Another kind of weight-loss surgery combines stomach restriction with a partial bypass of the small intestine. Such procedures create a direct connection from the stomach to the lower segment of the small intestine, literally bypassing portions of the digestive tract that previously absorbed more of the calories and the nutrients in food. These surgeries are known as malabsorptive operations.

Source: NIDDK: Gastrointestinal Surgery for Severe Obesity

Malabsorptive Operations

Malabsorptive operations are the most common weight-loss surgeries. They restrict both food intake and the amount of calories and nutrients the body absorbs.

Roux-en-Y gastric bypass (RGB), illustrated in Figure 1, is the most common and the most successful form of malabsorptive surgery and is the procedure that Dr. Gritsus will perform at Chilton. A small stomach pouch is created to restrict food intake. Then a Y-shaped section of the small intestine is attached to the pouch to allow food to bypass the lower stomach, the duodenum (the first segment of the small intestine) and the first part of the jejunum (the second segment of the small intestine). The bypass reduces the amount of calories and nutrients the body absorbs.

Biliopancreatic diversion (BPD) is a more complicated malabsorptive operation than RGB, where portions of the stomach are removed. The small pouch that remains is connected directly to the final segment of the small intestine, completely bypassing the duodenum and the jejunum. Although this procedure successfully promotes weight loss, it is less frequently used than other types of weight-loss surgery because of the high risk for nutritional deficiencies. A variation of BPD includes a "duodenal switch," which leaves a larger portion of the stomach intact, including the pyloric valve that regulates the release of stomach contents into the small intestine, as well as a small part of the duodenum.

Malabsorptive operations can produce greater weight loss than restrictive operations, and are considered more effective in reversing the serious health problems associated with severe obesity. Patients who have malabsorptive operations generally lose two-thirds of their excess weight within two years.

In addition to the risks of restrictive surgeries, malabsorptive operations also carry greater risk for nutritional deficiencies because foods bypass the duodenum and jejunum where most iron and calcium are absorbed. Menstruating women may develop anemia because not enough vitamin B-12 and iron are absorbed. Decreased absorption of calcium may also contribute to osteoporosis and metabolic bone disease. Patients are thus required to take nutritional supplements, which will usually prevent these deficiencies. Patients who have the biliopancreatic diversion surgery must also take the fat-soluble vitamins A, D, E and K in supplement form. RGB and BPD operations may also cause something called "dumping syndrome," where stomach contents move too rapidly through the small intestine. Symptoms include nausea, weakness, sweating and faintness, and sometimes diarrhea after eating. Because the duodenal switch operation keeps the pyloric valve intact, it can reduce the likelihood of dumping syndrome.

In general, the more extensive the bypass, the greater the risk for complications and nutritional deficiencies. Patients with extensive bypasses of the normal digestive process require close monitoring and lifelong adherence to special diets, supplements and medications.

Restrictive Operations

Restrictive operations, or gastric banding, severely limit food intake without otherwise interfering with the normal digestive process. In these procedures, physicians create a small pouch at the top of the stomach where food enters from the esophagus. Initially, the pouch holds about one ounce of food, eventually expanding to hold two to three ounces. The lower outlet of the pouch usually has a diameter of only about ¾ inch. This small outlet delays the emptying of food from the pouch and results in a feeling of fullness.

After such a surgery, the patient loses the ability to eat anything but very small amounts of food at any one time. The person will usually be able to consume only ¾ to 1 cup of food without discomfort or nausea. In order to be properly digested under these conditions, all food has to be very well chewed.

Adjustable gastric banding is where a hollow band made of specialized material is placed around the stomach near its upper end, creating a small pouch and a narrow passage into the remainder of the stomach. The band is then inflated with a saline solution. It can be tightened or loosened over time to change the size of the passage by increasing or decreasing the amount of solution.

Although restrictive operations lead to weight loss in about 80 percent of patients, they are less successful than malabsorptive operations in achieving substantial, long-term weight loss. Only about 30 percent of those who undergo ABG achieve normal weight and some patients will regain weight. Successful results depend on the patient's willingness to adopt a long-term plan of healthy eating and regular physical activity. Some patients who undergo restrictive operations fail to lose the desired weight because they fail to adjust their eating habits.

Common risks of restrictive operations include vomiting, caused by the small stomach being overly stretched by too much food or food that has not been sufficiently chewed. Band slippage and saline leakage can occur. In a small number of cases, stomach juices can leak into the abdomen, requiring an emergency operation. Infection or death from complications occur in less than one percent of all cases.

Source: NIDDK: Gastrointestinal Surgery for Severe Obesity