Power Calculation and statistical analysis The investigators will recruit 54 participants (27 each group). This will give us 80% power to detect an 0.8 Standard Deviation (SD) change in mean average glucose excursions (MAGE) (1.44 moll/L [35]), and an 18% absolute difference in glucose reduction with vildagliptin at the 5% level of significance between those with and without substantial endogenous insulin secretion.