Each subject will be asked to attend the clinical unit at approximately 20:00 in the evening on day 1. Thereafter the subject will receive an insulin and glucose infusion intravenously in order to obtain a steady state of a PG level of 5.5 mmol/L overnight until approximately 08:00 in the morning of day 2. At 05:00 hours D-[6,6-2H2] glucose (100 g/l) solution will be given i.v. as a primed (9.6 mg/kg/min) for one minute and a constant (0.08 mg/kg/min) infusion until the last blood sampling of the plasma glucose level of 4.0 mmol/L will be performed.