SUBCUTANEOUS ABDOMINAL FAT AND THIGH MUSCLE COMPOSITION PREDICT INSULIN SENSITIVITY INDEPENDENTLY OF VISCERAL FAT

Whether visceral adipose tissue has a uniquely powerful association wi th insulin resistance or whether subcutaneous abdominal fat shares thi s link has generated controversy in the area of body composition and i nsulin sensitivity. An additional issue is the potential role of fat d eposition within skeletal muscle and the relationship with insulin res istance. To address these matters, the current study was undertaken to measure body composition, aerobic fitness, and insulin sensitivity wi thin a cohort of sedentary healthy men (n = 26) and women (n = 28). Th e subjects, who ranged from lean to obese (BMI 19.6-41.0 kg/m(2)), und erwent dual energy X-ray absorptiometry (DEXA) to measure fat-free mas s (FFM) and fat mass (FM), computed tomography to measure cross-sectio nal abdominal subcutaneous and visceral adipose tissue, and computed t omography (CT) of mid-thigh to measure muscle cross-sectional area, mu scle attenuation, and subcutaneous fat. Insulin sensitivity was measur ed using the glucose clamp technique (40 mU . m(-2) . min(-1)), in con junction with [3-H-3]glucose isotope dilution. Maximal aerobic power ( VO2max) was determined using an incremental cycling test. Insulin-stim ulated glucose disposal (R-d) ranged from 3.03 to 16.83 mg . min(-1) . kg(-1) FFM. R-d was negatively correlated with FM (r = -0.58), viscer al fat (r = -0.52), subcutaneous abdominal fat (r = -0.61), and thigh fat (r = -0.38) and positively correlated with muscle attenuation (r = 0.48) and VO2max (r = 0.26, P < 0.05). In addition to manifesting the strongest simple correlation with insulin sensitivity, in stepwise mu ltiple regression, subcutaneous abdominal fat retained significance af ter adjusting for visceral fat, while the converse was not found. Musc le attenuation contributed independent significance to multiple regres sion models of body composition and insulin sensitivity, and in analys is of obese subjects, muscle attenuation was the strongest single corr elate of insulin resistance. In summary, as a component of central adi posity, subcutaneous abdominal fat has as strong an association with i nsulin resistance as visceral fat, and altered muscle composition, sug gestive of increased fat content, is an important independent marker o f insulin resistance in obesity.