Planetary Health Diet and Body Mass Distribution in Relation to Kidney Health: Evidence from NHANES 2003–2018

Background/Objectives: Chronic kidney disease (CKD) and diabetic kidney disease (DKD) are growing public health challenges. While diet and body composition influence metabolic and renal health, their combined role remains underexplored. This study investigates the association between the Planetary Health Diet Index (PHDI), body mass distribution, and the prevalence of CKD and DKD in U.S. adults. Methods: We analyzed data from 8093 adults aged ≥40 years from NHANES 2003–2018. PHDI was computed using two 24 h dietary recalls. Body composition was assessed using dual-energy X-ray absorptiometry (DXA), focusing on the android-to-gynoid fat ratio (AGFR) and lean mass ratio (AGLR). Survey-weighted linear and logistic regressions evaluated cross-sectional associations between PHDI score, body composition indices, and prevalence of CKD and DKD. Mediation analyses explored AGLR, AGFR, and body mass index (BMI) as potential mediators of the association between PHDI score and either CKD or DKD. Results: Higher PHDI scores were mildly associated with lower odds of CKD (OR per 10-point increase: 0.91; 95% CI: 0.83–0.99) and DKD (OR: 0.86; 95% CI: 0.76–0.97). Greater PHDI scores correlated with lower BMI, AGFR, and AGLR. Among participants with diabetes, AGLR mediated 17% of the relationship between a 10-point increase in PHDI score and decreased DKD prevalence, suggesting central lean mass distribution as a relevant pathway. No significant mediation was observed for AGFR, BMI, or for CKD. Conclusions: Adherence to PHD is associated with healthier body composition and lower prevalence of CKD and DKD. These findings support the promotion of dietary strategies that enhance metabolic and renal health in middle-aged and older individuals.