Skeletal muscle lipid content and insulin sensitivity in black versus white obese adolescents: is there a race differential?

OBJECTIVE: We tested the hypothesis that skeletal muscle lipid content (SMLC) is higher in obese black adolescents compared with their white peers and assessed the relationship between SMLC and insulin sensitivity (IS).
METHODS: Subjects were healthy obese black (n = 42) and white (n = 38) adolescents. Measurements included an oral glucose tolerance test, IS by a 3-h hyperinsulinemic-euglycemic clamp, abdominal adipose tissue (AT) by magnetic resonance imaging and midthigh SMLC by computed tomography.
RESULTS: All measures of SMLC including intermuscular AT (IMAT), low-density muscle, and thigh sc AT increased (P < 0.05) with increasing total adiposity independent of race. For a given total body adiposity or thigh circumference, SMLC did not differ between black and white adolescents; however, for a given visceral adipose tissue, IMAT was higher in blacks. Consistent with prior observations, IS did not differ between black and white obese adolescents despite lower visceral fat in blacks. In whites, all markers of SMLC were associated (P < 0.05) with IS, whereas in blacks, only IMAT correlated (P < 0.05) with IS. However, in both races, these relationships did not remain significant after accounting for total fat (kilograms).
CONCLUSIONS: SMLC is not different between black and white obese adolescents who have similar total body adiposity but lower visceral fat in blacks. The lack of association between IS and SMLC after adjusting for total adiposity suggest that muscle fat does not make a unique contribution to IS in this group of obese adolescents regardless of race.