Vegan/Vegetarian and Mental Health

Recent evidence suggests that vegetarian and vegan diets may increase the risk and symptoms of depression, a mental illness that affects 350 million people worldwide. In this systematic review by Jain et al. (2022), the authors investigated the literature available on the association of vegetarian and/or vegan diets with the risk or symptoms of depression, using evidence from observational and intervention studies. Three independent reviewers extracted data, assessed the risk of bias, and performed quality assessments of observational cohorts, cross-sectional studies, and controlled studies using the National Heart, Lung, and Blood Institute of the National Institutes of Health for Quality Assessment of Observational Cohort and Cross-Sectional Studies and Controlled Studies. Following the PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-analysis), a search was conducted on Medline, Embase, The Cochrane Library, and Web of Science to systematically document relevant cohort, cross-sectional, case-control, or randomized controlled trials examining the association between a vegetarian or vegan diet and depression in adults. Evidence was aggregated and narratively synthesized by type of diet analyzed as vegetarian, vegan, or both. A total of 23 studies (18 cross-sectional, 3 prospective cohorts, and 2 randomized controlled studies) were included in this review with 25 appraisable outcomes. Analysis of the results demonstrated conflicting evidence linking a vegetarian or vegan diet with depression. Seven (28%) outcomes showed a positive effect of diet on depression, while seven (28%) outcomes found no association between vegetarian and vegan diets and depression, although two of the studies found an increased risk of depression in some groups. On the other hand, 11 (48%) outcomes demonstrated a negative impact of vegetarian and vegan diets on the rates of depression. The quality of the evidence was rated as good in four studies and moderate in the remaining 19 studies. The authors conclude that the evidence regarding the effects of vegetarian and vegan diets on depression is conflicting, possibly due to the heterogeneity of the studies analyzed, and that further research is required. [NPID: Adults, depression, systematic review, vegan diet, vegetarian diet]

Previous studies have reported conflicting results that intake of a vegetarian diet is associated with mental health effects, particularly anxiety, depression, and stress. Askari et al. (2022) conducted their systematic review to summarize the current state of the literature on this relationship. A literature search was performed to identify relevant articles, yielding prospective cohort and cross-sectional studies, conducted on adults for risk estimation of vegetarian diet, depression, anxiety, and stress using Scopus, PubMed, and Web of Science for relevant articles published before July 2020. A total of 13 publications (4 cohort studies and 9 cross-sectional studies) examining the association between a vegetarian diet and depression, anxiety, and stress were included. Analysis of the included studies revealed no association between a vegetarian diet and depression. Furthermore, the pooled effect size from the four studies suggests that the vegetarian diet is not associated with anxiety. Results could not be summarized due to insufficient data on stress. Overall, the authors discovered no significant association was observed between a vegetarian diet and depression or anxiety. Future cohort studies are needed to further explore the impact of vegetarian diets on these mental health effects. [NPID: Fear, depression, stress, vegetarianism]

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In this cross-sectional study by Kohl et al. (2023), the authors investigated the potential relationship between depressive episodes and consuming a meatless diet, using data from a population of 14216 adults (participants of the ELSA-Brasil cohort, ages 35-74). Depressive episodes were evaluated using the Clinical Interview Schedule-Revised (CIS-R), while dietary adherence was evaluated using a validated food frequency questionnaire. After adjusting for potential confounders, the results revealed a two-fold increase in the prevalence of depressive episodes with adherence to a meatless diet, compared to meat consumers. The authors conclude that participants who did not eat meat were twice as likely to suffer from depressive episodes compared to their peers, regardless of lifestyle or socioeconomic factors. Further studies (especially longitudinal ones) are necessary to understand the mechanism behind this relationship. [NPID: Vegetarian diet, depression, mental health, meat]

Several publications highlight the beneficial impacts of vegetarian diets on health, including those that contrast the vegetarian population against others from a socio-psychological point of view. In this systematic review by Holler et al. (2021), the authors examined the dissimilarities between omnivores and vegetarians with regard to values, personality profiles, and empathy skills. After searching three electronic databases, 25 studies (n = 23,589) were found eligible, having met the inclusion criteria and passed a risk of bias assessment, and were evaluated using a shortened version of the Newcastle-Ottawa Scale. Analysis of the studies revealed a substantial dissimilarity in the personalities, empathic drive, and values of vegetarians and omnivores, with omnivores tending to be more socially dominant, prejudiced, and had stronger right-wing authoritarianism. On the other hand, vegetarianism was linked to more openness and empathy, with values rooted in universalism, stimulation, hedonism, and self-direction. Omnivore values, on the other hand, were found to be rooted more in the idea of power. The authors comment that the findings of their review, in which concepts like animal ethics, environmental protection, and animal rights were out of scope, demonstrate the significant personality dissimilarities that can be attributed to dietary preferences, and how the current worldwide trends in consuming plant-based diets highlight the necessity for future research on vegetarianism. [NPID: Diet, empathy, omnivore, personality, plant-based, values, vegetarian]

Vegetarianism has a contentious relationship with mental health. In this cross-sectional study, Bègue & Shankland (2022) looked at the links between vegetarianism, depression, and anxiety in a sample of 6,578 participants (70.8% female, 18-90 years of age). The participants submitted data through a self-reported questionnaire, which was then analyzed while taking several variables into account (age, body mass index, gender, income, education level, and size of city), revealing no substantial differences in the levels of anxiety and depression experienced by vegetarians and non-vegetarians. Thus, the authors demonstrate no potential relationships between plant-based diets and anxiety or depression. [NPID: Anxiety, cross-sectional studies, depression, vegetarian diet]

The focus of this 2021 study was on vegan and vegetarian diets, since it is not yet fully understood how plant-based diets are interlinked with mood disorders such as depression. These plant-based dietary patterns are often considered to be “healthy” and are said to provide broad health benefits. This present article assessed the quality of the plant-based diet and explored its association with depression. There was a total of 219 adult participants, all aged 18–44 years. Results showed a connection between overall plant-based diet quality and depressive symptoms in vegans and vegetarians. Among the individuals without depression, higher diet quality provided protection against depressive symptoms. However, Lee et al. could not identify a connection between diet quality and depression among those subjects with depression. Thus, a high-quality plant-based diet may be protective against depressive symptoms in vegans and vegetarians. Also, this finding supports the link between higher-quality dietary patterns with lower risk of depressive symptoms also reported by other research studies investigating food and mental health. Since more and more vegan and vegetarian food products are becoming available in Australia, it is important that we start to understand the mechanisms by which plant-based diets can influence depressive symptoms. [NPID: plant-based diets, vegetarian diet, vegan diet, depression, Australia, mental health, food, nutrition]

This 2021 study aimed to determine whether the Taiwanese vegetarian diet reduces the likelihood of having depression. Data was taken from another study called the Tzu Chi Vegetarian Study (TCVS), which recruited a total of 12,062 individuals from the Buddhist Tzu Chi Foundation of Taiwan. Dietary intake was assessed using a food frequency questionnaire. Data on depression prevalence was available on the National Health Institute Research Database (NHIRD) of Taiwan since they had claim records with the International Classification of Diseases. This study was able to gain access to the records of 3571 vegetarians and 7006 non-vegetarians. Regression analysis results demonstrated that the vegetarian group were at lower risk of depressive disorders than the non-vegetarians. Taiwanese vegetarians were less likely to develop subsequent depressive disorders when compared with non-vegetarians. Diet appears to play a crucial role in the prevention of depression, but more studies are needed to reach a general conclusion for the global population. [NPID: vegetarian diet, depression, Taiwan, Taiwanese, Buddhist, plant-based diet]

The aim of this 2020 study was to assess the relationship between eating disorders and vegetarian diets in adolescents and young adults. Sergentanis et al. identified that the prevalence rates of eating disorders are rising among adolescents and young adults, while the number of vegetarians is also increasing in these age groups. To find a connection between vegetarian diets and incidence of eating disorders, a systematic review was conducted on related articles published in PubMed, PsychInfo and Google Scholar up to 30 May 2019. Twenty studies met the inclusion criteria for this review, providing data of 14,391 trial participants. Most articles reported significant links between vegetarianism and eating disorders. However, it could not be confirmed whether vegetarian diets cause eating disorders because the included cohorts were cross-sectional studies (an observational study that analyzes data at one given time point). Although vegetarianism appears to be interlinked with eating disorders, we will need longitudinal data to establish these patterns between vegetarianism and the emergence of disordered eating. [NPID: vegetarian diet, vegetarianism, eating disorder, adolescents, young adults, review, systematic review]

In this 2019 study, participants completed an 8-week program in which they consumed a whole-food plant-based dietary pattern. Around 30% of the sample were already either vegetarian or vegan at baseline. The results demonstrated that subjects that lost the highest proportion of their body weight were obese at baseline. As baseline BMI increased, the percentage of body weight lost increased. Moreover, blood pressure and plasma lipid concentrations were lower after the 8-week program than before (systolic and diastolic blood pressure, total cholesterol and LDL levels dropped). This included individuals who started the study as vegans/vegetarians (reporting significant weight loss and reductions in total and LDL cholesterol). It was noted that their weight loss tended to be less than that of non-vegetarians at baseline but this relationship was not found to be significant. Also, there was no marked difference in total and LDL cholesterol reductions between the non-vegetarians and vegetarians/vegans at baseline. Two participants (2.6%) had to increase their dose of their chronic medication, while there were 21 subjects (26.9%) also that were able to reduce or stop at least one of their regular medications. It was concluded that a whole-food plant-based dietary intervention may at least provide great short-term benefits in non-vegetarians, vegetarians, and vegans alike. [NPID: plant based, whole foods, vegan, vegetarian, obesity, cholesterol]

This 2019 review looks at the effects of various diets and nutrients, especially plant-based diets, on gut microbiota composition, and evaluates the consequences of the microbial metabolites on host health. Tomova et al. explain that plant-based diets appear to be beneficial to human health by promoting more diverse and stable microbial systems. Compared to omnivores (people that eat a variety of food of both plant and animal origin), vegans and vegetarians have significantly higher populations of Bacteroidetes-related colonies. Fibers found exclusively in plants increase lactic acid bacteria and reduce Clostridium and Enterococcus species, while polyphenols (also very commonly found in plant foods) increase bacterial species that have protective properties, as well as anti-pathogenic and anti-inflammatory effects. A fiber-rich diet also encourages the growth of bacteria that ferment fibers and produce short-chain fatty acids (SCFAs) as a result. These fatty acids have numerous positive impacts on health, including enhancing immunity against pathogens, increasing the integrity of the blood-brain barrier, and regulating critical functions of the intestine. To conclude, the available evidence suggests that a vegetarian or vegan diet can help people develop a diverse ecosystem of beneficial bacteria that promote human gut microbiome and overall health. [NPID: plant based, whole foods, vegan, vegetarian, gut microbiota, gut-brain health, microbial metabolites, omnivores, Bacteroidetes, fiber, Clostridium, Enterococcus, microbiome]

With the rising popularity in whole-food plant-based (WFPB) and vegan diets today, this 2019 study checked whether these diets meet current food-based and nutrient-based recommendations. The WFPB and vegan diet followers who took part in the Adhering to Dietary Approaches for Personal Taste (ADAPT) Feasibility Survey were asked to reveal their main source of information on nutrition and cooking. These resources were used to create 30-day meal plans, which were then compared to various dietary recommendations. Both WFPB and vegan meal plans obtained a healthy eating index of 88 out of 100. Moreover, the whole-food plant-based diet was found to contain more total vegetables (180%), green leafy vegetables (238%), legumes (460%), whole fruit (100%), whole grains (132%), and less refined grains (-74%) than the MyPlate meal plan recommendations. But the amount of fiber in the diet exceeded adequate levels across all age groups. Also, the WFPB meal plans provided less vitamin B12 and D than the Recommended Dietary Allowances (RDAs) for these vitamins and was composed of inadequate calcium levels for women aged 51-70 (according to the RDA). To summarize, the whole-food plant-based diet meal plans were of higher diet quality than the typical U.S. diets with exceptions of vitamins B12 and D without supplementation, and of calcium in older women. [NPID: plant based, whole foods, vegan, vegetarian, ADAPT, fiber, vitamin B12, vitamin D, calcium, older women]