This operation induces controlled malabsorption. The operation involves removal of about 70% of the stomach and food is diverted to bypass a significant length of small bowel.

It works by reducing the absorption of nutrients due to the lack of enzymes needed to break down the larger fat, protein and carbohydrate molecules as well as reducing the amount of small intestine through which the ingested food passes. This results in less nutrients being absorbed.

The operation can be performed laparoscopically, but it is more demanding technically than other bariatric procedures and it is therefore usually performed open.

Although it produces more rapid weight loss than the other procedures and results in  greater food tolerance, it results in loose, foul smelling, bowel actions and malabsorption of fat soluble vitamins (A,D,E,K). Like Gastric Bypass, it also causes Dumping syndrome, but not as commonly.

The weight loss of about 65% is similar to that achieved by other, less risky procedures such as gastric lapbanding and sleeve gastrectomy which also do not cause the side effects common to the biliopancreatic diversion operation.