The way how we eat is obviously important. In the past, many researchers have conducted studies where they wanted to know the difference between people who were vegetarian, vegan, and omnivore. In this article, I cover a study where they were interested whether people differ in the rate of mental illnesses. The results may surprise you.
Researchers from the University of Hildesheim in Germany were investigating whether there were different rates of mental disorders in people who were either omnivores, vegetarians, or partial vegetarians. This was being assessed with a food frequency questionnaire, a common self-assessment tool.
While I don’t think self-assessment tools and self-report questionnaires are the best way of gathering data in nutritional studies, no other way was possible in this scenario.
In any case, if you like reading about nutrition, then you’ve surely come across studies where vegetarians were shown to live longer and with less disease compared to omnivores. One reason is the (health) superiority of a (predominately) plant-based diet, another were their counterparts themselves – omnivores who were mostly eating a Western diet. If you’ve read this blog then you know the typical Western diet is very unhealthy.
Another main reason is that vegetarians are, on average, more health-conscious and engage in behavior which promotes health, such as being physically active on a regular basis.
With all that said, little thought had been given to mental health. Until recently.
Omega-3 and mental disorders
I’ve written about the connection between omega-3 fatty acids and depression to an extent before. Nutritional evidence suggests that long-chain omega-3 fatty acids are a risk factor for major depressive disorder (MDD) [1, 2]. Vitamin b12 has some interesting implications, though smaller, in the pathophysiology of MDD as well.
The above-mentioned researchers further give weight to an interesting relationship; an increased prevalence of certain mental disorders in vegetarians when they were compared to people who described themselves as partial vegetarians (eating meat only occasionally) or omnivores.
Increased prevalence of mental disorders in vegetarians
What these researchers found was that the prevalence rate of depressive disorders were around 15% higher in the group of vegetarians, not a small percentage by any means. Moreover, the prevalence rate for anxiety disorders was higher by around 12% as well. And that’s not the end of it. While the prevalence rate of eating disorders in the omnivore group was around 1%, for vegetarians it was 5,6%.
These differences range from small; eating disorders, to rather high; depressive disorders. All of them were statistically significant – thus meaning it is highly unlikely they happened by chance. The interesting thing to note with the third group which was involved, partial vegetarians, was that they were always between the other two, as far as prevalence rates of different disorders go.
The last interesting factoid was that the female vegetarians in this study had a higher rate of mental disorders, there were also more of them in the sample itself (70%).
The authors conclude that, upon reviewing the available literature, there is a possibility that experiencing a mental disorder will increase your chance of choosing a vegetarian diet, or that certain psychological factors will influence either the possibility of you experiencing a certain mental disorder, becoming vegetarian, or both. 
This study obviously shows only a connection between vegetarianism and an increased prevalence of mental disorders. Nothing causal can be inferred from that, so we should stay vary of such conclusions.