflammatory processes ( 135 ).

Excess haem iron has been positively associated with non-communicable diseases, including colorectal cancer, type 2 diabetes and cardiovascular mortality ( 136 , 137 ). In a meta-analysis of prospective cohort studies by Hunnicutt et al. haem iron intake was positively associated with the incidence of coronary heart disease ( 138 ). In a prospective cohort study among 539 older Australian men aged 75 years and older, it was shown that higher haem iron intake was independently associated with an increased risk of adverse cardiovascular events, mortality from any cause, congestive heart failure and coronary revascularisation over 5 years ( 139 ). The maintenance of the right balance of iron in the body is essential for the maintenance of good health. It is therefore important that not only those who follow a plant-based diet, but also those who eat meat, monitor their iron levels on a regular basis and adjust their diet to include adequate amounts of iron ( 136 ).

7. Guidelines for adopting a vegan diet

Most guidelines on vegetarian and vegan diets have provided neutral advice on supplementing certain nutrients with plant sources. Guidelines such as those from the United Kingdom, Australia, Belgium, Lebanon, Malaysia and Malta indicate that all nutrients can be obtained from a vegetarian diet, including a vegan diet, by combining a variety of foods and consuming an appropriate amount of calories ( 140 ).

For adults aged 18 to 60 years, it is recommended to maintain a total energy intake ranging from 23 to 27 kcal/kg, while those over 60 years should target a range of 19 to 22 kcal/kg. To ensure a balanced carbohydrate and fiber intake, individuals should consume a minimum of 400 g (equivalent to five portions) of fruits and vegetables daily, excluding starchy root and vegetables. Dietary fat intake should be limited to less than 30% of total energy intake, with saturated fats kept below 10% and trans-fats below 1%. It is recommended to substitute saturated and trans fats with unsaturated fats. Protein intake should contribute to approximately 15% of total energy intake. Additionally, it is advised to limit free sugar intake to around 5% of energy and restrict salt intake to 1,500 mg/day when adhering to a vegan diet. To ensure adequate intake of vitamins B12 and D throughout the year can be achieved through vitamin-fortified meals or supplements, and EPA/DHA supplementation (alternate source of EPA/DHA algal oil) is also recommended ( 4 , 60 ).

People following a strict vegan diet can meet nutrient requirements as long as energy needs are met and an appropriate variety of plant foods are eaten throughout the day ( 140 ), and include fortified foods and/or supplements to get adequate amounts of vitamin D and vitamin B12 ( 4 , 60 ).

8. Obstacles to adopting a vegan diet and lifestyle

Individuals adopting a vegan diet can encounter a variety of difficulties. Many people fail to maintain a vegan diet in the long term and give up ( 133 ). This can be due to both physical and social obstacles that can affect the maintenance of this eating style.

The first barrier may be insufficient knowledge of the nutrients in a vegan diet, the principles of correct meal composition, or the implementation of supplementation ( 141 ). Another potential obstacle may be that veganism requires more dedicated time and commitment to cooking and preparing meals compared to meat-based options. This can be complicated by the perception that such a diet is tasteless and can easily become monotonous ( 142 ). Currently, the market offers a variety of meat and dairy substitutes that do not require much time to prepare ( 143 ). However, most plant-based meat alternatives are classified as ultra-processed foods (UPF) ( 144 ). Higher UPF intake is associated with an increased risk of obesity and diet-related non-communicable diseases (such as cardiovascular disease, diabetes, cancer) and even higher mortality ( 145 ).In addition, some people become attached to the taste of meat products, which can make it difficult to change eating habits, especially at the initial stage of changing their diet ( 146 ). One potential obstacle could be the difficulty of access to high-quality, fresh plant products and their higher cost compared to animal products ( 147 ). According to Fehér et al., meat prices have a clear impact on the willingness to switch to a plant-based diet ( 141 ).

Social pressure, especially from family, loved ones, and friends, is generally considered a significant influence on meat consumption. Some individuals may fear switching to a vegan diet because they expect stigma and ostracism from significant others ( 148 ). Adopting a vegan diet can affect family relationships, which may explain why those who choose this diet often experience a lack of understanding or even negative reactions from family members who consume animal products ( 149 ). Situations described as one of many factors seem to have an impact on mental health of people following a vegan diet, but scientific views on the impact of plant-based nutrition on mental health are divided. In the Dobersek et al. systematic review, the majority of studies, especially the higher-quality studies, found that people who avoided eating meat had significantly higher rates or risks of depression, anxiety and/or self-injurious behaviour ( 150 ). Forestell and Nezlek indicated that people who follow a plant-based diet are more likely to be depressed ( 151 ). Furthermore, women on a vegan diet are more likely than men to have disordered eating attitudes and practices ( 152 ).

One potential danger associated with a vegan diet is the risk of malnutrition, which can occur in individuals if the diet is not balanced and does not provide the body with sufficient essential nutrients. Although our review does not include studies on pregnant and breastfeeding women, it is worth mentioning that this is very important in the context of the impact on the fetus and child. According to international guidelines, a plant-based diet during pregnancy and lactation requires a high level of awareness to ensure complete intakes of essential key nutrients and vitamin supplements. Maternal undernutrition can potentially alter fetal growth trajectories by altering placental weight and nutrient transfer capacity, depending on the severity and timing of nutrient deprivation. Maternal malnutrition leading to vitamin B12, vitamin D, calcium and DHA deficiencies during lactation may contribute to low levels of these nutrients in breast milk ( 153 ).

Despite the barriers mentioned, many people successfully start and follow a vegan diet long-term and reap the health, ethical, and environmental benefits. Given the current growing interest in plant-based diets among the general population, it is crucial to understand both the barriers, risks, and benefits of such diets among clinicians, policy makers, and the general population ( 154 ). A food policy that combines health, sustainability, and affordability can effectively accelerate the promotion of plant-based diets and support the achievement of mitigation targets for potential barriers.

9. Conclusion

It is believed that a well-planned vegan diet, when combined with a healthy and active lifestyle, is a viable choice for healthy adults, especially those who follow it. This is because chronic diseases are significantly more common than they used to be and various strategies to address these public health challenges are insufficient.

Numerous studies have demonstrated the validity of this claim and any doubts have been attributed to an inadequately designed vegan diet, which is a potential problem with any kind of diet (such as omnivorous). As people age, their caloric needs tend to decrease, while their requirements for specific nutrients may increase.

A well-planned vegan diet must include adequate calories and nutrients, as well as the necessary supplements, such as vitamin B12 and vitamin D. To reduce the risk of vitamin deficiencies, fortified foods should be consumed by adults and the general population. Vegans are strongly encouraged to consult their doctors or dietitians before switching to a vegan diet.

Furthermore, the implementation of well-designed vegan diets and lifestyles requires greater awareness, greater social responsibility, and government involvement to ensure the fair cost of vegan food products. It should be emphasized that the advantages and drawbacks of vegan diets for adults are not fully covered in this review. The precise processes through which vegan diets work in many chronic diseases require further studies. Lastly, future studies should use large sample sizes that are accurately representative of the adult population.

Author contributions

EŁ: Conceptualization, Methodology, Resources, Writing – original draft, Writing – review & editing. FB: Conceptualization, Data curation, Methodology, Writing – original draft, Writing – review & editing. MZ: Data curation, Writing – original draft, Writing – review & editing. KD: Data curation, Resources, Writing – original draft, Writing – review & editing. AB: Data curation, Writing – review & editing. ŁO: Data curation, Writing – review & editing. AS: Data curation, Resources, Writing – review & editing.

Acknowledgments

We would like to express our sincere gratitude to Professor Gaëlle Arvisenet, for her valuable guidance and support throughout the research process. Her expertise, insights, and encouragement were invaluable in helping us to complete this work.

Funding Statement

The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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