Although optimal treatment for patients with type 2 diabetes involves tight glucose control, this is rarely achieved. Morbid obesity, defined as weighing at least 100 lb (45.5 kg) more than ideal body weight or more than 200 percent of ideal body weight, is associated with serious comorbid diseases such as hypertension, dyslipidemia, and diabetes. Obesity surgery, including gastric bypass (GBP), biliopancreatic diversion (BPD), and gastroplasties that reduce the volume of the stomach, can ease some of these comorbidities by bringing about a weight loss of 60 to 70 percent of excess body weight. Rates of operative mortality and major complications with these procedures are low. Rubino and Gagner review the literature and discuss the possibility that weight-reducing surgical procedures may have a positive effect on patients with type 2 diabetes.

Many patients who undergo GBP or BPD report long-term normalization of plasma glucose levels. The operations appear to restore insulin sensitivity, prevent progression from impaired glucose metabolism to frank diabetes, and decrease the rate of mortality from diabetes in persons who were previously morbidly obese. Potential mechanisms for this beneficial effect on glucose metabolism include weight loss or decreased food intake. However, the positive effect of surgery occurs before significant weight loss occurs, and the fact that gastroplasty has a significantly less beneficial effect on glucose metabolism makes these explanations appear unlikely.

A more likely reason for the positive effect of weight-reducing surgery on glucose control is the subsequent change in the pattern of secretion of gastrointestinal hormones, including enteroglucagon and leptin. When BPD is performed on persons who are not morbidly obese, the beneficial effects on glucose metabolism hint that a portion of the etiology of type 2 diabetes is probably the same among obese and nonobese patients. Bypassing of the duodenum and proximal jejunum, which is included in both procedures, probably decreases production of a hormone or neuronal signal secondary to the passage of food that is responsible for the impaired action or secretion of insulin that occurs in type 2 diabetes. This outcome is not related to a decrease in food intake or a drop in weight.

The authors conclude that morbid-obesity surgery may be a specific, primary treatment for type 2 diabetes. They recommend GBP over BPD in nonmorbidly obese patients with diabetes because of the lower complication rate and the lower incidence of important late metabolic sequelae, and because the procedure can be performed laparoscopically. Further studies of this surgical effect on diabetes are recommended.