Postprandial Duration Influences the Association of Insulin-Related Dietary Indexes and Plasma C-peptide Concentrations in Adult Men and Women

Background: The dietary insulin index (II) directly quantifies dietary effects on postprandial insulin secretion, whereas the empirical dietary index for hyperinsulinemia (EDIH), based on fasting C-peptide concentrations, is primarily reflective of insulin resistance. How these scores are related to nonfasting C-peptide in cohort studies has not been examined. Objective: We investigated the extent to which EDIH and II scores predict plasma C-peptide concentrations, in cross-sectional analyses by postprandial duration at blood collection from 1 to >= 15 h. Methods: Both EDIH and II scores were calculated from food-frequency questionnaire data reported by 3964 men in the Health Professionals Follow-up Study (1993-1995) and 6215 women in the Nurses' Health Study (1989-1990) who were not diabetic. We constructed 12 multivariable-adjusted linear regression models separately in men and women, by postprandial duration, to calculate relative differences and absolute values of plasma C-peptide concentrations in dietary index quintiles. Results: In both men and women, C-peptide concentrations were elevated 1-2 h after eating and declined with increasing postprandial duration. In men, percent differences in C-peptide concentration in the highest compared with lowest dietary index quintile were: EDIH: 0-1 h: 50%; 2 h: 22%; 14 h: 14%; >= 15 h: 30% (all P-trend< 0.05). II: 0-1 h: 19% (P-trend = 0.09); 2 h: 3% (P-trend = 0.09); 14 h: -6% (P-trend = 0.17); >= 15 h: -15% (P-trend = 0.02). Corresponding results among women were: EDIH: 0-1 h: 29% (P-trend = 0.002); 2 h: 33% (P-trend = 0.009); 14 h: 44% (P-trend < 0.0001); >= 15 h: 40% (P-trend < 0.0001). II: 0-1 h: -12% (P-trend = 0.09); 2 h: 17% (P-trend = 0.09); 14 h: -14% (P-trend = 0.009); >= 15 h: -3% (P-trend = 0.37). Conclusion: The EDIH was superior to the II in predicting both fasting and nonfasting C-peptide concentrations, suggesting that the EDIH may be better in assessing dietary effects of hyperinsulinemia on disease risk in adult men and women.