A total of 12 obese adolescents with NGT, 19 with IGT, and 17 with type 2 diabetes were studied; subjects were African-American and American Caucasian. All subjects had exogenous obesity and were not involved in any regular physical activity or weight-reduction programs. They were recruited through flyers posted in the community and the health center. The NGT and IGT adolescents had normal fasting glucose (<100 mg/dl), with a 2-h glucose value during an oral glucose tolerance test (OGTT) of <140 mg/dl in NGT and 140–199 mg/dl in IGT subjects. They were not on any medications that affect glucose metabolism. The adolescents with type 2 diabetes were clinically diagnosed according to American Diabetes Association and World Health Organization criteria (10 (link)), with a mean A1C of 10.1 ± 3.0% and glucose level of 277.2 ± 158.2 mg/dl at presentation and negative glutamic acid decarboxylase and islet cell autoantibodies. They all had adequate metabolic control, with an average A1C of 6.6 ± 0.2% (range 4.7–8.3%) and average duration of diabetes of 4.8 ± 5.7 months (0–18 months). They were on treatment consisting of lifestyle changes alone (n = 3), metformin (n = 6), metformin + insulin (n = 7), or insulin alone (n = 1). Metformin and long-acting insulin were discontinued 48 h before the clamp studies. All studies were approved by the institutional review board of the University of Pittsburgh. Informed consent was obtained. Characteristics of the study participants are summarized in Table 1.