Effects of Caloric Restriction Alone Versus Postoperative Caloric Restriction Following Bariatric Surgery on Glucose Metabolism in Patients With Diabetes Mellitus

Background Presently it is unknown whether the rapid normalization of glucose metabolism in obese patients with type 2 diabetes after bariatric surgery (before major weight loss occurs) is primarily due to acute postoperative caloric restriction or due to changes in intestinal effects on insulin secretion and sensitivity. We speculate that bypassing the stomach and proximal small intestine affects glucose metabolism beyond simple caloric restriction, and that the mechanisms are related to changes in hepatic and muscle insulin sensitivity, changes in vagal afferent signals, and changes in incretins and other gut hormones. Aim To compare the effects of pure caloric restriction with caloric restriction early after bariatric surgery (Roux-en-Y Gastric Bypass, RYGBP) in patients with type 2 diabetes, and to investigate the mechanisms that explain the observed difference in glucose metabolism Methods In patients with type 2 diabetes we will study the short-term changes in glucose metabolism, insulin sensitivity and gut hormone levels using a parallel group design. The non-surgical group will be studied before and after receiving a hypocaloric diet for 6 days mimicking the typical postoperative diet. The surgical group will be studied before and 6 days after bariatric surgery. The primary outcome will be the change in total body insulin sensitivity attributable to caloric restriction alone versus caloric restriction after RYGBP. Non-surgical subjects studied at NIH may enter an optional long-term weight loss phase.