What is Dietary Fiber?
Nuts and sultanas: a source of fiber
Dietary fiber (fibre) is a food substance derived from plants which is resistant to digestive enzymes in the human digestive system. The term `fiber’ covers a number of different substances of differing chemical structures.
There are many classifications of fiber which are based on the properties of these various substances. The classification below depends on whether a fiber is soluble or not, whether it undergoes fermentation or on its viscosity and chemical structure. 1
Solubility
Soluble fiber
- resistant starch
- beta-glucans
- gum (e.g. guar)
- plant mucilage (e.g. psyllium)
- pectines
- fructooligosaccharides
- certain hemicelluloses
Insoluble fiber
- cellulose
- lignin
- some pectines
- certain hemicelluloses
The fiber content of the average diet is approximately 67%-75% insoluble and 25%-33% soluble fiber.1
Fermentability
Fermentable fiber
- resistant starch
- pectines
- beta-glucans
- gums (e.g. guar)
- inulin and oligofructose
Non-fermentable fiber
Viscosity
Viscous or `sticky’ fiber
- pectines
- certain gums (e.g. guar)
- plant mucilage (e.g. psyllium)
Non viscous fiber:
- cellulose
- lignin
- certain hemicelluloses
Chemical structure
Polysaccharides
- cellulose
- hemicelllulose
- pectines
- beta-glucans
- resistant starch
- gums
- mucilage
- fructans
Non-polysaccharides
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References:
- 1. Kozłowska L. (2010) Rola błonnika pokarmowego w utrzymaniu prawidłowej pracy jelit, Żywność dla zdrowia 13(8):23-27.
