• Roux-en-Y gastric bypass (RGB): This operation is the most common gastric bypass surgery performed in the U.S. First, a small stomach pouch is created by stapling part of the stomach together or by vertical banding. This limits how much food you can eat. Next, a Y-shaped section of the small intestine is attached to the pouch to allow food to bypass the duodenum as well as the first portion of the jejunum. This causes reduced calorie and nutrient absorption. This procedure can now be done with a laparoscope (a thin telescope-like instrument for viewing inside the abdomen) in some people. This involves using small incisions and generally has a more rapid recovery time.

• Extensive gastric bypass (biliopancreatic diversion): In this more complicated gastric bypass operation, the lower portion of the stomach is removed. The small pouch that remains is connected directly to the final segment of the small intestine, thus completely bypassing both the duodenum and jejunum. Although this procedure successfully promotes weight loss, it is not as widely used because of the high risk for nutritional deficiencies.

Gastric bypass surgery that causes malabsorption and restricts food intake produces more weight loss than restriction operations, which only decrease food intake. People who have bypass surgery generally lose two-thirds of their excess weight within two years.

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