Fructose, glycemic load, and quantity and quality of carbohydrate in relation to plasma C-peptide concentrations in US women

Abstract

Background: Circulating C-peptide concentrations are associated with insulin resistance and the development of type 2 diabetes. However, associations between fructose and the quantity and quality of total carbohydrate intake in relation to C-peptide concentrations have not been adequately examined. Objective: We assessed the association of dietary fructose, glycemic load, and carbohydrate intake with fasting C-peptide concentrations. Design: Plasma C-peptide concentrations were measured in a cross-sectional setting in 1999 healthy women from the Nurses' Health Study I and II. Dietary fructose, glycemic load, and carbohydrate intake were assessed with the use of semiquantitative food-frequency questionnaires. Results: After multivariate adjustment, subjects in the highest quintile of energy-adjusted fructose intake had 13.9% higher C-peptide concentrations (P for trend = 0.01) than did subjects in the lowest quintile. Similarly, in the multivariate model, subjects in the highest quintile of glycemic load had 14.1% (P for trend = 0.09) and 16.1% (P for trend = 0.04) higher C-peptide concentrations than did subjects in the lowest quintile after further adjustment for total fat or carbohydrate intake, respectively. In contrast, subjects with high intakes of cereal fiber had 15.6% lower (P for trend = 0.03) C-peptide concentrations after control for other covariates. Conclusions: Our results suggest that high intakes of fructose and high glycemic foods are associated with higher C-peptide concentrations, whereas consumption of carbohydrates high in fiber, such as whole-grain foods, is associated with lower C-peptide concentrations. Furthermore, our study suggests that these nutrients play divergent roles in the development of insulin resistance and type 2 diabetes.