Fiber forms 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 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 the prevention of disease.
There is sufficient evidence to suggest that an artificial depletion of fiber as in the 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 a 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 a 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 tasted the same.
The 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 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 for 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.
Dietary fiber increases the bacteria in the large intestine which requires nitrogen for their growth. This in turn reduces the chances of cancerous changes in cells by reducing the amount of ammonia to 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 with diabetes mellitus.
Sources of Fiber
The most significant food sources of fiber are unprocessed wheat bran, all cereals such as wheat, rice, barley, rye, and millets; legumes such as potato, carrots, beet, and sweet potatoes fruits like mango and guava and leafy vegetables such as cabbage, lettuce, and celery.
Bran, the outer covering 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 grade real food value being rich in lime, iron, and vitamins and containing a considerable amount of protein. Legumes have high fiber content. Much of this fiber is water soluble, which makes legumes a likely agent for lowering cholesterol. Soybeans, besides this, can also help control glucose levels.
Types of fibers
There are 6 classes of fiber, they are Cellulose, Hemicellulose, Pectin, Gums and Mucilages, and Lignin. They differ in physiological properties and chemical interactions in the gut, though all except lignin are polysaccharides. The facts known so far about these forms of fiber as a result of various studies are discussed below.
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.
It is usually present whatever cellulose is and shares some of its traits like cellulose, it helps relieve constipation, water 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.
This form of fiber is highly beneficial in reducing serum cholesterol levels, however, does not influence the stool and does nothing to prevent constipation. It is found in apples, grapes, berries, citrus fruits, guava, raw papaya, and bran.
Gums and Mucilages
They are sticky fibers found in dried beans, bran, and oatmeal. Investigations have shown that they are useful in the dietary control of diabetes and cholesterol.
The main function of lignin is to escort bile acid and cholesterol out of the
intestine. There is some evidence that it may prevent the formation of gallstones. It is contained in cereals, parsley, bran wholemeal flour, raspberries, strawberries, cabbage, spinach, and tomatoes.
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 the 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.