A lack of sleep may be partly to be blame for childhood obesity, a leading UK expert claims.
Childhood obesity is increasing in Britain
Dr Shahrad Taheri and his team at Bristol University say sleep deprivation leads to hormonal changes.
They say these changes tell the body to eat sugary or starchy food to provide an energy boost. Over a prolonged period this leads to weight gain.
Experts want the government to take sleep-deprivation as seriously as diet and exercise in the obesity battle.
The researchers at Bristol University say the evidence is stark.
Dr Taheri told the BBC: "There is a really clear relationship between short sleep duration and obesity in children."
He said obesity occurs because of the "imbalance between the energy that we take in - the foods that we eat -and the energy we burn, which is our physical activity".
Dr Taheri added "there is a very good relationship between physical activity and good sleep".
The expert said this link was due to the fact that physical activity would make children tired, whereas youngsters were less likely to sleep well if they had been watching television or playing computer games.
He went on to say that children were "smart enough to learn about healthy foods and the importance of exercise", before adding that "we really should educate them about the importance of sleep".
One proposal is to start the school day later, so youngsters get a lie-in.
Another is to persuade parents to remove computers and mobile phones from their children's bedrooms, so they go to sleep on time.
Based on current trends, one million children in the UK will be obese by 2010, experts estimate.
Worldwide, more than 22 million children under five years old are obese or overweight, according to the World Health Organization.
Tam Fry, chairman of the Child Growth Foundation and a member of the National Obesity Forum, said the problem with obesity in the UK was "huge" and continuing to rise.
"The Department of Health wishes to halt the year on year rise of obesity by 2010," he said.
"I'm afraid that won't happen and really drastic measures now need to be put in place to try and reverse this situation."