Concentrated raw fibers enhance the fiber-degrading capacity of a synthetic human gut microbiome. Fiber-supplemented

Modulation of the human gut microbiome is a promising strategy to positively impact health; in this regards, consumption of prebiotic fibers holds promise. Nevertheless, given the compositional complexity of the gut microbiome and its inter-individual variances, generalized recommendations on the source or amount of fiber supplements remain vague. This problem is further compounded by availability of tractable models to validate certain fiber sources. We employed a gnotobiotic mouse model containing a priori characterized synthetic human gut microbiome (SM) for their ability to metabolize a suit of mono- and polysaccharides; the SM contains 14 different strains belonging to five different major bacterial phyla found in the human intestine. Since soluble purified fibers have been a common subject of studies, we specifically investigated the effects of concentrated raw fibers—containing concentrated fibers from apple, oat, wheat, pea and psyllium—on the compositional and functional alterations in the SM. We demonstrate that concentrated raw fiber supplementation compared to a fiber-free diet increased the abundance of certain fiber-degrading commensals in the SM such as Eubacterium rectale, Roseburia intestinalis and Bacteroides ovatus and decreased the abundance of the mucin-degrading bacterium Akkermansia muciniphila. These results were corroborated by a general increase of bacterial fiber-degrading glycosidase enzyme activity but failed to result in increased significantly concentrations of short-chain fatty acids (SCFA). Overall, our results highlight the ability of concentrated raw fibers to enhance the microbial fiber-degrading capacity.