In a biliopancreatic diversion with duodenal switch, a portion of the stomach is removed but the pylorus remains intact. The pylorus controls food drainage from the stomach. The pylorus is connected to a lower segment of the intestine. The upper part of the small intestine (duodenum) is connected to the lower part of the small intestine. The food you eat then bypasses much of the small intestine. This results in fewer calories absorbed and weight loss.