Impact of Plant-Based Diets on Gut Microbiota in Urban Adults

Thesis Abstract

Urban dietary patterns increasingly emphasize plant-based eating, yet the implications for gut microbiota composition and function in urban adult populations remain insufficiently understood. This study addresses the gap by examining how sustained plant-based diets influence gut microbial diversity, composition, and metabolite profiles, and how these microbiome changes relate to cardiometabolic risk markers in real-world urban settings. The aim is to determine whether adherence to plant-based diets modulates gut microbiota in ways associated with improved metabolic health, and to identify lifestyle or dietary factors that strengthen or weaken these effects. Specific objectives are (1) to compare alpha and beta diversity of gut microbiota between adults consuming predominantly plant-based diets (n=250) and omnivorous controls (n=250) over a 12-month period; (2) to characterize taxonomic shifts, particularly of SCFA-producing and bile-acid–metabolizing taxa, using 16S rRNA gene sequencing and metagenomic annotation; (3) to quantify fecal short-chain fatty acids (SCFAs) and secondary bile acids via gas chromatography–mass spectrometry and liquid chromatography–mass spectrometry; (4) to assess associations between microbial features and cardiometabolic markers (blood pressure, fasting glucose, lipid profile, waist circumference) and inflammatory markers (CRP, IL-6); (5) to explore the moderating roles of physical activity and dietary fiber intake on microbiota outcomes. A mixed-methods, longitudinal cohort design is employed. The population comprises adults aged 25–55 residing in three metropolitan districts with diverse socioeconomic backgrounds. A stratified random sampling approach yields 500 participants, with equal representation of plant-based and omnivorous dieters, confirmed by validated dietary questionnaires and 7-day dietary recalls at baseline, 6 months, and 12 months. Data collection integrates (i) stool samples for 16S rRNA sequencing, metagenomic profiling, and metabolomic analyses (SCFAs, bile acids); (ii) fasting venous blood for metabolic and inflammatory biomarkers; (iii) anthropometric measurements; (iv) accelerometer-based physical activity monitoring; and (v) comprehensive dietary assessments. Analytical methods include multivariate linear models and repeated-measures ANOVA to test microbiota and metabolite differences over time, controlling for confounders such as age, sex, BMI, antibiotic use, and physical activity. Differential abundance testing will identify taxa associated with plant-based diets, complemented by network analysis to reveal microbial interaction patterns. Structural equation modeling will explore pathways linking diet, microbiota, metabolites, and metabolic health outcomes. Theoretical framing draws on the holobiont concept and the dietary enterotype framework, with guidance from the Enteric Microbiota-Health Interaction theory to interpret diet-microbiome-host health linkages. Anticipated findings include higher microbial alpha diversity and enrichment of SCFA-producing taxa (e.g., Faecalibacterium, Roseburia) in plant-based dieters, along with elevated fecal butyrate and propionate levels; shifts in bile acid metabolism favoring secondary bile acids reduction; and favorable correlations between microbial features and improved insulin sensitivity, lipid profiles, and inflammatory status. The study is expected to contribute to the literature by providing longitudinal, population-based evidence on how plant-based eating patterns shape gut microbial ecology and its metabolic correlates in urban adults, with implications for dietary guidelines and public health strategies. It will advance understanding of dose–response relationships between plant-based dietary adherence and microbiome-mediated health benefits, and identify contextual factors that optimize microbiota-related outcomes, such as dietary fiber diversity and physical activity. Recommendations emphasize promoting diverse plant-based dietary patterns enriched in fermentable fibers, tailored to urban populations, and incorporating microbiome-conscious metrics into dietary counseling and chronic disease prevention programs. The main conclusion is that sustained plant-based diets in urban adults produce favorable gut microbiota configurations linked to improved cardiometabolic and inflammatory profiles, contingent upon adequate fiber intake and lifestyle factors, warranting integration into targeted public health interventions and individualized nutrition planning.