Impact of Fiber‐Bound Polyphenols on Gut Microbiome Metabolism is Influenced by Background Diet

Abstract

Dietary fiber, source of numerous metabolites produced by commensal gut microbiota, is a diverse mixture of polysaccharides, and in less‐processed forms also contains plant secondary metabolites (e.g. polyphenols) bound in this matrix. Typically, some of the fibers and polyphenols are not bioavailable in the upper gastrointestinal tract of animals consuming these fibers. However, commensal gut microbiota can catabolize fiber to liberate fiber‐bound polyphenols, and enzymatically convert both to postbiotics with health benefits. We sought to gain insight into the degree to which background diets impacted the production of microbiota postbiotics in canines. Two Test diets were formulated to contain equal amounts of sources of fiber and bound‐polyphenols, but to differ in their background composition to be representative of a typical hydrolyzed (HDT) or grain‐rich (GRT) diet. Further, two Control diets were produced to serve as controls for the hydrolyzed (HDC) and grain‐rich (GRC) diets. In these control diets, the fiber sources were removed and replaced with the main source of starch otherwise present in the Test diets. A single group of dogs was used to perform subsequent trials with washout periods separating them. Each trial was a randomized, crossover design with every dog consuming both Test and Control diets. Differences in endpoints were compared between each Test and Control diet after 4 week feeding periods, and then comparisons drawn between effects of fiber on either diet type. Dogs were housed in pairs, provided daily group exercise in outdoor grassy runs and had access to natural light that varied with season. Health was monitored via clinical and physical indices. Blood and fecal collections were carried out under IACUC approved protocols. Endpoints included serum and fecal metabolome and targeted chemical analyses, clinical measures and fecal microbiome. In general, the inclusion of fiber‐bound polyphenols into both hydrolyzed and grain‐rich diets improved fecal stool quality, acidified feces, increased saccharolytic postbiotics while decreasing microbial putrefaction, and increased levels of microbial taxa associated with production of beneficial postbiotics. Fecal bile acids were altered by Test diets, with increased fecal tauro‐conjugates and urso‐forms of these metabolites in feces. Fecal polyamines were decreased by fiber‐bound polyphenols, in a manner that indicated potential for increased bacterial catabolism. There was also a general decrease in fecal indoles, although HDT consumption intriguingly increased fecal levels of the benefical indoles‐indolelactate, indolepropionate and indoleacetate. In total, there was a difference in the degree to which the fiber‐bound polyphenols could impact these endpoints, which varied by background diet; be it hydrolyzed or grain‐rich.Support or Funding InformationHill's Pet Nutrition, Inc. Science and Technology Center, Topeka, KS 66601