It is estimated that up to 20% of patients who have Roux-en-Y Gastric Bypass (RYGB) surgery will not meet their weight loss goal, or may even regain some of the weight they initially lost. One possible explanation is that the opening between the stomach pouch and the intestine becomes stretched. If this opening becomes too wide, food may be able to pass from the stomach to the intestine too quickly - causing patients to feel less full after eating.