Gastric bypass surgery makes the stomach smaller and allows food to bypass part of the small intestine. You will feel full more quickly than when your stomach was its original size, which reduces the amount of food you eat and thus the calories consumed. Bypassing part of the intestine also results in fewer calories being absorbed. This leads to weight loss.

The most common gastric bypass surgery is a Roux-en-Y gastric bypass.

In normal digestion, food passes through the stomach and enters the small intestine, where most of the nutrients and calories are absorbed. It then passes into the large intestine (colon), and the remaining waste is eventually excreted.

In a Roux-en-Y gastric bypass, the stomach is made smaller by creating a small pouch at the top of the stomach using surgical staples or a plastic band. The smaller stomach is connected directly to the middle portion of the small intestine (jejunum), bypassing the rest of the stomach and the upper portion of the small intestine (duodenum).

This procedure can be done by making a large incision in the abdomen (an open procedure) or by making a small incision and using small instruments and a camera to guide the surgery (laparoscopic approach).

See an illustration of a Roux-en-Y gastric bypass.

What To Expect After Surgery

This surgery usually involves a 4- to 6-day hospital stay (2 to 3 days for a laparoscopic approach). Most people can return to their normal activities within 3 to 5 weeks.

Gastric bypass surgeries may cause dumping syndrome. This occurs when food moves too quickly through the stomach and intestines. It causes nausea, weakness, sweating, faintness, and possibly diarrhea soon after eating. These symptoms are made worse by eating highly refined, high-calorie foods (like sweets). In some cases you may become so weak that you have to lie down until the symptoms pass.

Why It Is Done

Although guidelines vary, surgery is generally considered when your body mass index is 40 or higher or you have a life-threatening or disabling condition related to your weight.

Your doctor may only consider doing gastric bypass surgery if you have not been able to lose weight with other treatments.

The following conditions may also be required or are at least considered:

• You have been obese for at least 5 years.
• You do not have a history of alcohol abuse.
• You do not have untreated depression or another major psychiatric disorder.
• You are between 18 and 65 years of age.

All surgeries have risk, and it is important for you and your health professional to discuss your treatment options to decide what is best for your situation.

How Well It Works

Most people who have gastric bypass surgery quickly begin to lose weight and continue to lose weight for up to 12 months. One study noted that people lost about one-third of their excess weight (the weight above what is considered healthy) in 1 to 4 years.¹ Some of the lost weight may be regained.

The laparoscopic approach showed similar results, with 69% to 82% of excess weight lost over 12 to 54 months.²

Risks

Risks common to all surgeries for weight loss include an infection in the incision, a leak from the stomach into the abdominal cavity or where the intestine is connected (resulting in an infection called peritonitis), and a blood clot in the lung (pulmonary embolism). About one-third of all people having surgery for obesity develop gallstones or a nutritional deficiency condition such as anemia or osteoporosis.^{3, 4}

Fewer than 3 in 200 (1.5%) people die after surgery for weight loss.³

After a Roux-en-Y gastric bypass:^{5, 3}

• An iron and vitamin B₁₂ deficiency occurs more than 30% of the time. About 50% of those with an iron deficiency develop anemia.
• The connection between the stomach and the intestines narrows (stomal stenosis) 5% to 15% of the time, leading to nausea and vomiting after eating.
• Ulcers develop 5% to 15% of the time.
• The staples may pull loose.
• Hernia may develop.
• The bypassed stomach may enlarge, resulting in hiccups and bloating.

What To Think About

In a gastric bypass, the part of the intestine where many minerals and vitamins are most easily absorbed is bypassed. Because of this, you may have a deficiency in iron, calcium, magnesium, or vitamins. This can lead to long-term problems, such as osteoporosis. To prevent vitamin and mineral deficiencies, you may need to work with a dietitian to plan meals, and you may need to take nutrient supplements and injections of vitamin B₁₂.

Early studies of the laparoscopic approach to surgery for obesity suggest that it reduces recovery time and postsurgery complications.²