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A Background to Dietary Fiber
Fiber is the part of the plant that is resistant to hydrolysis (A
chemical decomposition in which a substance is split into
simpler compounds by the addition or the taking up of the
elements of water) by human digestive enzymes and, with
the exception of lignin, fibers are complex carbohydrates.
These include pectin, gums, mucilages, hemicellulose,
polysaccharides cellulose, and nonpolysaccharide lignins.
Fibers are water-soluble except cellulose, hemicellulose,
and lignin, all of which form part of cell walls. Soluble fibers
are sticky and combine with water to form gel-like
substances. Pectin is a water-soluble fiber found in soft
fruits and vegetables. Gums that are common food
additives are also water-soluble, found in stems and seeds
of some tropical plants. In general, fruits are higher in
pectin and vegetables are higher in cellulose. Although
cellulose and hemicellulose are not hydrolyzed, intestinal
bacterial can digest some fiber to produce lipid fragments
known as short-chain fatty acids. These fatty acids are
absorbed in the colon and yield energy when metabolized.
Water Insoluble fibers pass through the gastrointestinal
track unchanged, absorbing up to 15 times their weight,
important since they provide the digestive tract with bulk
that helps facilitate food through the intestines to be
evacuated as solid waste; hence, fiber often is called
"natures natural laxative". Celluloses ability to absorb water
produces softer stools and regular bowel movements. Also,
insoluble fiber may prevent colon and rectal cancer and help
to control diverticulosis (A sac or pouch in the walls of a
canal or organ [e.g., GI tract] that becomes inflamed and
causes pain and stagnation of feces. Source: The American
Dietetic Association's Complete Food & Nutrition Guide, p.
145). Water-soluble fiber, as found in beans, fruit, and oat
bran lowers cholesterol by binding to the cholesterol found
in liver bile, to help control diabetes.
Overall, dietary fiber does not provide much nourishment to
the human diet because of the inability to break down these
carb sources for energy, yet reduces available kcalories by
providing a sense of satiety and by absorbing some
nutrients including fat. However, fiber also absorbs and
eliminates essential fatty acids, food substances that are
essential for good health and energy metabolism.
Also, dietary fiber may be a detoxifier since it binds with
some toxic substances before elimination. But a diet
extremely high in fiber is not a good idea since it impairs
calcium, iron, and zinc absorption in the intestine.
Increasing fiber should be a gradual process since the
majority of fiber products may cause unpleasant bloating,
cramps, gas, and other symptoms especially if they are
eaten in large amounts at once. It is best to add one high
fiber food at each eating session to judge whether the food
causes symptoms or not. For instance, some people who
have problems with brown rice may not have problems with
apples, oatmeal, whole wheat bread, or other sources of
similar fiber.
Many nutrition authorities estimate that 20-35 grams of fiber
daily is a desirable intake for the average individual. Note
that the amount of nutrients can vary in wheat products
since the refining of grains remove part of the seed (e.g.,
bran, endosperm, and germ). Here are some fiber-rich
sources:
1 ounce dry-roasted peanuts: 2.2 g
1/2 cup cooked broccoli: 2.2 g
1 potato with skin: 2.5 g
1 slice whole wheat bread: 2.8 g
1 cup carrots: 3.0 g
1/2 large grapefruit: 3.1 g
1 apple: 3.5 g
1 cup cooked long-grain brown rice: 3.3 g
1 cup cooked instant oatmeal: 3.5 g
3 cups air-popped popcorn: 3.7 g
1 pear: 4.3 g
_ cup raisins: 4.5 g
1 cup of whole wheat spaghetti cooked: 5 g
1 cup baked beans: 7.0 g
_ cup of chickpeas: 7 g
1 cup boiled lentils: 7.9 g
1 serving bran cereal: 11 g
Here are different sources of fiber and their uses in the
body:
CELLULOSE: Fruit legumes, nuts, oat bran, seeds, whole
grains, and vegetables. Adds bulk to stool to reduce
constipation; oat bran lowers cholesterol; may help control
blood sugar; helps weight loss by displacing kcalories.
GUMS: Algae, barley, fruits, legumes, oats, seaweed,
seeds, and vegetables. Adds bulk to stool to reduce
constipation; may lower blood cholesterol; helps control
blood sugar; helps weight loss by displacing kcalories.
HEMICELLULOSE: Fruits, legumes, nuts, oat bran, seeds,
whole grains, and vegetables. Adds bulk to stool to reduce
constipation; oat bran lowers cholesterol; may help control
blood sugar; helps weight loss by displacing kcalories.
LIGNINS: Woody parts of bran, fruit skins, nuts, seeds,
whole grains and vegetables. Adds bulk to stool to reduce
constipation; may lower blood cholesterol; may help control
blood sugar; helps weight loss by displacing kcalories.
MUCILAGES: Plant seeds and secretions. Adds bulk to
stool to reduce constipation; may lower blood cholesterol;
helps control blood sugar; helps weight loss by displacing
kcalories.
PECTINS: Algae, barley, fruits, legumes, oats, seaweed,
seeds, and vegetables. Adds bulk to stool to reduce
constipation; may lower blood cholesterol; helps control
blood sugar; helps weight loss by displacing kcalories.
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Brian D. Johnston is the Director of Education and President
of the I.A.R.T. fitness certification and education institute. He
has written over 12 books and is a contributing author to the
Merck Medical Manual. An international lecturer, Mr.
Johnston wears many hats in the fitness and health
industries, and can be reached at info@ExerciseCertification.com.
Visit his site at
http://www.ExerciseCertification.com for more free articles.
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