Food and Behaviour Research

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Vegetarianism and veganism compared with mental health and cognitive outcomes: a systematic review and meta-analysis

Iguacel I, Huybrechts I, Moreno L, Michels N (2021) Nutrition Reviews 79(4) 361-381. doi: 10.1093/nutrit/nuaa030 

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Vegetarian and vegan diets are increasing in popularity. Although they provide beneficial health effects, they may also lead to nutritional deficiencies. Cognitive impairment and mental health disorders have a high economic burden.


A meta-analysis was conducted to examine the relationship between vegan or vegetarian diets and cognitive and mental health.

Data sources: PubMed, Scopus, ScienceDirect, and Proquest databases were examined from inception to July 2018. 

Study selection: Original observational or interventional human studies of vegan/vegetarian diets were selected independently by 2 authors.

Data extraction: Raw means and standard deviations were used as continuous outcomes, while numbers of events were used as categorical outcomes.


Of 1249 publications identified, 13 were included, with 17 809 individuals in total. No significant association was found between diet and the continuous depression score, stress, well-being, or cognitive impairment.

Vegans/vegetarians were at increased risk for depression (odds ratio = 2.142; 95%CI, 1.105-4.148) and had lower anxiety scores (mean difference = -0.847; 95%CI, -1.677 to -0.018). Heterogeneity was large, and thus subgroup analyses showed numerous differences.


Vegan or vegetarian diets were related to a higher risk of depression and lower anxiety scores, but no differences for other outcomes were found.

Subgroup analyses of anxiety showed a higher risk of anxiety, mainly in participants under 26 years of age and in studies with a higher quality. More studies with better overall quality are needed to make clear positive or negative associations.