Plant polyphenols and gut microbiota: An interdependent relationship and its repercussions for human health

Dietary polyphenols are structurally diverse plant-derived bioactive compounds increasingly recognised for their interactions with the gut microbiota and their potential influence on human health. Although polyphenols include phenolic acids, flavonoids, stilbenes, lignans, and tannins, many exhibit limited absorption in the small intestine because of their glycosylation, polymerization, and association with the food matrix. Consequently, substantial quantities reach the colon, where gut microorganisms transform them through deglycosylation, hydrolysis, demethylation, dehydroxylation, reduction, and ring cleavage into more readily absorbed metabolites, including phenolic acids, phenyl-γ-valerolactones, urolithins, and enterolignans. This relationship is bidirectional, as polyphenols and their metabolites can also reshape microbial composition and function by promoting beneficial taxa, suppressing opportunistic pathogens, enhancing short-chain fatty acid production, and supporting intestinal barrier integrity. Their antimicrobial effects involve membrane disruption, enzyme inhibition, metal chelation, interference with adhesion and biofilm formation, and modulation of bacterial virulence. Microbiota-derived metabolites may subsequently enter systemic circulation and contribute to cardiometabolic, anti-inflammatory, and neuroprotective effects. Importantly, inter-individual differences in gut microbial composition and metabolic capacity generate distinct metabotypes, resulting in considerable variability in biological responses to polyphenol-rich foods. This review examines the chemistry, bioavailability, microbial biotransformation, microbiota-modulating properties, and health implications of dietary polyphenols, emphasizing the polyphenol- microbiota-metabolite axis. Greater integration of metabolomics, metagenomics, controlled human studies, and microbiome profiling is required to clarify causal mechanisms and facilitate the development of microbiota-informed personalized nutritional strategies for improving human health.