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Severe obesity is a chronic condition that is very difficult to treat. Surgery to promote weight loss by restricting food intake or interrupting digestive processes is an option for severely obese people. A body mass index (BMI) above 40--which means about 100 pounds of overweight for men and about 80 pounds for women--indicates that a person is severely obese and therefore a candidate for surgery . Surgery also may be an option for people with a BMI between 35 and 40 who suffer from life-threatening cardiopulmonary problems (for example, severe sleep apnea or obesity-related heart disease) or diabetes. However, as in other treatments for obesity, successful results depend mainly on motivation and behavior.


The Normal Digestive Process

Normally, as food moves along the digestive tract (see figure 1), appropriate digestive juices and enzymes arrive at the right place at the right time to digest and absorb calories and nutrients. After we chew and swallow our food, it moves down the esophagus to the stomach, where a strong acid continues the digestive process. The stomach can hold about 3 pints of food at one time. When the stomach contents move to the duodenum, the first segment of the small intestine, bile and pancreatic juice speed up digestion. Most of the iron and calcium in the foods we eat is absorbed in the duodenum. The jejunum and ileum, the remaining two segments of the nearly 20 feet of small intestine, complete the absorption of almost all calories and nutrients. The food particles that cannot be digested in the small intestine are stored in the large intestine until eliminated.


How Does Surgery Promote Weight Loss?

The concept of gastric surgery to control obesity grew out of results of operations for cancer or severe ulcers that removed large portions of the stomach or small intestine.

Because patients undergoing these procedures tended to lose weight after surgery, some physicians began to use such operations to treat severe obesity. The first operation that was widely used for severe obesity was the intestinal bypass. This operation, first used 40 years ago, produces weight loss by causing malabsorption. The idea was that patients could eat large amounts of food, which would be poorly digested or passed along too fast for the body to absorb many calories.

The problem with this surgery was that it caused a loss of essential nutrients and its side effects were unpredictable and sometimes fatal. The original form of the intestinal bypass operation is no longer used.

Surgeons now use techniques that produce weight loss primarily by limiting how much the stomach can hold. These restrictive procedures are often combined with modified gastric bypass procedures that somewhat limit calorie and nutrient absorption and may lead to altered food choices.

Two ways that surgical procedures promote weight loss are:

  1. By decreasing food intake (restriction). Gastric banding, gastric bypass, and vertical-banded gastroplasty are surgeries that limit the amount of food the stomach can hold by closing off or removing parts of the stomach. These operations also delay emptying of the stomach (gastric pouch).


  2. By causing food to be poorly digested and absorbed (malabsorption). In the gastric bypass procedures, a surgeon makes a direct connection from the stomach to a lower segment of the small intestine, bypassing the duodenum, and some of the jejunum.


Although results of operations using these procedures are more predictable and manageable, side effects persist for some patients.


What Are the Surgical Options?

Restriction Operations

Restriction operations are the surgeries most often used for producing weight loss. Food intake is restricted by creating a small pouch at the top of the stomach where the food enters from the esophagus. The pouch initially holds about 1 ounce of food and expands to 2-3 ounces with time. The pouch's lower outlet usually has a diameter of about 1/4 inch. The small outlet delays the emptying of food from the pouch and causes a feeling of fullness.

After an operation, the person usually can eat only a half to a whole cup of food without discomfort or nausea. Also, food has to be well chewed. For most people, the ability to eat a large amount of food at one time is lost, but some patients do return to eating modest amounts of food without feeling hungry.

Restriction operations for obesity include gastric banding and vertical banded gastroplasty. Both operations serve only to restrict food intake. They do not interfere with the normal digestive process.


  • Gastric banding. In this procedure, a band made of special material is placed around the stomach near its upper end, creating a small pouch and a narrow passage into the larger remainder of the stomach (figure 2). In the future, it may be possible to perform gastric banding with smaller incisions through a laparoscope, a flexible fiberoptic tube and light source through which some surgical instruments may be passed. Laparoscopic gastric banding has not yet been approved by the Food and Drug Administration.

  • Vertical banded gastroplasty (VBG). This procedure is the most frequently used restrictive operation for weight control. As figure 3 illustrates, both a band and staples are used to create a small stomach pouch.

Restrictive operations lead to weight loss in almost all patients. However, weight regain does occur in some patients. About 30 percent of persons undergoing vertical banded gastroplasty achieve normal weight, and about 80 percent achieve some degree of weight loss. However, some patients are unable to adjust their eating habits and fail to lose the desired weight. In all weight-loss operations, successful results depend on your motivation and behaviors.

A common risk of restrictive operations is vomiting caused by the small stomach being overly stretched by food particles that have not been chewed well. Other risks of VBG include erosion of the band, breakdown of the staple line, and, in a small number of cases, leakage of stomach juices into the abdomen. The latter requires an emergency operation. In a very small number of cases (less than 1 percent) infection or death from complications can occur.

Gastric Bypass Operations

These operations combine creation of small stomach pouches to restrict food intake and construction of bypasses of the duodenum and other segments of the small intestine to cause malabsorption.


  • Roux-en-Y gastric bypass (RGB). This operation (figure 4) is the most common gastric bypass procedure. First, a small stomach pouch is created by stapling or by vertical banding. This causes restriction in food intake. Next, a Y-shaped section of the small intestine is attached to the pouch to allow food to bypass the duodenum (the first segment of the small intestine) as well as the first portion of the jejunum (the second segment of the small intestine). This causes reduced calorie and nutrient absorption.

  • Extensive gastric bypass (biliopancreatic diversion). In this more complicated gastric bypass operation (figure 5), portions of the stomach are removed. The small pouch that remains is connected directly to the final segment of the small intestine, thus completely bypassing both the duodenum and jejunum. Although this procedure successfully promotes weight loss, it is not widely used because of the high risk for nutritional deficiencies.

Gastric bypass operations (figures 4 and 5) that cause malabsorption and restrict food intake produce more weight loss than restriction operations (figures 2 and 3) that only decrease food intake. Patients who have bypass operations generally lose two-thirds of their excess weight within 2 years.

The risks for pouch stretching, band erosion, breakdown of staple lines, and leakage of stomach contents into the abdomen are about the same for gastric bypass as for vertical banded gastroplasty. However, because gastric bypass operations cause food to skip the duodenum, where most iron and calcium are absorbed, risks for nutritional deficiencies are higher in these procedures. Anemia may result from malabsorption of vitamin B12 and iron in menstruating women, and decreased absorption of calcium may bring on osteoporosis and metabolic bone disease. Patients are required to take nutritional supplements that usually prevent these deficiencies.

Gastric bypass operations also may cause "dumping syndrome," whereby stomach contents move too rapidly through the small intestine. Symptoms include nausea, weakness, sweating, faintness, and, occasionally, diarrhea after eating, as well as the inability to eat sweets without becoming so weak and sweaty that the patient must lie down until the symptoms pass.

The more extensive the bypass operation, the greater is the risk for complications and nutritional deficiencies. Patients with extensive bypasses of the normal digestive process require not only close monitoring, but also life-long use of special foods and medications.


Explore Benefits and Risks

Surgery to produce weight loss is a serious undertaking. Each individual should clearly understand what the proposed operation involves. Patients and physicians should carefully consider the following benefits and risks:


  • Immediately following surgery, most patients lose weight rapidly and continue to do so until 18 to 24 months after the procedure. Although most patients then start to regain some of their lost weight, few regain it all.


  • Surgery improves most obesity-related conditions. For example, in one study blood sugar levels of most obese patients with diabetes returned to normal after surgery. Nearly all patients whose blood sugar levels did not return to normal were older or had had diabetes for a long time.


  • Ten to 20 percent of patients who have weight-loss operations require followup operations to correct complications. Abdominal hernias are the most common complications requiring followup surgery. Less common complications include breakdown of the staple line and stretched stomach outlets.


  • More than one-third of obese patients who have gastric surgery develop gallstones. Gallstones are clumps of cholesterol and other matter that form in the gallbladder. During rapid or substantial weight loss a person's risk of developing gallstones is increased. Gallstones can be prevented with supplemental bile salts taken for the first 6 months after surgery.


  • Nearly 30 percent of patients who have weight-loss surgery develop nutritional deficiencies such as anemia, osteoporosis, and metabolic bone disease. These deficiencies can be avoided if vitamin and mineral intakes are maintained.


  • Women of childbearing age should avoid pregnancy until their weight becomes stable because rapid weight loss and nutritional deficiencies can harm a developing fetus.


Is the Surgery for You?

For patients who remain severely obese after nonsurgical approaches to weight loss have failed, or for patients who have an obesity-related disease, surgery may be the best next step. But for other patients, greater efforts toward weight control, such as changes in eating habits, behavior modification, and increasing physical activity, may be more appropriate. Answers to the following questions may help in your decision to undergo surgery for weight loss.

Are you:

  • unlikely to lose weight successfully with (further) nonsurgical measures?


  • well informed about the surgical procedure and the effects of treatment?


  • determined to lose weight and improve your health?


  • aware of how your life may change after the operation (adjustment to the side effects of the surgery, including need to chew well and inability to eat large meals)?


  • aware of the potential for serious complications, the associated dietary restrictions, and the occasional failures?


  • committed to lifelong medical followup?

Do you:

  • have a BMI of 40 or more?


  • have an obesity-related physical problem (such as body size that interferes with employment, walking, or family function)?


  • have high-risk obesity-related health problems (such as severe sleep apnea or obesity-related heart disease)?

Remember: There are no guarantees for any method, including surgery, to produce and maintain weight loss. Success is possible only with your fullest cooperation and commitment to behavioral change and medical followup--and this cooperation and commitment should be carried out for the rest of your life.


Additional Reading

Gastrointestinal Surgery for Severe Obesity. Consensus Statement, NIH Consensus Development Conference, March 25-27, 1991; Public Health Service, National Institutes of Health, Office of Medical Applications of Research, Building 1, Room 260, Bethesda, MD 20892. This publication, written for health professionals, summarizes the findings of a conference discussing treatments for severe obesity.

Understanding Adult Obesity. NIH Publication No. 94-3680. This fact sheet describes what obesity is, its causes, how it is measured, and associated health risks.