Waist-to-height ratio more accurate than BMI for detecting childhood obesity

Body mass index (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.

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.

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; 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.

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."

Andrew Agbaje, 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.

"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.

Agbaje's research is supported by research grants from Jenny and Antti Wihuri Foundation, the Finnish Cultural Foundation Central Fund, the Finnish Cultural Foundation North Savo Regional Fund, the Orion Research Foundation, the Aarne Koskelo Foundation, the Antti and Tyyne Soininen Foundation, the Paulo Foundation, the Yrjö Jahnsson Foundation, the Paavo Nurmi Foundation, the Finnish Foundation for Cardiovascular Research, Ida Montin Foundation, Eino Räsänen Fund, Matti and Vappu Maukonen Fund, Foundation for Pediatric Research, Alfred Kordelin Foundation, and Novo Nordisk Foundation.