Statistical Analysis Subject characteristics will be expressed as the mean (SD). 13C-glucose oxidation as 13CO2 will be the primary outcome measured, as this best describes the whole body oxidation capacity for glucose. Area under the curve (AUC) for each subject's 13CO2 oxidation from t0 to t240, the time to reach maximum 13CO2 oxidation (tmax) and the maximum peak enrichment in13CO2 oxidation (Cmax) will be calculated. A repeated-measures analysis using restricted maximum likelihood estimation will be used to get the estimated parameters with the MIXED procedure using SAS software (SAS/STAT; Version 9.2). A paired t-test will be used to compare the 13CO2 oxidation at each time point without and with U-13C-glucose. All values will be presented for individual subjects, and significance is set at P<0.05. Statistical analysis will be performed using GraphPad Prism 4.0 (GraphPad Software Inc, CA).