The widely used body mass index (BMI) system may incorrectly categorise a significant number of people as overweight or obese, according to new research.
BMI is a common method used to estimate body fat based on a person’s height and weight. NHS figures show that in 2024, around 30% of adults in England were classified as obese, while 66% were considered either overweight or obese.
However, researchers in Italy have questioned the accuracy of the measure after comparing BMI results with more detailed body composition scans that assess fat, muscle and bone.
BMI Accuracy Questioned By Body Composition Scan Findings
The study analysed 1,351 adults, initially categorised using BMI as follows: 19 underweight, 787 normal weight, 354 overweight and 191 obese.
Participants were then reassessed using dual-energy X-ray absorptiometry (DXA) scans, a more advanced method for measuring body composition.
Findings revealed notable discrepancies. More than a third (34%) of individuals classified as obese by BMI were found to belong in the overweight category when assessed using scans. Meanwhile, 53% of those labelled overweight were also misclassified.
Among this group, three-quarters were actually within a normal weight range based on scan results, while the remaining individuals fell into the obese category.
Experts Urge Combined Measures Beyond BMI
The research, conducted on adults referred to the Department of Neurosciences, Biomedicine and Movement Sciences at the University of Verona, highlights limitations in relying solely on BMI.
Despite BMI appearing relatively accurate for identifying normal weight individuals, researchers noted that “over a third of the general population was misclassified”.
They added that the current BMI classification “appears to inflate the prevalence of underweight, overweight and obesity among the general population”.
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Experts involved in the study recommend that healthcare professionals should not depend exclusively on BMI when assessing patients.
Instead, they suggest combining BMI with additional measures, such as body fat percentage calculations or waist circumference, particularly for individuals who fall within the normal BMI range. The findings were published in the journal Nutrients.
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