In adults with obesity and type 2 diabetes, marked weight loss of approximately 20% achieved through behavioral diet therapy results in double the increase in insulin-mediated glucose disposal after a mixed meal compared to equivalent weight loss achieved through Roux-en-Y gastric bypass surgery, leading to greater reductions in postprandial blood glucose levels despite similar improvements in insulin sensitivity and insulin secretion.

When people lose weight by eating less, their muscles become better at responding to insulin, allowing more sugar to leave the blood and enter muscle cells after meals. But when weight loss happens through surgery, food moves too quickly into the bloodstream, flooding it with sugar before insulin can act slowly and effectively. Even though insulin works normally in both cases, the sugar spike from surgery happens too fast for the body to clear it properly, leaving blood sugar high after eating.