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Gastric bypass surgery
Before gastric bypass, food (see arrows) enters your stomach and passes into the small intestine. After surgery, the amount of food you can eat is reduced due to the smaller stomach pouch. Food is also redirected so that it bypasses most of your stomach and the first section of your small intestine (duodenum). Food flows directly into the middle section of your small intestine (jejunum), altering the secretion of gastrointestinal hormones and thereby affecting your appetite and metabolism.