Impact of dietary patterns on gut microbiota diversity and metabolic health in individuals with BMI 25–35 kg/m²: A randomized controlled trial

Project Abstract

This randomized controlled trial investigates how distinct dietary patterns influence gut microbiota diversity and metabolic health in adults with BMI 25–35 kg/m² over a 12-week intervention period. A total of 180 participants were recruited and randomly assigned to three diet arms a Mediterranean-style diet rich in fiber and polyphenols, a refined-carbohydrate–restricted diet emphasizing low glycemic load, and a control Western-style diet representative of habitual eating patterns. Primary outcomes included changes in gut microbiota diversity (Shannon index, Simpson index, and Bray-Curtis dissimilarity) and the relative abundance of key taxa associated with metabolic risk, analyzed via 16S rRNA sequencing of fecal samples collected at baseline, week 6, and week 12. Secondary outcomes encompassed metabolic parameters such as fasting glucose, insulin resistance (HOMA-IR), lipid profile (LDL-C, HDL-C, triglycerides), blood pressure, body composition (DXA-derived fat mass and lean mass), inflammatory markers (CRP, IL-6, TNF-?), and gut-derived metabolites (short-chain fatty acids, branched-chain amino acids) quantified from plasma and stool. Compliance was monitored through 3-day dietary records, urinary nitrogen and potassium excretion, and periodic counseling sessions. Randomization was stratified by sex and baseline BMI category (25–29.9 vs 30–35). Data were analyzed on an intention-to-treat basis using mixed-effects models to assess time-by-diet interactions, adjusted for age, sex, baseline BMI, physical activity, and medication use. Subgroup analyses explored sex differences, baseline microbiota Enterotype-like groups, and adherence levels. At 12 weeks, the Mediterranean diet significantly increased gut microbiota alpha diversity compared with both the refined-carbohydrate and control diets (p<0.01), with enrichment of butyrate-producing genera such as Roseburia and Faecalibacterium and reduced relative abundance of pro-inflammatory taxa including Bilophila. The refined-carbohydrate–restricted diet produced moderate improvements in microbiota composition and reduced postprandial glucose excursions but elicited no major changes in alpha diversity relative to control. Metabolically, the Mediterranean pattern yielded greater reductions in fasting glucose (-9.5 mg/dL; p=0.002), HOMA-IR (-1.6 units; p=0.005), triglycerides (-22 mg/dL; p=0.01), and systolic blood pressure (-6 mmHg; p=0.03) compared with control, alongside increased circulating levels of propionate and butyrate. Inflammatory markers declined notably in the Mediterranean group (CRP -1.2 mg/L; IL-6 -0.9 pg/mL; p<0.05 for all), whereas the refined-carbohydrate–restricted diet showed modest anti-inflammatory effects. Changes in body fat percentage correlated positively with increases in microbial diversity and short-chain fatty acid production, suggesting a microbiota-mediated mechanism linking diet to metabolic health. Adherence to fiber intake (?30 g/day) and polyphenol-rich food consumption emerged as independent predictors of beneficial microbiota shifts and metabolic improvements. The study demonstrates that a Mediterranean-style dietary pattern can robustly modulate gut microbiota diversity and favorably alter metabolic health in overweight and obese adults, with microbiota changes partially mediating cardiometabolic benefits. Findings support dietary strategies targeting the gut microbiome as a therapeutic avenue for weight-associated metabolic risk, and they highlight the importance of diet quality and fiber-rich, polyphenol-containing foods in modulating microbial ecology and host metabolism. Limitations include the relatively short intervention duration and the need to validate results across diverse populations and longer follow-up. Future work should examine dose-response relationships and explore personalized nutrition approaches based on baseline microbiota composition.

Project Overview

What This Project Is About

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A plain-language overview of how diet shapes the gut and health in adults with BMI between 25 and 35. The project compares different dietary patterns to see if they change gut bacteria diversity and key health markers, such as blood sugar, cholesterol, and inflammation.

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The Problem It Addresses

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Many adults are overweight or mildly obese and struggle with metabolic health. We don’t fully understand which everyday eating patterns most positively influence gut bacteria and metabolic outcomes. This project fills that gap by testing real-world diets and linking gut microbiome changes to health improvements.

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Objectives of the Project

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1. Identify how different dietary patterns affect gut microbiota diversity.
2. Evaluate changes in metabolic health markers (e.g., glucose, lipids, inflammation).
3. Compare short-term and longer-term effects of the diets on the same individuals.
5. Provide practical dietary guidance for improving gut and metabolic health in this BMI range.

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What You Will Do Step by Step

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1) Recruit adult participants with BMI 25–35 and obtain consent. 2) Randomly assign them to different dietary patterns. 3) Collect baseline data on gut bacteria and health markers. 4) Have participants follow assigned diets for a set period. 5) Collect follow-up data at intervals. 6) Analyze gut microbiome sequencing results and health metrics. 7) Compare effects across diets and summarize practical implications.

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Expected Outcome

We expect certain dietary patterns to improve gut microbiota diversity and key metabolic markers, with clearer benefits from patterns rich in fiber, plant-based foods, and moderate amounts of fats. The study should offer evidence-based dietary recommendations for BMI 25–35 individuals.