Leptin, an adipocyte-derived hormone, informs neuroendocrine pathways about the status of energy stores in adipose tissue. The integration of this peripheral signal in hypothalamic networks results in activation of peripheral metabolic pathways that control energy build-up and expenditure. Firing of the reproductive cascade of hormones at puberty and its regulation in adults is tightly associated with energy metabolism and is thus regulated by leptin. This article provides an update of past and present theories that link nutrition and reproduction in light of new research.