New framework reveals fewer children meet clinical obesity criteria than BMI measures suggest

A recent international study indicates that clinical obesity affects a smaller proportion of children and adolescents than BMI-based estimates suggest, prompting calls for revised diagnostic approaches to improve early intervention and treatment strategies.

A new international analysis suggests that far fewer children meet the threshold for clinical obesity than are counted under commonly used body mass index measures, raising questions about how doctors identify, monitor and treat excess weight in young people.

The study, led by the Murdoch Children’s Research Institute, examined data from 786,557 people in Australia, Canada, Estonia, Finland, the Netherlands, the UK and the US. Published in eClinicalMedicine, it is described as the first large study to track the prevalence of clinical obesity from early childhood into older age. The researchers found that among children and adolescents, clinical obesity affected only 2.1% to 4.9%, compared with 7% to 10.8% classified as obese using BMI alone.

Clinical obesity, as defined by a recent Lancet Commission framework, goes beyond BMI by considering whether excess body fat is already causing health problems or limiting everyday activities. That approach reflects a broader medical view that obesity is not simply a question of weight relative to height. The World Health Organisation defines obesity as abnormal or excessive fat accumulation that poses a risk to health, while the US Centers for Disease Control and Prevention still uses BMI as a population-level screening tool for overweight and obesity.

The Australian-led research found that clinical obesity became more common with age, overtaking BMI-defined obesity from the 55 to 64 age group and reaching 52% among people aged 65 to 74. It was also more common among men in early and middle adulthood, before rates became higher among women later in life. Dr Danielle Longmore of the Murdoch Children’s Research Institute said BMI remained useful for comparing populations, but did not capture the full health picture for an individual. She said the new definition could help clinicians make better-informed decisions about treatment, including when to consider weight-loss medicines or dietary changes.

The study’s authors also argued that childhood and adolescence are a crucial window for prevention, because obesity-related problems can feed into later heart disease, type 2 diabetes, hypertension, stroke and some cancers. David Burgner of the Murdoch Children’s Research Institute said identifying which children are already showing signs of obesity-related complications could improve future prevention and treatment strategies. At the same time, he cautioned that the available cohort data did not include every diagnostic element needed under the Lancet definition, meaning more long-term studies will be needed before the true prevalence of clinical obesity can be pinned down.