The study will also examine the response of the pancreas (the insulin-producing organ) to a sugar load, as well as to a hormone called Glucagon Like Peptide 1 (GLP-1), which is released from your gut to maximally stimulate your pancreas. The release of this hormone increases when you eat food and it causes the pancreas to release more insulin than does sugar alone. Volunteers will have 22 visits over a two year period. Only people having Roux-en-Y gastric bypass surgery, gastric sleeve surgery, duodenal switch gastric surgery or lap-band/gastric banding surgery may join. Seventy volunteers will be recruited to take part in this study.