Biological clocks shape metabolism, but how circadian programs govern nutrient processing is unclear. Here, using human metabolomics and 13 C 6 -glucose tracing in Drosophila , we delineate previously under characterized daily oscillations in glucose-derived metabolic networks, providing a mechanistic framework for a purpose-built isotope-tracing approach. In flies, we reveal a pronounced “rush hour” of glucose utilization early in the light phase, with carbons directed to biosynthetic and energetic pathways. By contrast, a dopamine reuptake-deficient hyperactive mutant ( fumin ) with elevated metabolic rate shows phase-shifted and amplified metabolic peaks, indicating that altered neural signaling reshapes temporal glucose flux. Neither altered feeding schedules nor short-term fasting disrupt these intrinsic metabolic rhythms, strongly suggesting that circadian timing, rather than nutrient availability, orchestrates temporal homeostasis. By integrating human metabolite profiling with isotope-tracing in flies, we define a conserved temporal architecture of glucose utilization and demonstrate that metabolic flux is dynamically gated across the day. Our findings establish a framework for understanding how circadian misalignment contributes to metabolic dysfunction and disease.
Malik et al. (Thu,) studied this question.