2.1. Procedures. Participants arrived at the General Clin- ical Research Center (GCRC) where a licensed pediatric health care provider conducted a medical/family history and physical examination which included an assessment of Tanner stage [22, 23]. Body composition was measured by air displacement plethysmography (BodPod; Life Measurement Instruments, Concord, CA). Total dietary intake was assessed with three-day dietary records given to participants to com- plete at home, which were later returned to research staff for nutritional analysis. Three-Day Physical Activity Recall was used to assess self-reported physical activity [24].
A frequently sampled insulin-modified intravenous glu- cose tolerance test (FSIGT) was used to assess type 2 diabetes risk [25]. Fasting plasma insulin and glucose concentrations were used to estimate insulin resistance using homeostasis model assessment (HOMA-IR), which was calculated as HOMA-IR = [(FPI × FPG)/22.5] [11]. Plasma collected during the FSIGT was analyzed for glucose and insulin, and values were entered into the MINMOD Millennium 2003 computer program (version 5.16, Bergman, USC) to calculate SI, AIRG, and DI. SI was defined as the net capacity for insulin to promote the disposal of glucose and to inhibit the endogenous production of glucose. AIRG was defined as the area under the plasma insulin curve between 0 and 10 minutes. DI, an index of beta-cell function, was calculated