Assessing the Impact of Dietary Polyphenols on Human Gut Microbiota Composition

Thesis Abstract

The escalating interest in the influence of diet on human health underscores the significance of understanding how specific dietary components modulate gut microbiota composition, a critical determinant of overall well-being. Despite growing evidence linking polyphenol-rich foods to various health benefits, the precise shifts in microbial populations attributable to dietary polyphenols remain inadequately characterized, particularly within diverse populations. This study aims to systematically assess the impact of dietary polyphenol intake on the composition and diversity of the human gut microbiota, elucidating potential mechanisms underlying health outcomes associated with polyphenol consumption. The primary objectives include identifying specific microbial taxa responsive to increased dietary polyphenol intake, quantifying changes in microbial diversity indices, and exploring correlations between polyphenol intake levels and shifts in microbiota composition. An explanatory sequential mixed-methods research design was employed, integrating a quantitative intervention component with qualitative dietary assessments. The study population comprised 200 healthy adult volunteers aged 25-45 years from urban healthcare centers, randomly assigned into an intervention group receiving a high-polyphenol diet (based on berries, dark chocolate, and green tea) and a control group maintaining their habitual diets over a 12-week period. Sample size determination was guided by power analysis to detect a minimum effect size of 0.3 with 80% power at a 5% significance level, utilizing stratified random sampling to ensure demographic representation. Data collection involved fecal samples at baseline, 6 weeks, and 12 weeks, analyzed via 16S rRNA gene sequencing on an Illumina MiSeq platform to characterize microbial taxa. Dietary intake was monitored through 3-day food diaries complemented by 24-hour dietary recalls, validated by dietary pattern analysis. The validity and reliability of microbiota sequencing were confirmed through technical replicates, with data quality control performed using QIIME2 software. Quantitative data analyses employed repeated-measures ANOVA and linear regression models to assess temporal changes and associations between polyphenol intake and microbiota composition. Thematic analysis was applied to qualitative dietary data to explore participants' adherence and perceptions. Expected findings include significant increases in beneficial microbial genera such as Bifidobacterium and Lactobacillus in the intervention group, alongside enhanced microbial diversity indices (Shannon and Simpson). A dose-response relationship between polyphenol intake and microbiota modulation is anticipated, supported by positive correlations between specific polyphenol subclasses and microbial taxa. These results will suggest that dietary polyphenols favorably alter gut microbiota structure, contributing to improved host health outcomes. This study provides novel insights into dietary modulation of the gut microbiome, advancing understanding of nutrient-microbe interactions. Its contribution to knowledge lies in the detailed characterization of microbiota shifts in response to controlled dietary polyphenol interventions within an urban adult population. The findings have potential implications for dietary guidelines and therapeutic strategies targeting microbiome health. Conclusions emphasize the importance of incorporating polyphenol-rich foods into regular diets to promote gut microbial diversity and resilience. Recommendations include integrating specific polyphenol-rich foods into public health policies and encouraging further longitudinal studies to examine long-term effects and functional microbiome changes. Overall, this research underscores the pivotal role of diet in shaping microbiota composition and opens avenues for personalized nutritional interventions aimed at optimizing gut health.