Dietary Glycemic Index and Glycemic Load Are Positively Associated with Oxidative Stress among Premenopausal Women.

Background: Diets with a high glycemic index (GI) and glycemic load (GL) have been hypothesized to increase oxidative stress, but the limited human studies are inconsistent. Objective: The aim of this cross-sectional study was to investigate associations between dietary GI, GL, and carbohydrate intake and oxidative stress, as measured by F2-isoprostanes (F2-IsoPs). Methods: Concentrations of F2-IsoP and its metabolite (15-F2t-IsoP-M) were measured in urine samples collected at enrollment from 866 premenopausal women (aged 35-54 y) participating in the Sister Study. Total carbohydrate intake and dietary GI and GL were assessed using a validated food frequency questionnaire. Urinary F2-IsoP and 15-F2t-IsoP-M concentrations were compared across quintiles of carbohydrate intake, GI, and GL using multivariable linear regression models. Results: Urinary F2-IsoP concentrations were positively associated with dietary GI (P-trend = 0.023), and both F2-IsoP and 15-F2t-IsoP-M concentrations were positively associated with GL (F2-IsoP: P-trend < 0.001; 15-F2t-IsoP-M: P-trend < 0.001) and total carbohydrate intake (F2-IsoP: P-trend = 0.012; 15-F2t-IsoP-M: P-trend < 0.001). Stratified analyses suggested that a positive association between GI and urinary 15-F2t-IsoP-M concentrations was present among women with a body mass index [BMI (in kg/m2)] ≥30.0, but not among those with a BMI of <25.0 or 25.0-29.9 (P-interaction = 0.01). Conclusions: Our cross-sectional analyses in a sample of premenopausal women support hypothesized relations between high dietary GI and GL and oxidative stress, as assessed by urinary F2-IsoP and 15-F2t-IsoP-M concentrations. Given potential associations between oxidative stress and the development of cardiovascular disease and type 2 diabetes, our findings may have important implications for reducing chronic disease risk.