Duodenal switch is a surgery with two components. First, a smaller, tubular stomach pouch is created by removing a portion of the stomach, similar to the sleeve gastrectomy. Next, a large portion of the small intestine is bypassed.
The duodenum, or the first portion of the small intestine, is divided just past the outlet of the stomach. A segment of the distal (last portion) small intestine is then brought up and connected to the outlet of the newly created stomach, so that when the patient eats, the food goes through a newly created tubular stomach pouch and empties directly into the last segment of the small intestine. Roughly three-fourths of the small intestine is bypassed by the food stream.
The bypassed small intestine, which carries the bile and pancreatic enzymes that are necessary for the breakdown and absorption of protein and fat, is reconnected to the last portion of the small intestine so that they can eventually mix with the food stream. The procedure reduces the amount of food that is consumed; however, over time this effect lessens and patients are able to eventually consume near “normal” amounts of food. Unlike the other procedures, there is a significant amount of small bowel that is bypassed by the food stream.
Additionally, the food does not mix with the bile and pancreatic enzymes until very far down the small intestine. This results in a significant decrease in the absorption of calories and nutrients (particularly protein and fat) as well as nutrients and vitamins dependent on fat for absorption (fat soluble vitamins and nutrients).
Lastly, similar to the gastric bypass and sleeve gastrectomy, this surgery affects guts hormones in a manner that impacts hunger and satiety as well as blood sugar control. Therefore, it is considered to be the most effective surgery for the treatment of diabetes.
Source: American Society for Metabolic and Bariatric Surgery