[HuShifang]

Ok, one more anecdote for you: I've been vegan for about five years, for ethical reasons. (Which is to say, I basically have eaten a similar diet to what I did before, only vegan -- so vegan ice cream in lieu of dairy ice cream, sofritas Chipotle burritos rather than steak Chipotle burritos, Beyond burgers rather than cow burgers.) I've taken the occasional multivitamin but nothing special -- I get B12 and all that from fortified soy milk and other foods. I'm physically larger -- at six foot, my weight has ranged from 202 to 185 lbs as a vegan rather than 185 to 170 lbs as it did when I was omnivorous -- and run (my main form of exercise) faster, farther, and more frequently than when I ate omnivorously (I.e. it's not that I've gotten fat). Blood work has always been perfect, recovery times much lower, energy levels fine, etc. Zero health issues.

Your friends were doing it wrong. Probably, they were eating nothing but salads, or stacking dietary restrictions (e.g. gluten-free or raw).