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Dietary fiber

The medical and nutritional communities have long recognized the health benefits of a high fiber diet. Low intake of dietary fiber is associated with high incidents of several diseases including coronary heart disease, diabetes, obesity, and colon cancer.High fiber diets are reported to reduce the risk of colon and rectal cancers and to reduce blood serum cholesterol levels. Dietary fiber is not a single substance, but is a term used to identify plant polysaccharides and lignins that are not hydrolyzed by the endogenous secretions of the human digestive system. Numerous types of dietary fibers are currently available. Dietary fiber consists of the non-digestible polysaccharide fractions of plant fiber and is classified as water soluble (pectin or guar), and water insoluble products such as wheat bran. These fibers all have different characteristics and subsequently different metabolic and physiologic effects. Plant components which make up dietary fiber include, among others: structural polysaccharides (cellulose and hemicellulose), nonstructural polysaccharides (pectines, B-glucans; gums and mucilages) and structural non-polysaccharides (lignin). Dietary fibers are commonly characterized by their water solubility and their relative susceptibility to microbial degradation into fermentable and nonfermentable fiber fractions. In general, pectines, gums and mucilages are water soluble, while lignin, cellulose and hemicellulose are water insoluble. The roles of dietary fiber as an alexeteric for protecting the gastrointestinal tract from diseases have also been documented. These include reduction in gastrointestinal cancer incidence, constipation, hiatal hernia, appendicitis, diverticular disease, and hemorrhoids. There are also implications of its use in the treatment or prevention of "irritable bowel syndrome". Basically, dietary fiber passes through the small intestine undigested by enzymes and is a kind of natural and necessary laxative. Dietary fiber is understood to be all of the components of a food that are not broken down by enzymes in the human digestive tract to produce small molecular compounds which are then absorbed into the bloodstream. These components are mostly celluloses, hemicelluloses, pectin, gums, mucilages, lignin and lignin material varying in different plants according to type and age. These fibers differ significantly in their chemical composition and physical structure and subsequently their physiological function. The modes of action of dietary fiber in the human gastrointestinal tract include providing mechanical distention through its water holding activity, stimulating bowel movement, slowing down the gastrointestinal transition and digestion process, modifying fat absorption, increasing bile acids excretion, and detoxicating toxic substances. Soluble dietary fibers are found to have cholesterol-lowering and leveling postprandial glycemic response effects in clinical studies.

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