We compared the utility of different adiposity measures in predicting indices of insulin sensitivity and secretion. At their pre-randomization visit for a 1 year, randomized, double masked, placebo controlled trial of metformin extended release, 47 (to date, of a planned 135) obese adolescents had a 7 point, 180 minute, 75-gm OGTT. Inclusion criteria included a BMI greater than the 95th centile and weight of less than 137 kg. Subjects had a mean age of 14.6 (13-18) years. 21 (45%) were male and 55% were non-Hispanic white. Insulin sensitivity was estimated using the Composite Insulin Sensitivity Index [CISI, 1/((mg/dL)(μU/mL))]. Insulin secretion was calculated using the Corrected Insulin Release at glucose peak [CIRgp, ((μU/L)/(mg/dL)2)]. Total adiposity was measured using BMI and dual energy x-ray absorptiometry (DXA-whole body (WB)). Trunk adiposity was measured by DXA-TK and a CT slice aligned with the L4-L5 intervertebral disk. This CT slice was also used to partition intraperitoneal (CT-IP) and subcutaneous (CT-SQ) fat. While the mean body weights were similar (98.9 vs 100 kg), girls, as expected, had greater adiposity than boys (DX-WB 42[138}6% vs 36±6% fat). Moreover, non-Hispanic whites, while having similar adiposity, had greater insulin sensitivity (CISI 3.88±3.00 vs 3.38±4.55). CISI was highly correlated with fasting insulin concentrations (r = -0.95, p ≤ 0.0001). Intraperitoneal fat (CT-IP), while constituting only 14% of abdomen fat, had the strongest correlation with CISI of all the measures of adiposity (Table).
Of the adiposity indices, only abdomen CT quantitated intraperitoneal fat and this was the only measure that significantly correlated with insulin sensitivity in these obese adolescents.
Supported by: Glaser Pediatric Research Network and CRCs at Baylor (M01-RR-00188), Harvard (M01-RR- 02172), Stanford (M01-RR-000070), UCLA (M01-RR-00865), and UCSF (M01-RR-01271).