A combined Finnish and UK study has shown that two-thirds of children who would be classified as overweight according to their Body Mass Index (BMI), had normal fat when estimated when using the waist-to-height ratio. BMI and weight-to-height indices are universally employed as markers of childhood obesity. However, BMI does not distinguish muscle mass from fat mass, and may misclassify children as overweight.
The BMI was almost three times more likely to classify children as overweight than waist circumference-to-height ratio, according to a new study. Published in Obesity and Endocrinology, the study was based on collaboration between the University of Eastern Finland and the Universities of Bristol and Exeter in the UK.
The difference between muscle mass and fat mass
BMI and weight-to-height indices are universally employed as markers of childhood obesity. However, BMI does not distinguish muscle mass from fat mass, and may misclassify children as overweight.
Picture caption: Waist circumference-to-height ratio is a non-invasive and inexpensive tool for measuring fat mass overweight and obesity (adiposopathy) in paediatric practice. The QR code links to a waist-to-height ratio calculator developed on the basis of this study. Image: Andrew Agbaje.
With regard to adult obesity, the Lancet Commission on Obesity and the European Association for the Study of Obesity (EASO) have recently recommended that obesity in adults should not be diagnosed with BMI alone but confirmed with another measure, such as waist-to-height ratio. The UK National Institute for Health Care and Excellence has also recommended waist-to-height ratio as a tool to predict health risks associated with central adiposity in children.
The present study is the largest follow-up pediatric study comparing BMI and waist-to-height ratio in the world. The study included 7,600 children drawn from the University of Bristol’s Children of the 90s cohort who were followed up from ages 9 until 24 years. Of the 1,431 children classified as BMI-overweight at age 9 years, 25% had waist-to-height ratio high fat, 11% had waist-to-height ratio excess fat, and 64% had waist-to-height ratio normal fat according to the cutpoints used in the study. However, of the 517 children classified as having waist-to-height ratio high fat, 70% were BMI-overweight, 24% had BMI-obesity, and only 6% had normal BMI.
Dual-energy X-ray absorptiometry (DEXA) is considered the gold-standard for accurate body fat measure with major benefits for people in training; however, this expensive device is not universally available in primary health care. It was previously reported from the same data that waist-to-height ratio can assess body fat to a maximum of 85% accuracy compared to DEXA results. The waist-to-height ratio cutpoints for high, excess and normal body fat used in this study were developed from earlier results in the same children and adolescents.
New parameters needed for predicting diabetes
In the present study, these waist-to-height ratio cutpoints were also externally validated for type 2 diabetes prediction in 3,329 US adults. Waist-to-height ratio high fat was associated with higher odds of prediabetes, while waist-to-height ratio excess fat predicted higher odds of type 2 diabetes.
“Waist-to-height ratio is an affordable and universally accessible, accurate and precise tool for detecting high and excess fat in children and adolescents,” says Andrew Agbaje, who is a physician and associate professor (docent) of Clinical Epidemiology and Child Health at the University of Eastern Finland. His earlier research has also shown that waist-to-height ratio predicts both total body adiposity and central adiposity.
Combined tests needed to diagnose overweight and obesity in children
“Overweight and obesity in children and adolescents should not be diagnosed with BMI alone but could be confirmed with waist-to-height ratio where a DEXA scan is lacking,” Agbaje concludes.
About Children of the 90s
Based at the University of Bristol, Children of the 90s, also known as the Avon Longitudinal Study of Parents and Children (ALSPAC), is a long-term health research project that enrolled more than 14,000 pregnant women in 1991 and 1992. It has been following the health and development of the parents, their children and now their grandchildren in detail ever since. It receives core funding from the Medical Research Council, the Wellcome Trust and the University of Bristol.
University of Eastern Finland
The University of Eastern Finland, UEF, is the most multidisciplinary university in Finland. The university’s high standard of interdisciplinary research and education responds to global challenges, building a sustainable future. Research conducted at UEF is ranked among the best in the world in several fields. The university is home to 17,000 students and 3,200 staff.
References:
Agbaje AO. BMI triples overweight prevalence in 7600 children compared with waist-to-height ratio: The ALSPAC Study. Obesity and Endocrinology 2025.
Other relevant article:
Agbaje AO. Waist-circumference-to-height-ratio had better longitudinal agreement with DEXA-measured fat mass than BMI in 7237 children. Pediatr Res. 2024.
