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Gastric Bypass

Gastric Bypass

Normal results


A gastric bypass is one type of elective bariatric (weight-loss) surgery done on the digestive system to help morbidly obese people lose weight. Gastric bypass surgery is also called malabsorptive surgery because it creates an alternate route for food traveling through the digestive system that bypasses a section of the small intestine where many nutrients are absorbed.


Gastric bypass surgery is intended to treat severe (morbid) obesity in people who have tried unsuccessfully to lose weight and whose excess weight threatens their health and well being. Obesity is defined by the body mass index (BMI). The BMI calculation compares weight to height. Adults age 20 and older are evaluated as follows:

  • BMI below 18.5: underweight
  • BMI 18.5-24.9: normal weight
  • BMI 25.0-29.9: overweight
  • BMI 30 and above: obese
  • BMI 40 and above: morbidly or severely obese

Obesity is linked to an increased likelihood of developing over 20 different diseases and disorders, including high blood pressure (hypertension), type 2diabetes, heart disease, stroke, deep vein blood clots, fatty liver disease, sleep apnea, heartburn, gastroesophageal reflux disease (GERD), gallstone disease, arthritis, colon cancer, breathing problems, and depression. Gastric bypass surgery reduces the amount of nutrients that are absorbed from food. It is performed in conjunction with bariatric restriction surgery in which the size of the stomach is reduced through surgical application of a band or stomach staples that close off a portion of the stomach. People who have had restriction surgery can eat only small amounts at a time before feeling full. Reduced food intake along with reduced nutrient absorption can lead to dramatic weight loss.


Obesity is the second leading cause (after tobacco use) of preventable death in the United States. The number of overweight and obese Americans has steadily increased since 1960. According to the National Institutes of Health, in 2006, 34% of Americans were overweight and 27% were obese. Of these, 15 million were morbidly obese, however, less than 1% chose to undergo a surgical weight-loss procedure.

The number of all surgical weight-loss procedures has increased rapidly. In 1995, only 20,000 weight-loss surgeries were performed in the United States. By 2006, 170,000 of these surgeries were done, and the number is expected to continue to increase. In 2006, the United States government agreed to pay for certain bariatric surgeries for individuals who qualified for Medicare. At that time, about 395,000 Americans ages 65-69 were medically eligible for obesity surgery. This number is expected to grow to 475,000 persons by 2010. With Medicare coverage, it is likely that more older people will have weight-loss surgery. In 2006, the average patient having bariatric surgery was a woman in her late 30s who weighed about 300 pounds (135 kg).


There are several different variations on gastric bypass, all of which are malabsorptive surgeries designed to lower caloric intake by reducing the amount of nutrients absorbed by the digestive system. These include:

  • gastric bypass with long gastrojejunostomy
  • Roux-en-Y (RNY) gastric bypass
  • transected (Miller) RNY bypass
  • laparoscopic RNY bypass
  • vertical (Fobi) gastric bypass
  • distal RNY bypass
  • biliopancreatic (BPD) diversion

All bariatric procedures create an alternate route for food through the digestive system so that the food bypasses part of the intestine. These procedures are accompanied by a procedure to reduce the size of the stomach so that less food can be comfortably consumed. Choice of procedure relies on the patient’s overall health status and on the surgeon’s judgment and experience.

In the operating room, the patient is put under general anesthesia by the anesthesiologist. Once the patient is asleep, an endotracheal tube is placed through the mouth into the trachea (windpipe) to connect the patient to a respirator during surgery. A urinary catheter is also placed in the bladder to drain urine during surgery and for surgeon to monitor the patient’s hydration. A nasogastric (NG) tube is also placed through the nose to drain secretions and is typically removed the morning after surgery.

The most common gastric bypass operation is the Roux-en-Y (RNY) gastric bypass. In this surgery, a small stomach pouch is created by stapling and banding the stomach. The pouch is about the size of an egg


Gastrojejunostomy— A surgical procedure in which the stomach is surgically connected to the jejunum (middle portion of the small intestine).

Gastroesophageal reflux disease (GERD)— A condition in which gastric juice from the stomach backs up into the bottom of the esophagus and causes irritation, inflammation, or erosion of the cells lining the esophagus.

Heartburn— A pain in the center of the chest behind the breastbone caused by the contents of the stomach flowing backwards (refluxing) into the lower end of the esophagus and causing irritation.

Hernia— The protrusion of a loop or section of an organ or tissue through an abnormal opening.

Laparoscopy— The examination of the inside of the abdomen through a lighted tube (endoscope), sometimes accompanied by surgery done through a small incision.

Malabsorption— Poor absorption of materials in the digestive system.

Morbidly obese— Definition of a person who is 100 lb (45 kg) or more than 50% overweight and has a body mass index above 40.

Osteoporosis— A condition found in older individuals in which bones decrease in density and become fragile and more likely to break. It can be caused by lack of vitamin D and/or calcium in the diet.

Sleep apnea— A temporary interruption in breathing during sleep.

Small intestine Consists of three sections: duodenum (nearest the stomach), jejunum, and ileum (nearest the colon or large intestine). Different nutrients are absorbed in different sections of the small intestine.

Type 2 diabetes Sometimes called adult-onset diabetes, this disease prevents the body from properly using glucose (sugar), but can often be controlled with diet and exercise.

and initially can hold 1-2 oz (30-60 ml), as compared to the 40-50 oz (1.2-1.51) held by a normal stomach. It is created along the more muscular side of the stomach, which makes it less likely to stretch over time.

Next, a Y-shaped piece of intestine is attached to the pouch on one end, and the jejunum, or middle part of the small intestine, on the other. This allows food to bypass the duodenum, or first part of the small intestine, where nutrients are absorbed. The food then continues normally through the rest of the small intestine and the large intestine.

The RNY gastric bypass can also be performed laparoscopically. The result is the same as an open surgery RNY, except that instead of opening the patient with a long incision on the stomach, surgeons make a small incision and insert a pencil-thin optical instrument called a laparoscope, to project a picture to a TV monitor. The laparoscopic RNY results in smaller scars, as usually only three to four small incisions are made. The average time required to complete the laparoscopic RNY gastric bypass is approximately two hours.

The great advantage of Roux-en-Y gastric bypass is that individuals lose, on average, 60-70% of their excess weight and are able to maintain the weight loss for 10 years or more. As a result, most obesity-related health problems are substantially reduced or cured when weight is lost and that weight loss is maintained. As of 2006, Medicare would usually pay for this surgery.

However, Roux-en-Y surgery also has some serious disadvantages, including:

  • This surgery is more difficult for the surgeon than restrictive surgeries, and involves permanently altering the digestive system.
  • Many vitamins and minerals are absorbed in the part of the small intestine bypassed by this surgery. The individual must commit to a lifetime of taking nutritional supplements to prevent serious vitamin and mineral deficiencies.
  • Tearing, bleeding, and infection at the sites where the incisions and reconnections are potentially fatal complications.
  • Dumping syndrome may occur in response to meals high in sugar. Dumping occurs when food moves too fast through the intestine and causes symptoms of nausea, bloating, weakness, sweating, fainting, and diarrhea.

Biliopancreatic diversion (BPD), another type of malabsorptive surgery, bypasses an even longer section of the small intestine. In BPD, about two-thirds of the stomach is surgically withdrawn, leaving a pouch that can hold about 3 cups of food. A bypass is then created to the ileum, or final portion of the small intestine. In all, about 9 ft (3 m) of intestine are bypassed. As a result, many fewer calories and nutrients are absorbed. The main advantage of BPD is the large amount of excess weight—between 75% and 80%—that is lost over the first two years and the health benefits that this loss brings. As of 2006, Medicare would usually pay for this surgery. Disadvantages are the same as for Roux-en Y surgery, but nutrient deficiencies are greater. Because fat is poorly digested as a result of this surgery, bowel movements are frequent and stools are especially foul smelling.


A diagnosis of obesity relies on a body weight assessment based on the body mass index (BMI) and waist circumference measurements. Waist circumference exceeding 40 in (101 cm) in men and 35 in (89 cm) in women increases disease risk. Gastric bypass as a weight-loss treatment is considered only for morbidly obese patients whose health is impaired by their obesity. To be candidates for gastric bypass surgery, individuals need to have failed at serious attempts to lose weight in the past, be in good mental health, demonstrate an understanding of the risks associated with this surgery, and be willing to make a lifetime commitment to changing eating habits.

Before the surgery, the patient will undergo a physical and psychological examination and receive nutritional counseling. To prepare for the surgery itself, an intravenous (IV) line is placed, and the patient may be given a sedative to help relax before going to the operating room.


Patients experience postoperative pain and the other common discomforts of major surgery, such as the NG tube and a dry mouth. Pain is managed with medication. A large dressing covers the surgical incision on the abdomen of the patient and is usually removed by the second day in the hospital. Short showers 48 hours after surgery are usually allowed. Patients are also fitted with special socks to improve blood flow in their legs and prevent blood clot formation. At the surgeon’s discretion, some patients may have a gastrostomy tube (g-tube) inserted during surgery to drain secretions from the larger bypassed portion of the stomach. After a few days, it will be clamped and will remain closed. When inserted, the g-tube usually remains for another four to six weeks. It is kept in place in the unlikely event that the patient may need direct feeding into the stomach.

By the evening after surgery or the next day at the latest, patients are usually able to sit up or walk around. Gradually, physical activity may be increased, with normal activity resuming three to four weeks after surgery. Patients are also taught breathing exercises and are asked to cough frequently to clear their lungs of mucus. Postoperative pain medication is prescribed to ease discomfort and initially administered by a epidural. At the time patients are discharged from the hospital, they will be given oral medications for pain. Most patients will typically have a three-day hospital stay if their surgery is uncomplicated.

After gastric bypass or BPD, the individual does not eat anything for one or two days, giving the bowel time to rest. During this time, all nutrition is given intravenously. Once the person begins eating, the diet will include:

  • liquids such as juice, broth, milk, or diluted cooked cereal for two or three days
  • pureed foods that have the texture of baby food for two or three weeks while the stomach heals; these foods must be smooth and contain no large pieces
  • soft foods such as ground meat and soft-cooked fruits and vegetables for about eight weeks
  • regular food can be eaten in very small amounts

Most people begin by eating six tiny meals a day. These meals should be high in protein. Food must be chewed thoroughly. Liquids are drunk between meals, not with them. Vitamin and mineral supplements are essential.


Gastric bypass surgery has many of the same risks associated with other major abdominal operations. Life-threatening complications or death are rare, occurring in less than 1% of patients. Significant side effects, such as wound healing problems, difficulty in swallowing food, infections, and extreme nausea, can occur in 10–20% of patients. Blood clots after major surgery are rare, but extremely dangerous; if they occur, they may require re-hospitalization and anticoagulants (blood-thinning medications).

Some risks are specific to gastric bypass surgery, including:

  • Dumping syndrome. Usually occurs when sweet foods are eaten or when food is eaten too quickly. When the food enters the small intestine, it causes cramping, sweating, and nausea.
  • Abdominal hernias. These are the most common complications, requiring follow-up surgery. Incisional hernias occur in 10–20% of patients and require follow-up surgery.
  • Narrowing of the stoma. The stoma, or opening between the stomach and intestines, can sometimes become too narrow, causing vomiting. The stoma can be repaired by an outpatient procedure that uses a small endoscopic balloon to stretch it.
  • Gallstones. They develop in more than a third of obese patients undergoing gastric surgery. Gallstones are clumps of cholesterol and other matter that accumulate in the gallbladder. Rapid or major weight loss increases a person’s risk of developing gallstones.
  • Leakage of stomach and intestinal contents. Leakage of stomach and intestinal contents from the staple and suture lines into the abdomen can occur. This is a rare occurrence and sometimes seals itself. If not, another operation is required.

Nutritional deficiencies. People who have gastric bypass surgery or BPD need extensive nutritional counseling and must take vitamin and mineral supplements for the rest of their lives. Most iron and calcium is absorbed in the duodenum, the first part of the intestine that is bypassed by these operations. Calcium deficiency can lead to osteoporosis, and iron deficiency can cause anemia.

In BPD, only 25% of the fat in food is absorbed because so much of the small intestine is bypassed. The fat-soluble vitamins A, D, E, and K are absorbed along with fat. When the body absorbs too little fat, inadequate amounts of these fat-soluble vitamins are absorbed, so dietary supplements containing these vitamins must be taken. Other vitamins that may not be absorbed in adequate amounts are vitamin B12, folic acid, and vitamin B1 (thiamine). Research published in the journal Neurology in March 2007 found that a very small number of people developed a brain disorder called Wernicke encephalopathy 4–12 weeks after bariatric surgery. This disorder is caused by a deficiency of vitamin B1. Most of the people who developed the disorder had failed to take their vitamin supplements as prescribed after surgery.

Normal results

Most people who have surgery for obesity lose anywhere from 50-80% of their excess weight. However, quite a few put pounds back on beginning several years after surgery. The main reason for weight gain is noncompliance with their nutrition and exercise plan. Also, over time the size of the stomach pouch in restrictive surgeries tends to stretch, allowing people to eat more and still feel comfortable. On the positive side, people who lose weight through surgery almost always see great improvement in any obesity-related diseases they have.


Surgical alternatives

Lap-band and adjustable gastric band restrictive surgery used alone represent alternatives to gastric bypass surgery. Lap-Band surgery achieves restriction by placing a saline (salt water) filled bag around the stomach, pinching off a portion of it leaving only a small pouch at the top. The exit to the pouch is narrowed so that the rate at which the pouch empties is slowed. Because the pouch is so small, the individual can only eat about half a cup of food at a time without feeling nauseated. Since there is no cutting, stapling, or stomach rerouting involved, the procedure is the least invasive of all weight-loss surgeries. Patients generally experience less pain and scarring, and their hospital stay is shorter than with malabsorptive surgeries. In addition, a port allows access to the saline bag, so that the size of the stomach pouch can be adjusted without additional surgery. This surgery is reversible; the band or saline bag can be removed and the digestive system will function normally. Weight loss averages 50–65% of the excess body weight during the first two years. The procedure is often covered by Medicare.

Gastric band surgery uses a different technique to reduce the size of the stomach. The United States Food and Drug Administration (FDA) approved this surgery in 2001. Its long-term effects have not been studied.

Vertical banded gastroplasty (VBG) is also known as stomach stapling. This surgery is performed less often than lap-band surgery. With VBG, part of the stomach is stapled shut, making it smaller so that individuals feel full sooner. The advantage of VBG is that the procedure is quick and has few complications. Disadvantages are that average weight loss is less than with other weight-loss surgeries, and staples can pull out allowing small leaks between the stomach and the abdomen to develop. Infection is possible, but rare (less than 1%).

Nonsurgical alternatives

Diet and nutrition counseling is the main nonsurgical method of weight loss. Diet therapy involves instruction on how to adjust a diet to reduce the number of calories eaten. Reducing calories moderately is essential in achieving gradual and steady weight and in maintaining the loss. Strategies of diet and nutrition therapy include teaching individuals about the calorie content of different foods, food composition (fats, carbohydrates, and proteins), reading nutrition labels, types of foods to buy, and how to prepare foods. To be healthful, a diet must provide balanced nutrition along with calorie reduction.


A board-certified bariatric surgeon or a general surgeon who has specialized in the surgical treatment of obese patients performs gastric bypass surgery. An anesthesiologist is responsible for administering anesthesia. The operation is performed in a hospital setting. A registered dietitian usually provides dietary counseling before and after the procedure.

Physical activity, especially when combined with a healthy low-calorie diet is another nonsurgical way to lose weight. Moderate physical activity, progressing to 30 minutes or more five or more days a week, is recommended for weight loss. Physical activity has also been reported to be a key part of maintaining weight loss. Abdominal fat and, in some cases, waist circumference can be modestly reduced through physical activity. Strategies of successful weight loss through long-term physical activity involve selecting enjoyable activities that can be scheduled into a regular daily routine.

Behavior therapy aims to improve diet and physical activity patterns and develop habits and new behaviors that promote weight loss. Behavioral therapy strategies for weight loss and maintenance include keeping a food and exercise diary, identifying high-risk situations such as having high-calorie foods in the house and learning to avoiding these situations, using non-food rewards for specific actions such as exercising regularly, developing realistic goals and modifying false beliefs about weight loss and body image, developing a social support network (family, friends, or colleagues), and joining a support group that will encourage weight loss in a positive and motivating manner.

Drug therapy is another nonsurgical alternative option for treating obesity. The United States Food and Drug Administration (FDA) has approved three prescription drugs for treating obesity: orlistat (Xenical), phentermine (an appetite suppressant available under more than a dozen trade names), and sibutramine (Meridia in the United States, Reductil in Europe). In 2007, orlistat became available in the United States as an over-the-counter (nonprescription) drug under the name Alli. These drugs alone are not magic bullets for weight loss and should be used in addition to calorie reduction and regular exercise.


  • What type of bariatric surgery is best for me?
  • What benefits can I expect from this surgery?
  • When can I expect to return to work and/or resume normal activities?
  • What are the risks associated with a the type of gastric bypass surgery I plan to have?
  • How many gastric bypass surgery do you perform in a year?
  • What is the rate of post-surgery complications among your patients?
  • Will my insurance cover this procedure?
  • What are the alternatives to this surgery?



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Leach, Susan M. Before &amp: After, Revised Edition: Living and Eating Well After Weight-Loss Surgery. New York: Morrow Cookbooks, 2007.


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American Society for Bariatric Surgery. 7328 West University Avenue, Suite F, Gainesville, FL 32607. (352) 331-4900. (accessed March 30, 2008).

Weight-control Information Network (WIN). 1 WIN Way, Bethesda, MD 20892-3665. Telephone: (877)946-4627 or (202) 828-1025. Fax: (202) 828-1028. (accessed March 30, 2008).


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“Gastrointestinal Surgery for Severe Obesity.” Weight-control Information Network (WIN), December 2004 [cited January 5, 2008]. (accessed March 30, 2008).

Monique Laberge, PhD

Tish Davidson, AM

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