Microbial Biotransformation of Polyphenols and Bioactive Substrates: Implications for Metabolite-Guided Synbiotics

Dietary bioactive compounds-including polyphenols, alkaloids, lignans, and amino acid-derived substrates-exert well-established effects on human health but are constrained by poor bioavailability. Only 5%-10% of ingested polyphenols are absorbed in the proximal gastrointestinal tract, while the remainder undergoes biotransformation by colonic microbiota into a diverse repertoire of bioactive metabolites. Accumulating evidence indicates that these microbially derived metabolites, rather than their parent compounds, are the primary mediators of systemic benefits due to superior bioavailability, metabolic stability, anti-inflammatory and antioxidant activity, and greater specificity in modulating host metabolic and signaling pathways.

This review aimed to synthesize recent advances in the microbial biotransformation of dietary polyphenols, amino acids, glucosinolates, and related substrates, and to evaluate how these pathways influence metabolic, cardiometabolic, neurocognitive, and immune outcomes, as well as the potential of targeted synbiotic strategies to enhance metabolite production.

We conducted a narrative synthesis of recent literature examining microbial conversion pathways of dietary bioactives and their associated physiological effects, with a specific focus on interindividual variability in metabolite production and emerging evidence on synbiotic interventions combining probiotics with selected bioactive precursors.

Production of microbial metabolites varied markedly among individuals due to differences in gut microbiota composition, giving rise to distinct metabolic phenotypes (metabotypes) that influenced clinical and nutritional responsiveness. Evidence showed that microbially derived metabolites were key mediators of systemic benefits. Studies evaluating targeted synbiotics demonstrated the capacity to convert non-producers into producers, reduce interindividual variability in metabolite output, and improve clinically relevant outcomes in metabolic dysfunction, inflammation-driven disorders, and aging.

Metabolite-guided synbiotics represent a promising paradigm for precision nutrition by enhancing the consistency and efficacy of bioactive compound metabolism. Integration of metagenomics, metabolomics, and computational modeling will enable individualized prediction of metabolite-production capacity and accelerate the translation of microbiota-targeted interventions into practice.