Meal patterning of rats with changes in day length and food availability

Feeding activity in rats is mainly nocturnal, with about 70–90% of the total daily intake eaten in the dark phase. During this phase, feeding has a typical biomodal pattern, i.e. a high level of feeding activity early and late in the night. The aim of the present study was to investigate the effects of temporary food restriction at dawn and dusk, and advanced light onset on the bimodal feeding pattern of male rats. It was found that suppression of food intake by restricting access to food or altering light onset act in radically different ways on the circadian meal patterning. It is argued that food restriction led to a general metabolic deficit, which was compensated by an increase in intake, especially after deprivation. Advancing light onset shifted the “dawn peak” of food intake to precede light onset. The results suggest that under these experimental conditions advancing light onset but not temporary food restriction can “reset” the circadian pacemaker.