The team scanned the genetic code of more than 100,000 women, reporting their findings in the journal Nature Genetics.
In the UK, girls as young as 10 are now showing the first signs of puberty.
A specialist said early puberty was linked to an increased risk of female cancers later in life.
The reasons why girls are going through puberty several years earlier than a century ago are not well understood by scientists.
Some have suggested a relationship between early puberty and obesity, and the latest research, carried out by the Reprogen consortium of scientists from the US, Europe and Australia, supports this idea.
Among the 30 genes highlighted by their genome research were some already linked to fat metabolism and weight regulation.
However, it is still not clear whether being obese or overweight in childhood is itself the cause of early puberty, or just another consequence of a different mechanism.
In addition, the study does not show how much of the risk is due to genes, and how much other environmental factors such as diet and upbringing are responsible.