There are three mechanisms by which patients lose weight after gastric bypass:
The pouch is very small and can only hold tiny portions of food. This helps you to feel full quickly and eat less.
The opening from the pouch to the small intestine is small, so food moves through your system slowly. This gives you the sensation of feeling full/satisfied for longer.
Many patients cannot tolerate large amounts of refined sugar after gastric bypass. Eating very little sugar contributes to weight loss.