Fitness is a stronger predictor of fasting insulin levels than fatness in overweight male middle-school children

Objective: We studied the relationship between % body fat (%BF), cardiovascular fitness (CVF), and insulin resistance (IR) in overweight middle-school children. Study design: Middle school-children (n = 106, body mass index [BMI] > 95(th) percentile for age) underwent evaluation of body composition, maximal volume of oxygen utilization (Vo(2)) uptake/kg lean body mass (Vo(2)max/kgLBM), and fasting glucose and insulin (FI) concentrations and derived homeostasis model assessment index (HOMA(IR)). Results: Both %BF (r = .33, P < .001) and Vo(2)max/kgLBM (r = -0.42, P < .0001) were significantly correlated with FI. Bivariate regression analysis revealed %BF (P = .008 vs FI, P = .035 vs HOMA(IR)) and VO(2)max/kgLBM (P < .001 vs FI, P = .009 vs HOMA(IR)) to be independent predictors of insulin sensitivity. In males, VO(2)max/kgLBM was a better predictor of FI and HOMA(IR) than %BF. Conclusions: in obese middle-school children, both %BF and VO(2)max/kgLBM are independent predictors of FI levels. The relationship between CVF and FI levels was significant in both sexes but was particularly profound and stronger than %BF in males. Efforts to reduce risk of type 2 diabetes mellitus in an increasingly obese child population should include exercise intervention sustained enough to improve CVF.