/sci/ - Science & Math

One of my buddies who recently was discharged from the military just became a vegan. Despite all the 'oh the poor animals' bullshit he queefs all over facebook, he does make some good points about health and wellness. And he never neglects to back up his assertions with sources. SO what does /sci/ think about veganism?
I've been doing some research myself but this kind of thing is not my forte. I'm more of a historyfag, and I can't come to any conclusions that I'm willing to trust myself on.
I wasn't sure where else to post this, and I don't think /fit/ would be much help. So, can you guys help me achieve enlightenment on the matter?