Dietary quality, insulin resistance, and preserved ratio impaired spirometry in postmenopausal women: a cross-sectional study with exploratory mediation analysis.

BACKGROUND: Preserved ratio impaired spirometry (PRISm) is a clinically relevant pulmonary phenotype with metabolic heterogeneity. Whether multidimensional dietary quality is associated with PRISm in postmenopausal women remains unclear. OBJECTIVE: To examine associations of dietary quality with PRISm and evaluate the exploratory role of insulin resistance. METHODS: This cross-sectional study included 678 postmenopausal women attending routine health examinations at a single hospital in Taian, China, from June 2024 to December 2025. Dietary quality was assessed using the Healthy Eating Index (HEI), Dietary Inflammatory Index (DII), Composite Dietary Antioxidant Index (CDAI), and Diet Index for Gut Microbiota (DI-GM). Insulin resistance was evaluated using HOMA-IR and METS-IR. PRISm was defined as FEV1 < 80% predicted with FEV1/FVC > =0.70. Multivariable regression, restricted cubic splines, exploratory mediation analysis, false-discovery-rate sensitivity analysis, hierarchical adjustment models, quartile-based analyses, restriction to never-smokers, and additional HOMA-IR-adjusted models were performed. RESULTS: PRISm was identified in 67 participants (9.88%). Higher HEI, DI-GM, and CDAI were associated with lower odds of PRISm, whereas higher DII was associated with higher odds. HOMA-IR was associated with PRISm continuously and categorically. HOMA-IR statistically explained 7.92-10.69% of diet-PRISm associations, but mediation findings did not remain significant after false-discovery-rate correction and should be considered exploratory. Diet-PRISm associations were consistent across hierarchical models and among never-smokers and remained statistically significant after additional adjustment for HOMA-IR. Quartile analyses supported graded associations for HEI, DII, and DI-GM, whereas the categorical CDAI trend was less precise. CONCLUSION: In this single-center cross-sectional study, dietary quality and insulin resistance were associated with PRISm in postmenopausal women. The associations were robust across complementary sensitivity analyses; however, the findings remain hypothesis-generating and require longitudinal and multicenter validation.