SCFAs are known to have crucial health functions, such as the regulation of water and mineral absorption, and the reduction of colonic pH to inhibit potential pathogens and encourage the growth of good bacteria.
Based on this, researchers at Kobe University conducted a study to examine how various prebiotics — indigestible dextrins, dextran and α-cyclodextrin — would affect human colonic microbiota if taken in a daily dose of 6g per person.
Model testing
They first created an in vitro human colonic microbiota model based on batch fermentation starting from a faecal inoculum, which they named the Kobe University Human Intestinal Microbiota Model (KUHIMM).
The KUHIMM was reported as capable of hosting over 500 microbial species found in a human faecal inoculum (similar to the 400 to 1,000 species previously found in human faecal samples) and of effectively mimicking human colonic microbiota.
The researchers wrote that it was "able to reproduce the bifidogenic effects of prebiotic materials (i.e., fructo-, galacto-, iso-malto- and xylo-oligosaccharides), in line with the results from human clinical trials".
Using the KUHIMM, they were able to carry out gene sequence analysis to show that adding 0.2% / 6g prebiotics did not alter colonic microbiota composition or diversity, but did improve SCFA production, with the prebiotics lowering colonic pH and increasing acetate and propionate generation.
They added that a human intervention study conducted to compare the effects of daily dietary fibre intake on healthy human microbiota with KUHIMM data confirmed the study results.
This led the researchers to state that even in "such relatively low amounts", prebiotics seemed able to activate colonic microbiota metabolism.
Colonic considerations
They noted that the KUHIMM lacked epithelial and immune cells, and as such, adding enterocytes and / or immune cells to an in vitro model would improve current knowledge of how different microbial metabolite patterns affect host cells.
They concluded: "These results suggest that the positive effect of prebiotics seen in vitro using our human colonic microbiota model can be achieved also in vivo in human subjects, upon administration of 6g of prebiotics per day, although increased SCFA production is difficult to detect in the human intestine.
"This amount represents a realistic intake and does not pose a burden on a person's eating habits."
Source: Scientific Reports
https://doi.org/10.1038/s41598-017-18877-8
"Low amounts of dietary fibre increase in vitro production of short-chain fatty acids without changing human colonic microbiota structure"
Authors: Daisuke Sasaki, et al.