A specific group of plant and animal oligosaccharides does not suffer enzymatic digestion in the human upper intestinal tract, achieving the colon microbial ecosystem in intact form. The reason for that is their diverse glycosidic bond structure, in comparison with common energetic polysaccharides as starch or glycogen. In this complex ecosystem, these molecules serve as energy sources, via fermentation, of distinctive beneficial bacterial groups, mainly belonging to the Anaerostipes, Bifidobacterium, Coprococcus, Faecalibacterium, Lactobacillus, Roseburia and other genera. The main catabolic products of these fermentations are short-chain fatty acids (SCFA) as acetate, propionate and butyrate, which appear in high concentrations in the lumen around the colon mucosa. Acetate and propionate are associated to energetic purposes for enterocytes, hepatocytes and other cells. Butyrate is the preferred energy source for colonocytes where it controls their cell cycle; butyrate is able to induce cell cycle arrest and apoptosis in tumor colonocytes. These oligosaccharides that increase beneficial colon bacterial populations and induce SCFA production in this ecosystem are called prebiotics. Here, different sources and chemical structures for prebiotics are described, as well as their modulatory effect on the growth of specific probiotic bacterial groups in the colon, and how their fermentation renders diverse SCFA, with beneficial effects in gut health.

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