Answer
Dietary fibers include animal and plant materials that are not digestible, or that resist digestion. Examples of plant fibers are cellulose, pectins, gums, mucilage. psyllium and hemicellulose. The RDA for fiber is about 30 grams. However, there is great variation in the amount of fiber consumed daily by national and regional cultural and ethnic groups. East Indian and African countries cuisines include more vegetable and less animal material than American cuisines do. Whereas American diets have only about 12 grams of fiber/day, in African and Indian diets the amount of dietary fiber ranges from 40-150 gm/day
Fibers do not constitute a class of nutrients but they are necessary in the diet, and serve essential gastrointestinal functions.
Work Step by Step
Dietary fiber is usually classified as water soluble or water-insoluble. The water-soluble type includes
pectins, gums, mucilages, and psyllium; some water-insoluble example are cellulose, hemicellulose, and lignin.
Some sources of water-soluble fibers are oats, bean, carrots, seeds,nuts and fruits. Some sources of water-insoluble fibers are whole wheat, whole grain, vegetables, wheat bran, Brussels sprouts, turnips, cauliflower, fruit skins.
Both types of fibers confer certain health benefits.
Water soluble fibers are known to decrease the amount of cholesterol and low density lipoprotein adsorbed from the diet. In doing so they benefit the cardiovascular system and decrease the risks of atherosclerosis, heart attacks, and strokes.
Water insoluble fibers by absorb water, soften stool, and increase its bulk by 40-100%. The increase in the bulk of stool normally stretches the the colon. This stimulates peristalsis and quickens the rate of passage of feces through the colon. The benefits of this faster movement and evacuation of undigested food and waste are the lowering of rates of constipation and a decrease in the risk of developing diverticulitis.
While fibers are clearly necessary for good health, too much fiber can decrease the absorption of essential micronutrients like iron (Fe), calcium, magnesium, phosphorus, and traces element--zinc, selenium chromium etc.
