SADI-S (single anastomosis duodeno–ileal bypass) is the surgical procedure that involves duodenal bypass, which is performed with a single anastomosis, and sleeve gastrectomy. It can also be defined as an integrated form of biliopancreatic diversion surgery or duodenal switch surgery. In this procedure, the stomach obtained as a result of sleeve gastrectomy is separated from the duodenum by cutting. An anastomosis, that is, a joining operation, is performed to connect the separated duodenum section to the second part of the small intestine called the ileum.

The sleeve stomach created in SADI-S surgery, which can also be performed laparoscopically, restricts the amount of food intake, and also aim at reducing the utilization of these foods. In addition, absorption is also reduced by inactivating a section of the small intestine that provides absorption. Thus, the procedure can help lose weight by reducing the weight gain of the patient. This surgical procedure is usually performed on people who have metabolic diseases such as hypertension, diabetes and high cholesterol, and those who cannot achieve weight loss at the planned rates or to the extent close to these rates. After the procedure, patients may experience a condition in which they need to take vitamin and mineral supplements for life.