The outcomes of caloric restriction are driven by enhanced glucocorticoid rhythms.

Caloric restriction extends lifespan and healthspan across species, with feeding times synchronized to circadian rhythms further maximizing its benefits. However, the mechanisms linking diet, diurnal rhythms, and lifespan are not fully understood. In mice, the time point most strongly tied to dietary effects on lifespan coincides with the peak of glucocorticoid secretion (ZT12, lights-off). Caloric restriction raises circulating glucocorticoid hormone levels, but their functional relevance remains untested. We show that the glucocorticoid receptor (GR) is critical for the effects of caloric restriction. Hepatocyte-specific GR mutant mice fail to respond to caloric restriction indicating that increased glucocorticoid amplitudes support its benefits. Using multiomics techniques in murine liver, we find that nutrient deprivation elicits a nuclear switch from active STAT signaling to increased FOXO1 activity, enabling the GR to activate a unique diet-specific gene expression program. Taken together, our results suggest that glucocorticoid rhythms are crucial for caloric restriction-induced metabolic reprogramming.