Glucose is dynamically regulated by time of day in humans and Drosophila

Biological clocks shape metabolism, but how circadian programs govern nutrient processing is unclear. Here, using human metabolomics and 13C6-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.