Nondigestible polysaccharides (NDP) and nondigestible oligosaccharides (NDO) occur naturally in many foods. The physicochemical and biological properties of these compounds, as they relate to dietary fiber, are associated with physiological actions in the small and large intestine, having important implications in human health. These properties include water dispersibility and solubility, viscosity effects, bulk, absorption and fermentability, and binding of other compounds. These features may lead to various physiological actions such as reducing cholesterol and attenuating blood glucose, maintaining gastrointestinal health, and positively affecting calcium bioavailability and immune function. Moreover, based on their physiochemical properties, many of the new oligosaccharides can help improve the organoleptic properties and nutritional value of foods.

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The bifidogenic effect of inulin and oligofructose is now well established in various studies, not only in adult participants but also in other age groups. This bifidogenic shift in the composition of the colonic microbiota is likely the basis for the impact of these prebiotic compounds on various parameters of colonic function. Mainly from animal and in vitro studies and also from some human trials, there are indications, for instance, that inulin-type fructans may reduce the production of potentially toxic metabolites and may induce important immune-mediated effects. This review discusses how these changes in the composition and activity of the colonic microbiota may affect gut health in healthy people, including in those who may experience some form of gastrointestinal discomfort.

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Objective: To evaluate the bifidogenic efficacy of two inulin doses in healthy human adults. Design: A double-blind, placebo-controlled, crossover human study. Setting: Food Microbial Sciences Unit, The University of Reading, Reading, UK. Subjects: Thirty healthy volunteers, 15 men, 15 women (age range 19-35).Interventions: Subjects consumed a chocolate drink containing placebo (maltodextrin, 8 g/day), 5 g/day inulin and 8 g/day inulin for a 2-week treatment period. Each treatment was followed by a 1-week washout at the end of which volunteers progressed to the next treatment. Faecal samples were obtained at the start of the study (baseline) and at the end of each treatment and washout period. Fluorescent in situ hybridization was used to monitor populations of Bifidobacterium genus, Bacteroides -Prevotella, Lactobacillus -Enterococcus and Clostridium perfringens -histolyticum subgroup. Results: Bifidobacterial levels increased significantly upon ingestion of both the low (9.7870.29 log 10 cells/g faeces, Po0.05) and the high inulin dose (9.7970.38 log 10 cells/g faeces, P ¼ 0.05) compared to placebo (9.6470.23 log 10 cells/g faeces).Conclusions: Both inulin doses exhibited a bifidogenic effect but a higher volunteer percentage responded to the high dose. A dose response effect was not observed but the magnitude of increase in bifidobacteria levels depended on their initial numbers. The higher the initial concentrations the smaller was the increase upon ingestion of the active treatments. Sponsorship: Financial support for the completion of this project was provided by Sensus (Roosendaal, The Netherlands).