Dietary fiber is grouped into two categories: water-insoluble and water-soluble. Insoluble fibers—cellulose, lignin, and most hemi- celluloses are found in vegetables, wheat, and other grains. Soluble fibers—pectin, gums, and some hemicelluloses are contained in fruits, oats, barley, and legumes .
Fibers have the capacity to hold water and improve transit time through the gut resulting in less constipation and less abdominal straining for the colon that may cause hemorrhoids, varicose veins, and diverticular disease. Soluble fiber combines with liquid in the diet to form a gel that delays emptying time and enhances satiety, which can be helpful in adjustable gastric banding and vertical sleeve gastrectomy. Both soluble and insoluble fiber delays glucose absorption from the small intestine and is useful in diabetes management [8, p. 212].
Adverse effects of dietary fiber usually are related to gastrointestinal symptoms such as abdominal pain. Of particular concern for bariatric patients postsurgery is the use of guar gum (extract of guar bean) products in constipation management that can swell 20 times its original size. Bowel and esophageal obstructions have been reported to the U.S. Food and Drug Administration .
Fiber-rich foods like whole grains, fresh fruits, raw vegetables, nuts, and seeds may be consumed prior to surgery but need to be discontinued postsurgery until advised by health-care professionals that it is safe to consume these foods.
An easy way to evaluate fiber content in the diet and review modifications that can help relieve constipation issues postsurgery is as follows:
- • Legumes (lentils, beans) 1/2 cup = 7 g
- • Bran cereals 1/2 cup = 3 g
- • Vegetables, raw 1 cup = 2 g
- • Vegetables, cooked 1/2 cup = 1 g
- • Fruit, raw 1 small piece/1/2 banana = 2 g
- • Fruit, canned/frozen 1/2 cup = 1 g
- • Bread, white 1 slice = 1 g
- • Bread, whole grain 1 slice = 2 g
The dietary intervention of adding soluble fiber from oat bran, pectin, or psyllium is frequently mentioned to bariatric patients s truggling with constipation. Other patients may have used these fibers to improve insulin sensitivity and lower lipids. But according to a 2005 article in the American Journal of Gastroenterology, only 20% of the patients with slow transit benefited from adding more fiber . For some patients and possibly bariatric surgery patients, adding more fiber could worsen constipation symptoms.
A 2012 meta-analysis  reviewed the role of fiber on constipation and determined that it does increase stool frequency but does not improve stool consistency or painful defecation. A review published in the Cleveland Clinic Journal of Medicine  points out that increasing physical activity is not always helpful.
Since constipation results from other disorders like hypothyroidism and food sensitivities, the primary disorder needs to be treated before evacuation problems are resolved. Dietary changes to increase fiber levels in the diet need to be done over 2-3 weeks according to the Cleveland Clinic study authors. In addition, nutrition supplements— calcium and iron—can cause constipation and may need to be modified to improve bowel function.