Duodenal Switch

This surgery, also called biliopancreatic diversion with duodenal switch, is more complex than the others. The duodenal switch involves two separate surgeries. The first is similar to gastric sleeve surgery. The second surgery redirects food to bypass most of your small intestine. The surgeon also reattaches the bypassed section to the last part of the small intestine, allowing digestive juices to mix with food.
This type of surgery allows you to lose more weight than the other three. However, this surgery is also the most likely to cause surgery-related problems and a shortage of vitamins, minerals, and protein in your body. For these reasons, surgeons do not perform this surgery as often.
 
Source  https://www.niddk.nih.gov/health-information/weight-management/bariatric-surgery/types