At the end of each period (Visit 8, 15) a hypoglycaemic clamp will be performed. After the subject completed the MMTT on day 1, the subject will stay in the clinical unit to prepare for the hypoglycaemic clamp with an variable insulin infusion intravenously in order to obtain a steady state of a plasma glucose (PG) level of 5.5 mmol/L overnight until approximately 08:00. At 05:00 hours 10%-[6,6-2H2] glucose solution will be given i.v. as a primed (9.6mg/kg/min) for one minute and a constant (0.08 mg/kg/min) infusion until the last blood sampling of the plateau 4.0 mmol/L will be performed.