Roux-en-Y gastric bypass surgery uses a combination of restriction and malabsorption. During the procedure, the surgeon creates a smaller stomach pouch. The surgeon then attaches a Y-shaped section of the small intestine directly to the pouch. This allows food to bypass a large portion of the small intestine, which absorbs calories and nutrients. Having the smaller stomach pouch may cause patients to feel fuller sooner and eat less food, and bypassing a portion of the small intestine means the patient’s body may absorb fewer calories.