Prebiotics are substances that preferentially favor the growth and dominance within the G.I. tract of the beneficial components of the microflora, such as the lactobacilli and bifidibacteria. The most well known and well proven prebiotic are the fructooligosaccharides (FOS).
FOS are non-digestible plant sugars derived from asparagus, Jerusalem artichokes and soybeans. FOS pass undigested through the small intestine and are fermented in the colon, where they specifically and selectively promote the growth of some species of the indigenous microflora, especially Bifidobacterium and Lactobacillus.
FOS are not hydrolyzed by human digestive enzymes but, as they are not recovered from the feces, this suggests complete colonic metabolism. Colonic fermentation leads to increased fecal biomass, decreased ceco-colonic pH, and production of short-chain fatty acids. The short-chain fatty acids exert systemic effects on lipid metabolism similarly to dietary fiber.
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