Dietary fiber is the indigestible portion of plant parts such as seed husks. Dietary fibers—and their function after eating food containing them—have been described in ancient herb books and medicinal literature up to the recent emergence of the dietary fiber hypothesis, putting forward the idea that indigestible, fibrous residues of seeds and vegetables play a significant role in human nutrition and health [1-3].
AACC International (AACC stands for American Association of Cereal Chemists), a non-profit professional organization of grain scientists, adopted the following definition :
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 plants substances. Dietary fibers promote beneficial physiological effects including laxation, and/or blood cholesterol attenuation, and/or blood glucose attenuation.
Instead of merely being a formal definition, this text underlines the nutritional and nutraceutical (a portmanteau of the words nutrition and pharmaceutical) aspects of dietary fibers.
Keywords: biomedical sciences, physiology, gastroenterology, health, food science, macromolecules.
References and more to explore
 Steve W. Cui and Keisha T. Roberts. Chapter 13. Dietary Fiber: Fulfilling the Promise of Added-Value Formulations. In Stefan Kasapis, Ian T. Norton and Johan B. Ibbing (Eds.), Modern Biopolymer Science: Bridging the Divide Between Fundamental Treatise and Industrial Application.(pp. 399-447), London (UK), Burlington (MA) and San Diego (CA): Academic Press, 2009.
 Thomas P. Amy: The dietary fiber hypothesis. Am. J. Clin. Nutr. 1981, 34 (3), pp. 432-433 [http://ajcn.nutrition.org/content/34/3/432.full.pdf+html].
 Low-Carb for You: The Fiber Hypothesis. May 4, 2010 [lowcarb4u.blogspot.com/2010/05/fiber-schmiber.html].
 AACC International: AACCnet > Scientific Initiatives > AACCI Standard Definitions > Dietary Fiber [www.aaccnet.org/initiatives/definitions/Pages/DietaryFiber.aspx].