Association of the dietary carbohydrate-to-fiber ratio with prevalent rheumatoid arthritis in NHANES 2009–2018

This study examines the cross-sectional association between the carbohydrate-to-fiber ratio (CFR), an indicator of carbohydrate quality, and prevalent rheumatoid arthritis (RA) in the National Health and Nutrition Examination Survey (NHANES). The exposure was overall CFR, calculated from 2 days of dietary recall and categorized into population-wide quartiles. RA diagnosis was the outcome. Survey-weighted logistic regression was used to evaluate the CFR–RA association, adjusting for demographic, lifestyle, dietary, and metabolic covariates. Generalized additive models, subgroup analyses, and interaction tests were performed. An exploratory survey-weighted mediation analysis evaluated SII as a hypothesized intermediate factor. The study ultimately included 19,260 participants aged ≥ 20 years with valid 2-day dietary weights, with a survey-weighted RA prevalence of 4.31%. Higher CFR was significantly associated with increased RA odds, with the highest quartile showing 67% higher odds than the lowest ( P < .001). After exclusion of CFR values above the upper fence defined using the interquartile range, the model 4 GAM showed an effectively linear positive association. A sensitivity analysis retaining all CFR observations showed curvature in the sparsely populated upper tail with wide uncertainty. In the exploratory model 4 mediation analysis, the estimated indirect association through SII was small (4.77% of the total association; 95% confidence interval: −5.33% to 14.87%), and its confidence interval included the null. Higher CFR was associated with greater odds of prevalent self-reported RA. Longitudinal and genetically informed studies are needed before causal or preventive interpretations can be made.