More than 100,000 young Scots are now obese, with current methods of measuring weight at risk of underestimating the scale of the problem by as much as half, researchers said.
Experts at the University of Strathclyde warned there are “large numbers of children and adolescents” whose weight is “apparently healthy” when their Body Mass Index (BMI) is calculated - but who despite this have “an excessively high body fat content”.
Rather than using BMI - which is based on height and weight - the researchers said using an alternative method to measure obesity would provide a “far more accurate picture of the scale of the problem”.
However they said the method would also be “more costly” to use, with more time needed to establish if youngsters are a healthy weight or not.
Despite this, Professor John Reilly of Strathclyde’s School of Psychological Sciences and Health said it “could be worth the consideration and investment”.
He recently led a study of obesity in Africa, which involved 1,500 primary schoolchildren across eight separate countries.
This found a significant disparity between the level of children defined as obese by BMI (9 percent) and those classed as obese by excessive fatness as measured by total body water - with this deuterium dilution method resulting in 29 percent being put in this group.
Prof Reilly spoke out as the Active Healthy Kids Global Alliance (AHKGA) report, which assesses trends in childhood physical activity in 49 countries was published.
The Strathclyde University expert was the Scottish lead for AHKGA study, which gave Scotland a D+ rating - placing the country in the lower half of the rankings.
Slovenia had the best ranking of any of the nations, with a B, while England was given a C overall.
Scotland’s ranking however was better than the USA which was awarded a D, while China was given a D-.
While Scotland scored a B for organised sport and physical activity, it was given an F for high levels of sedentary behaviour amongst youngsters.
Professor Reilly said: “BMI is a straightforward and cost-effective way of measuring obesity in children. It has become widely-used in national surveys and in public health information but it is a very crude proxy measure. Large numbers of children and adolescents with an apparently healthy BMI for their age have an excessively high body fat content.
“Childhood obesity is at least twice as prevalent as reported in national surveys and official publications; in fact, more than 100,000 Scottish children and young people will have obesity at present.
“The deuterium dilution measure would be more costly and would take longer than BMI - three to four hours compared with 15 to 20 minutes for BMI - but it would present us with a far more accurate picture.”