The Roux-Y gastric bypass is the standard procedure. In the first two years after the gastric bypass, this can reduce obesity by 60 to 70%. On the one hand, this is due to the fact that the body absorbs food more poorly as a result of the stomach's altered approach to the intestines. The fact that the operation lowers ghrelin levels, on the other hand, plays a role. This hormone, among other things, is responsible for the sensation of hunger.