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Step 5: Gastric bypass surgery
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Weight loss surgery involves one or both of the following approaches:

  • Restrictive procedures result in a smaller stomach pouch. Normally, the stomach can hold about 6 1/2 cups of food. Because a surgically modified, smaller stomach pouch holds less (usually about 1/2 cup), you must eat considerably smaller portions. Food then passes much more slowly from the stomach into the intestine. This allows you to feel full much longer after eating.
  • Malabsorptive procedures alter the pattern of flow from your stomach to your intestine, decreasing the number of calories absorbed by the intestine.

The next few steps explain some of the most common forms of weight loss surgery.

Gastric bypass surgery

Gastric bypass surgery uses both restriction and malabsorption to achieve weight loss. Roux-en-Y gastric bypass is the most common type of weight loss surgery performed.

In Roux-en-Y gastric bypass, staples are used to permanently close off part of the stomach. This leaves only a small stomach pouch for the food you eat. Additionally, a Y-shaped piece derived from an upper portion of the small intestine is then attached to this small stomach pouch. As a result, food from your stomach pouch bypasses the rest of the stomach and the first part of the intestine, which normally would absorb some calories and nutrients after eating.

Gastric bypass surgery can be performed using a traditional open technique or through laparoscopic surgery, depending on your circumstances and the decision of your surgeon. The traditional open technique involves an incision in the abdomen that allows the surgeon to visualize and access your stomach and intestine. Most gastric bypass surgery is done with laparoscopic surgery, which uses smaller incisions and a small video camera that projects views of your stomach and intestine onto a monitor in the operating room. Both methods are routinely performed. Talk to your doctor about these two approaches and which would be appropriate for you.

Not surprisingly, there are numerous other variations on the gastric bypass approach. (Click here to learn more about biliopancreatic diversion, and biliopancreatic diversion with duodenal switch.)

Biliopancreatic diversion takes longer than gastric bypass, and is technically more difficult. The complication rate is similar to gastric bypass when an experienced surgeon performs the procedure. After this operation, people can enjoy a wider variety of foods and eat about half as much as they did before the operation, without fear of experiencing dumping syndrome. In addition, calcium loss does not follow the duodenal switch. Although some behavioral change is still needed, this procedure may offer better quality of life for some people.

The benefits of gastric bypass surgery

  • The procedure is a proven, accepted long-term weight control tool with established health benefits.
  • Gastric bypass surgery (malabsorptive techniques) tends to produce greater weight loss than do surgeries that use only restrictive techniques, such as the adjustable gastric band.
  • Patients lose about two-thirds of their excess weight within a year. While some weight rebound may occur, most patients can keep off roughly 100 pounds of the weight they've lost over the long-term.
  • Many of the serious complications of obesity may resolve or improve after weight loss, including diabetes, high blood pressure, sleep apnea, joint pain, and incontinence.

The potential complications of gastric bypass surgery

The risks include, but are not limited to, the usual risks of any surgery (which involves general anesthesia), including problems with:

  • Breathing, pneumonia
  • Blood clots
  • Bleeding
  • Hernias at the site of the incision
  • Infection
  • Heart problems

The risks from gastric bypass surgery include:

  • Leaking or rupture along the stapled area of the stomach pouch and small intestine
  • Gallstones with rapid weight loss
  • Stomach ulcers
  • Nausea and vomiting, especially if you overeat
  • Dumping syndrome (a condition in which you eat too much sugar or fat, resulting in symptoms such as nausea, vomiting, diarrhea, dizziness, and sweating)
  • Nutritional deficiencies (such as iron, calcium, vitamin B12, and folic acid)
  • Blocked intestine (bowel obstruction)
  • Stretching of the stomach pouch - if you repeatedly overeat, you may slowly increase the size of the stomach pouch, thus defeating the purpose of having undergone gastric bypass surgery in the first place, and therefore gain weight.
  • Hair loss
  • Constipation
  • Excess skin after weight loss
The formation of gallstones is a possible risk following gastric bypass surgery.

Although you may not be able to avoid all complications, here is how to minimize risks after surgery:

  • Closely follow recommended meal size.
  • Take small bites.
  • Chew slowly and thoroughly.
  • Take 20 - 30 minutes to eat each meal.
  • Follow recommended amounts of protein at each meal.
  • Stay away from fatty foods and sugars.
  • Consult a dietitian for how to maintain the most nutritious diet possible, advice on nutritional supplements, and information on taking fiber to avoid constipation.


Richards WO. Morbid Obesity. In: Townsend Jr. CM, Beauchamp RD, Evers BM, Mattox KL. Sabiston Textbook of Surgery. 19th ed. Philadelphia,Pa: Saunders; 2012; chap 15.

Pontiroli AE, Morabito A. Long-term prevention of mortality in morbid obesity through bariatric surgery: A systematic review and meta-analysis of trials performed with gastric banding and gastric bypass. Ann Surg. 2011;253:484-487.


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Review Date: 12/16/2012
Reviewed By: Robert A. Cowles, MD, Associate Professor of Surgery, Yale University School of Medicine, New Haven, CT. Review provided by VeriMed Healthcare Network.
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