Abstract
Bile acids (BAs) act as signaling molecules in various physiological processes, and are related to colonic microbiota composition as well as to different types of dietary fat and fiber. This study investigated whether guar gum and pectin—two fibers with distinct functional characteristics—affect BA profiles, microbiota composition, and gut metabolites in rats. Low- (LM) or high-methoxylated (HM) pectin, and low-, medium-, or high-molecular-weight (MW) guar gum were administered to rats that were fed either low- or high-fat diets. Cecal BAs, short-chain fatty acids (SCFA) and microbiota composition, and plasma lipopolysaccharide-binding protein (LBP) levels were analyzed, by using novel methodologies based on gas chromatography (BAs and SCFAs) and 16S rRNA gene sequencing on the Illumina MiSeq platform. Strong correlations were observed between cecal BA and SCFA levels, microbiota composition, and portal plasma LBP levels in rats on a high-fat diet. Notably, guar gum consumption with medium-MW increased the cecal amounts of cholic-, chenodeoxycholic-, and ursodeoxycholic acids as well as α-, β-, and ω-muricholic acids to a greater extent than other types of guar gum or the fiber-free control diet. In contrast, the amounts of cecal deoxycholic- and hyodeoxycholic acid were reduced with all types of guar gum independent of chain length. Differences in BA composition between pectin groups were less obvious, but cecal levels of α- and ω-muricholic acids were higher in rats fed LM as compared to HM pectin or the control diet. The inflammatory marker LBP was downregulated in rats fed medium-MW guar gum and HM pectin; these two fibers decreased the cecal abundance of Oscillospira and an unclassified genus in Ruminococcaceae, and increased that of an unclassified family in RF32. These results indicate that the molecular properties of guar gum and pectin are important for their ability to modulate cecal BA formation, gut microbiota composition, and high-fat diet induced inflammation.
Highlights
Bile acids (BAs) act as signaling molecules in a number of physiological processes associated with host health [1, 2]
We report here that among the investigated dietary fiber (DF) medium-MW guar gum and HM pectin had the greatest effects on cecal BA formation, gut microbiota composition, and high-fat diet-induced inflammation
The contribution of group II secondary BAs (LCA, DCA, and hyodeoxycholic acid (HDCA)) was lower with DF in the diet (7–9%) than without (25%), while the opposite was true for group I secondary BAs (UDCA, β-muricholic acids (MCA), and ω-MCA, 67–69% with DF vs. 52% without DF)
Summary
Bile acids (BAs) act as signaling molecules in a number of physiological processes associated with host health [1, 2]. Gut microbiota regulate the composition of BAs via deconjugation and dehydroxylation reactions, and can thereby modulate their signaling functions [2]. Supplementation with very low amounts of chenodeoxycholic acid (CDCA) changed BA metabolism, highlighting the importance of diet in this process [7]. Other factors influence the composition and metabolic activity of colonic microbiota: availability of nutrients— dietary fiber (DF) and to some extent protein—is important for the formation of shortchain fatty acids (SCFAs), with different types of DF giving rise to different SCFA amounts and profiles during colonic fermentation [8]. It is of interest to determine whether BA composition can be modulated by diet, in relation to SCFAs derived from fermentable ingested DF
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