Laparoscopic gastric bypass is an effective treatment for obesity, but a new study finds that patients who undergo the surgery often complain of gastrointestinal problems. The study included 249 obese patients who underwent the surgery and 295 obese controls, all of whom completed a questionnaire. Surgical patients completed the questionnaire two years after surgery. Surgical patients often experienced indigestion. Also, food intolerance, especially for food with a high fat or sugar content and for red meat, was a common side-effect of the surgery: food intolerance for specific products was reported by 70.7 per cent of postoperative patients compared with 16.9 percent of controls.