Roux-en-Y (RNY) gastric bypass is a weight loss surgery, or bariatric surgery, that is performed on patients who have tried and failed to lose weight losing using traditional methods. In Roux-en-Y gastric bypass, a small pouch at the top of the stomach is the only part of it that receives food, limiting intake. The small intestine is cut a short distance below the main stomach and connected to the new pouch. Food flows directly from the pouch into this part of the intestine. Because food now bypasses a portion of the small intestine, fewer calories are absorbed.