Can an unhealthy diet cause puberty to start earlier?

Excess weight is the most well-supported factor: girls with obesity more often begin puberty earlier, probably because fatty tissue produces hormones such as leptin and insulin that accelerate the maturation process. In boys the picture is less clear: some studies find an earlier onset, while others find a delay.

Eating a lot of animal protein as a child considerably increases the likelihood of an early first menstruation: for each extra gram per day, menarche occurs on average roughly two months earlier, and girls with the highest protein intake had more than three times the risk of early menstruation. High calorie intake has also been linked to earlier onset in several studies, though the results varied considerably. Both associations are observational, so they do not prove a direct cause-and-effect relationship.

Not all dietary components work in the same direction. Girls who ate a lot of fibre and olive-oil-like fats (monounsaturated fatty acids) actually had a lower likelihood of early menarche. Yoghurt was also associated with later puberty, though it is unclear why. Soy feeding in infancy had no demonstrable effect on the timing of puberty in several studies.

Another factor to take into account is hormone-disrupting substances, such as phthalates and bisphenol A (BPA). These enter the body through packaging materials and processed food. Some studies link them to earlier puberty in girls, but the findings contradict each other enough that no firm conclusion is yet possible. Children are probably more sensitive to these substances.

The practical takeaway: a diet high in calories, high in animal protein and low in fibre increases the likelihood of early puberty in girls, primarily through excess weight. The most concrete actionable approach supported by the evidence is a varied diet with adequate fibre, moderate animal protein and as little processed food in packaging as possible. That is no guarantee, but it points in a favourable direction.