Waist-to-height ratio identified as a more precise indicator of childhood obesity than BMI, study finds

A recent study has highlighted the limitations of body mass index (BMI) in accurately identifying overweight and obesity in children and adolescents. Researchers found that BMI was nearly three times more likely to classify children as overweight when compared to waist-to-height ratio, a measurement that better reflects body fat distribution. The study, a collaborative effort between the University of Eastern Finland and the Universities of Bristol and Exeter in the United Kingdom, was published in Obesity and Endocrinology. 

BMI is widely used as a screening tool for childhood obesity, as it is a simple calculation based on weight and height. However, one of its key limitations is that it does not differentiate between fat mass and lean muscle mass. This means that children with a higher proportion of muscle could be mistakenly classified as overweight or obese.

In contrast, waist-to-height ratio takes into account central adiposity—the accumulation of fat around the abdomen—which is a more reliable predictor of obesity-related health risks. Recognising this, leading health organisations have begun to shift their recommendations regarding obesity assessment. The Lancet Commission on Obesity and the European Association for the Study of Obesity (EASO) have both advised that BMI alone should not be used as the sole diagnostic measure for obesity in adults. Instead, they recommend confirming obesity using waist-to-height ratio or other indicators. Similarly, the UK’s National Institute for Health and Care Excellence (NICE) has endorsed waist-to-height ratio as a useful tool for predicting obesity-related health risks in children, particularly those linked to central fat accumulation.

Largest Longitudinal Study Comparing BMI and Waist-to-Height Ratio in Children

This latest study represents the most extensive follow-up research globally to compare BMI and waist-to-height ratio in paediatric populations. The study followed 7,600 children from the University of Bristol’s Children of the 90s cohort, tracking their growth and body composition changes from the age of 9 years through to 24 years.

At the age of 9, researchers identified 1,431 children as overweight based on BMI. However, when these same children were assessed using waist-to-height ratio, the findings were markedly different:

• 25% were classified as having high fat
• 11% had excess fat
• 64% had normal fat levels, according to the study’s waist-to-height ratio cutpoints

Conversely, among the 517 children classified as having high fat based on waist-to-height ratio:

• 70% were classified as overweight by BMI
• 24% were classified as having obesity by BMI
• Only 6% were within the normal BMI range

These findings underscore the risk of BMI misclassifying children’s weight status, either overestimating or underestimating body fat levels.

Waist-to-Height Ratio as a More Accessible Alternative to DEXA Scanning

For precise measurement of body fat, dual-energy X-ray absorptiometry (DEXA) is considered the gold standard. However, this technology is expensive and not widely available in primary care settings. Previous research using the same dataset demonstrated that waist-to-height ratio can predict body fat with up to 85% accuracy when compared to DEXA results. The cutpoints for high, excess, and normal body fat used in this study were derived from earlier findings in the same cohort of children and adolescents.

Furthermore, the validity of these cutpoints was externally tested in a separate population of 3,329 adults in the United States to assess their predictive value for metabolic health outcomes. Researchers found that:

• High waist-to-height ratio fat levels were associated with increased odds of prediabetes
• Excess waist-to-height ratio fat levels correlated with a higher risk of developing type 2 diabetes

These results highlight the potential for waist-to-height ratio to serve as a universal and cost-effective screening tool for obesity-related health risks across different age groups and populations.

Expert Perspective: Waist-to-Height Ratio as a More Reliable Metric for Childhood Obesity

Dr Andrew Agbaje, a physician and associate professor (docent) of Clinical Epidemiology and Child Health at the University of Eastern Finland, emphasised the advantages of waist-to-height ratio as a more precise measure of adiposity in young people.

“Waist-to-height ratio is an affordable and universally accessible, accurate, and precise tool for detecting high and excess fat in children and adolescents,” he stated.

His previous research has demonstrated that waist-to-height ratio is a strong predictor of both total body fat and central fat distribution, reinforcing its value in obesity assessment.

“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 concluded.

Research Funding and Support

Agbaje’s research has been made possible through financial support from multiple organisations, including:

• Jenny and Antti Wihuri Foundation
• Finnish Cultural Foundation (Central Fund and North Savo Regional Fund)
• Orion Research Foundation
• Aarne Koskelo Foundation
• Antti and Tyyne Soininen Foundation
• Paulo Foundation
• Yrjö Jahnsson Foundation
• Paavo Nurmi Foundation
• Finnish Foundation for Cardiovascular Research
• Ida Montin Foundation
• Eino Räsänen Fund
• Matti and Vappu Maukonen Fund
• Foundation for Paediatric Research
• Alfred Kordelin Foundation
• Novo Nordisk Foundation

Implications for Future Obesity Screening and Management

The findings of this study contribute to the growing body of evidence suggesting that waist-to-height ratio should be incorporated into routine obesity screening in children and adolescents. Given its affordability, accessibility, and stronger correlation with body fat distribution, it presents a valuable alternative to BMI in both clinical and public health settings.

As global obesity rates continue to rise, ensuring the accuracy of diagnostic tools is essential for early intervention and effective management. This research reinforces the need for a shift in obesity screening practices, with waist-to-height ratio emerging as a more reliable and equitable measure of adiposity in young people.