[Why patients lose weight after bariatric operations].

The obesity epidemic is in Germany as well as worldwide a major health problem which is associated with increased morbidity and mortality. Bariatric surgery is currently the most effective therapy for significant and sustained weight loss. The most common form of bariatric surgery worldwide is Roux-en-Y gastric bypass surgery. The underlying mechanisms behind the superiority of this procedure are unclear and remain to be elucidated, but recent findings suggest that gastrointestinal hormones play an important role rather than malabsorption or restriction. It appears that gastric bypass surgery alters the physiology of weight regulation and eating behaviour in patients who have undergone the procedure. Gastrointestinal hormones have recently been found to be an important element in the physiology of appetite regulation due to the signals from the periphery to the brain. It is the purpose of this article to review the current knowledge about the regulation of body weight and eating behaviour by gastrointestinal hormones and how their levels are altered after bariatric surgery.