High-level dietary fibre up-regulates colonic fermentation and relative abundance of saccharolytic bacteria within the human faecal microbiota in vitro.

BACKGROUND: Health authorities around the world advise citizens to increase their intake of foods rich in dietary fibre because of its inverse association with chronic disease. However, a few studies have measured the impact of increasing mixed dietary fibres directly on the composition of the human gut microbiota. AIMS OF THE STUDY: We studied the impact of high-level mixed dietary fibre intake on the human faecal microbiota using an in vitro three-stage colonic model.
METHODS: The colonic model was maintained on three levels of fibre, a basal level of dietary fibre, typical of a Western-style diet, a threefold increased level and back to normal level. Bacterial profiles and short chain fatty acids concentrations were measured.
RESULTS: High-level dietary fibre treatment significantly stimulated the growth of Bifidobacterium, Lactobacillus-Enterococcus group, and Ruminococcus group (p < 0.05) and significantly increased clostridial cluster XIVa and Faecalibacterium prausnitzii in vessel 1 mimicking the proximal colon (p < 0.05). Total short chain fatty acids concentrations increased significantly upon increased fibre fermentation, with acetate and butyrate increasing significantly in vessel 1 only (p < 0.05). Bacterial species richness changed upon increased fibre supplementation. The microbial community and fermentation output returned to initial levels once supplementation with high fibre ceased.
CONCLUSIONS: This study shows that high-level mixed dietary fibre intake can up-regulate both colonic fermentation and the relative abundance of saccharolytic bacteria within the human colonic microbiota. Considering the important role of short chain fatty acids in regulating human energy metabolism, this study has implications for the health-promoting potential of foods rich in dietary fibres.