Evidence is mounting for the use of bariatric surgery to treat type 2 diabetes mellitus in patients whose body mass index (BMI) is 35 kg/m 2 or higher. In obese patients who also have type 2 diabetes, bariatric surgery sends it into remission (defined as normoglycemic control without the need for diabetic medications) in more than three-fourths of cases, with higher rates with the Roux-en-Y gastric bypass procedure than with the laparoscopic adjustable gastric banding procedure.
However, data on the effects of this surgery on type 2 diabetes come primarily from observational studies that lacked appropriate control groups, and the relative benefit of bariatric surgery vs aggressive medical antidiabetic therapy is not yet known. Needed are randomized trials comparing the two types of therapy (and the various types of bariatric surgery) in diabetic patients with less-severe obesity.
Further, why would bariatric surgery help with diabetes, and why would one procedure do it better than another? To be honest, we are not sure, but evidence points not only to weight loss but also to better insulin sensitivity and to alterations in levels of hormones secreted by the gut that increase insulin secretion.
OBESITY PROMOTES DIABETES; WEIGHT LOSS COUNTERACTS IT
Type 2 diabetes mellitus is a complex metabolic disease characterized by insulin resistance and progressive failure of pancreatic beta cells, resulting in hyperglycemia. 1,2
Obesity, a potent risk factor for type 2 diabetes, contributes to its development by inducing insulin resistance and inflammation, which in turn impair glucose regulation. 3,4 Fat deposits in the abdomen, muscles, and liver contribute to elevations of circulating free fatty acids and adipocyte-derived cytokines that mediate insulin resistance and inflammatory pathways. 5
In the Diabetes Prevention Program, 6 modest weight loss (5% to 10% of body weight) through diet and exercise reduced the incidence of type 2 diabetes, and in the ongoing Action for Health in Diabetes (Look AHEAD) study of the National Institutes of Health, it improved glucose homeostasis. 7,8
The current medical approach to type 2 diabetes includes advising the patient to lose weight through lifestyle modification, and prescribing drugs that restore glycemic control by reducing insulin resistance (biguanides, glitazones) and improving insulin secretion (incretin mimetics and analogues and sulfonylureas). 9,10
However, several factors make type 2 diabetes challenging to treat in obese people. Patients who lose weight via behavioral changes and weight-loss drugs tend to gain the weight back. Antidiabetic drugs pose the risk of hypoglycemia. Moreover, although many new classes of drugs have been developed to treat type 2 diabetes, most patients fail to achieve the American Diabetes Association goal for glycemic control, ie, a hemoglobin A 1c level lower than 7%. 11
BARIATRIC PROCEDURES AND THEIR EFFECT ON DIABETES CONTROL
After bariatric surgery, patients lose more weight than with traditional weight-loss methods—up to 25% of their total body weight. Furthermore, of those with type 2 diabetes, 87% achieve at least better glucose control and need fewer antidiabetic medications, 12 and an average of 78% achieve normal glycemic control without taking any antidiabetic medications at all. 12,13