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, 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 three-fold 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