Dietary insulin index and insulin load in relation to biomarkers of glycemic control, plasma lipids, and inflammation markers

Background: Dietary glycemic index and load are widely used to estimate the effect of carbohydrate-containing foods on postprandial blood glucose concentrations and as surrogates for insulin response. The food insulin index (II) directly quantifies the postprandial insulin secretion of a food and takes into account foods with a low or no carbohydrate content. Objective: We investigated the average dietary II and insulin load (IL) in relation to biomarkers of glycemic control, plasma lipids, and inflammation markers. Design: In a cross-sectional setting and with the use of data from the Nurses' Health Study and the Health Professionals Follow-Up Study, we measured plasma concentrations of C-peptide, glycated hemoglobin (Hb A_1c), HDL cholesterol, LDL cholesterol, triglycerides, C-reactive protein (CRP), and interleukin-6 (IL-6) in fasting blood samples of 4002 healthy men and women. The dietary II and IL were assessed from food-frequency questionnaires by using directly analyzed or published food II data. Results: After multivariate adjustment, participants in the highest quintile of II had 26% higher triglyceride concentrations than did participants in the lowest quintile of II (P for trend < 0.0001). This association was strongest in obese [body mass index (in kg/m2) ≥30] participants (difference between highest and lowest quintiles in the II: 72%; P for trend = 0.01). Dietary II was inversely associated with HDL cholesterol in obese participants (difference: 218%; P for trend = 0.03). Similar associations were seen for the IL. Dietary II and IL were not significantly associated with plasma C-peptide, Hb A1c, LDL cholesterol, CRP, or IL-6. Conclusion: Dietary II and IL were not associated with fasting biomarkers of glycemic control but may be physiologically relevant to plasma lipids, especially in obese individuals.