What Is Gastric Bypass Surgery?

Roux-en-Y gastric bypass surgery is one of the most common weight loss surgeries, accounting for about 47% of all weight loss surgeries. The procedure has two parts:

Part One: Making a Small Pouch in the Stomach

The surgeon divides the stomach into a large portion and a much smaller one. Then, in a process sometimes called "stomach stapling,” the small part of the stomach is sewn or stapled together to make a pouch, which can hold only a cup or so of food.

With such a small stomach, people feel full quickly and eat less. This strategy is also called "restrictive," because the new stomach size restricts how much food it can hold.

Part Two: Bypass

The surgeon disconnects the new, small stomach pouch from the majority of the stomach and first part of the small intestine (the duodenum), and then connects it to a part of the small intestine slightly farther down (the jejunum). This surgical technique is called a "Roux-en-Y."

After a Roux-en-Y, food passes directly from the stomach into the jejunum, bypassing the duodenum. This curbs your absorption of calories and nutrients. This weight loss method is called "malabsorptive."

Stomach stapling and Roux-en-Y are typically done during the same surgery and together are called a "Roux-en-Y gastric bypass."

Usually, surgeons do both laparoscopically (using tools inserted through small cuts in the belly). When laparoscopy isn’t possible, surgeons may do a laparotomy (involving a large cut in the middle of the belly).

Recovery and Potential Complications

After gastric bypass surgery, people typically stay in the hospital for 2 to 3 days and return to normal activity within 2 to 3 weeks. About 10% of people have complications that may include:

  • Wound infections
  • Digestive problems
  • Ulcers
  • Bleeding

Nearly 1% to 5% of people have serious or life-threatening complications, such as:

  • Blood clot (pulmonary embolism)
  • Heart attack
  • Leak in the surgical connections with the intestines
  • Serious infection or bleeding

The risk of complications is lower at centers that do more than 100 weight loss surgeries per year. Deaths in the month following gastric bypass surgery are very rare (about 0.2% to 0.5%, or less than one in 200 people) when the procedure is done by a highly experienced surgeon.

Other health problems can also happen as a result of the surgery. For example, not absorbing as much of nutrients like iron and calcium can cause anemia and osteoporosis. But taking nutritional supplements and getting blood tests can make that less likely.


What to Expect After Gastric Bypass

Post-surgery weight loss is often dramatic. On average, patients lose 60% of their extra weight. For example, a 350-pound person who is 200 pounds overweight would drop about 120 pounds.

Many weight-related health problems improve or even disappear after gastric bypass surgery. The most common are diabetes, high blood pressure, asthma, and obstructive sleep apnea.

But losing weight and keeping it off takes lasting lifestyle changes, like eating several small meals a day and getting regular exercise.

Other Types of Weight Loss Surgery

If you’re considering weight-loss surgery, gastric bypass isn’t your only option. Others include:

  • Adjustable gastric banding(also called laparascopic gastric banding, or lap band surgery) is the least invasive weight loss surgery. It accounts for about 15%-20% of procedures. In gastric banding, a surgeon places a silicone ring around the upper stomach.

The surgeon can adjust the ring's tightness by injecting saline through the skin to fill up the band or extracting saline to loosen it. This fine-tunes the exact size of the stomach. For example, if a too-tight stomach is causing side effects, the bands can be loosened. Tightening the bands can shrink the stomach.

If necessary, the procedure can often be reversed. Gastric banding is also less likely to cause nutritional problems. It usually results in less weight loss than gastric bypass surgery.

  • Sleeve gastrectomy (gastric sleeve surgery) where more than half of your stomach is removed, leaving a thin vertical sleeve, or tube. This is also a “restrictive” strategy and can be performed laparoscopically.
  • Vertical banded gastroplasty combines stomach stapling with gastric banding. Because of its higher complication rate and lower rates of weight loss, it’s rarely done.
  • Biliopancreatic diversionis similar to the Roux-en-Y gastric bypass, except the surgeon reconnects the stomach pouch to a portion of the small intestine that's much farther down (the ileum). Since more of the small intestine is bypassed, you absorb even fewer calories. This surgery is difficult to do and often leads to nutritional problems. This procedure accounts for a fraction of all U.S. weight loss surgeries.
WebMD Medical Reference Reviewed by Nayana Ambardekar, MD on January 23, 2020



American Society for Metabolic and Bariatric Surgery: "Brief History and Summary of Bariatric Surgery;" "Rationale for the Surgical Treatment of Morbid Obesity;" "Gastric Banding and Laparoscopic Adjustable Gastric Banding;" and "Bariatric Surgery." 

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Virji, A. American Family Physician, April 15, 2006.

Kral, J.  British Medical Journal, Oct. 28, 2006.

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