Obesity, a causative factor in a variety of serious medical conditions, is highly prevalent in the United States. A modest planned weight loss of 5 percent of initial body weight can improve many of the medical conditions related to obesity, as well as prevent or delay the onset of other obesity-related conditions, including diabetes. The American Gastroenterological Association presents official recommendations for the management of obesity.

The need to treat obesity and the aggressiveness of treatment is dependent on obesity-related health risks, the presence of other disease risk factors, and the presence of complications of obesity. Eating fewer calories than are used by the body for daily activities is the best way to encourage the use of endogenous fat as fuel. Weight-loss treatment is not recommended for persons with a body mass index (BMI) of less than 25 kg per m², although recommendations about a healthy diet and physical activity are appropriate for people who have or are at risk for future adiposity-related diseases.

Treatment of obesity is dependent on a patient's willingness to receive therapy and ability to comply with recommendations, access to appropriate clinicians who can supervise management, and ability to pay for specialized services. Stepwise treatment involves medical evaluation, including BMI measurement, to identify potential causes and risks of obesity; assessment of weight-loss readiness to determine whether it is the best time to focus on weight loss; and treatment, including either preventing additional weight gain or efforts to lose weight. Treatment goals should be carefully and realistically constructed, with regular medical follow-up included. The aggressiveness of the treatment program should depend on the level of obesity-related health risk. Fundamental bases of treatment include behavior modification and changes in dietary intake and physical activity. Pharmacotherapy and bariatric surgery can be useful adjuncts in certain patients.

Basic diet intervention involves decreasing energy intake by about 500 kcal per day, which will result in a weight loss of 1 lb (0.45 kg) per week. Patients who are more obese should be managed more aggressively, with a calorie deficit of up to 1,000 kcal per day. The goal is a 10 percent weight loss at six months. Popular dietary strategies include portion-controlled servings, prepackaged meals, and ingestion of a low-energy density diet (i.e., low fat and increased water content). About 60 to 90 minutes of daily, moderate-intensity activity (such as brisk walking) or 30 to 45 minutes of daily, high-intensity activity (such as fast bicycling or aerobics) is necessary for successful weight maintenance. Activity levels can be slowly increased until the target is reached. Useful behavior-modification techniques are noted in the accompanying table.

Pharmacotherapy is most useful when used in conjunction with behavior modification and should be considered a long-term therapy. Stopping pharmacotherapy too early results in weight gain. Currently, only sibutramine and orlistat are approved for the treatment of obesity, but studies of pharmacotherapeutically induced weight loss compared with placebo show only a modest benefit.

Bariatric surgery is the most effective technique for achieving long-term weight loss in the more obese patients and those with multiple severe obesity-related conditions. Gastric bypass is the most common surgical technique, achieving long-term weight loss of approximately one half of excess weight. Gastroplasty can be performed, but weight loss generally is less than that achieved with gastric bypass. Malabsorptive procedures with diversion can provide even greater weight loss and may be used in very obese patients.