The Manichaeans, followers of
Mani, were split into two groups: the "hearers" and the "elect." The elect had to follow very strict rules, mostly concerning the taking of life.
Any life. So not only were they
not allowed to eat meat, they also weren't allowed to kill any plants for food.
They still ate, it was just a matter of having hearers to prepare their food for them. And when they ate the food that had been prepared for them they said to it, "It was not I who reaped or ground or baked thee; may they who did so be reaped and ground and baked in their turn!"
The idea being that the guy who actually killed the grain would be reincarnated as grain in his next life, until he had worked off all his sins and could eventually be born as an elect after a few spins on the karmic wheel. The elect, when he dies, gets to leave the reincarnation cycle and return to heaven, from whence all human souls originally came.
St. Augustine served as a hearer of the Manicheans for nine years, but got disillusioned by their hypocrisy and left.
source: Sketches of Church History, Book 1: A.D. 33 - 604