The biliopancreatic diversion with duodenal switch procedure begins with the surgeon removing a large part of the stomach. This is called a sleeve gastrectomy. The valve that releases food into the small intestine is left, along with the first part of the small intestine, called the duodenum. The surgeon then closes off the middle section of the intestine and attaches the last part directly to the duodenum. This is the duodenal switch. The separated section of the intestine isn't removed from the body. Instead, it's reattached to the end of the intestine, allowing bile and pancreatic digestive juices to flow into this part of the intestine. This is the biliopancreatic diversion. As a result of these changes, food bypasses most of the small intestine, limiting the absorption of calories and nutrients. This, together with the smaller size of the stomach, leads to weight loss.