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

Background: Dietary glycemic index and load have been widely used to estimate the effect of carbohydrate-containing foods on postprandial increase in blood-glucose levels and as a surrogate for insulin response. The recently developed food insulin index (II) directly quantifies the postprandial insulin secretion of a food, also taking into account foods with low or no carbohydrate content. The aim of this study was to investigate the association of average dietary II and insulin load (IL) with plasma biomarkers of glycemic control, and plasma lipids. Methods: In a cross-sectional setting, plasma concentrations of C-peptide, hemoglobin A1c (HbA1c), HDL cholesterol, LDL cholesterol, and triacylglycerol were measured in fasting blood samples of 2707 healthy men and women (participants from the Health Professional Follow-up Study and Nurses' Health Study). Dietary II and IL were assessed from semi-quantitative food frequency questionnaires using analytical data on the food II provided by the University of Sydney, Australia. Results: In multivariate regression models, dietary II and IL were not associated with plasma C-peptide or HbA1c. Participants in the highest quintile of both II and IL had 23.4% higher triacylglycerol concentrations than participants in the lowest quintile (ptrend <0.0001 and 0.003, respectively). The positive association with plasma triacylglycerol was stronger among overweight (BMI ≥25kg/m²) participants (percent difference highest versus lowest quintile 34%, ptrend=0.0001 for II and 32.2%, ptrend=0.004 for IL). II and IL were inversely associated with HDL cholesterol among overweight participants (percent difference –8.7%, ptrend=0.04 for II and –9.7%, ptrend=0.05 for IL). Dietary II and IL were not associated with LDL cholesterol. Conclusion: Dietary II and IL were not associated with markers of glycemic control, at least in the fasting state, but may be physiologically relevant to plasma lipids, especially in overweight subjects.