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):
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
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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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The information presented in Aisle7 is for informational purposes only.
It is based on scientific studies (human, animal, or in vitro), clinical experience,
or traditional usage as cited in each article. The results reported may not necessarily occur
in all individuals. For many of the conditions discussed, treatment with prescription or over
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for any health problem and before using any supplements or before making any changes in
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