What is "dietary fiber"

Fiber \Fi"ber\, Fibre \Fi"bre\,, n. [F. fibre, L. fibra.]

1. One of the delicate, threadlike portions of which the tissues of plants and animals are in part constituted; as, the fiber of flax or of muscle.

2. Any fine, slender thread, or threadlike substance; as, a fiber of spun glass; especially, one of the slender rootlets of a plant. [WordNet sense 1]

3. the inherent complex of attributes that determine a person's moral and ethical actions and reactions; sinew; strength; toughness; as, a man of real fiber. [WordNet sense 2]

   Syn: character, fibre.

   Yet had no fibers in him, nor no force.
   --Chapman.

4. A general name for the raw material, such as cotton, flax, hemp, etc., used in textile manufactures.

5. (Nutrition) that portion of food composed of carbohydrates which are completely or partly indigestible, such as cellulose or pectin; it may be in an insoluble or a soluble form. It provides bulk to the solid waste and stimulates peristalsis in the intestine. It is found especially in grains, fruits, and vegetables. There is some medical evidence which indicates that diets high in fiber reduce the risk of colon cancer and reduce cholesterol levels in the blood. It is also called dietary fiber, roughage, or bulk.

6. a leatherlike material made by compressing layers of paper or cloth. [WordNet sense 3]

   Syn: fibre, vulcanized fiber.

   Fiber gun, a kind of steam gun for converting, wood, straw, etc., into fiber. The material is shut up in the gun with steam, air, or gas at a very high pressure which is afterward relieved suddenly by letting a lid at the muzzle fly open, when the rapid expansion separates the fibers.

   Fiber plants (Bot.), plants capable of yielding fiber useful in the arts, as hemp, flax, ramie, agave, etc.

n. (context US English) (alternative spelling of dietary fibre English)

Dietary fiber or roughage is the indigestible portion of food derived from plants. It has two main components:

• Soluble fiber, which dissolves in water, is readily fermented in the colon into gases and physiologically active byproducts, and can be prebiotic and viscous.
• Insoluble fiber, which does not dissolve in water, is metabolically inert and provides bulking, or it can be prebiotic and metabolically ferment in the large intestine. Bulking fibers absorb water as they move through the digestive system, easing defecation.

Dietary fibers can act by changing the nature of the contents of the gastrointestinal tract and by changing how other nutrients and chemicals are absorbed. Some types of soluble fiber absorb water to become a gelatinous, viscous substance which is fermented by bacteria in the digestive tract. Some types of insoluble fiber have bulking action and are not fermented. Lignin, a major dietary insoluble fiber source, may alter the rate and metabolism of soluble fibers. Other types of insoluble fiber, notably resistant starch, are fully fermented. Some but not all soluble plant fibers block intestinal mucosal adherence and translocation of potentially pathogenic bacteria and may therefore modulate intestinal inflammation, an effect that has been termed contrabiotic.

Chemically, dietary fiber consists of non- starch polysaccharides such as arabinoxylans, cellulose, and many other plant components such as resistant starch, resistant dextrins, inulin, lignin, chitins, pectins, beta-glucans, and oligosaccharides. A novel position has been adopted by the US Department of Agriculture to include functional fibers as isolated fiber sources that may be included in the diet. The term "fiber" is something of a misnomer, since many types of so-called dietary fiber are not actually fibrous.

Food sources of dietary fiber are often divided according to whether they provide (predominantly) soluble or insoluble fiber. Plant foods contain both types of fiber in varying degrees, according to the plant's characteristics.

Advantages of consuming fiber are the production of healthful compounds during the fermentation of soluble fiber, and insoluble fiber's ability (via its passive hygroscopic properties) to increase bulk, soften stool, and shorten transit time through the intestinal tract. A disadvantage of a diet high in fiber is the potential for significant intestinal gas production and bloating.