The "obese insulin-sensitive" adolescent: importance of adiponectin and lipid partitioning.

There is a wide interindividual variation in peripheral insulin sensitivity at any given body mass index or percent body fat among obese adolescents with normal glucose tolerance. The goals of this study were to determine whether variability in insulin sensitivity is associated with differences in patterns of lipid partitioning or substrate use under fasting and hyperinsulinemic conditions. We compared 14 obese insulin-resistant adolescents with 14 obese insulin-sensitive controls, pair matched for age, gender, pubertal stage and body composition. Insulin sensitivity was assessed by the hyperinsulinemic-euglycemic clamp, intramyocellular lipid content by (1)H-nuclear magnetic resonance and visceral fat by magnetic resonance imaging. Obese insulin-sensitive subjects had lower intramyocellular (1.64 +/- 0.68 vs.2.26 +/- 0.62% of water peak, P = 0.017) and visceral lipid deposition (45 +/- 23 vs. 77 +/- 52 cm(2), P = 0.04) and a higher level of adiponectin, compared with their obese-resistant counterparts (8.8 +/- 3.6 vs. 6.5 +/- 1.8 mug/dl, P = 0.015). Glycerol fluxes were similar between the two obese groups yet occurred in the face of different concentrations of insulin. Intramyocellular lipid and visceral fat were negatively related to insulin sensitivity. Obese insulin-sensitive adolescents are characterized by lower lipid deposition in the intramyocellular and visceral compartments and greater levels of adiponectin, despite similar degree of adiposity.