If you undergo gastric bypass surgery you are at risk for pouch stretching, a condition whereby the stomach enlarges over time, and stretching back to its normal size before surgery. Band erosion of some part of the stomach disintegrate or the breakdown of some staple lines which involve the falling apart of band and stable thereby reversing the procedure.
There are two types of gastric bypass surgery, the Roux-en Y Gastric Bypass (RGB) which is the most common. Here the stomach pouch is formed by stapling part of the stomach together. The other one is the extensive gastric bypass which is a more complicated bypass operation whereby the lower portion of the stomach is removed and the part that remains is connected directly to the small intestines thus completing bypassing of the duodenum and jejunum. This type of operation helps in promoting weight loss but it is not used widely because of the high risk of nutritional deficiencies.