Writing a story in which most alien races digest food physically, not useing any chemical stuff. Is this even possible? I know that some lizards and chickens eat rocks for similar reasons, but they've got stomach acid as well. If they are weak and need to eat all the time, it's a plus, story wise, so.
Edit because I wasn't clear enough: I know that it's not posible for there to be NO chemical reaction, what I mean is that they lack bile. I want to know if such a creature can survive, and what the effects of it's odd digestive system would be.