Just 15 minutes of exercise a day could be enough for children to keep their weight at healthy levels, a joint UK/US study has found.
The study, conducted by the Universities of Bristol and Bath and their colleagues in the US, found that short bursts of daily exercise seemed to be best at cutting obesity.
More than 5,500 children with an average age of 12 took part in the study, wearing motion sensors to record their daily levels of exercise.
Those who completed 15 minutes of exercise daily, equivalent to a brisk walk, were up to 50 per cent less likely to be obese than inactive children, said the researchers.
"This study provides some of the first robust evidence on the link between physical activity and obesity in children," said co-author Professor Chris Riddoch of Bath University.
"We know that diet is important, but what this research tells us is that we mustn't forget about activity. It's been really surprising to us how even small amounts of exercise appear to have dramatic results."
Obesity is one of the leading causes of cancer after smoking, and is thought to be related to around a quarter of all cancer deaths.
The study is published in the Public Library of Science journal PLoS Medicine.
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