A Novel Dietary Index for Gut Microbiota ( <scp>DI</scp> ‐ <scp>GM</scp> ) is Associated With Inflammation, Mental Health, and Tumor Biomarkers in Adults: A Cross‐Sectional Study

The interplay between diet, gut microbiota, and mental health has garnered increasing attention. This study aimed to examine the association of a novel Dietary Index for Gut Microbiota (DI-GM) with depression, anxiety, and intestinal tumor biomarkers, and to explore whether gut microbiota composition mediates these associations. A cross-sectional study was conducted among 650 Chinese adults aged 18-65 years. DI-GM scores were calculated based on habitual dietary intake. Mental health was assessed using PHQ-9, STAI-A, PSQI, and WHO-5. Gut microbiota metrics (Firmicutes/Bacteroidetes [F/B] ratio, alpha diversity), inflammatory markers (CRP, calprotectin, TMAO), brain-derived neurotrophic factor (BDNF), and carcinoembryonic antigen (CEA) were measured. Linear regression and structural equation modeling were used to assess associations and mediation effects. Higher DI-GM scores were significantly associated with lower BMI, improved lipid profiles (↑ HDL-C: <i>β</i> = 0.41; 95% CI: 0.39-0.44), reduced insulin resistance (↓ HOMA-IR: <i>β</i> = -2.11; 95% CI: -2.15 to -2.07), and increased BDNF (<i>β</i> = 0.25; 95% CI: 0.19-0.30). Participants in the higher quartiles had lower depressive (PHQ-9: <i>β</i> = -0.32; 95% CI: -0.46 to -0.17) and anxiety scores (STAI-A: <i>β</i> = -0.08; 95% CI: -0.10 to -0.06). Inflammatory markers including CRP, TMAO, and CEA were significantly reduced. The F/B ratio was inversely associated with DI-GM (<i>p</i> < 0.001) and partially mediated its relationship with depression (<i>β</i> = -0.013) and anxiety (<i>β</i> = -0.07). The DI-GM score is a promising dietary tool linked to favorable metabolic, inflammatory, and psychological outcomes, partially mediated by gut microbiota.