The onset of puberty in adolescents and whether it is related to obesity is an ongoing topic for debate. Epidemiological cross-sectional and longitudinal studies show a shift towards earlier onset of puberty in girls who are obese; however, the situation is less clear in boys. Boys who are overweight seem to mature earlier, and boys who are obese mature later, than boys at a healthy weight. The underlying mechanisms are not yet fully understood, and whether earlier onset of puberty in obese girls is based on the activation of the hypothalamic-pituitary-gonadal axis is unclear. The most promising link between obesity and puberty is the adipokine leptin and its interaction with the kisspeptin system, which is an important regulator of puberty.
Source: Is there a causal relationship between obesity and puberty?