Via the New York Times, an ex-Vegan Speaks:
Indigenous cuisines offer clues about what humans, naturally omnivorous, need to survive, reproduce and grow: traditional vegetarian diets, as in India, invariably include dairy and eggs for complete protein, essential fats and vitamins. There are no vegan societies for a simple reason: a vegan diet is not adequate in the long run.
While my views on Veganism are not as…ah…pointed as Michael Ruhlman‘s, I do belive that the weakest part of the vegan stance was in regard to nutrition. But as I live in a very large glass house when it comes to nutrition, I try to toss as few stones as possible.
At any rate, the Op-ed by Nina Plank is a thought provoking read.