Fiber, found in foods like bran, popcorn, raw vegetables, and dried beans, is also limited on the gastric bypass diet. There is less space in the stomach to hold these bulky foods, and less gastric acid available to digest them. Some kinds of fiber could get stuck in the pouch itself, or block the narrow opening into the small intestine. Do not take any fiber pills or laxatives without the advice of a physician. Since the diet allows only small amounts of a limited variety of foods, it may be difficult to get enough vitamins and minerals from food alone.
Deficiencies can develop in a matter of months.
Iron, folate, vitamin B-12, and calcium are the nutrients most affected. Special Considerations Gastric bypass surgery creates dramatic changes in the size and shape of the stomach. It may take awhile to get used to these changes. Patients report a wide variety of complications after surgery. Some of these will go away with time, while others can be lessened with adjustment of the diet.