There are a whole slew of research linking not eating meat to depression, but questions still remain about why.
Is it predisposition? People who are predisposed to depression also select vegetarian/vegan status?
Is it social? Being vegan or vegetarian limits people’s social opportunities, thus driving depression?
Is it chemical? Something in the lack of animal protein contributes to the depression?
What ever the cause, more research is necessary before ruling out vegan and vegetarian lifestyles.