Hyperinsulinemic-Euglycemic Clamp

Insulin sensitivity was measured using a two-step hyperinsulinemic-euglycemic clamp. Insulin was infused for 180 min at 10 mU/min m² (low-dose insulin), followed by 150 min at 50 mU/min m² (high-dose insulin). Infusion of a 20% glucose solution was adjusted to maintain plasma glucose at 90 mg/dL. Insulin sensitivity was assessed as the glucose infusion rate (GIR) during the final 30 min of each step of the clamp (steady-state) (33) and was expressed per kg of estimated metabolic weight (fat-free mass + 17.7 kg) (34). Resting metabolic rate and RQ were measured using a DeltaTrac hood indirect calorimeter (Sensor Medics, Yorba, CA) for 30 min fasting and for 30 min during each steady-state period of the clamp. The oxidative component of GIR was calculated as described by Jequier et al (31) while the nonoxidative component was calculated as the difference between total GIR and its oxidative component. Clamp whole-body metabolic flexibility was defined as the difference between the high-dose or low-dose steady-state RQ and the fasting RQ.