Restrictive procedures like gastric banding, temporarily decrease the capacity of the stomach. Weight loss occurs because the amount of food that can be comfortably ingested is drastically reduced.

Restrictive/malabsorptive procedures like gastric bypass combine both principles of the previously described weight loss surgery methods. Weight loss occurs not only because the capacity of the stomach is greatly reduced, but because digestion and metabolism is altered from changes in stomach hormones and the absorption of nutrients.

Malabsorptive procedures prevent the body from absorbing calories and nutrients from ingested food. Weight loss occurs because surgery changes the way food is digested.

Duodenal switch/Biliopancreatic diversion is a malabsorptive procedure in which the stomach is surgically divided so that food is rerouted directly to the latter part of the small intestine. Food is passed through the system much more quickly than usual because there is less contact with digestive juices from the liver and pancreas.

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This procedure can be performed with either an open or laparoscopic approach. The advantages to malabsorptive procedures include a significant degree of excess weight loss and overall patient satisfaction because when compared to other procedures, this surgery allows them to eat much larger meals.

However, the principles which induce weight loss with this procedure type are often related to the most frequent complications. Patients are at risk for developing problems with malnutrition of nutrients and essential vitamins and minerals. Without compliance close lifelong monitoring for protein malnutrition, anemia and bone disease, it has been observed that at least 25% of patients develop problems that require treatment.