Pubertal alterations in growth and body composition. VI. Pubertal insulin resistance: relation to adiposity, body fat distribution and hormone release

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Abstract
Objective: To investigate the independent influence of alterations in fat mass, body fat distribution and hormone release on pubertal increases in fasting serum insulin concentrations and on insulin resistance assessed by the homeostasis model (HOMA). Design and Subjects: Cross-sectional investigation of pre- (n=11, n=8), mid- (n=10, n=11), and late-pubertal (n=10, n=11) boys and girls with normal body weight and growth velocity. Measurements: Body composition (by a four-compartment model), abdominal fat distribution and mid-thigh interfascicular plus intermuscle (extramyocellular) fat (by magnetic resonance imaging), total body subcutaneous fat (by skinfolds), mean nocturnal growth hormone (GH) release and 06:00 h samples of serum insulin, sex steroids, leptin and insulin-like growth factor-I (IGF-I). Results: Pubertal insulin resistance was suggested by greater (PPr=0.59, Pr2=0.36). Sequential addition of fat mass (FM) increased r2 (r2(inc)remental=0.08, r2=0.44, Pr2inc=0.11, r2=0.55, P0.05) did not reliably improve r2 beyond the physical characteristic and adiposity variables. In a second model, differences in sex and pubertal maturation were again held constant (r2=0.25), but body size differences were accounted for using percentage fat data. Sequential addition of percentage body fat (r2(inc)remental=0.11, r2=0.36, Pr2inc=0.08, r2=0.44, P=0.058), and then a block of serum IGF-I and log(10) leptin concentrations (r2inc=0.07, r2=0.51, Pr2. Mean nocturnal GH release was not related to HOMA (r=−0.04, P=0.75) and therefore was not included in the hierarchical regression models. Conclusion: Increases in insulin resistance at puberty were most related to FM. Accumulation of fat in the abdominal visceral, subcutaneous and muscular compartments may increase insulin resistance at puberty beyond that due to total body fat. Serum concentrations of leptin and IGF-I may further modulate HOMA beyond the effects of adiposity and fat distribution. However, the results are limited by the cross-sectional design and the use of HOMA rather than a criterion measure of insulin resistance.