Dietary Fiber Can Increase Short-Chain Fatty Acids Without Altering the Gut Microbiome


Humans cannot digest prebiotic fiber alone; it passes intact through the small intestine and into the colon where it is fermented by gut microbes into short-chain fatty acids such as butyrate and propionate.


These short-chain fatty acids have a number of important health functions, such as regulating mineral absorption, reducing colonic pH, stopping pathogens (bad bacteria) and promoting the growth of beneficial bacteria.


Indigestible dextrin, alpha-cyclodextrin, and dextran are types of prebiotics that have been shown to affect the composition of healthy gut bacteria at high doses (more than 30 g per day), but not at normal dietary doses (less than 10 g per day). 


So, a group of Japanese researchers set out to test the effects of these potential prebiotics at normal dietary levels and compare them to well-studied prebiotics such as inulin (FOS) and XOS.


The results of the study are published in the journal Scientific Reports.


The researchers used a fermentation model containing human feces (containing gut bacteria) so that they could rule out factors other than the prebiotics, and closely monitor the production of short-chain fatty acids by the gut bacteria.


The researchers added the prebiotics at the equivalent of 6 g per day (comparable to a normal dietary intake), which is low enough to avoid dietary discomfort (such as bloating or diarrhea that can be caused when prebiotics are consumed in high doses).


They found that each of the prebiotics lowered the pH in the fermentation system. Interestingly, the production of acetate and propionate short-chain fatty acids increased, but butyrate levels were unaffected. Finally, the composition of the gut bacteria (i.e., Bifidobacteria and Lactobacilli) was unchanged.


The findings of the study suggest that low doses of indigestible dextrin, alpha-cyclodextrin, and dextran can produce the beneficial prebiotic effects of increased production of short-chain fatty acids and lowered pH in the colon without changing the composition of the gut microbiome.