What is it?
Dietary fiber comes from the thick cell wall of plants. It is an indigestible complex carbohydrate. Fiber is divided into two general categories-water soluble and water insoluble.
Where is it found?
Whole grains are particularly high in insoluble fiber. Oats, barley, beans, fruit (but not fruit juice), psyllium, and some vegetables contain significant amounts of both forms of fiber and are the best sources of soluble fiber. The best source of lignan, by far, is flaxseed (not flaxseed oil, regardless of packaging claims to the contrary).
What do the advocates say?*
Unlike laxatives, fiber can truly help regulate bowel patterns. If you choose to take a fiber supplement, be sure you don’t inadvertently purchase a laxative supplement instead. The labels on both types of supplements may say something like “regulates bowel patterns.” While the featured ingredient of fiber supplements will likely be an ingredient such as psyllium, the featured ingredient of laxatives tend to be herbal-based. Such supplements are designed only for short-term constipation.
While there is weak evidence that fiber may promote a feeling of fullness, it seems to be necessary to use it in conjunction with a diet and exercise program in order to be effective for contributing to weight loss.
The best way to get fiber is from food. However, if you don’t include enough fiber-rich food in your diet and choose to use a fiber supplement instead, choose a product that has different types of fiber in it—both soluble and insoluble. When taking a fiber supplement, be sure to stay well hydrated.
How much is usually taken by dieters?
Fiber supplements are one way to add fiber to a weight-loss diet. Several trials have shown that supplementation with fiber from a variety of sources accelerated weight loss in people who were following a low-calorie diet.1 2 3 4 Other researchers found, however, that fiber supplements had no effect on body weight, even though it resulted in a reduction in food intake.5 Supplementation with 3 to 4 grams per day of a bulking agent called glucomannan, with or without a low-calorie diet, has promoted weight loss in overweight adults,6 7 8 while 2 to 3 grams per day was effective in a group of obese adolescents in another controlled trial.9 However, guar gum, another type of fiber supplement, has not been effective in controlled studies for weight loss or weight maintenance.10 11 12
Are there any side effects or interactions?
While people can be allergic to certain high-fiber foods (most commonly wheat), high-fiber diets are more likely to improve health than cause any health problems. Beans, a good source of soluble fiber, also contain special sugars that are often poorly digested, leading to gas. Special enzyme products are now available in supermarkets to reduce this problem by improving digestion of these sugars.
Fiber reduces the absorption of many minerals. However, high-fiber diets also tend to be high in minerals, so the consumption of a high-fiber diet does not appear to impair mineral status. However, logic suggests that calcium, magnesium and multimineral supplements should not be taken at the same time as a fiber supplement.
Bran, an insoluble fiber, reduces the absorption of calcium enough to cause urinary calcium to fall.13 In one study, supplementation with 10 grams of rice bran twice a day reduced the recurrence rate of kidney stones by nearly 90% in recurrent stone formers.14 However, it is not known whether other types of bran would have the same effect. Before supplementing with bran, people should check with a doctor, because some people—even a few with kidney stones—do not absorb enough calcium. For those people, supplementing with bran might deprive them of much-needed calcium.
People with scleroderma (systemic sclerosis) should consult a doctor before taking fiber supplements or eating high-fiber diets. Although a gradual introduction of fiber in the diet may improve bowel symptoms in some cases, there have been several reports of people with scleroderma developing severe constipation and even bowel obstruction requiring hospitalization after fiber supplementation.15
Are there any drug interactions?
Certain medicines may interact with fiber. Refer to drug interactions for a list of those medicines.
*Dieters and weight-management advocates may claim benefits for fiber based on their personal or professional experience. These are individual opinions and testimonials that may or may not be supported by controlled clinical studies or published scientific articles on fiber. For more complete and detailed information, including references and safety information, see Fiber as a nutritional supplement.
References
1. Marquette CJ Jr. Effects of bulk producing tablets on hunger intensity in dieting patients. Obes Bariatr Med 1976;5:84–8.
2. Rossner S, von Zweigbergk D, Ohlin A, Ryttig K. Weight reduction with dietary fibre supplements. Acta Med Scand 1987;222:83–8.
3. Ryttig KR, Tellnes G, Haegh L, et al. A dietary fibre supplement and weight maintenance after weight reduction: a randomized, double-blind, placebo-controlled long-term trial. Int J Obes 1989;13:165–71.
4. Solum TT, Ryttig KR, Solum E, Larsen S. The influence of a high-fibre diet on body weight, serum lipids and blood pressure in slightly overweight persons. A randomized, double-blind, placebo-controlled investigation with diet and fibre tablets (DumoVital). Int J Obes 1987;11 Suppl 1:67–71.
5. Hylander B, Rössner S. Effects of dietary fiber intake before meals on weight loss and hunger in a weight-reducing club. Acta Med Scand 1983;213:217–20.
6. Biancardi G, Palmiero L, Ghirardi PE. Glucomannan in the treatment of overweight patients with osteoarthritis. Curr Ther Res 1989;46:908–12.
7. Vita PM, Restelli A, Caspani P, Klinger R. Chronic use of glucomannan in the dietary treatment of severe obesity. Minerva Med 1992;83:135–9 [in Italian].
8. Walsh DE, Yaghoubian V, Behforooz A. Effect of glucomannan on obese patients: a clinical study. Int J Obes 1984;8:289–93.
9. Livieri C, Novazi F, Lorini R. The use of highly purified glucomannan-based fibers in childhood obesity. Pediatr Med Chir 1992;14:195–8 [in Italian].
10. Kovacs EM, Westerterp-Plantenga MS, Saris WH, et al. The effect of addition of modified guar gum to a low-energy semisolid meal on appetite and body weight loss. Int J Obes Relat Metab Disord 2001;25:307–15.
11. Beattie VA, Edwards CA, Hosker JP, et al. Does adding fibre to a low energy, high carbohydrate, low fat diet confer any benefit to the management of newly diagnosed overweight type II diabetics? Br Med J (Clin Res Ed) 1988;296:1147–9.
12. Pasman WJ, Westerterp-Plantenga MS, Muls E, et al. The effectiveness of long-term fibre supplementation on weight maintenance in weight-reduced women. Int J Obes Relat Metab Disord 1997;21:548–55.
13. Shah PJR. Unprocessed bran and its effect on urinary calcium excretion in idiopathic hypercalciuria. Br Med J 1980;281:426.
14. Ebisuno S, Morimoto S, Yoshida T, et al. Rice-bran treatment for calcium stone formers with idiopathic hypercalciuria. Br J Urol 1986;58:592–5.
15. Gough A, Sheeran T, Bacon P, Emery P. Dietary advice in systemic sclerosis: the dangers of a high fibre diet. Ann Rheum Dis 1998;57:641–2.
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2006-09-07
