Quality of dietary carbohydrate is more important than its quantity in lipid peroxidation

Background High glycemic index (GI) diets have been linked to elevated risk of cardiometabolic diseases. One possible underlying mechanism comes from high GI diet's potential to promote lipid peroxidation. Objectives We aim to evaluate whether and to what extent dietary carbohydrate quality and quantity are associated with systemic levels of lipid peroxidation in females. Methods In this cross-sectional analysis of 2163 middle-aged women, a subset of the Shanghai Women's Health Study, we measured lipid peroxidation biomarkers F-2-isoprostanes (F-2-IsoPs) and its metabolite, 2,3-dinor-5,6-dihydro-15-F-2t-IsoP (F-2-IsoP-M), in urine. The quality of carbohydrate was defined by dietary GI, assessed using a validated FFQ via in-person interviews. A multivariable linear regression model with restricted cubic spline functions was used to evaluate the association of measured biomarkers with carbohydrate intake and dietary GI. Results After adjustment for potential confounding factors such as cigarette smoking, BMI, and comorbidities, among others, we found that F-2-IsoP-M concentrations were positively associated with both carbohydrate intake and dietary GI. Carbohydrate intake and dietary GI were weakly correlated (r = 0.12). When further mutually adjusted for the 2 factors, the positive association with F-2-IsoP-M remained statistically significant for GI (P = 0.004) but not for carbohydrate intake (P = 0.50). Compared with those in the 10th percentile of dietary GI, fold increases (95% CI) in F-2-IsoP-M concentrations for those in the 30th, 50th, 70th, and 90th percentiles were 1.03 (1.00, 1.07), 1.06 (1.01, 1.10), 1.09 (1.03, 1.14), and 1.13 (1.05, 1.21), respectively. Moreover, there appeared a threshold regarding the association between dietary GI and F-2-IsoP-M concentrations, with the dose-effect slope of GI being 2.3 times greater when GI was >= 75 relative to GI Conclusions This study provides evidence that the quality of dietary carbohydrate may be more important than the quantity of the intake with regard to systemic lipid peroxidation.