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Vegetarian diet and mental disorders (2016-01-03)

A small but increasing number of people in Western countries are choosing to restrict meat for various reasons. While in countries such as India a high proportion (35%) of the population follows a vegetarian diet due to cultural and religious traditions, rates in Western countries are much lower.

Although our knowledge about the association between vegetarian diet and physical health is based on numerous studies, relatively little data is available on the associations between vegetarian diet and mental health.
A german study investigated associations between vegetarian diet and mental disorders. Participants were drawn from the representative sample of the German Health Interview and Examination Survey and its Mental Health Supplement (GHS-MHS).

Vegetarians displayed elevated prevalence rates for depressive disorders, anxiety disorders and somatoform disorders. Due to the matching procedure, the findings cannot be explained by socio-demographic characteristics of vegetarians (e.g. higher rates of females, predominant residency in urban areas, high proportion of singles).

The analysis of the respective ages at adoption of a vegetarian diet and onset of a mental disorder showed that the adoption of the vegetarian diet tends to follow the onset of mental disorders.
Diverse processes could in principle produce differences between vegetarians and non-vegetarians in rates of mental disorders.

On a biological level, nutrition status resulting from vegetarian diet may affect neuronal function and synaptic plasticity, which in turn influences brain processes relevant for onset and maintenance of mental disorders. For example, there is strong evidence that long-chain n-3 fatty acids causally affect risk for major depressive disorders.
Moreover, although evidence is less unequivocal, vitamin B12 levels appear to be causally linked to major depressive disorders.
Studies have reported that vegetarians show lower tissue concentrations of long-chain n-3 fatty acids and vitamin B12 which may elevate risk for major depressive disorder.

Besides differences in nutrition status, vegetarians and non-vegetarians differ in a number of psychological and socio-demographic characteristics that may influence their risk for mental disorders.
Vegetarians are predominantly female, are more likely to live in urban areas and to be single. All these socio-demographic factors are correlates of the presence of mental disorders.

A number of studies have shown that vegetarians tend to be slimmer, drink less alcohol, and exercise more than non-vegetarians; they tend to define themselves negatively by emphasizing what they do not do; they tend to stress their dissimilarity from others and thereby accentuate their differences from the general society; some vegetarians base the choice of their diet more on an ethical motivation.

On the whole, results strongly corroborate the past findings in smaller samples of adolescents and young adults, which have demonstrated that in contrast to physical health, a vegetarian diet is not associated with better mental health.
Whether compared with a control group of non-vegetarians matched for important socio-demographic characteristics, or with non-vegetarians in general, vegetarians show elevated prevalence rates of diverse mental disorders.

Importantly, researchers found no evidence for a causal role of vegetarian diet in the etiology of mental disorders.
Rather, the results are more consistent with the view that the experience of a mental disorder increases the probability of choosing a vegetarian diet, or that psychological factors influence both the probability of choosing a vegetarian diet and the probability of developing a mental disorder.

For more information
The International Journal of Behavioral Nutrition and Physical Activity
Vegetarian diet and mental disorders: results from a representative community survey
Johannes Michalak1, Xiao Chi Zhang and Frank Jacob.