For decades, body mass index has been one of the main tools used to identify obesity in children. But a newer definition asks a broader question: Is excess body fat actually affecting a child’s health?
In a study of nearly 787,000 children and adults from seven countries, researchers found that about 2% to 5% of children and adolescents met the newer definition of clinical obesity, compared with about 7% to 11% classified as having obesity based on BMI alone.
The findings do not mean excess body fat in childhood is harmless or that BMI should be ignored. Instead, they suggest BMI alone may not tell the full story.
The newer definition, developed by a Lancet Commission, separates obesity into two categories. Clinical obesity means excess body fat is accompanied by health problems linked to it, while preclinical obesity means excess body fat is present without those complications.
That distinction could matter when deciding which children need more intensive treatment.
“People can have a similar BMI but develop very different health outcomes related to excess body fat,” said Dr. Danielle Longmore of Murdoch Children’s Research Institute.
The study, published in eClinicalMedicine, combined data from 11 large studies in Australia, Canada, Estonia, Finland, the Netherlands, the United Kingdom and the United States.
Among children and adolescents, the newer clinical definition consistently identified fewer cases than BMI alone.
BMI is useful for tracking weight across large groups of people, but it has limits when applied to individuals. It does not directly measure body fat or show whether a person is experiencing health problems related to excess fat.
The newer approach adds information such as waist measurements, blood pressure, blood sugar, cholesterol and other signs that excess body fat may be affecting the body.
“The distinction could have implications for how obesity is assessed and treated, including decisions about weight-loss medications and dietary recommendations,” Longmore said.
But researchers stressed that children who do not meet the clinical definition may still face future health risks. Excess body fat that begins in childhood can continue into adulthood and has been linked with a higher risk of several chronic diseases later in life.
Professor David Burgner of Murdoch Children’s Research Institute said identifying which children are already showing health complications could help doctors better target treatment.
“Understanding which children are already showing signs of obesity-related health complications will help inform future prevention and treatment strategies,” Burgner said.
The study also has important limitations. None of the datasets included every measure required by the new definition, so the estimates are considered preliminary. The study also looked at people at different ages rather than following everyone over time.
Interestingly, the pattern changed later in life. Clinical obesity became more common than BMI-defined obesity in older adults, suggesting the newer definition may identify different health concerns at different ages.
The researchers reported no study-specific funding. Some authors reported outside research support, speaking fees or travel support from organizations including Novo Nordisk and Lilly.