The molecular clockwork in mammals involves various clock genes with specific temporal patterns of expression. Synchronization of the master circadian clock located in the suprachiasmatic nuclei is accomplished mainly via daily resetting of the phase of the clock by light stimuli. Phase shifting responses to light are correlated with induction of Per1 and Per2 within the suprachiasmatic cells. The timing of peripheral oscillators is controlled by the suprachiasmatic clock when food is available ad libitum. Time of feeding, as modulated by temporal restricted feeding, is a potent Zeitgeber (synchronizer) for peripheral oscillators with no clear synchronizing influence on the suprachiasmatic clockwork. However, a timed calorie restriction (i.e. when only a hypocaloric diet is given each day at the same time) can modify the temporal organization generated by the suprachiasmatic nuclei and reset by the light-dark cycle. Such a situation of conflict between photic and feeding synchronizers alters timing of clock gene expression within the suprachiasmatic nuclei and timing of circadian outputs, indicating that the suprachiasmatic clock is sensitive to nutritional cues.