Energy homeostasis at the organismal level requires signaling between different cell types, tissues, and organs to coordinate energy uptake and expenditure. The larval stage of Drosophila development provides a powerful model to study the mechanisms at play. Among the various sources of signals that control fat storage in the fat body, the brain has been studied primarily as a regulator of relevant behaviors such as feeding and exercise. Here, I briefly review what is known about a brain-fat-body axis for communication in the context of energy homeostasis in Drosophila larvae and introduce a protocol for rapidly identifying changes in body fat resulting from manipulation of gene or neuronal function.