A new study from the Avon Longitudinal Study of Parents and Children (ALSPAC) is challenging long-held assumptions about how we measure overweight and obesity in children. According to findings published in Obesity and Endocrinology in January 2025, body mass index (BMI) — the most commonly used tool for assessing weight status — may dramatically overestimate overweight prevalence in children when compared with a more nuanced measure: waist-to-height ratio (WHtR).
The study, “Body mass index triples overweight prevalence in 7,600 children compared with waist-to-height ratio: the ALSPAC study,” analyzed data from 7,600 British children at ages 9, 15, and 24 and found that BMI overclassified overweight status by nearly three times compared to WHtR in childhood, 2.3 times in adolescence, and 2.6 times in early adulthood.
“This isn’t just a statistical curiosity,” said Andrew O. Agbaje, MD, MPH, FESC, the study’s lead author. “It has real-world consequences for how we label children, how we intervene, and how we track population health.”
Calculated by dividing waist circumference by height, WHtR has emerged as a more precise measure of both total body fat and central adiposity — what some researchers refer to as adiposopathy, or “sick fat.” This approach offers not just a better snapshot of body composition but also correlates more strongly with future metabolic risks.
To classify fat levels using WHtR, Agbaje introduced sex-specific cutoffs. For example, a WHtR above 0.53 in boys and 0.54 in girls was considered “excess fat” (adiposopathy grade 2), while slightly lower values were categorized as “high fat” (grade 1). These thresholds align more closely with risks for conditions like prediabetes and type 2 diabetes.
The ALSPAC data revealed that of 1,431 children classified as overweight by BMI, 64% actually had normal fat levels according to WHtR. Only 25% had high fat, and just 11% had excess fat. In contrast, of the 517 children with WHtR-defined high fat, only 6% had normal BMI, highlighting WHtR’s ability to identify high-risk children that BMI might miss — or misclassify.
To validate the WHtR approach, researchers examined U.S. data from the National Health and Nutrition Examination Survey (NHANES), involving over 3,300 adults. Those classified with WHtR excess fat had more than six times the odds of having type 2 diabetes compared to those with normal fat distribution. Even those with high fat—but not excess—had over twice the odds of prediabetes.
The findings suggest that WHtR could serve as a universal, low-cost, and more accurate method for identifying children and adults at risk for metabolic diseases.
BMI has long been criticized for failing to distinguish between fat and muscle mass, and for ignoring fat distribution — especially the abdominal fat most strongly linked to health risks. Yet it remains the default measure in schools, clinics, and public health guidelines.
This study adds to the growing consensus that it may be time to replace — or at least supplement — BMI with more sensitive and specific tools like WHtR.
“If we’re serious about tackling childhood obesity and preventing lifelong metabolic disease,” said Agbaje, “we need to start using the right tools.”
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