Velingkaar, N.; Astafev, A. A.; Prabahar, A.; Trokhimenko, E.; Rom, J.-M. B.; Asi, G. J.; Jiang, P.; Kondratov, R. V.

Interest in fasting-based dietary interventions to improve metabolic health is growing. Caloric restriction (CR) with one meal per day includes an extended fasting component that contributes to its metabolic and longevity benefits, yet the specific role of fasting within CR remains unclear. Here, we compared mice under CR with those subjected to a fasting-refeeding-fasting (FRF) regimen while controlling pre-fasting food intake and fasting duration. Simultaneous comparison of diet induced changes in plasma insulin and free fatty acids, hepatic mTOR signaling and ketogenesis, total body metabolic rhythms with kinetics of food digestion suggested that gastric emptying served as a primary metabolic trigger in acute fasting. In contrast, in CR, fasting responses were actively regulated and suggested anticipatory mechanisms. At the transcriptomic level, CR enhanced circadian rhythmicity and metabolic gene coordination, whereas FRF disrupted it. In agreement with the expression data, CR improves glucose and fatty acid metabolism while fasting leads to glucose intolerance and fat accumulation in the liver induced glucose intolerance and hepatic steatosis. These findings reveal that CR engages clock-aligned, anticipatory metabolic control, while fasting-refeeding cycles rely on direct nutrient cues. This mechanistic distinction between active and passive metabolic regulation may underlie the superior metabolic and longevity outcomes of caloric restriction.