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Dietary fiber

Foods rich in fibers: fruits, vegetables and grains
Wheat bran has a high content of dietary fiber.

Dietary fiber (fibre in Commonwealth English) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes.[1] 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.[2] Dietary fiber has two main subtypes: soluble fiber and insoluble fiber which are components of plant-based foods such as legumes, whole grains, cereals, vegetables, fruits, and nuts or seeds.[2][3] A diet high in regular fiber consumption is generally associated with supporting health and lowering the risk of several diseases.[2][4] Dietary fiber consists of non-starch polysaccharides and other plant components such as cellulose, resistant starch, resistant dextrins, inulins, lignins, chitins, pectins, beta-glucans, and oligosaccharides.[1][2][3]

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.[1][5] Advantages of consuming fiber depend upon which type is consumed.[6] Bulking fibers – such as cellulose and hemicellulose (including psyllium) – absorb and hold water, promoting bowel movement regularity.[7] Viscous fibers – such as beta-glucan and psyllium – thicken the fecal mass.[7] 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.[8][9][10]

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 – soluble, viscous, and non-fermented 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.[2] Inulin (in chicory root), wheat dextrin, oligosaccharides, and resistant starches[11] (in legumes and bananas) are soluble non-viscous fibers.[2] Regular intake of soluble fibers such as beta-glucans from oats or barley has been established to lower blood levels of LDL cholesterol.[2][4][12] Soluble fiber supplements also significantly lower LDL cholesterol.[13][14][15]

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. However, finely ground insoluble fiber does not have this effect and instead can cause a constipation.[2] Some forms of insoluble fiber, such as resistant starches, can be fermented in the colon.[16]

  1. ^ a b c "Dietary fibre". British Nutrition Foundation. 2018. Archived from the original on 26 July 2018. Retrieved 26 July 2018.
  2. ^ a b c d e f g h "Fiber". Linus Pauling Institute, Oregon State University. March 2019. Retrieved 3 February 2021.
  3. ^ a b Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids (2005), Chapter 7: Dietary, Functional and Total Fiber. US Department of Agriculture, National Agricultural Library and National Academy of Sciences, Institute of Medicine, Food and Nutrition Board. 2005. doi:10.17226/10490. ISBN 978-0-309-08525-0.
  4. ^ a b Veronese N, Solmi M, Caruso MG, et al. (March 2018). "Dietary fiber and health outcomes: an umbrella review of systematic reviews and meta-analyses". The American Journal of Clinical Nutrition. 107 (3): 436–444. doi:10.1093/ajcn/nqx082. PMID 29566200.{{cite journal}}: CS1 maint: overridden setting (link)
  5. ^ Institute of Medicine (2001). Dietary Reference Intakes, Proposed Definition of Dietary Fiber. Washington, D.C.: Institute of Medicine Press. p. 25. ISBN 978-0-309-07564-0.
  6. ^ Gallaher DD (2006). "8". Present Knowledge in Nutrition (9 ed.). Washington, D.C.: ILSI Press. pp. 102–110. ISBN 978-1-57881-199-1.
  7. ^ a b Institute of Medicine (2001). Dietary Reference Intakes: Proposed Definition of Dietary Fiber. Washington, D.C.: National Academy Press. p. 19. ISBN 978-0-309-07564-0.
  8. ^ Bedford A, Gong J (June 2018). "Implications of butyrate and its derivatives for gut health and animal production". Animal Nutrition. 4 (2): 151–159. doi:10.1016/j.aninu.2017.08.010. PMC 6104520. PMID 30140754.
  9. ^ Cummings JH (2001). The Effect of Dietary Fiber on Fecal Weight and Composition (3 ed.). Boca Raton, Florida: CRC Press. p. 184. ISBN 978-0-8493-2387-4.
  10. ^ Ostrowski MP, La Rosa SL, Kunath BJ, et al. (April 2022). "Mechanistic insights into consumption of the food additive xanthan gum by the human gut microbiota". Nature Microbiology. 7 (4): 556–569. doi:10.1038/s41564-022-01093-0. hdl:11250/3003739. PMID 35365790. S2CID 247866305.{{cite journal}}: CS1 maint: overridden setting (link)
  11. ^ Keenan MJ, Zhou J, Hegsted M, et al. (March 2015). "Role of resistant starch in improving gut health, adiposity, and insulin resistance". Advances in Nutrition. 6 (2): 198–205. doi:10.3945/an.114.007419. PMC 4352178. PMID 25770258.
  12. ^ Cite error: The named reference FDAc was invoked but never defined (see the help page).
  13. ^ Jovanovski E, Yashpal S, Komishon A, et al. (1 November 2018). "Effect of psyllium (Plantago ovata) fiber on LDL cholesterol and alternative lipid targets, non-HDL cholesterol and apolipoprotein B: a systematic review and meta-analysis of randomized controlled trials". The American Journal of Clinical Nutrition. 108 (5): 922–932. doi:10.1093/ajcn/nqy115. ISSN 1938-3207. PMID 30239559.
  14. ^ Ho HV, Jovanovski E, Zurbau A, et al. (May 2017). "A systematic review and meta-analysis of randomized controlled trials of the effect of konjac glucomannan, a viscous soluble fiber, on LDL cholesterol and the new lipid targets non-HDL cholesterol and apolipoprotein B". The American Journal of Clinical Nutrition. 105 (5): 1239–1247. doi:10.3945/ajcn.116.142158. ISSN 1938-3207. PMID 28356275.
  15. ^ Ghavami A, Ziaei R, Talebi S, et al. (1 May 2023). "Soluble Fiber Supplementation and Serum Lipid Profile: A Systematic Review and Dose-Response Meta-Analysis of Randomized Controlled Trials". Advances in Nutrition. 14 (3): 465–474. doi:10.1016/j.advnut.2023.01.005. ISSN 2161-8313. PMC 10201678. PMID 36796439.
  16. ^ Lockyer S, Nugent AP (2017). "Health effects of resistant starch". Nutrition Bulletin. 42: 10–41. doi:10.1111/nbu.12244.

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