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Fibre
What is it ? Dietary
fibres are structural components of plants. The type and amount of
fibre in plants vary from species to species. |
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A common misconception about fiber is that it
is not digested by enzymes in the body and therefore provides no
calories or nutrients. But the category "fibre" includes
chemicals that are not fibrous, materials that can be dissolved, and
some substances that can be digested partially. We eat quite a complex
mixture of fibers.
Dietary fibre is a broad generic term; it
includes the following chemicals, which form the structural components
of plants, including many of the plant foods we eat:
- cellulose
- hemicellulose
- lignin
- pectin's
- mucilage's
- gums
The first three are insoluble fibers which can
absorb and hold water in the digestive system. The others are soluble
fibers, which are partially broken down in digestion to a gel-like
substance, which also retains water.
What does it do?
Fiber's ability to hold water and to bind minerals
and cholesterol-like materials results in a number of physiological
effects which vary depending on the type of fiber and/or where it is in
the digestive tract.
- In the mouth, fiber stimulates the flow of
saliva.
- In the stomach and small intestine, fiber
dilutes the contents and delays the emptying of food and the
absorption of nutrients; this promotes a feeling of fullness.
- In the large intestine, fiber dilutes the
contents and provides a place for bacterial growth and digestion.
The water-holding capacity of insoluble fiber in the lower intestine
softens the stool and increases stool size, so that the process of
elimination is easier and faster.
- In the large intestine, fibre also acts to
bind certain chemicals. Different kinds of fiber have different
binding capacities: when fiber binds cholesterol-like compounds, it
lowers cholesterol, a healthy result; when fiber binds minerals, it
decreases their absorption, a less desirable result.
Because of these physiological effects, fiber
is considered beneficial in preventing, alleviating or curing a number
of diseases and conditions, including:
- arteriosclerosis (hardening of the arteries)
- excess food intake
- diverticular disease
- irritable bowel syndrome
- Crohn's disease
- gallstone formation
- constipation
Where do you get it?
Recent recommendations suggest that we should be
getting fiber from a variety of foods high in different types of fibers,
rather than from dietary supplements. A healthy diet should provide a
mixture of both soluble and insoluble fibers.
About eight grams of daily fiber intake should
be in the form of soluble fibers, such as:
- fruits, especially apples and citrus
- vegetables, especially leafy green varieties
- oats
Major sources of insoluble fibers include:
- wheat bran
- whole grains
- legumes
- most fruits and vegetables
A good source of fiber should have at least
three grams of fiber. High-fiber foods provide five grams or more. The
accompanying chart lists a variety of foods and their fiber content.
Sources of Fibre
| Food |
Amount
of fibre (in gms) in a 100g
(3.5 ounce) serving |
| Bread |
| bagel |
2.1 |
| bran
bread |
8.5 |
pita
bread
(white) |
1.6 |
pita
bread
(whole white) |
7.4 |
| white
bread |
1.9 |
| Cereals |
| bran
cereal |
35.3 |
| bran
flakes |
18.8 |
| cornflakes |
2.0 |
| oatmeal |
10.6 |
| wheat
flakes |
9.0 |
| Grains |
barley,
pearled
(minus its outer covering) |
15.6 |
| cornmeal,
whole grain |
11.0 |
| de-germed |
5.2 |
| oatbran,
raw |
6.6 |
| rice,
raw (brown) |
3.5 |
| rice,
raw (white) |
1.0-2.8 |
| rice,
raw (wild) |
5.2 |
| wheat
bran |
15.0 |
| Fruits |
| apple
(with skin) |
2.8 |
| apricots
(dried) |
7.8 |
| figs
(dried) |
9.3 |
| kiwifruit |
3.4 |
| pears
(raw) |
2.6 |
| prunes
(dried) |
7.2 |
| prunes
(stewed) |
6.6 |
| raisins |
5.3 |
| Vegetables |
| beans |
|
|
7.7 |
|
|
5.4 |
|
|
7.2 |
| broccoli,
raw |
7.7 |
| brussels
sprouts, (cooked) |
2.6 |
cabbage
(white)
raw |
2.4 |
| cauliflower,
raw |
2.4 |
| corn,
sweet, cooked |
3.7 |
peas
with edible
pods, raw |
2.6 |
potatoes,
white,
baked, w/skin |
5.5 |
| sweet
potato, cooked |
3.0 |
| tomatoes,
raw |
1.3 |
| Others |
| corn
chips, toasted |
4.4 |
| nuts |
|
|
11.2 |
|
|
9.0 |
|
|
6.4 |
|
|
8.0 |
|
|
10.8 |
| tahini |
9.3 |
| tofu |
1.2 |
Source: Provisional
table on the dietary fibre content of selected foods (Washington, D.C.:
U.S. Department of Agriculture,1988).
How much do we need?
A healthy adult should get 20-25 grams of fiber a
day, based on the assumption that we need 10-13 grams of fiber a day for
every 1,000 calories consumed. Unfortunately, most Americans consume
only about 10 grams.
Children ages 3-18 need less fiber than adults,
and they need different amounts at different ages. To calculate a
child's daily fiber requirements, add the child's age to the number five
(for five grams). For example, a four-year-old needs nine grams of fiber
a day.
To get the appropriate amount of fiber, adults
should include the following in their diets:
- two to three servings of whole grains (as
part of the 6-11 recommended daily servings)
- five servings of fruits and vegetables a day
- one or two servings of legumes every week
Is it safe?
Yes. However, increasing your fiber intake to
recommended levels may cause some unpleasant effects unless you do it
gradually and drink plenty of water. This can help you avoid:
- gas, distention and/or diarrhea resulting
from increases in fiber intake
- colon obstruction caused by very large
intakes of fiber
- interference with the absorption of some
minerals (though this should not be a problem if you eat a healthy
diet.)
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