Dietary Fiber

[michael edward badolato jr]

Dhingra D. et al. Dietary fibre in foods: a Review. J Food Sc Technol 49;3: 255–266 2012

Dietary fiber consists of polysaccharides (usually non starch), oligosaccharides, and lignin - which is not classified as a carbohydrate - all resist digestion and absorption in the small intestine - instead relying on bacterial fermentation in the large intestine. There is also digestion resistant starch (RS) - especially in wheat.

Insoluble, often hydrating, slowly or nonfermenting fibers include:

cellulose - 50-80% fermented, 17% of grain, 31% of vegetables;

hemicellulose - 50-80% fermented predominating in whole grain rice and wheat;

and lignin very resistant to fermentation and present in whole grain

Soluble viscous fibers are gel forming, adhering, or gummy:

pectins, gums, and mucilages predominate in vegetables and fruit - pectin most common - gums from leguminous seed plants (guar, locust bean), seaweed extract, and microbrial (xanthan, gellan); mucilages from plant extracts such as gum acacia, gum karaya, gum tragacanth (Dhingra 2012) - excessive pectin has been shown to adversely affect the small intestinal villi contrasting with beneficial cellulose. It is important to balance soluble vegetable fiber with the insoluble hydrating fiber of whole grain. Hydrating fiber contributes more to fecal bulk than does soluble fiber (Priebe 2010, Cummings 1987, Paulini I. 1987, Tasman-Jones 1986, 1978, Schwartz 1982, Owen 1977, Chako 1969, Cook 1969).

Data of Dhingra 2012 illustrates the excessive bulk experienced with whole wheat compared to brown rice. 

fiber per 100 gram dry (uncooked)

rice: 1.0 gram insoluble, .3 soluble

wheat: 12.6 and 2.3, ten-fold difference