Medical illustration representing 3 types of bariatric surgery to fight overweight and obesity: sleeve gastrectomy, bypass, gastric band. The sleeve (gastrectomy) consists of removing about 2/3 of the stomach and, in particular, the part containing the cells that secrete the appetite stimulating hormone (ghrelin). The stomach is reduced to a vertical tube and food passes quickly through the intestine. Appetite is greatly reduced and the digestion of food is not disturbed. Longitudinal gastrectomy is sometimes the first step in a gastric bypass or a biliopancreatic bypass. The bypass reduces the capacity of the stomach and bypasses much of the intestinal digestion. Thus, the bolus is reduced in volume and is only partially digested. The principle of this method is therefore restrictive (as for gastroplasty) and poorly absorptive. The gastric ring consists of putting a silicone ring, whose caliber is easily modifiable, around the upper part of the stomach. It reduces the size of the stomach and slows down the passage of food.