Dietary Fiber
Importance of Dietary Fiber
Fibers form the skeletal system of plants. Without it
no plant or tree would be able to stand upright. Dietary fiber, the roughage of
yesteryears, consists of those parts of the plant foods that cannot be digested
by enzymes or other digestive secretions in the alimentary canal. Dietary fiber
plays an important role in the maintenance of health and prevention of
diseases. There is sufficient evidence to suggest that an artificial depletion
of fiber as in case of refined cereals and sugar has over the last 100 years
contributed to several degenerative diseases. Recent studies in this area
indicate that sufficient intake of fiber-rich diet may help prevent obesity,
colon cancer, heart disease, gallstones, irritable bowel syndrome,
diverticulosis and diabetic conditions. Studies have also established that
dietary fiber is a collection of elements with a variety of functions rather
than a single substance with single function as was assumed earlier. This new insight
into the true nature of fiber has given the lie to old beliefs that bran is
synonymous with fiber, that all fiber is fibrous or stringy and that all fiber
tastes the same.
Physiological effects
Fiber in the diet promotes more frequent bowel
movements and softer stools having increased weight. The softness of stools is
largely due to the presence of emulsified gas which is produced by the
bacterial action on the fiber. A high fiber intake results in greater
efficiency in the peristaltic movement of the colon. This helps in relieving
the constipation which is the main cause of several acute and chronic diseases.
Recent studies suggest that increasing the dietary fiber intake may be
beneficial for patients with irritated bowel syndrome who have diarrhea and
rapid colonic transit, as well as to those who have constipation and slow transit.
The high fiber diet, like bran, thus regulates the condition inside the colon
so as to avoid both extremes - constipation and diarrhea. Investigations have shown
that several potential carcinogens are produced in the faeces. Their production
is related to the acidity of the gut content. The greater the acidity in the
bowel content, the less is the production of these carcinogens. The breaking
down of the fiber by bacteria renders the faeces more acidic. This reduces the
amount of possible carcinogenic substances. Fiber also reduces the possibility
of formation of harmful toxins in the large intestine by reducing the
intestinal transit time of the food contents. Dietary fiber increases the
bacteria in the large intestines which require nitrogen for their growth. This
in turn reduces the chances of cancerous changes in cells by reducing the
amount of ammonia in the large bowel. Fiber reduces the absorption of cholesterol
in the diet. It also slows down the rate of absorption of sugars from the food
in the digestive system. Certain types of fiber increase the viscosity of the
food content. This increased viscosity indirectly reduces the need for insulin
secreted by the pancreas. Thus, a fiber-rich diet can help in diabetes mellitus.
Sources of Fiber
The most significant food sources of fiber are
unprocessed wheat bran, whole cereals such as wheat, rice, barley, rye, millets; legumes such as potato, carrots, beet , turnip and sweet potato; fruits like
mango and guava and leafy vegetables such as cabbage, lettuce and celery. The percentage
of fiber content per 100 gms. of some foods are: bran 10.5-13.5, whole grain cereals
1.0-2.0, nuts 2.0-5.0, legumes 1.5-1.7, vegetables 0.5-1.5, fresh fruits
0.5-1.5, and dried fruits 1.0-3.0. The foods which are completely devoid of
fiber are meat, fish, eggs, milk, cheese, fats and sugars. Bran, the outer
coverings of grains, is one of the richest sources of dietary fiber. And it
contains several types of fiber including cellulose, hemicellulose and pectin.
Wheat and corn bran are highly beneficial in relieving constipation.
Experiments show that oat bran can reduce cholesterol levels substantially.
Corn bran is considered more versatile. It relieves constipation and also lowers
LDL cholesterol, which is one of the more harmful kinds. Besides being rich in
fiber, bran has a real food value being rich in time, iron and vitamins and
containing a considerable amount of protein.
Dr.Dennis P. Burkitt, a noted British physician
remarks, "Grain roughages, such as
rich bran and wheat bran, are an essential part of a healthy diet, and a
preventive against diseases like piles, constipation, bowel cancer, varicose
veins and even coronary thrombosis." Dr. Burkitt worked for many years
in Africa and found after a series of
observations that rural Africans who eat bulk of fibrous foods rarely suffer
from any of these diseases. Legumes have high fiber content. Much of this fiber
is water- soluble, which makes legumes likely agents for lowering cholesterol.
Soybeans, besides this, can also help control glucose levels. The types of fiber contained in vegetables
and fruits contribute greatly towards good health. The vegetables with the
biggest fiber ratings include sweet corn, carrots, potatoes, parsnips and peas.
And among the high ranking fruits are raspberries, pears, strawberries and
guavas.
Types of Fibers
There are six classes of fiber. They are cellulose,
hemicellouse, pectin, gums, mucilages and legnin. They differ in physical
properties and chemical interactions in the gut, though all except legnin are poly-saceharides. The facts known
so far about these forms of fibre as a result of various studies are discussed
below.
Cellulose - It is
the most prevalent fiber. It is fibrous and softens the stool. It abounds in
fruits, vegetables, bran, whole-meal bread and beans. It is also present in
nuts and seeds. It increases the bulk of intestinal waste and eases it quickly
through the colon. Investigations indicate that these actions may dilute and
flush cancer-causing toxins out of the intestinal tract. They also suggest that
cellulose may help level out glucose in the blood and curb weight gain.
Hemicellulose - It is
usually present wherever cellulose is and shares some of its traits. Like cellulose,
it helps relieve constipation, waters down carcinogens in the bowel and aids in
weight reduction. Both cellulose and hemicellulose undergo some bacterial
breakdown in the large intestine and this produces gas.
Pectin - This
form of fiber is highly beneficial in reducing serum cholesterol levels. It,
however, does not have influence on the stool and does nothing to prevent
constipation. Researches are being conducted to ascertain if pectin can help
eliminate bile acids through the intestinal tract thereby preventing gallstones
and colon cancer. It is found in apples, grapes, berries, citrus fruits, guava,
raw papaya and bran.
Gums and Mucilages - They are
the sticky fibers found in dried beans, oat bran and oatmeal. Investigations
have shown that they are useful in the dietary control of diabetes and
cholesterol.
Legnin - The main
function of legnin is to escort bile acid and cholesterol out of the
intestines. There is some evidence that it may prevent the formation of
gallstones. It is contained in cereals, bran, whole meal flour, raspberries,
strawberries, cabbage, spinach, parsley and tomatoes. The best way to increase
fiber content in the diet is to increase the constipation of whole meal bread, brown
rice, peas, beans, lentils, root vegetables and sugar -containing fruits, such
as dates, apples, pears and bananas. The intake of sugar, refined cereals,
meat, eggs and dairy products should be reduced. Candies, pastries, cakes which
are rich in both sugar and fat, should be taken sparingly. White processed
bread should be completely eliminated from the diet.
Requirement :
There are divergent views as to the requirement of
dietary fiber for good health. There is no recommended daily dietary allowance
for it and hardly any data about optimum amounts. Some Africans known for lower
incidence of degenerative diseases take about 150 grams of fiber a day. In
Europe and North America , where there is a
high incidence of such diseases, people take 25 grams or less a day. Dr. John
H. Cummings, a noted fiber expert in England , considers that a fiber
intake of 30 grams (about one ounce) per day is sufficient for good health. Excessive
consumption of fiber, especially bran, should however, be avoided. Due to its
content of crude fiber, bran is relatively harsh and it may irritate the delicate
functioning of the digestive system, especially in the sick and the weak.
Excessive use of fiber may also result in loss of valuable minerals like
calcium, phosphorus, magnesium and potassium from the body through excretion
due to quick passage of food from the intestine.
Source: www.healthlibrary.com through
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