The worldwide rise in obesity levels has led to an explosion in the number of operations performed for weight loss. Even with dietary and lifestyle modifications, most individuals are only able to lose about 10 % of excess body weight, and relapse is extremely common. On the other hand, bariatric surgery usually results in rapid and dramatic weight loss that can be long lasting. The appeal of bariatric surgery is clear, however these procedures can be associated with significant morbidity, making patient selection and education critical to surgical success.

The body mass index (BMI), which incorporates both weight and height, is a more accurate measure of obesity than weight alone. Most medical organizations support the use of bariatric surgery in patients whose BMI is greater than 40 kg/m², or in those whose BMI is over 35 kg/m² if additional weight-related comorbidities such as hypertension, diabetes mellitus, hyperlipidemia, obstructive sleep apnea, or osteoarthritis are present.

Bariatric procedures are able to produce weight loss by at least two distinct mechanisms. Restrictive procedures decrease caloric intake by creating a physical reduction in stomach size. Purely restrictive procedures have a limited duration of effect because over time the gastric remnant will stretch to accommodate a larger volume of food. Malabsorptive procedures exert their effect by interrupting normal absorption of ingested calories. Most currently used bariatric procedures utilize both mechanisms: a restrictive component to initiate rapid weight loss, combined with a malabsorptive component to ensure long-lasting effects. In addition to these stated mechanisms, it is now increasingly clear that bariatric surgery induces profound metabolic changes via recently discovered hormones such as ghrelin that are involved in the feelings of hunger and satiety.

A number of different bariatric procedures exist, each with a particular risk/benefit profile that should be considered on a patient-by-patient basis. Gastric banding involves fitting an inflatable plastic cuff around the gastric cardia, thereby limiting the amount of food that can be consumed at one time (Fig. 12.1). The degree of gastric constriction can be adjusted by the addition or removal of saline through a subcutaneous port. This procedure is almost purely restrictive in its effects, and therefore has a limited ability to produce long-term weight loss. However the procedure is associated with a low rate of surgical complications, and—since no alterations in anatomy are created—is reversible with removal of the device.

Another bariatric procedure is the sleeve gastrectomy, in which most of the gastric body is resected, leaving only a thin channel of stomach (Fig. 12.2). This procedure also relies on restriction of food intake for its efficacy. However, removal of a large portion of the stomach has been shown to result in lower levels of circulating ghrelin. Therefore, some of the weight loss seen after sleeve gastrectomy is likely due a decrease in the sensation of hunger.

There are several types of gastric bypass procedures; the Roux–en–Y gastric bypass is the most commonly performed version of this operation. Gastric bypass procedures combine both restrictive and malabsorptive properties by creating a small gastric pouch that is then anastomosed to the downstream small bowel, thereby reducing the opportunity for caloric absorption. While advantageous for weight loss, bypassing portions of the small intestine interferes with the normal absorption of various vitamins and minerals. Most patients who undergo gastric bypass require lifelong nutritional supplementation.

Patients qualifying for bariatric surgery typically undergo an intense preoperative program including a comprehensive nutritional assessment and psychological evaluation. Bariatric centers typically also require completion of an educational program that teaches about postoperative dietary restrictions and potential medical and nutritional complications.