How much weight can be lost on a juice fast?

There is no definite answer but when the body doesn't receive solid food for a while it slows down one's metabolism so when you do decide to eat, your body will convert it all to fat, thus undoing what you tried to do in the first place. The key (as I see it) is to eat small amounts of food. 2000 calories will keep you at the same weight. Eat less than that or burn more via exercize and you lose weight!