Severe obesity is a chronic condition that is very difficult to treat. For some people, surgery to promote weight loss by restricting food intake or interrupting digestive processes is an option. But keep in mind that surgery to produce weight loss is a serious undertaking. You should clearly understand the pros and cons associated with the procedures before making a decision.

How Does Weight Loss Surgery Work?

The surgery helps you lose weight by changing the way your body digests and absorbs food. Your body digests food to break down what you eat into small pieces of nutrients (carbohydrates, proteins, fats, vitamins and minerals). When the pieces are small enough, the cells of your body absorb the nutrients to give you energy to live.

Normally, as food moves along the digestive tract, appropriate digestive juices and enzymes arrive at the right place and 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 juices 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 (made up of the ascending colon, transverse colon, descending colon, sigmoid colon and rectum) until eliminated.

Obesity surgery involves making changes to the stomach and/or small intestine.

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 doctors began to use such operations to treat severe obesity. The first operation that was widely used for severe obesity was a type of intestinal bypass. This operation, first used 40 years ago, caused weight loss through malabsorption (decreased ability to absorb nutrients from food because the intestines were removed or bypassed).

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 (malnutrition) and its side effects were unpredictable and sometimes fatal. The original form of the intestinal bypass operation is no longer used.

Surgeons now use other techniques that produce weight loss primarily by limiting how much the stomach can hold. Two types of surgical procedures used to promote weight loss are:

Restrictive surgery. During these procedures the stomach is made smaller. A section of your stomach is removed or closed which limits the amount of food it can hold and causes you to feel full.
Gastric bypass. Most of digestion and absorption takes place in the small intestine. Surgery to this area shortens the length of the small intestine and/or changes where it connects to the stomach, limiting the amount of food that is completely digested or absorbed (causes malabsorption).

Through food intake restriction, malabsorption or both, you can lose weight since less food either goes into your stomach or stays in your small intestine long enough to be digested and absorbed.

What Are the Benefits and Risks Associated With Weight Loss Surgeries?

Surgery to produce weight loss is a serious undertaking. Before making a decision, talk to your doctor about the following benefits and risks.

Benefits

Weight loss. 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.
Obesity-related conditions improve. 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 diabetes for a long time.

Risks and Side Effects

Vomiting. This is a common risk of restrictive surgery caused by the small stomach being overly stretched by food particles that have not been chewed well.
"Dumping syndrome." Caused by gastric bypass surgery , this is when 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 extremely weak.
Nutritional deficiencies. Nearly 30% 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.
Complications. Ten to 20% of patients who have weight-loss operations require follow-up operations to correct complications. Abdominal hernias (ruptures) are the most common complications requiring follow-up surgery. Less common complications include breakdown of the staple line (used to make the stomach smaller) and stretched stomach outlets (when the stomach returns to its normal size).
Gallstones. 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 increases. Gallstones can be prevented with supplemental bile salts taken for the first 6 months after surgery.
Need to temporarily avoid pregnancy. Women of childbearing age should avoid pregnancy until their weight becomes stable because rapid weight loss and nutritional deficiencies can harm a developing fetus.
Side effects. These include nausea, vomiting, bloating, diarrhea, excessive sweating, increased gas and dizziness.
Lifestyle changes. Patients with extensive bypasses of the normal digestive process require not only close monitoring, but also life-long use of special foods and medications.

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Am I a Candidate?

If you have a body mass index (BMI) above 40 -- which is about 100 pounds overweight for men and about 80 pounds for women -- you are considered severely obese and therefore a candidate for surgery.

Surgery may also 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. For these people, the risk of death from not having the surgery is greater than the risks from the possible complications from undergoing the procedures.

Keep in mind that as in other treatments for obesity, successful results depend mainly on motivation and behavior. In many cases, patients are required to show proof that their attempts at dietary weight loss have been ineffective before surgery will be approved. A psychological evaluation is considered essential by most doctors to determine your potential response to weight loss and change in body image. Most surgeons require patients to demonstrate serious motivation and a clear understanding of the extensive dietary, exercise and medical guidelines that must be followed for the remainder of their lives after having weight loss surgery. In addition, studies are performed to assess the health of your heart and hormonal systems. Nutritional counseling is also a must before surgery.

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 an appropriate treatment option. But for most patients, greater efforts toward weight control, such as changes in eating habits, lifestyle changes, and increasing physical activity, are more appropriate. The following questions may help you decide if weight loss surgery is right for you.

Have you tried to lose weight through conventional methods of weight loss. group classes, one-on-one counseling, calorie controlled meal plans, food journals, exercise?
Are you well informed about the surgical procedure and the effects of treatment?
Are you determined to lose weight and improve your health?
Are you aware of how your life may change after the operation (adjustment to the side effects of the surgery, including dramatically different eating habits)?
Are you aware of the potential for serious complications from the procedure, the associated dietary restrictions, and the slight chance that the procedure will not help you lose weight?
Are you committed to life-long medical follow-up?

Reviewed by the Department of Nutrition Therapy at The Cleveland Clinic.

Weight Loss:
Is Weight Loss Surgery for You?

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