Weight loss through gastric bypass or diet improved insulin sensitivity in patients with type 2 diabetes

The same amount of weight loss in people with type 2 diabetes, prompted by either gastric bypass surgery or by dietary changes, led to nearly identical improvements in metabolic function in a recent study.

Researchers compared the metabolic effects of marked weight loss (about 18%) induced by Roux-en-Y gastric bypass with the effects of the same weight loss induced by a low-calorie diet alone in 22 patients with obesity and type 2 diabetes. They analyzed data before and after weight loss for 11 participants (four men and seven women) in the diet group (mean age, 54±9 years; mean time since diabetes diagnosis, 9.1±5.6 years) and for 11 participants (three men and eight women) in the surgery group (mean age, 49±12 years; mean time since diabetes diagnosis, 9.6±9.6 years). The primary outcome was the change in hepatic insulin sensitivity, as assessed by infusion of insulin at low rates (i.e., stages 1 and 2 of a 3-stage hyperinsulinemic euglycemic pancreatic clamp procedure). Secondary outcomes were changes in muscle insulin sensitivity, beta-cell function (insulin secretion relative to insulin sensitivity), and 24-hour plasma glucose and insulin profiles. Results were published online on Aug. 20 by the New England Journal of Medicine.

Both groups saw metabolic benefits, including marked improvements in liver, adipose, and muscle insulin sensitivity, which did not significantly differ by intervention. Weight loss was associated with increases in mean suppression of glucose production from baseline, by 7.04 µmol per kg of fat-free mass per minute (95% CI, 4.74 to 9.33) in the diet group and by 7.02 µmol per kg of fat-free mass per minute (95% CI, 3.21 to 10.84) in the surgery group during clamp stage 1, and by 5.39 (95% CI, 2.44 to 8.34) and 5.37 (95% CI, 2.41 to 8.33) µmol per kg of fat-free mass per minute in the two groups, respectively, during clamp stage 2. Weight loss was associated with increased insulin-stimulated glucose disposal, from 30.5±15.9 to 61.6±13.0 µmol per kg of fat-free mass per minute in the diet group and from 29.4±12.6 to 54.5±10.4 µmol per kg of fat-free mass per minute in the surgery group. Weight loss increased beta-cell function by 1.83 units (95% CI, 1.22 to 2.44) in the diet group and by 1.11 units (95% CI, 0.08 to 2.15) in the surgery group, and it decreased the areas under the curve for 24-hour plasma glucose and insulin levels in both groups, with no significant differences between groups for either outcome. No major complications occurred in either group.

Limitations of the study include that treatment assignment was not randomized and that it is possible that unique benefits of surgery were not detected because of inadequate statistical power and a large proportion of participants who withdrew or were withdrawn from the study (seven in the diet group and four in the surgery group), the authors noted. In addition, the study had a low number of participants, and because those in the surgery group all had Roux-en-Y procedures, extrapolation to other types of gastric bypass (e.g., vertical sleeve gastrectomy) must be done with caution, an accompanying editorial noted.

Taken together, the findings suggest that the metabolic benefits of gastric bypass were principally a result of weight loss, owing to reduced overall adiposity, the editorialists said. “[The study] delivers a straightforward and important message for both clinicians and patients—reducing adipose tissue volume, by whatever means, will improve blood glucose control in persons with type 2 diabetes,” they wrote.