Insulin sensitivity indices of glucose and free fatty acid metabolism in obese children and adolescents in relation to serum lipids.

OBJECTIVE: Most studies concerning the association between insulin resistance and the features of metabolic syndrome in obese children are based on measurement of insulin sensitivity indices (ISI) of glucose metabolism and not of fat metabolism.
METHODS: We studied fasting low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides, insulin, free fatty acids (FFA), blood glucose, ISI of glucose (homeostasis model assessment [HOMA] %S), and FFA metabolism (ISI-FFA) in 124 obese children aged 6 to 16 years. ISI-FFA was calculated based on the formula 2/(insulin x FFA + 1). Stepwise forward regression analyses were performed with triglycerides, HDL-C and LDL-C as dependent variables and age, sex, stage of puberty, body mass index, insulin, FFA, and blood glucose as independent variables. Direct multiple regression analyses were conducted with the dependent variables triglycerides, HDL-C, and LDL-C including age, sex, stage of puberty, body mass index, HOMA %S, and ISI-FFA as independent variables. Furthermore, ISI-FFA was measured in 13 normal-weight children aged 6 to 16 years.
RESULTS: ISI-FFA (median 0.30) was significantly (P < .05) reduced in obese children compared with normal-weight children (median ISI-FFA 0.64). In stepwise regression analyses, triglycerides were significantly correlated with insulin and FFA (P < .05), LDL-C levels were significantly correlated with FFA (P < .05), and HDL-C was related to stage of puberty (P < .05), whereas all other variables demonstrated no significant associations with triglycerides, LDL-C, and HDL-C levels. In contrast to HOMA %S, ISI-FFA was significantly (P < .05) related to triglycerides and LDL-C in direct multiple regression analysis.
CONCLUSIONS: Insulin resistance in respect to FFA metabolism is already detectable in childhood. Insulin sensitivity index of FFA metabolism seems to be a better tool for describing insulin resistance in lipid metabolism than ISI of glucose metabolism, because FFA and partially insulin but not glucose were related to triglycerides and LDL-C.