 The recent expansion in understanding of the metabolic effects of surgery has largely been driven by the study of bariatric better termed metabolic surgery. It is well known that Roux-en-Y gastric bypass RYGB can result in early remission of diabetes in 85 of cases and elevated levels of gut hormones such as glucagon-like peptide 1 GLP-1, but there is considerable debate around whether the gut hormones changes contribute to the reductions in plasma glucose and appetite after surgery. Whereas studies in rodent models appear to indicate that gut hormones are largely redundant after bypass surgery, data from humans strongly support the idea that increased post-prandial GLP-1 and Peptide YY PYY levels underlie improvements in insulin secretion and reduced appetite. Studies from bariatric cohorts are confounded by the requirement for dietary restriction before surgery and massive weight loss after surgery. 