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Diet versus surgery for metabolic health: weighing the benefits for people with obesity and type 2 diabetes

New research shows that the metabolic benefits of gastric bypass surgery and diet in people with obesity and type 2 diabetes are similar and related to weight loss itself with no evidence of clinically significant effects independent of weight loss.

Studies have suggested that surgical procedures to treat obesity that involve bypass of part of the gastrointestinal tract, such as Roux-en-Y gastric bypass, have unique therapeutic effects on blood glucose (sugar) control that are independent of weight loss. However, results of such studies are complicated by the differences in weight loss among people who undergo procedures. To investigate these effects further, researchers in this study evaluated markers of glucose control before and after matched amounts of weight loss induced either by gastric bypass surgery or diet alone in 22 women and men with obesity and type 2 diabetes. The scientists used techniques to measure how well an individual metabolizes glucose and how sensitive an individual is to insulin. Following weight loss of about 18 percent of their initial weight, participants had their blood glucose tested after a meal. Levels of blood glucose were lower in both the surgery and diet groups than before weight loss, indicating metabolic improvements. There was a higher initial peak, followed by a decrease, in blood glucose in the surgery group after food consumption, likely due to the marked increase in rate of delivery of nutrients into circulation due to a restructured gastrointestinal tract. The researchers also found that insulin sensitivity (a measure of how well the body responds to insulin) in the liver, skeletal muscle, and adipose (fat) tissue increased similarly in both groups after weight loss. In addition, beta cell function (a measure of insulin secretion relative to insulin sensitivity) increased similarly in both groups.

The nearly identical benefits of matched weight loss in the surgery and diet groups underscore the profound effects of substantial weight loss on metabolic function in people with type 2 diabetes, and these results challenge the notion that gastric bypass surgery has clinically meaningful effects on metabolic health that are independent of weight loss. However, there remains difficulty in achieving and maintaining substantial weight loss with diet and other lifestyle changes alone. Therefore, further research is needed to attain the same long-term metabolic outcomes in people with obesity and type 2 diabetes without surgical intervention.

Yoshino M, Kayser BD, Yoshino J,…Klein S. Effects of diet versus gastric bypass on metabolic function in diabetes. N Engl J Med 383: 721-732, 2020.

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