Steroid hormones are crucial regulators of life-stage transitions during development in animals. However, the molecular mechanisms by which developmental transition through these stages is coupled with optimal metabolic homeostasis remains poorly understood. Here, we demonstrate through mathematical modelling and experimental validation that ecdysteroid-induced metabolic remodelling from resource consumption to conservation can be a successful life-history strategy to maximize fitness in Drosophila larvae in a fluctuating environment. Specifically, the ecdysteroid-inducible protein ImpL2 protects against hydrolysis of circulating trehalose following pupal commitment in larvae. Stored glycogen and triglycerides in the fat body are also conserved, even under fasting conditions. Moreover, pupal commitment dictates reduced energy expenditure upon starvation to maintain available resources, thus negotiating trade-offs in resource allocation at the physiological and behavioural levels. The optimal stage-specific metabolic shift elucidated by our predictive and empirical approaches reveals that Drosophila has developed a highly controlled system for ensuring robust development that may be conserved among higher-order organisms in response to intrinsic and extrinsic cues.