I do think our diet needs vary between people and in each individual over time but I don't think our basic physiology changes. That said, almost-vegetarianism (still eating insects) has been found to be sustainable within traditional cultures but veganism has not so I do agree that vegetarianism is possible long term. Personally I felt very healthy- also never got sick, had healthy pregnancies, BF long-term and didn't have low levels of iron. But I'm discovering a deeper level of nutrition that I think is better provided for on an omnivore diet.

But I don't really want to debate this with a vegetarian at the moment. There is a vegetarian chat thread if you would like to discuss it more there. I made this thread for former vegetarians.