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A prebiotic was first defined as a "non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health".[1] However, a prebiotic nature has been attributed to many food components without due consideration to the criteria required. In particular, almost every food oligosaccharide and polysaccharide (including dietary fiber) has been claimed to have prebiotic activity, but not all dietary carbohydrates are prebiotics. There is, therefore, a need to establish clear derivatives for classifying a food ingredient as prebiotic. Such classification requires a scientific demonstration that the food component or ingredient:
As with most functional foods or ingredients[2], the final demonstration must be carried out in vivo, either humans or in domestic animals or pets through appropriate clinical feeding trials. The methodologies used should be validated and supported by sound scientific approaches. Although each of these criteria is equally important, the third, concerning the selective stimulation of growth and/or activity of one or a limited number of bacteria, remains the most important and probably the most difficult to fulfill. This leads to a consideration of fermentable substrates in the human diet, availability for the microflora and selective metabolism. The following oligomers have been suggested as having prebiotic potential:[3]