Comparative Effect of Insulin Resistance Reduction and Hormonal Alterations on Type 2 Diabetes Remission After Bariatric Surgery

<b>Background:</b> Bariatric surgery is known to induce weight loss and diabetes remission in patients with type 2 diabetes (T2D), but the exact mechanism of glycemic normalization needs to be defined. <b>Methods:</b> The study included patients with BMI ≥ 35 kg/m², obesity history ≥ 10 years, and planned bariatric surgery. At baseline and 3 and 6 months after surgery, all patients underwent anthropometric measurements, body composition and blood tests (including insulin, glucagon, and incretins during oral glucose tolerance test (OGTT)), and hyperinsulinemic euglycemic clamp tests. Diabetes remission was defined if the person reached HbA1c < 6.5% after surgery and glucose-lowering therapy withdrawal. <b>Results:</b> The study included 86 patients, divided into groups with no diabetes (control group, <i>n</i> = 44) and T2D (<i>n</i> = 42). Most patients with T2D reached normoglycemia at 6 months. BMI and insulin resistance (according to M-index) decreased in T2D group comparably to people without diabetes. At 6 months, people with T2D at baseline had less insulin and GLP-1 secretion and higher glucagon level during OGTT when compared to the control group. <b>Conclusions:</b> We conclude that weight and insulin resistance reduction is sufficient for T2D remission. The absence of insulin, glucagon, and incretin restoration is not crucial for the glucose metabolism in the short-term, but it may explain the relapse of T2D years after bariatric surgery.