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Dietary fiber


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

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.


Organization (reference) Definition
Institute of Medicine Dietary fiber consists of nondigestible carbohydrates and lignin that are intrinsic and intact in plants. Functional fiber consists of isolated, nondigestible carbohydrates that have beneficial physiologic effects in humans. Total fiber is the sum of dietary fiber and functional fiber.
American Association of Cereal Chemists Dietary fiber is the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine, with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin, and associated plant substances. Dietary fibers promote beneficial physiologic effects including laxation, and/or blood cholesterol attenuation, and/or blood glucose attenuation.
Codex Alimentarius Commission Dietary fiber means carbohydrate polymers with ≥10 monomeric units, which are not hydrolyzed by the endogenous enzymes in the small intestine of humans.
Nutrient Food additive appearance / preparationi
water-insoluble dietary fibers
β-glucans (a few of which are water-soluble)
   Cellulose E 460 cereals, fruit, vegetables (in all plants in general)
   Chitin in fungi, exoskeleton of insects and crustaceans
Hemicellulose cereals, bran, timber, legume
   Hexoses wheat, barley
   Pentose rye, oat
Lignin stones of fruits, vegetables (filaments of the garden bean), cereals
Xanthan gum E 415 production with Xanthomonas-bacteria from sugar substrates
Resistant starch Can be starch protected by seed or shell (type RS1), granular starch (type RS2) or retrograded starch (type RS3)
   Resistant starch high amylose corn, barley, high amylose wheat, legumes, bananas, etc.
water-soluble dietary fibers
Arabinoxylan (a hemicellulose) psyllium
Fructans replace or complement in some plant taxa the starch as storage carbohydrate
   Inulin in diverse plants, e.g. topinambour, chicory, etc.
Polyuronide
   Pectin E 440 in the fruit skin (mainly apples, quinces), vegetables
   Alginic acids (Alginates) E 400–E 407 in Algae
      Natriumalginat E 401
      Kaliumalginat E 402
      Ammoniumalginat E 403
      Calciumalginat E 404
      Propylenglycolalginat (PGA) E 405
      agar E 406
      carrageen E 407 red algae
Raffinose legumes
Xylose monosacharide, pentose
Polydextrose E 1200 synthetic polymer, ca. 1kcal/g
Lactulose synthetic disaccharide
Food group Serving Mean fiber g/serving
Fruit 0.5 cup 1.1
Dark-green vegetables 0.5 cup 6.4
Orange vegetables 0.5 cup 2.1
Cooked dry beans (legumes) 0.5 cup 8.0
Starchy vegetables 0.5 cup 1.7
Other vegetables 0.5 cup 1.1
Whole grains 28 g (1 oz) 2.4
Meat 28 g (1 oz) 0.1
Effects
Increases food volume without increasing caloric content to the same extent as digestible carbohydrates, providing satiety which may reduce appetite.
Attracts water and forms a viscous gel during digestion, slowing the emptying of the stomach and intestinal transit, shielding carbohydrates from enzymes, and delaying absorption of glucose, which lowers variance in blood sugar levels
Lowers total and LDL cholesterol, which may reduce the risk of cardiovascular disease
Regulates blood sugar, which may reduce glucose and insulin levels in diabetic patients and may lower risk of diabetes
Speeds the passage of foods through the digestive system, which facilitates regular defecation
Adds bulk to the stool, which alleviates constipation
Balances intestinal pH and stimulates intestinal fermentation production of short-chain fatty acids, which may reduce risk of colorectal cancer

edible parts of plants
indicates that some parts of a plant we eat—skin, pulp, seeds, stems, leaves, roots—contain fiber. Both insoluble and soluble sources are in those plant components.
carbohydrates
complex carbohydrates, such as long-chained sugars also called starch, oligosaccharides, or polysaccharides, are sources of soluble fermentable fiber.
resistant to digestion and absorption in the human small intestine
foods providing nutrients are digested by gastric acid and digestive enzymes in the stomach and small intestine where the nutrients are released then absorbed through the intestinal wall for transport via the blood throughout the body. A food resistant to this process is undigested, as insoluble and soluble fibers are. They pass to the large intestine only affected by their absorption of water (insoluble fiber) or dissolution in water (soluble fiber).
complete or partial fermentation in the large intestine
the large intestine comprises a segment called the colon within which additional nutrient absorption occurs through the process of fermentation. Fermentation occurs by the action of colonic bacteria on the food mass, producing gases and short-chain fatty acids. It is these short-chain fatty acids—butyric, acetic (ethanoic), propionic, and valeric acids—that scientific evidence is revealing to have significant health properties.
  • Soluble fiber, which dissolves in water, is readily fermented in the colon into gases and physiologically active byproducts, and can be prebiotic and viscous. It delays gastric emptying which in turn can cause an extended feeling of fullness.
  • 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.
  • The cells of cooked potatoes and legumes are gels filled with gelatinized starch granules. The cellular structures of fruits and vegetables are foams with a closed cell geometry filled with a gel, surrounded by cell walls which are composites with an amorphous matrix strengthened by complex carbohydrate fibers.
  • Particle size and interfacial interactions with adjacent matrices affect the mechanical properties of food composites.
  • Food polymers may be soluble in and/or plasticized by water. Water is the most important plasticizer, particularly in biological systems thereby changing mechanical properties.
  • The variables include chemical structure, polymer concentration, molecular weight, degree of chain branching, the extent of ionization (for electrolytes), solution pH, ionic strength and temperature.
  • Cross-linking of different polymers, protein and polysaccharides, either through chemical covalent bonds or cross-links through molecular entanglement or hydrogen or ionic bond cross-linking.
  • Cooking and chewing food alters these physicochemical properties and hence absorption and movement through the stomach and along the intestine
  • Both Applies to both soluble and insoluble fiber
  • Soluble Applies to soluble fiber only
  • Insoluble Applies to insoluble fiber only
  • Oat bran
  • Rolled oats
  • Whole oat flour
  • Oatrim
  • Whole grain barley and dry milled barley
  • Soluble fiber from psyllium husk with purity of no less than 95%
  • 3 g or more per day of beta-glucan soluble fiber from either whole oats or barley, or a combination of whole oats and barley
  • 7 g or more per day of soluble fiber from psyllium seed husk.
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Wikipedia

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