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).
Fiber has been used in connection with the following conditions (refer to the individual health concern for complete information):
| Science Rating | Health Concerns |
|---|---|
 | Constipation Diverticular disease High cholesterol Type 1 diabetes Type 2 diabetes |
 | Cirrhosis (combination of beta-glucan, inulin, pectin, and resistant starch) Diarrhea Hemorrhoids High blood pressure Weight loss |
 | High triglycerides Irritable bowel syndrome (fiber other than wheat) Kidney stones Peptic ulcer Premenstrual syndrome |
| Reliable and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit. For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit. | |
Who is likely to be deficient?
Most people who consume a typical Western diet are fiber-deficient. Eating white flour, white rice, and fruit juice (as opposed to whole fruit) all contribute to this problem. Many so-called whole wheat products contain mostly white flour. Read labels and avoid “flour” and “unbleached flour,” both of which are simply white flour. Junk food is also fiber depleted. The diseases listed above are more likely to occur with low-fiber diets.
The benefits of eating whole grains are largely derived from the beneficial constituents present in the outer layers of the grains, which are stripped away in making white flour and white rice. Preliminary research has found that women who ate mostly whole grain fiber had a lower mortality rate than women who ate a comparable amount of refined grains.1
How much is usually taken?
Western diets generally provide approximately 10 grams of fiber per day. People in less-developed countries consume 40 to 60 grams per day. Increasing fiber intake to the amounts found in such diets may be desirable.
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.2 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.3 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.4
Are there any drug interactions?
Certain medicines may interact with fiber. Refer to drug interactions for a list of those medicines.
References
1. Jacobs DR, Pereira MA, Meyer KA, Kushi LH. Fiber from whole grains, but not refined grains, is inversely associated with all-cause mortality in older women: the Iowa women’s health study. J Am Coll Nutr 2000;19(3 Suppl):326S–30S.
2. Shah PJR. Unprocessed bran and its effect on urinary calcium excretion in idiopathic hypercalciuria. Br Med J 1980;281:426.
3. 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.
4. 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
