The mechanism of diabetes resolution after RYGB is not completely understood and there is evidence that it might not be dependent on weight loss only. Improvements in glycemic control have been found within days after surgery, while significant weight loss has not yet been achieved at this time. There are several hypotheses concerning the weight-independent effects of bariatric surgery on insulin secretion. The most popular are the 'hindgut-hypothesis', which states that expedited delivery of nutrients to the distal intestine enhances the secretion of intestinal peptides like glucagon-like-peptide 1 (GLP1) and peptide YY and the 'foregut hypothesis', which states that the exclusion of the duodenum and proximal jejunum from the transit of nutrients results in changes in secretion of intestinal peptides. However, several other mechanisms, both in- and outside the intestines might play a role.