According to the latest research the notion that 'puppy fat' in children disappears as they progress to adolescence is a myth, and possibly puts the future health of children at risk.
Professor John Toy, Cancer Research UK, says the study found 29% of 11-year-old girls could be classed as overweight or obese, compared to 20% of boys.
Professor Jane Wardle, of Cancer Research UK's heath behaviour unit who led the study, says a poor diet is one factor which affects teens' weight and "Puppy fat" can have lifelong health implications and should not be dismissed as a temporary childhood problem.
Previous studies have shown that adolescence is a crucial time, since excess weight during teenage years pre-disposes adults to continued weight problems along with all the associated health risks.
In a five year longitudinal study of an ethnically and socioeconomically diverse sample of young people in Britain, 5863 children were tracked as they developed into young adults.
It was seen that the problems with weight are established before the teenage years since those with excess weight by the age of 11 continued with it during adolescence.
The researchers looked at annual measurements of weight, height, Body Mass Index (BMI) and waist circumferences of children aged between 11/12 and 16/17 throughout 36 schools across South London, giving them a broad ethnic and social mix.
They found that overall, girls had higher rates of excess weight problems than boys.
Black girls had particularly high levels, with an average of 38% being overweight or obese over the study period, compared to 28% for white girls or 20% for Asian girls.
For boys, however, ethnicity made little difference to excess weight levels.