Refeeding after a 24-hour fasting deepens NREM sleep in a time-dependent manner

► Feeding affects sleep regulation. ► EEG delta power in NREM sleep is a parameter of sleep depth and intensity. ► Refeeding at ZT1, but not at ZT7 or ZT12, following the 24-h fasting enhances EEG delta power. ► Timing of refeeding is an important factor affecting sleep quality.