Contrary to conventional wisdom, this link is surprisingly weak. Most kids who abuse animals become normal adults and most serial killers and school shooters do not have a history of animal abuse. (See Animal Cruelty Does Not Predict Who Will Be a School Shooter).
Similarly, only a small fraction of people who suffer from depression are vegetarians and most vegetarians are not depressed. However, the existence of multiple studies involving thousands of subjects by researchers in different countries suggests that the connection between vegetarianism and depression is not a statistical fluke.
Does Vegetarianism Cause Depression?
What is going on?
I can think of a couple of possibilities.
First, it could be the case that vegetarian diets actually produce biological changes in brain chemistry, or even the microbiome, that causes some people to be depressed. I am a bit skeptical of this explanation, but the German study mentioned above found that 34 percent of people with depression started on a vegetarian diet before the onset of their mental disorders, compared to 9 percent of people with anxiety disorders.
I think it is more likely that some traits may predispose some people to both depression and to vegetarianism. Women, for example, are twice as likely as men to suffer from depression, and there are also more female vegetarians than male vegetarians.
And, while the evidence is mixed, some personality types may also be particularly drawn to vegetarianism.
In addition, vegetarian diets can be isolating. A woman who recently became a vegan told me that she suddenly gets fewer dinner invitations from old friends: They don’t know how to cook for her. And one young woman told me, “I won’t go out with anyone who is not a vegetarian. It limits my pool of possible men.”
Further, social reasons rank high when former vegetarians and vegans are asked why they returned to meat. (See Why Do Most Vegetarians Go Back To Eating Meat?)
Finally, as several animal activists pointed out to me after this post was initially written, the vegetarian-depression link could be the result of moral commitment. As Lori Marino, executive director of the Kimmela Center for Animal Advocacy wrote on Facebook, vegetarians and vegans are more aware of the cruelties of the world and this is more depressing than living in a state of ignorant bliss.
Lori is right. Indeed, the emotional and psychological costs of devoting your life to animal protection was a major theme in one of my first studies of human-animal relationships. (Full text here.)
In short, we don’t know why the rates of depression seem substantially higher among vegetarians than in omnivores. But we do know that “correlation does not imply causality” and “more research is needed.”
Written by Hal Herzog
Originally appeared in Animal and Us Blog on PsychologyToday
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