The doctor generally performs the following three types of bariatric surgery:

1. Gastric bypass Surgery:  In this surgery, the surgeon transforms the stomach into a small pouch and attaches the small intestine into the pouch. It is a common method and is usually irreversible. After this procedure, the food bypasses most of the stomach and the initial part of the small intestine.  
2. Sleeve gastrectomy: During this procedure, the surgeon eliminates most parts of the stomach to make the stomach a thin-tube like structure. Thus, the new stomach would be unable to hold much food. There is also lesser secretion of the hormone ghrelin resulting in lesser appetite. 
3. Biliopancreatic diversion with duodenal switch: This procedure is done in two steps. The first step is similar to sleeve gastrectomy. The surgeon makes the stomach into a tube-like structure. In the second step, the surgeon bypasses a significant portion of the intestine.
4. Gastric band: The surgeon, during this procedure, places a silicone band around the upper stomach to reduce its size. The surgeon also attaches this silicone band to a tube and extends it under the abdominal skin. The surgeon inflates the silicone band by injecting the saline solution into the tube.