New research has found BMI to be a highly inaccurate measure of childhood obesity, leading current thinking and policy based on it into question

Waist circumference-to-height ratio is a more reliable measure of obesity in children and adolescents than BMI, according to a new study, published in the journal Pediatric Research.

For nearly a generation, weight-to-height ratio charts and BMI for age and sex have been used to diagnose children with obesity, but they have been proven to be an inaccurate measure since they don’t distinguish fat mass from muscle mass, with many children being classified as obese, when they are in fact muscular.

These diagnoses – with the accompanying confusion and distress for parents – have the potential to lead to the development of eating disorders and body dysmorphia, while also calling into question the accuracy of current published numbers about childhood obesity which may now be found to be flawed, given they’ve been based on BMI.

International collaboration
The new study – conducted at the University of Exeter, in collaboration with the University of Bristol and University of Eastern Finland – has discovered waist circumference-to-height ratio is a more accurate measure of obesity, which is currently impacting almost one in four children according to the BMI measure.

Dr Andrew Agbaje of the Children’s Health and Research Centre at the University of Exeter says: “Unlike BMI, the average waist circumference-to-height ratio in childhood, adolescence, and young adulthood does not vary with age or among individuals, which is why it might be preferable to BMI assessment for use in child and adolescent clinics as an inexpensive tool for detecting excess body fat.

“It also means parents can easily and quickly confirm whether any increase that occurs in their child’s BMI or weight is due to excess fat or increases in muscle mass, by examining their child’s waist circumference-to-height ratio.”

Meta study underpins results
This study is the largest and the longest follow-up DEXA-measured fat mass and muscle mass study undertaken in the world, using the University of Bristol’s ‘Children of the 90s’ data.

The study followed 7,237 children, 51-per cent of whom were female, from aged nine to the age of 24. Their BMI and waist circumference-to-height ratio were measured at ages nine, 11, 15, 17, and 24 to establish the accuracy of the waist circumference-to-height ratio measure.

• Read the study, Waist-circumference-to-height-ratio had better longitudinal agreement with DEXA-measured fat mass than BMI in 7,237 children at www.HCMmag.com/BMIflaw