Investigating the Impact of Dietary Polyphenols on Human Gut Microbiota Composition

Thesis Abstract

The escalating prevalence of diet-related non-communicable diseases underscores the critical need to understand the intricate interactions between dietary components and human gut microbiota, a dynamic microbial community integral to host health. Among dietary constituents, polyphenols—bioactive compounds abundant in fruits, vegetables, teas, and red wine—have garnered considerable research interest due to their potential prebiotic effects and capacity to modulate gut microbial composition. Nevertheless, comprehensive, empirical data elucidating the specific impact of dietary polyphenols on human gut microbiota remain limited, particularly regarding differential responses among diverse populations and the underlying microbial mechanisms involved. This study aims to investigate the influence of dietary polyphenols on the composition and diversity of human gut microbiota, with a focus on identifying specific microbial taxa responsive to polyphenol intake and elucidating potential microbial pathways associated with polyphenol metabolism. The specific objectives include (1) quantifying changes in gut microbial diversity following controlled polyphenol supplementation; (2) identifying shifts in key microbial taxa associated with polyphenol-rich diets; (3) analyzing correlations between plasma polyphenol metabolites and microbial alterations; and (4) exploring the functional implications of microbiota modulation via metagenomic pathway analysis. Employing a randomized controlled trial (RCT) design, the study will recruit 120 healthy adult participants aged 25-45 years, stratified into an intervention group receiving a standardized polyphenol-rich extract derived from berries, green tea, and cocoa, and a control group receiving a placebo. Participants will adhere to their usual diets for six weeks, with dietary intake monitored via 7-day food diaries to control confounding variables. Fecal samples will be collected at baseline, three weeks, and six weeks for microbiota analysis using 16S ribosomal RNA gene sequencing on an Illumina MiSeq platform. Plasma samples will be obtained concomitantly to quantify polyphenol metabolites through liquid chromatography-mass spectrometry (LC-MS). Data on microbial composition will be analyzed with bioinformatics pipelines, including QIIME2, and statistical analyses such as repeated measures ANOVA, multiple regression, and multivariate correspondence analysis will be employed to identify significant changes and associations. The study expects to find that polyphenol supplementation significantly enhances microbial diversity and selectively enriches beneficial taxa such as Bifidobacterium and Lactobacillus, while suppressing potentially pathogenic bacteria like Escherichia coli. Correlation analyses are anticipated to reveal that higher plasma concentrations of polyphenol metabolites correspond with favorable microbial shifts, suggesting effective microbial biotransformation of polyphenols. Functional pathway analysis through PICRUSt will likely demonstrate upregulation of pathways involved in short-chain fatty acid production and polyphenol metabolism, indicating enhanced microbial functional capacity. The findings will contribute novel empirical evidence to the understanding of diet-microbiota interactions, advancing knowledge on how specific dietary polyphenols influence gut microbial ecology and function. This research will inform dietary guidelines and the development of functional foods aimed at optimizing gut health, as well as providing a scientific basis for personalized nutrition strategies. The study underscores the importance of dietary polyphenols as modulators of gut microbiota and highlights their potential therapeutic role in preventing and managing metabolic and inflammatory disorders. In conclusion, the study will provide robust evidence on the modulatory effects of dietary polyphenols on gut microbial composition and function, advocating for increased intake of polyphenol-rich foods within balanced diets. Future research avenues include exploring long-term impacts of polyphenol-rich diets, examining inter-individual variability in microbial responses, and integrating metabolomic and microbiomic data for comprehensive mechanistic insights. Recommendations will emphasize dietary strategies that leverage polyphenol-mediated microbiota modulation for improved health outcomes.