[johnohara]

While I can't speak to the issue of mental health effects, I can say with certainty that being purely vegan requires a very high level of knowledge and understanding about the human body's intrinsic dietary needs and metabolic processes.

Most vegans I know have acquired this knowledge over time. A vegan diet demands physiological due diligence and truthful self-discovery. Neither of which is a bad thing.

[PerfectElement]

I think that's true for anyone aiming at being healthy. I'd say that eating meat and not having any nutrition knowledge is even worse. If you don't know anything about nutrition, sticking with fruits, legumes, grains, nuts, seeds and greens is a pretty safe choice.