There is an urgent need to obtain more knowledge about the influence of weight and metabolism on the timing and progression of puberty. The age of pubertal onset has been constantly declining during the last decades and extremely early maturation may have yet unseen consequences for the psychosocial development of the child as well as detrimental long-term health consequences. Studies have shown that girls with early-onset puberty are more likely than their peers to enter sexual relationships at a younger age, to experience more psychological distress, and to engage in risk-taking behaviors. In addition, early maturation may have long-term health consequences since earlier menarche is associated with an increased risk of all-cause mortality and cardiovascular disease later in life in large epidemiological studies. The exact aetiology for the earlier onset of puberty in the general population remains to be elucidated, and the cause is probably to be found in a complex interplay between genetic, epigenetic, environmental and metabolic factors. However, world-wide there is a concerning increasing prevalence of overweight in childhood and early puberty is one of many consequences of this. Environmental factors such as endocrine disrupting chemicals have been suggested to play a role for both obesity and precocious puberty either directly or through epigenetic moderation. The current study of a Danish National cohort will explore the incidence and aetiology of precocious puberty for better treatment and prevention. Furthermore, a placebo-controlled randomized controlled trial may give a novel mechanistic insight of the interplay between insulin sensitivity and sex steroids. To our knowledge this study is the first of its kind and may lead to novel alternative treatment strategy for overweight girls with early puberty that may have beneficial effects on long-term morbidity and mortality.