A study conducted found a correlation between the adaptation of a vegetarian diet and an elevated risk of mental illness (neuroticism, major depression, OCD, phobias, etc) in comparison to a matched non-vegetarian group which took socio-economic factors into account (so that it wasn't just elite, financially well-off vegetarians vs. trailer trash junk food eaters). One of the possible reasons listed for the high-rate of depression and social anxiety was how vegetarians negatively define themselves by what they don't eat (ie, meat).
What would they find if they polled the Paleo community?
Vegetarian diet and mental disorders: results from a representative community survey
