Dose-response effects of inulin and oligofructose on intestinal bifidogenesis effects

Recent studies have identified several beneficial attributes of inulin (I) and oligofructose (OF) in human health. However, most of the studies pertaining to the physiologic role of these compounds have been conducted at higher concentrations (8-40 g/d) as a source of dietary fiber. There is growing interest in using I and OF as a substrate for the selective growth of beneficial gastrointestinal bacteria such as the bifidobacteria. In vitro fermentation studies using fecal inoculums have shown that I and OF are utilized rapidly and completely by intestinal microflora and that the degree of polymerization of the substrate influenced its rate of disappearance. In these and other studies, I and OF were shown to be efficient substrates for the growth of most strains of bifidobacteria compared with glucose. In vivo studies have also shown that when human volunteers ingested I or OF, the number of fecal bifidobacteria increased. However, when results from the reported studies are combined and analyzed, a dose-response relationship in terms of log increases in the count of bifidobacteria cannot be demonstrated. Initial numbers of bifidobacteria in the feces, independent of the dose of the fructo-oligosaccharides, seem to influence the results. Future investigations should consider this relationship carefully.