Impact of plant-derived polyphenols on gut microbiome metabolism in a rural population

Thesis Abstract

In rural populations, limited access to diverse diets and chronic exposure to plant-based foods rich in polyphenols may influence gut microbiome composition and metabolic activity, thereby affecting host energy balance, immune function, and nutrient utilization. This study investigates how habitual intake of plant-derived polyphenols modulates gut microbial metabolism and its systemic repercussions in a representative rural cohort. The aims are to quantify polyphenol intake, characterize gut microbiome structure and function, and assess associations with microbial metabolite profiles and host markers of inflammation and metabolic health. Specific objectives include (1) to determine the relationship between polyphenol-rich dietary patterns and fecal short-chain fatty acid (SCFA) concentrations; (2) to evaluate changes in microbial gene pathways related to polyphenol metabolism using shotgun metagenomics; (3) to measure circulating polyphenol metabolites and inflammatory cytokines; (4) to examine associations between microbial functional capacity and host metabolic parameters such as fasting glucose, HOMA-IR, and lipid profile; and (5) to explore potential mediating roles of microbiome-derived metabolites in linking polyphenol intake to host health outcomes. A cross-sectional observational design will be employed, complemented by a targeted metabolomics analysis to capture polyphenol-derived metabolites. The study will recruit 300 adults aged 25–65 years from three rural communities with varying levels of fruit, vegetable, and legume consumption, ensuring adequate representation of sex, BMI, and socioeconomic status. Data collection will involve (i) a validated semi-quantitative food frequency questionnaire to estimate habitual polyphenol intake, (ii) fecal samples for 16S rRNA gene sequencing, shotgun metagenomics, and targeted metabolomics of short-chain fatty acids and microbial phenolic metabolites, (iii) fasting blood samples for inflammatory markers (CRP, IL-6, TNF-?), polyphenol-derived metabolites, glucose, insulin, and lipid panels, and (iv) anthropometric measurements and basic clinical data. Questionnaires will capture lifestyle variables and antibiotic or probiotic use to adjust for confounders. Data analysis will proceed in three tiers. First, descriptive statistics will summarize demographics, dietary polyphenol intake, microbiome composition, and host biomarkers. Second, multivariable linear and logistic regression models will test associations between polyphenol intake and microbial community structure (alpha and beta diversity), SCFA concentrations, and host outcomes, adjusting for age, sex, BMI, energy intake, physical activity, and antibiotic history. Third, integrative analyses will combine metagenomic functional profiles with host metabolomics using canonical correlation analysis and mediation modeling to evaluate whether microbial pathways for polyphenol metabolism mediate effects of dietary polyphenols on inflammation and insulin resistance. Sensitivity analyses will stratify by baseline BMI and by high versus low polyphenol consumers. Expected findings include a positive association between higher intake of polyphenol-rich foods and increased abundance of microbial pathways involved in polyphenol transformation, elevated fecal SCFA levels, and higher circulating levels of specific polyphenol metabolites (e.g., urolithins, phenyl-?-valerolactones) correlated with reduced inflammatory markers and improved insulin sensitivity. It is anticipated that rural populations with diverse polyphenol sources will exhibit distinct microbiome-metabolome signatures, highlighting the role of habitual diet in shaping host–microbe interactions. The study will contribute to knowledge by elucidating mechanistic links between plant-derived polyphenols, microbial metabolism, and cardiometabolic health in a rural context, informing dietary guidance and community nutrition interventions that leverage local food systems. The study’s findings are expected to advance theoretical understanding of diet–microbiome–host health relationships by integrating microbial ecology with metabolomics and clinical biomarkers within an ecologically valid rural setting. Practical implications include evidence-based recommendations for polyphenol-rich dietary patterns tailored to rural populations, consideration of microbiome-targeted strategies to optimize polyphenol bioavailability, and policy guidance for agricultural and food programs that enhance access to polyphenol-rich foods. Limitations include the cross-sectional design precluding causal inference and potential residual confounding from unmeasured dietary factors. Recommendations for future work include longitudinal cohorts and randomized trials evaluating polyphenol interventions with microbiome-centered endpoints in diverse rural communities.