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, the deuterium dilution measure, to measure obesity would provide a ‘far more accurate picture’.

However, they said the method would also be ‘more costly’ to use.

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 countries.

This found a significant disparity between the level of children defined as obese by BMI and those classed as obese by excessive fatness as measured by total body water.

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 official publications. 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 but it would present us with a more accurate picture.”