Abstract: Aim: This study aimed to evaluate changes in gut microbiota composition and their impact on metabolic physiology in obese patients undergoing a structured dietary intervention program.

Materials &Methods: A prospective cohort study was conducted with 100 obese adults (BMI ≥ 30 kg/m², aged 25–55 years). Participants followed a 12-week structured dietary intervention divided into three phases: caloric restriction (Weeks 1–4), macronutrient-balanced diet (Weeks 5–8), and maintenance (Weeks 9–12). Anthropometric measurements, blood samples (fasting glucose, HbA1c, insulin, lipid profile, CRP), and stool samples for gut microbiota analysis were collected at baseline (Week 0), Week 6, and Week 12. Microbiota composition was analyzed using 16S rRNA gene sequencing, and metabolic parameters were evaluated using standard clinical assays. Correlation analysis was performed to assess the association between gut microbiota changes and metabolic markers.

Results: Significant improvements were observed in weight (95.5 kg to 87.0 kg, p<0.001), BMI (35.6 kg/m² to 32.1 kg/m², p<0.001), waist circumference (102.3 cm to 94.1 cm, p<0.001), fasting glucose (110 mg/dL to 97 mg/dL, p<0.001), and HOMA-IR (4.1 to 2.5, p<0.001). Microbiota diversity increased, with Shannon Index improving from 3.5 to 4.1 (p=0.002) and a favorable shift in the Firmicutes-to-Bacteroidetes ratio observed. Lactobacillus and Bifidobacterium abundance increased significantly, while Proteobacteria levels decreased. Correlation analysis revealed strong associations between microbial shifts and metabolic improvements.

Conclusion: A structured dietary intervention significantly improved metabolic health and gut microbiota composition in obese individuals. Changes in gut microbiota, including increased microbial diversity and favorable taxonomic shifts, were strongly correlated with improvements in weight, glucose metabolism, and inflammatory markers. These findings emphasize the potential of microbiota-targeted dietary interventions in obesity management.