What Is Gastric Bypass Surgery?

Medically Reviewed by Melinda Ratini, MS, DO on April 26, 2024
3 min read

Roux-en-Y gastric bypass surgery was once the most common weight loss surgeries, but it is far outpaced by the sleeve gastrectomy. Gastric bypass accounts for only 18% of weight loss surgeries. The procedure has two parts:

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.

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).

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.

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.

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

  • Sleeve gastrectomy(gastric sleeve surgery) is the most commonly performed weight loss surgery in the U.S., accounting for almost 60% of weight loss procedures in 2021. Half the stomach is removed, with the remaining section formed into a sleeve, or tube. This is also a “restrictive” strategy; the smaller stomach can't hold as much food. It 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.