Obesity is a major health problem worldwide and has reached an epidemic proportion in the Western society. Evidence continues to accumulate that obesity is a major risk factor for many diseases and is associated with significant morbidity and mortality.
The most widely accepted measure of obesity is the body mass index (BMI). This number is calculated by dividing a patient’s mass (kg) by his or her height (m2). A normal BMI is considered in the range of 18.5-24.9 kg/m2. A BMI of 25-29.9 kg/m2 is considered overweight. A BMI of 30 kg/m2 or greater is classified as obese; this classification is further subdivided into class I, II, or III obesity.
Considering other factors (eg, total muscle mass, waist circumference) besides the BMI may be important. For example, an extremely muscular individual may have an elevated BMI without being considered overweight. Waist circumference has been shown to be an excellent indicator of abdominal fat mass. A circumference of greater than 88 cm (35 in.) in women or greater than 102 cm (40 in.) in men strongly correlates with an increased risk of obesity-related disease.
Bariatric surgery is currently the only modality that provides a significant, sustained weight loss for morbidly obese patients, with resultant improvement in obesity-related comorbidities. A prospective, controlled Swedish study involving 4047 obese patients, half of whom had undergone bariatric procedures, followed up over 14.7 years, found that compared to usual care, bariatric surgery was associated with a significantly reduced number of cardiovascular deaths and a lower incidence of cardiovascular events in obese adults. 
In 1954, Kremen and Linner introduced jejunoileal bypass, the first effective surgery for obesity in the United States. In this procedure, the proximal jejunum was connected directly to the distal ileum, bypassing 90% of the small intestine out of the intestinal stream of ingested nutrients (blind loop). The procedure induced a state of malabsorption, which led to significant weight loss.
However, many patients developed complications secondary to malabsorption (eg, steatorrhea, diarrhea, vitamin deficiencies, oxalosis) or due to the toxic overgrowth of bacteria in the bypassed intestine (eg, liver failure, severe arthritis, skin problems). Consequently, many patients have required reversal of the procedure, and the procedure has been abandoned. This led to a search for better operations.
Modifications in the original procedures and the development of new techniques led to the following three basic concepts for bariatric surgery (see Surgical Therapy):
- Gastric restriction (adjustable gastric banding, sleeve gastrectomy)
- Gastric restriction with mild malabsorption (Roux-en-Y gastric bypass)
- Combination of mild gastric restriction and malabsorption (duodenal switch)
In recent years, the field of bariatric surgery has been enriched by data from numerous clinical investigations and experience. The direction of future clinical investigations are proceeding in a number of directions, including the following:
- Controlled, prospective, intervention studies
- Establishment of a major prospective database to study bariatric surgery outcomes
- Establishment of a pediatric (adolescent) bariatric surgery registry
- Performance of randomized clinical trials to compare the safety and efficacy of different operative procedures
- Controlled studies of new operative modalities (eg, gastric pacing) and nonoperative modalities of treatment
- Study by meta-analysis of outcomes of comorbid conditions of morbid obesity
- Study of the socioeconomic outcomes of bariatric surgery
- Study by stratified risk assessment of the risk-to-benefit ratio of treating morbid obesity with bariatric surgery and without bariatric surgery
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