Comparative mediation roles of body shape indices in the association between Healthy Eating Index-2015 and phenotypic age acceleration

Aging is a universal physiological process, yet the rate of aging varies significantly among individuals. Phenotypic Age is a biomarker-based measure that reflects biological aging by quantifying the deviation of an individual's physiological state from their chronological age. Diet quality, as a modifiable factor, may influence the aging process; however, its association with phenotypic aging and the underlying mechanisms remain unclear. We analyzed data from 12,511 U.S. adults aged ≥ 20 years from the National Health and Nutrition Examination Survey 2005-2010. Diet quality was assessed using the Healthy Eating Index-2015 (HEI-2015), and phenotypic age acceleration was derived from 9 clinical biomarkers. Survey-weighted multivariable linear and logistic regression models were used to examine the association between HEI-2015 and phenotypic age acceleration. Mediation analysis was conducted to compare the indirect effects of 4 body shape indices: body mass index, waist-to-height ratio (WHtR), Body Roundness Index (BRI), and A Body Shape Index. Multivariable logistic regression showed that each 1-point increase in HEI-2015 was associated with lower odds of accelerated aging (odds ratio = 0.98, 95% confidence interval: 0.97-0.98, P < .001). All 4 body shape indices exhibited partial mediation effects, with WHtR and BRI showing the largest mediation proportions (29.23% and 28.90%, respectively). Subgroup and sensitivity analyses yielded consistent results, supporting the robustness of the findings. Higher diet quality is associated with lower odds of biological age acceleration, partially mediated through improved body shape, particularly indicators of central adiposity such as WHtR and BRI. These findings support a dual-targeted strategy integrating dietary improvement and body shape management to more precisely mitigate aging acceleration.