A new study led by Professor Marwan El Ghoch of the University of Modena and Reggio Emilia reports on Mar. 27 that the World Health Organization's body mass index (BMI) classification system misidentifies a significant number of people as overweight or obese when compared to measurements using dual-energy X-ray absorptiometry (DXA). The findings will be presented at the European Congress on Obesity in May and published in the journal Nutrients.
The study highlights ongoing concerns about BMI’s accuracy, which is widely used in healthcare and policy settings despite criticism for not capturing true body fat percentage or distribution. Accurate identification of weight status is important for public health guidance, clinical care, and insurance policies.
Researchers from Italy and Lebanon analyzed data from 1,351 adults aged 18 to 98 years who had their body fat measured by DXA at the University of Verona. All participants were White Caucasian. According to BMI classifications, about 41% were categorized as overweight or obese—a figure consistent with local population estimates. However, DXA-based analysis showed that more than one third (34%) classified as obese by BMI should have been labeled overweight instead. Among those labeled overweight by BMI, over half (53%) were misclassified; most should have been considered normal weight according to DXA results.
Professor El Ghoch said: "Our main finding highlights the fact that a large proportion of individuals, exceeding one-third of adults among the Italian general population, is misclassified and placed in an incorrect weight status category, when relying on the traditional WHO BMI classification resulting in an overestimation of the prevalence of underweight, overweight, and obesity when compared to the classification based on body fat percentage as measured by the gold standard technique of dual-energy X-ray absorptiometry (DXA)."
Study co-author Professor Chiara Milanese noted: "Another key finding of our study is that, even though both systems identify a similar overall prevalence of overweight and obesity, we are talking in some cases about different people - or in other words the individuals identified by DXA are not all the same as those from BMI classification. This is due to the disagreement between WHO BMI and DXA-derived BF% classification systems in determining weight status in the general population among body weight ranges and age groups of both genders."
The authors conclude that public health guidelines should consider combining direct measures such as skinfold measurement or waist-to-height ratio with BMI for better assessment accuracy. They also call for further research across different countries and ethnicities to determine if similar patterns exist elsewhere.
