Association between carbohydrate-to-fiber ratio and endometriosis in U.S. women: mediating role of neutrophil-percentage-to-albumin ratio

Associations between carbohydrate and fiber intake and endometriosis (EM) have been inconsistent, and no study has evaluated the combined effect of the carbohydrate-to-fiber ratio (CFR) or its inflammatory mechanisms. TThis cross-sectional study used data from two NHANES cycles (2003-2004 and 2005-2006), including 2,400 women aged 20-54 years. Weighted multivariable logistic regression assessed associations between CFR and physician-diagnosed EM, with restricted cubic splines used to identify non-linear relationships. The neutrophil percentage-to-albumin ratio (NPAR) was examined as a potential inflammatory mediator. CFR was positively associated with EM in all models (fully adjusted OR: 1.02, 95% CI: 1.01-1.04). A non-linear relationship emerged, with a turning point at CFR 17.3 (p for nonlinearity = 0.037): below this threshold, a one-unit increase in CFR raised EM odds by 11% (OR: 1.11, 95% CI: 1.00-1.22), while no significant association was observed above it (OR: 1.02, 95% CI: 1.00-1.04). The fully adjusted OR for the highest CFR quartile (≥23.1) was 2.17 (95% CI: 1.06-4.14). NPAR partially mediated the CFR-EM association (proportion mediated: 5.16%). Subgroup analyses showed a consistent positive association, with a significant interaction only for hypertension status (p for interaction = 0.040). This study identifies a novel association between CFR and EM prevalence, partially mediated by NPAR. It is the first to apply CFR as a specific dietary measure, offering a clinically actionable tool for dietary assessment and patient counseling. Given the cross-sectional design, causal inference cannot be drawn, and prospective studies are needed to confirm these findings. CFR may be a useful dietary metric associated with EM prevalence, with a specific threshold of 17 for risk stratification. CFR offers a simple, actionable metric for dietary counseling that emphasizes reducing refined carbohydrates and increasing fiber intake.