Longitudinal changes in body fat in African American and Caucasian children: Influence of fasting insulin and insulin sensitivity

Obesity is associated with hyperinsulinemia and reduced insulin sensitivity , both risk factors for type 2 diabetes. However, it, is not clear whether these risk, factors occur as a result of obesity or whether they contribute to the development of obesity. The aims of this study were to determine wh ether baseline (first visit) or changes in insulin measures over time were associated with longitudinal changes in body fat mass during growth in chil dren. The study group consisted of 137 children (83 Caucasian and 54 Africa n American) with a mean age of 8.1 yr at baseline; The children returned fo r 3-6 annual visits for measurement of fasting insulin,; insulin sensitivit y (Si), and acute insulin response (AIR) from the tolbutamide-modified freq uent sampling iv glucose tolerance test and for determination of body compo sition by dual energy x-ray absorptiometry. Data were analyzed using SAS Pr oc mixed growth models. Total fat mass increased with time by 15.6%/yr (P = 0.013), but the rate of increase was not significantly influenced by race, sex, or Tanner stage. However, fasting insulin (positive effect), Si (nega tive effect), and AIR (positive effect) were significantly associated with the rate of increase in fat mass. In conclusion, in this cohort of children , growth-related increases in body fat were significantly associated with i ncreases in fasting insulin and AIR and decreases in Si.