Lipolysis in African-American children: is it a metabolic risk factor predisposing to obesity?

Rates of obesity and type 2 diabetes are higher in African-American (AA), compared with American white (AW), adults and children. It is not known whether biologic and/or environmental differences are responsible for this racial disparity. We and others have demonstrated that AA children are hyperinsulinemic, compared with their AW peers. This investigation tested the hypothesis that hyperinsulinemia in AA children is associated with lower rates of lipolysis, which could be a risk factor for future obesity. Forty prepubertal children (20 AA and 20 AW) with comparable body composition (assessed by dual-energy x-ray absorptiometry) and visceral adiposity (evaluated with computed tomography scan) were studied. Total body lipolysis was measured with [(2)H(5)]glycerol after overnight fasting. Basal lipolysis was approximately 40% lower in AA vs. AW children, whether the data were expressed for total body (85.7 +/- 8.9 vs. 130.3 +/- 14.1 micromol/min, P = 0.011) or per-kilogram BW (2.4 +/- 0.2 vs. 3.8 +/- 0.4 micromol/min.kg, P = 0.002) or per kilogram fat free mass (FFM) (3.3 +/- 0.3 vs. 5.2 +/- 0.5 micromol/min.kg FFM, P = 0.004), or per kg fat mass (FM) (13.7 +/- 1.6 vs. 21.3 +/- 3.3 micromol/min.kg FM, P = 0.046). Fasting insulin levels were higher in AA children (99.6 +/- 7.8 vs. 77.4 +/- 5.9 pmol/L, P = 0.032). Lipolysis correlated positively with fat mass, percent body fat, and abdominal fat mass. However, in multiple-regression analysis models after controlling for insulin and body composition, race remained a significant contributor to the variance in lipolysis. In summary, the present study demonstrates that rates of lipolysis are significantly lower in AA children, compared with their white peers. This may constitute an early metabolic phenotype that may mediate fat trapping and susceptibility to obesity in a specific environmental context of energy excess conducive to fat accretion.