I have done the vegan DIET in the past and must admit, it can be a very healthy diet. I learned a lot about food, and I think it is possibly one of the best ways of eating.
HOWEVER, if your friend is into vegetarianism/veganism because of some MORAL IMPERATIVE, this could be a problem. Although I do "get" the moral issues behind veganism (factory farming, animals have some form of consciousness) that was not my sole reason for trying veganism- it was more for health reasons. I discontinued mainly for social reasons (none of my friends were vegan) and impracticality (poor availability of fresh and varied produce). If I lived in the East Village with a bunch of vegan hipsters, I could eat vegan very day.