Overweight teens 'do not see themselves as too heavy'
More than a third of overweight teenagers do not regard themselves as too heavy and think they are about the right weight, a study in England shows.
This might lead some teens to underestimate the need for healthier diets and exercise, researchers warn.
But they say there is some good news - most normal-weight teenagers recognised their weight was fine.
The study, funded by the charity Cancer Research UK, appears in the International Journal of Obesity.
Concern and celebration
Over the last few decades, studies in adults have hinted that fewer people are able to spot when they are overweight.
And scientists speculate that the rising levels of obesity across the population might have "normalised" the idea of being overweight or obese, making it harder to recognise the extra pounds.
But others argue that a constant barrage of media and cultural messages encouraging people to be thin might lead some to overestimate their weight.
To see how this might affect teenagers, the researchers looked at nearly 5,000 adolescents aged between 13 and 15.
They used data collected from the Health Survey for England spanning 2005-2012, which included the following question.
"Given your age and height, would you say that you are about the right weight, too heavy or too light?"
Separately, researchers recorded teenagers' heights and weights and calculated their body mass index - a ratio of weight to height.
Their responses were then compared against categories of BMI.
Eight out of 10 teenagers of normal weight according to the BMI measure, identified themselves as about the right weight.
But there were differences between sexes, with normal-weight girls more likely to consider themselves as too heavy.
And in adolescents whose weight put them in the overweight category, 39% said they were about the right weight.
Researchers say their results bring up challenging questions about how best to tackle weight in teenagers, without causing unnecessary concern in those whose weight is healthy.
Prof Jane Wardle, from the Cancer Research UK Health Behaviour Research Centre at University College London, said: "This study was a cause for celebration and concern.
"Young people who think they're overweight when they're not can sometimes develop devastating eating disorders, so we're delighted that most of the normal-weight teenagers had a realistic view of their body size.
"But we need to find effective ways of helping too-heavy teenagers slim down and maintain a healthier weight, and it is vitally important that we find out whether it helps if they are more aware of their weight status."
Eustace De Sousa, at Public Health England, said a healthy weight could help protect against disease in later life.
He added: "Children and teenagers consume more sugar than anyone else, so cutting back and being more active will help to maintain a healthy weight and protect against developing type 2 diabetes, heart disease and some cancers later in life."