A gastric bypass is one of the surgical weight loss procedures offered to morbidly obese patients as a last resort, when all other weight loss methods have failed.

Bariatric surgery is the collective term used to refer to these weight loss procedures which include gastric bypass surgery and gastric banding.

It is estimated that 200,000 gastric bypasses were performed in 2008 in the United States. The surgery has since become more popular owing to the minimally invasive approaches used such as keyhole surgery or laparoscopy.

For laparoscopic surgery, several small incisions are made in the abdomen through which a telescope attached to a camera and various other specialized surgical instruments can be inserted. The operating surgeon can then perform the bypass while watching the operation on a video screen.

Gastric bypass procedure

For the surgery, a thumb-sized pouch with an approximate capacity of around 15 to 30 ml is created in the upper stomach. This pouch is then connected to a segment of the small intestine, meaning the rest of the stomach and bowel is bypassed.

Because the pouch is small, the stomach size is effectively reduced, leading to a reduction in its functional volume and therefore the amount of food that can be ingested at any one time.

The surgery can reduce the size of the stomach by as much as 90% or more. The patient then requires less food to feel full as well as absorbing less calories from any food they do eat.

Variations of the surgery

These include:

• Gastric bypass, Roux en-Y (proximal) - This is the most common form of gastric bypass surgery in the United States. For this operation, the small intestine is divided about 18 inches below the lower stomach outlet to create a Y shaped configuration that allows food to flow from the small stomach pouch via a “Roux limb.”
• Gastric bypass, Roux en-Y (distal) - In this variation, the Y-configuration is made further down in the small intestine, much closer to the lower end. This reduces the amount of bowel available to absorb the fat, starches and other components of food.