When you were in Vietnam, how old were you? Youth may have had a lot to do with your ability to flourish on the proffered fare. And if you continued to eat that way up to the current day, do you think it would still be benefitting you?
I absolutely am at the crossroads of reintroducing some flesh back into my diet after nearly 30 years of being a veghead. I don't do this lightly by any means. I am admittedly still waffling back & forth.
However, the point you bring to the fore is notable. It would be wise to adapt our bodies to ALL types of food in the event that the food our body's have adapted to (such as vegetarianism) became unavailable.