The underlying mechanism of HH is not completely understood and several potential causes have been proposed, including, 1) An inappropriate increase of beta cell mass and function, that is persisting despite the increased insulin sensitivity after RYGB, 2) late dumping syndrome, i.e. an inappropriate insulin secretion following rapid food entry into the small intestine, 3) an inappropriate counter-regulatory glucagon response and 4) post-RYGB an increase in the incretin secretion (GLP1 and GIP).