In the first phase of the surgery, 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.
Around 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. Similar to the other surgeries described above, the BPD/DS initially helps to reduce 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.
The food does not mix with the bile and pancreatic enzymes until it reaches the small intestine. Therefore a significant decrease in the absorption of calories and nutrients occur .
Lastly, the BPD/DS, , affects guts hormones in a manner that impacts hunger and satiety as well as blood sugar control.
The BPD/DS is considered to be the most effective surgery for the treatment of diabetes also.