Gastric bypass is a bariatric operation for morbid obesity in which the surgeon creates a small pouch from the top of the stomach and connects it directly to the middle of the small intestine, bypassing most of the stomach and the upper gut. Food therefore fills a tiny pouch and skips the main absorptive stretch of intestine, so patients both eat far less and absorb fewer calories — a combination of restriction and malabsorption that typically produces substantial, lasting weight loss. The rerouting also alters gut hormones in ways that often rapidly improve type 2 diabetes. It is major surgery with lifelong consequences: patients need permanent vitamin and mineral supplementation, careful protein intake, and monitoring for dumping syndrome and deficiencies.