Bariatric surgery is the most effective weight loss therapy for obesity. Moreover, the early improvement in insulin sensitivity and the resolution of type 2 diabetes after bariatric surgery has led to the hypothesis that bariatric surgery has specific beneficial effects on glucose homeostasis beyond weight loss alone. However, this hypothesis has never been adequately evaluated in human subjects. Therefore, the primary goal of this proposal is to provide a better understanding of the effect of bariatric surgery-induced weight loss on insulin action and pancreatic beta cell function.