dietary fiber dietary fiber dietary fiber (in commonwealth english fibre) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes. dietary fibers are diverse in chemical composition, and can be grouped generally by their solubility, viscosity, and fermentability, which affect how fibers are processed in the body. dietary fiber has two main components: soluble fiber and insoluble fiber, which are components of plant-based foods, such as legumes, whole grains and cereals, vegetables, fruits, and nuts or seeds. a diet high in regular fiber consumption is generally associated with supporting health and lowering the risk of several diseases. dietary fiber consists of non-starch polysaccharides and other plant components such as cellulose, resistant starch, resistant dextrins, inulin, lignins, chitins (in fungi), pectins, beta-glucans, and oligosaccharides. foods rich in fibers: fruits, vegetables and grains wheat bran has a high content of dietary fiber. food sources of dietary fiber have traditionally been divided according to whether they provide soluble or insoluble fiber. plant foods contain both types of fiber in varying amounts, according to the fiber characteristics of viscosity and fermentability. advantages of consuming fiber depend upon which type of fiber is consumed and which benefits may result in the gastrointestinal system. bulking fibers – such as cellulose and hemicellulose (including psyllium) – absorb and hold water, promoting regularity. viscous fibers – such as beta-glucan and psyllium – thicken the fecal mass. fermentable fibers – such as resistant starch, xanthan gum, and inulin – feed the bacteria and microbiota of the large intestine, and are metabolized to yield short-chain fatty acids, which have diverse roles in gastrointestinal health. soluble fiber (fermentable fiber or prebiotic fiber) – which dissolves in water – is generally fermented in the colon into gases and physiologically active by-products, such as short-chain fatty acids produced in the colon by gut bacteria. examples are beta-glucans (in oats, barley, and mushrooms) and raw guar gum. psyllium – a soluble, viscous, nonfermented fiber – is a bulking fiber that retains water as it moves through the digestive system, easing defecation. soluble fiber is generally viscous and delays gastric emptying which, in humans, can result in an extended feeling of fullness. inulin (in chicory root), wheat dextrin, oligosaccharides, and resistant starches (in legumes and bananas), are soluble non-viscous fibers. regular intake of soluble fibers, such as beta-glucans from oats or barley, has been established to lower blood levels of ldl cholesterol, a risk factor for cardiovascular diseases. insoluble fiber – which does not dissolve in water – is inert to digestive enzymes in the upper gastrointestinal tract. examples are wheat bran, cellulose, and lignin. coarsely ground insoluble fiber triggers the secretion of mucus in the large intestine, providing bulking. finely ground insoluble fiber does not have this effect and can actually have a constipating effect. some forms of insoluble fiber, such as resistant starches, can be fermented in the colon. definition dietary fiber is defined to be plant components that are not broken down by human digestive enzymes. in the late 20th century, only lignin and some polysaccharides were known to satisfy this definition, but in the early 21st century, resistant starch and oligosaccharides were included as dietary fiber components. the most accepted definition of dietary fiber is "all polysaccharides and lignin, which are not digested by the endogenous secretion of the human digestive tract". currently, most animal nutritionists are using either a physiological definition, "the dietary components resistant to degradation by mammalian enzymes", or a chemical definition, "the sum of non-starch polysaccharides (nsp) and lignin". 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 fermented to produce short-chain fatty acids, which are sources of energy for colonocytes. a diet rich in dietary fiber and whole grains may lower rates of coronary heart disease, colon cancer, and type 2 diabetes. definition of dietary fiber varies among institutions: organizationdefinition institute of medicine (2001)dietary fiber consists of nondigestible carbohydrates and lignin that are intrinsic and intact in plants. "added fiber" consists of isolated, nondigestible carbohydrates that have beneficial physiological effects in humans. american association of cereal chemists (2001)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 (2014; adopted by the european commission and 10 countries internationally)dietary fiber means carbohydrate polymers with more than 10 monomeric units, which are not hydrolyzed by digestive enzymes in the small intestine of humans. british nutrition foundation(2018)dietary fibre refers to a group of substances in plant foods which cannot be completely broken down by human digestive enzymes. this includes waxes, lignin and polysaccharides such as cellulose and pectin. originally it was thought that dietary fibre was completely indigestible and did not provide any energy. it is now known that some fibre can be fermented in the large intestine by gut bacteria, producing short chain fatty acids and gases. european unionfibre means carbohydrate polymers with three or more monomeric units, which are neither digested nor absorbed in the human small intestine. according to the european commission's joint research centre, "the eu and us definitions differ from the codex alimentarius definition (fao 2009) on the number of monomers that constitute the carbohydrate polymer; while the eu and us includes three or more monomeric units, the codex definition specifies ten or more, leaving national authorities to decide whether to include as fibre also carbohydrates with 3–9 monomers." dietary fiber 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. some types of insoluble fiber have bulking action and are not fermented, while some insoluble fibers like wheat bran may be slowly fermented in the colon in addition to the fecal bulking effect. generally, soluble fibers are fermented more than insoluble fibers in the colon. types and sources nutrientfood additivesource/comments water-insoluble dietary fibers β-glucans (a few of which are water-soluble) cellulosee 460cereals, fruit, vegetables (in all plants in general) chitin—in fungi, exoskeleton of insects and crustaceans hemicellulosecereals, bran, timber, legumes hexoses—wheat, barley pentose—rye, oat lignin—stones of fruits, vegetables (filaments of the garden bean), cereals xanthan gume 415production with xanthomonas-bacteria from sugar substrates resistant starchcan 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, raw bananas, cooked and cooled pasta and potatoes water-soluble dietary fibers arabinoxylan (a hemicellulose)—psyllium fructansreplace or complement in some plant taxa the starch as storage carbohydrate inulin—in diverse plants, e.g. topinambour, chicory, etc. polyuronide pectine 440in the fruit skin (mainly apples, quinces), vegetables alginic acids (alginates)e 400–e 407in algae sodium alginatee 401 potassium alginatee 402 ammonium alginatee 403 calcium alginatee 404 propylene glycol alginate (pga)e 405 agare 406 carrageene 407red algae raffinose—legumes polydextrosee 1200synthetic polymer, c. 1 kcal/g contents in food children eating fiber-rich food dietary fiber is found in fruits, vegetables and whole grains. the amounts of fiber contained in common foods are listed in the following table: food groupserving meanfibermass per serving fruit120 ml (0.5 cup)1.1 g dark green vegetables120 ml (0.5 cup)6.4 g orange vegetables120 ml (0.5 cup)2.1 g cooked dry beans (legumes)120 ml (0.5 cup)8.0 g starchy vegetables120 ml (0.5 cup)1.7 g other vegetables120 ml (0.5 cup)1.1 g whole grains28 g (1 oz)2.4 g meat28 g (1 oz)0.1 g dietary fiber is found in plants, typically eaten whole, raw or cooked, although fiber can be added to make dietary supplements and fiber-rich processed foods. grain bran products have the highest fiber contents, such as crude corn bran (79 g per 100 g) and crude wheat bran (43 g per 100 g), which are ingredients for manufactured foods. medical authorities, such as the mayo clinic, recommend adding fiber-rich products to the standard american diet (sad) because it is rich in processed and artificially sweetened foods, with minimal intake of vegetables and legumes. plant sources some plants contain significant amounts of soluble and insoluble fiber. for example, plums and prunes have a thick skin covering a juicy pulp. the skin is a source of insoluble fiber, whereas soluble fiber is in the pulp. grapes also contain a fair amount of fiber. soluble fiber found in varying quantities in all plant foods, including: legumes (peas, soybeans, lupins and other beans) oats, rye, chia, and barley some fruits (including figs, avocados, plums, prunes, berries, ripe bananas, and the skin of apples, quinces and pears) certain vegetables such as broccoli, carrots, and jerusalem artichokes root tubers and root vegetables such as sweet potatoes and onions (skins of these are sources of insoluble fiber also) psyllium seed husks (a mucilage soluble fiber) and flax seeds nuts, with almonds being the highest in dietary fiber insoluble fiber sources include: whole grain foods wheat and corn bran legumes such as beans and peas nuts and seeds potato skins lignans vegetables such as green beans, cauliflower, zucchini (courgette), celery, and nopal some fruits including avocado, and unripe bananas the skins of some fruits, including kiwifruit, grapes and tomatoes supplements these are a few example forms of fiber that have been sold as supplements or food additives. these may be marketed to consumers for nutritional purposes, treatment of various gastrointestinal disorders, and for such possible health benefits as lowering cholesterol levels, reducing risk of colon cancer, and losing weight. soluble fiber soluble fiber supplements may be beneficial for alleviating symptoms of irritable bowel syndrome, such as diarrhea or constipation and abdominal discomfort. prebiotic soluble fiber products, like those containing inulin or oligosaccharides, may contribute to relief from inflammatory bowel disease, as in crohn's disease, ulcerative colitis, and clostridium difficile, due in part to the short-chain fatty acids produced with subsequent anti-inflammatory actions upon the bowel. fiber supplements may be effective in an overall dietary plan for managing irritable bowel syndrome by modification of food choices. insoluble fiber one insoluble fiber, resistant starch from high-amylose corn, has been used as a supplement and may contribute to improving insulin sensitivity and glycemic management as well as promoting regularity and possibly relief of diarrhea. one preliminary finding indicates that resistant corn starch may reduce symptoms of ulcerative colitis. inulins chemically defined as oligosaccharides and occurring naturally in most plants, inulins have nutritional value as carbohydrates, or more specifically as fructans, a polymer of the natural plant sugar, fructose. inulin is typically extracted by manufacturers from enriched plant sources such as chicory roots or jerusalem artichokes for use in prepared foods. subtly sweet, it can be used to replace sugar, fat, and flour, is often used to improve the flow and mixing qualities of powdered nutritional supplements, and has potential health value as a prebiotic fermentable fiber. as a prebiotic fermentable fiber, inulin is metabolized by gut flora to yield short-chain fatty acids (see below), which increase absorption of calcium, magnesium, and iron. the primary disadvantage of inulin is its fermentation within the intestinal tract, possibly causing flatulence and digestive distress at doses higher than 15 grams/day in most people. individuals with digestive diseases have benefited from removing fructose and inulin from their diet. while clinical studies have shown changes in the microbiota at lower levels of inulin intake, higher intake amounts may be needed to achieve effects on body weight. vegetable gums vegetable gum fiber supplements are relatively new to the market. often sold as a powder, vegetable gum fibers dissolve easily with no aftertaste. in preliminary clinical trials, they have proven effective for the treatment of irritable bowel syndrome. examples of vegetable gum fibers are guar gum and gum arabic. activity in the gut many molecules that are considered to be "dietary fiber" are so because humans lack the necessary enzymes to split the glycosidic bond and they reach the large intestine. many foods contain varying types of dietary fibers, all of which contribute to health in different ways. dietary fibers make three primary contributions: bulking, viscosity and fermentation. different fibers have different effects, suggesting that a variety