Abstract Roux-en-Y gastric bypass leads to a marked improvement of glucose control. The mechanisms are only partly known. Gastrointestinal hormones may play a role. Of these, glucagon-like peptide 1 and peptide YY have been most consistently associated with the beneficial effects of gastric bypass on glucose metabolism and weight. In this paper, a short review of the topic is presented and a suggestion of the improvement of glucose metabolism is made based on the current published work.