Lean body mass (lbm) is estimated using Hume's formula [12] which correlates well with tritiated water or electrical bioimpedance measures [13]. Secr1.phase is calculated as the area under serum insulin vs. time curve (AUC, trapezoidal rule) during the first 10 min of the clamp procedure, and Secr2.phase is calculated as the insulin AUC during the last hour (120-180 min) of the clamp procedure. The same calculations were also performed for C-peptide concentrations. Glucose disposal rate (GDR) is calculated from the amount of glucose infused during the last hour of the clamp. The IS index (ISI) is calculated as GDR [mmol/kg (lbm)*min] divided by mean serum insulin (pmol/l) in the same period. Glucose clearance is calculated as ISI divided by mean serum glucose during the last 60 min of the clamp [14].