Almost everyone has struggled with trying to lose those last 5 to 10 unwanted pounds. For people who are severely obese, not being able to lose weight can have dangerous health risks.

A body mass index (BMI) above 40--which means about 100 pounds overweight for men and about 80 pounds for women--indicates that a person is severely obese and therefore a candidate for gastric surgery.

Surgery also may be an option for people with a BMI between 35 and 40 who suffer from life-threatening heart and lung problems for example, severe sleep apnea, heart disease or diabetes.

Severe obesity is a chronic disease that is very difficult to treat. Surgery to promote weight loss by restricting food intake or decreasing the absorption of food is an option for severely obese people, who have tried diets, medications and behavioral modification without success.

What happens when I eat?

After we chew and swallow our food, it moves down the esophagus to the stomach, where a strong acid begins the digestion of food. The stomach can hold about three pints of food at one time.

The stomach contents then move to the duodenum, the first segment of the small intestine, where bile and pancreatic juice aid in digestion. Most of the iron and calcium in the foods we eat are 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 that cannot be digested in the small intestine is stored in the large intestine until the next bowel movement.

How does gastric surgery control obesity?

The idea for gastric surgery to control obesity stemmed from operations for cancer that removed large portions of the stomach or small intestine. Because people with cancer tended to lose weight after the surgery, some physicians began to use such operations to treat severe obesity.

The first procedure that was widely used was the intestinal bypass. This operation, first used 40 years ago, produces weight loss by causing malabsorption. The idea was that one could eat large amounts of food, which would be passed along too fast for the body to absorb many calories. The problem with this surgery was that its side effects were sometimes fatal. The original form of the intestinal bypass operation is no longer used.

What are the types of procedures used now?

Restriction operations

Techniques primarily used now limit how much the stomach can hold (restriction operations), and do not interfere with the normal digestive process. The types of procedures include gastric banding and vertical banded gastroplasty. With these procedures, a small pouch at the top of the stomach (where the food enters from the esophagus) is created.

By creating this pouch, food intake is restricted. 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. Also, food has to be well chewed.

For most people, the ability to eat a large amount of food is lost. This operation leads to weight loss in almost all 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.

A common risk of restrictive operations is vomiting caused by the small stomach being overly stretched by food that has not been chewed well. Other risks of vertical banded gastroplasty include erosion of the band, breakdown of the staple line and, in a small number of cases, leakage of stomach juices into the abdomen.

Gastric bypass operations

Gastric bypass operations combine the creation of small stomach pouches to restrict food intake with the construction of a bypass. The created bypass makes a direct connection from the stomach to a lower segment of the small intestine, bypassing the duodenum and some of the jejunum.

Gastric bypass operations that cause malabsorption and restrict food intake produce more weight loss than restriction operations. Patients who have bypass operations generally lose two-thirds of their excess weight within two years. 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. Patients are required to take nutritional supplements that usually prevent these deficiencies.

Gastric bypass operations also may cause "dumping syndrome," in which 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.

Is gastric surgery for me?

Surgery to produce weight loss is a serious undertaking. Anyone considering weight loss surgery should clearly understand what the operation involves. For those 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.

Remember: There are no guarantees for any method, including surgery, to produce and maintain weight loss. Success is possible only with your fullest commitment to behavioral change and medical follow-up--and this needs to continue for the rest of your life.

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