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
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. So-called
“primitive societies” consume 40–60 grams per day. Increasing fiber intake
to the amounts found in primitive 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
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
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
Certain medicines may interact with fiber. Refer to drug interactions for a list of those medicines.
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
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.