Weight loss-independent associations of body composition changes with device-derived metabolic age during Mediterranean diet follow-up

OBJECTIVE: The aim of this study was to investigate whether changes in body composition over 6 months of Mediterranean diet follow-up were associated with corresponding changes in device-derived metabolic age after adjustment for weight change. METHODS: This retrospective observational study analyzed body composition records of 414 adults who completed routine 6-month follow-up after Mediterranean diet counseling between June 2024 and June 2025. Metabolic age and body composition parameters were assessed using the Tanita MC-580 body composition analyzer at baseline and after 6 months. Hierarchical multiple linear regression analysis was used to evaluate the associations between changes in body composition parameters and metabolic age change after adjustment for weight change, age, sex, and baseline metabolic age. RESULTS: Tanita-derived metabolic age decreased by 0.94 years (p<0.001). Changes in muscle-fat ratio (β=-0.585), visceral fat (β=-0.556), and protein mass (β=-0.339) were significantly associated with metabolic age change after adjustment, whereas weight-adjusted waist index was not significantly associated with metabolic age change in the adjusted model. Inclusion of body composition variables increased the explained variance of the model from 20.4 to 45.7% (adjusted R2 from 0.196 to 0.446). CONCLUSION: Favorable changes in Tanita-derived metabolic age were observed during follow-up. The associated body composition changes may partly reflect shared components of the device algorithm because metabolic age is a composite surrogate rather than a direct measure of biological aging. Given the retrospective uncontrolled design, causal effects of the Mediterranean diet cannot be established.