Leptin signals ample body fat and influences hypothalamic circuits controlling puberty.

“Leptin (which signals ample body fat) may be the signal but there are other signals too, and ultimately the hypothalamic circuits that flip the puberty switch include hormones from within that signal body/nutrient availability status, as well as olfactory (not neccesarily pheromonal) cues and there is an interesting role of melatonin becoming more cyclic too.”