Association Between the Dietary Index for Gut Microbiota and Frailty: Mediating Role of Body Mass Index

Dietary composition and quality have been linked to the onset of frailty. Although the recently developed Dietary Index for Gut Microbiota (DI-GM) offers a means to evaluate diet quality based on its impact on the gut microbiota, its relevance to frailty has yet to be determined. This cross-sectional study utilized data from the NHANES collected between 2007 and 2020. DI-GM scores were determined based on 14 dietary components, with higher scores indicating a diet more supportive of gut microbiota health. Frailty was evaluated using a validated 49-item frailty index, with frailty defined as a score of 0.21 or higher. Weighted logistic regression, restricted cubic spline models, and mediation analyses were employed to examine the relationship between DI-GM scores and frailty. A total of 27,026 eligible participants were included in the analysis. Higher DI-GM scores were significantly associated with a lower risk of frailty. After full adjustment (Model 3), each one-point increase in the DI-GM scores corresponded to a 4% reduction in the odds of frailty (OR: 0.96, 95% CI: 0.92-1.00). Compared to the lowest quartile (Q1), individuals in the highest quartile (Q4) demonstrated significantly lower odds of frailty (OR: 0.81, 95% CI: 0.67-0.99). A nonlinear relationship between DI-GM scores and frailty was identified (p for nonlinearity = 0.031). Age, sex, education level, and smoking status were found to potentially moderate this association. Mediation analyses further revealed that body mass index (BMI) partially mediated the relationship, accounting for 24.83% of the effect (p < 0.001). These results indicate that higher DI-GM scores are linked to a lower risk of frailty, with BMI partially mediating this relationship. Future longitudinal studies are needed to establish causality and further investigate the underlying mechanisms.