Patients who are extremely obese may have a Biliopancreatic diversion procedure performed in order to permanently reduce their ability to absorb food, thereby forcing them to lose weight.
In the operation (see diagram) the stomach is cut away from its lower end just above the pylorus, and attached to a long loop of ileum (lower small intestine) that drains into the colon (large intestine). The upper end of the remaining small intestine is closed off, but continues to drain bile and pancreatic juices, while the lower end of the remaining small intestine is connected to the piece of ileum running from the stomach about 50 cm. from the colon.
After the operation the patient has difficulty in absorbing the food that they eat. The main side effects may be excessive weight loss and diarrhoea.