Supplementation with soluble or insoluble rice-bran fibers increases short-chain fatty acid producing bacteria in the gut microbiota in vitro

Authors: Mahalak, Karley; Liu, Linshu; BOBOKALONOV, JAMSHED - Oak Ridge Institute For Science And Education (ORISE); Narrowe, Adrienne; Firrman, Jenni; BITTINGER, KYLE - The Children'S Hospital Of Philadelphia; HU, WEIMING - The Children'S Hospital Of Philadelphia; JONES, STEVEN - The Children'S Hospital Of Philadelphia; MUSTAFA, AHMED - The Children'S Hospital Of Philadelphia

Submitted to: Frontiers in Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2024
Publication Date: 5/10/2024
Citation: Mahalak, K.K., Liu, L.S., Bobokalonov, J., Narrowe, A.B., Firrman, J., Bittinger, K., Hu, W., Jones, S.M., Mustafa, A.M. 2024. Supplementation with soluble or insoluble rice-bran fibers increases short-chain fatty acid producing bacteria in the gut microbiota in vitro. Frontiers in Nutrition. https://doi.org/10.3389/fnut.2024.1304045.
DOI: https://doi.org/10.3389/fnut.2024.1304045

Interpretive Summary: Rice bran is a by-product of rice processing done to create white rice, which is popular with consumers. Rice bran is most frequently used as an additive to animal feed and has potential as a human dietary supplement due to its high fiber content. The digestion of fiber in the colon by the gut microbiota produces beneficial compounds called short-chain fatty acids that promote gut and immune health. The two main types of dietary fiber are insoluble and soluble fibers, both of which are important for normal bodily function. Soluble and insoluble fibers are sometimes sold separately as supplements, but the different effects on the human gut microbiota of these two fiber types from rice bran are not well known. To address how these rice bran fibers may impact the gut microbiota, we used the Simulator of the Human Intestinal Microbial Ecosystem (SHIME) to see how human gut microbial communities develop differently following supplementation with different fibers from rice bran. We found that both fiber types increased the population of beneficial bacteria and short-chain fatty acids that are known to help protect against IBD and other digestive disorders.

Technical Abstract: Studies have shown that a diet high in fiber and prebiotics has a positive impact on human health due largely to the fermentation of these compounds by the gut microbiota. One underutilized source of fiber may be rice bran, a waste product of rice processing that is used most frequently as an additive to livestock feed but may be a good source of fibers and other phenolic compounds as a human diet supplement. Previous studies focused on specific compounds extracted from rice bran showed that the soluble fibers extracted from rice bran can improve glucose response and reduce weight gain in mouse models. However, less is known about changes in the human gut microbiota in response to regular rice bran consumption. In this study, we used a Simulator of the Human Intestinal Microbial Ecology (SHIME®) to cultivate the human gut microbiota in conditions containing either soluble or insoluble fiber fractions from rice bran. Using 16S rRNA amplicon sequencing and targeted metabolomics, we explored how the gut microbial communities developed when provided with different supplemental fiber sources. We found that insoluble and soluble fiber fractions increased short-chain fatty acid production, indicating that both fractions were fermented. Both soluble and insoluble rice bran fractions increased the abundance of Bifidobacterium and Lachnospiraceae taxa. Overall, soluble and insoluble rice bran fractions had similar effects on the in vitro human gut microbiota, with differences highly dependent on the region and donors of the gut microbiota.