 The aim of the current study is to test the hypothesis that the concurrence of meal timing with elevated endogenous melatonin concentrations results in impaired glucose control and that this effect is stronger in homozygous MTNR1B risk carriers than in non-carriers. To do so we will test glucose tolerance using identical mixed meals under two dinner conditions: a delayed dinner or Late Eating LE: starting1 hour before usual bed time, b advanced dinner or Early Eating EE: starting 4 hours before habitual bed time, in a randomized, cross-over study design. 