 The increased prevalence of obesity and type 2 diabetes T2DM has resulted in a surge in the number of patients seeking surgical weight loss. Gastric bypass surgery GBP results in 30-40 body weight loss with resolution of T2DM in 40-80 of cases. The mechanisms by which T2DM improves after GBP are unclear. Glycemic control occurs long before significant weight loss, suggesting that the nature of the procedure, rather than the weight loss, is responsible for the T2DM improvement. Recent data have singled out the role of the gut hormones known as incretins in diabetes improvement after GBP. The current proposal will study 1 whether the short and long term change in the gut hormone incretins after GBP results in improved insulin secretion in response to the administration of oral and IV glucose, in patients with diabetes undergoing GBP surgery; 2 the factors responsible for diabetes remission - or lack of - after GBP. The investigators wish to apply our finding to define better surgical outcome on diabetes. 