Quite often. The Pythagoreans went so far as to avoid beans, it's said, because they were supposed to be reincarnated animals and people - as evidenced by their souls escaping when we fart.

Greek ascetics were probably influenced by Hindu and Buddhist sects, and influenced others in the Greco-Roman world in turn: many early Christians were vegetarians, including a Jewish-Christian sect of Nazarenes that has as good a claim as any of being the one founded by Jesus himself.