Association of the newly proposed dietary index for gut microbiota and depression: the mediation effect of phenotypic age and body mass index

Gut microbiota and depression have garnered attention. The dietary index for gut microbiota (DI-GM) is a newly proposed index that reflects the diversity of gut microbiota, yet its association with depression remains unstudied.

Data from the National Health and Nutrition Examination Survey were analyzed. Depression was assessed using Patient Health Questionnaire (PHQ-9). Dietary recall data were used to calculate the DI-GM (including components beneficial and unfavorable to gut microbiota). Multivariable weighted logistic and linear regression were employed to investigate the association of DI-GM with depression and total PHQ-9 score. The potential mediating role of phenotypic age and body mass index (BMI) was explored. Secondary analyses included subgroup analyses, restricted cubic spline (RCS), and multiple imputation.

A higher DI-GM and beneficial gut microbiota score were associated with a lower prevalence of depression (DI-GM: OR = 0.94, 95% CI = 0.89, 0.99; beneficial gut microbiota score: OR = 0.88, 95% CI = 0.82, 0.94) and lower total PHQ-9 score (DI-GM: β=-0.09, 95% CI=-0.14, -0.04; beneficial gut microbiota: β=-0.15, 95% CI=-0.21, -0.08). RCS indicated a non-linear relationship between DI-GM and depression. A significant mediating effect of phenotypic age (proportion of mediation: 19.81%, 95% CI: 12.86–63.00%) and BMI (proportion of mediation: 16.49%, 95% CI: 12.87–62.00%) was observed.

The newly proposed DI-GM was negatively associated with the prevalence of depression and total PHQ-9 score. Mediation analyses demonstrated a significant mediating effect of phenotypic age and BMI.