Prior to discoveries relating the composition and function of the gut microbiome to human health, plant polyphenols were thought to provide benefit mainly as antioxidants. Recent meta-analyses are beginning to characterize how dietary polyphenols influence the makeup and overall diversity of the gut microbiota. Only a small proportion of ingested polyphenols, on the order of 5-10%, are absorbed by the small intestine, with the balance delivered to the colon and its crucial microbial communities.
Through selective support or inhibition of particular microbial species’ growth, dietary polyphenols have the potential to reshape the human gut microbiota and microbiome, with subsequent effects on metabolism and overall health. Lactobacillus, Bifidobacterium, and Clostridium species figure prominently in human health. Clostridial species include butyrogens (butyrate producers) such as C. butyricum and others displaying health benefits along with disease-causing pathogens like C. perfringens, C. difficile, and C. histolyticum.
For this systematic review and meta-analysis, researchers evaluated clinical and preclinical studies of polyphenol intakes or supplementation showing effects on the abundance of major gut microbial species at daily intake levels of total polyphenols ranging from <1 mg/day to 2364 mg/day. Data were analyzed by dosage level and food source, and microbial species found to be influenced by dietary polyphenol intake were assessed in greater detail for associations with specific polyphenols. After initial analysis, gut microbe species examined further included Bacteroides, Lactobacillus, Bifidobacterium, and the following Clostridium species: Clostridium cluster XIVa species as a group, C. coccoides, and C. leptum as health-promoting/probiotics, and Clostridium pathogens as a group, C. perfringens, and C. histolyticum as pathogens.
Dietary Polyphenols Affect Both Commensals and Pathogens in the Gut
Greater consumption of dietary polyphenols (like quercetin and anthocyanidins) is strongly associated with superior cardiovascular, metabolic, and cognitive health outcomes. Polyphenols can act as prebiotic substances for beneficial gut microbes that, in turn, provide the human host with health-promoting metabolites, and this relationship is increasingly recognized as contributing to the benefits of dietary polyphenols. Increasing intakes of polyphenols through polyphenol-rich foods and supplements may improve gut microbiome function and long-term human health.