Sex differences in the body fat percentage pathway linking dietary fat energy ratio to sleep quality in older adults: a cross-sectional study

Background: Poor sleep quality is common among older adults and may be related to modifiable dietary and body-composition factors. However, it remains unclear whether body fat percentage is involved in the association between dietary macronutrient structure and sleep quality, and whether this pathway differs by sex. Methods: This cross-sectional study included 726 older adults (mean age 72.26 ± 5.14 years; 49.7% male). Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI), dietary intake was evaluated using repeated 24-hour dietary recalls, and body composition was measured by bioelectrical impedance analysis. Regression-based mediation and sex-moderated mediation analyses were conducted with adjustment for relevant covariates. Results: Poor sleep quality was identified in 43.8% of participants. Dietary fat energy ratio was positively associated with body fat percentage (PBF) and PSQI score. PBF showed a statistically significant partial mediation pattern between dietary fat energy ratio and sleep quality (indirect effect = 0.480, 95% bias-corrected bootstrap confidence interval [CI]: 0.068--1.282). Sex moderated the PBF-PSQI pathway (index of moderated mediation = 0.843, 95% CI: 0.070--2.289). The conditional indirect effect was significant in women (effect = 0.860, 95% CI: 0.179-2.006) but not in men (effect = 0.017, 95% CI: -0.587-0.727). Conclusions: A higher dietary fat energy ratio was associated with poorer sleep quality among older adults, and this association was partly accounted for by body fat percentage. The indirect pathway was statistically evident in women but not in men. These findings suggest that combined dietary and body-composition assessment may help identify potentially modifiable profiles related to poor sleep quality in older women. Longitudinal studies are needed to clarify temporal and potential causal relationships.