While academics have been quick to note that the age of girls hitting puberty has fallen by five years in the past century, the reason why has been harder to establish - until now.
Speaking at the Cheltenham Science Festival this week, Professor Richard Sharpe, an expert in early puberty at the Medical Research Council, underlined the clear link between obesity and young girls reaching puberty as early as five years old.
When a child's fat tissue level reaches a certain point, a hormone signal is sent to the brain instructing puberty to begin, Professor Sharpe explains to Huffpost Lifestyle.
"You get these occasional children who have a genetic mutation that means their bodies can't send that signal. So they continue to eat and eat, but don't go into puberty," he explains. "But they're the exception."
Two years ago, a Danish study observed that breast development now begins on average a year earlier than 20 years ago - around the age of nine years and ten months.
"If girls mature early, they run into teenage problems at an early age and they're more prone to diseases later on.
"We should be worried about this, regardless of what we think the underlying reasons might be.
"It's a clear sign that something is affecting our children; whether it's junk food, environmental chemicals or lack of physical activity."
According to Professor Sharpe, advancement of puberty is more likely to occur in females because they bear the "burden of reproduction".
As girls have to support a foetus, and then baby, so the onset of her reproductive system is triggered by her fat levels, he explains.
Professor Sharpe adds: "The only point we’re trying to emphasise is that obesity is the one modifiable known factor that we can do something about.
"Parents need to make sure that children are on a health diet from birth, not just leading up to puberty."
In a blog for The Huffington Post last year, family doctor joel Fuhrman pointed out that in the US, about 16% of girls enter puberty by the age of 7, and about 30% by the age of 8.
Professor Sharpe also suggested environmental factors and social factors, such as family breakdown, could also be 'puberty accelerators' - but their influence was far harder to determine.
"Social factors might trigger a stress response that could alter hormone levels in young girls. But you can't investigate these delicate subjects with any great ease, so they're difficult to tie down. "