Study Reveals BMI Misclassifies Weight Categories in Adults

A recent study conducted on a cohort of 1,351 white Caucasian adults in Italy has revealed significant inaccuracies in the Body Mass Index (BMI) as a tool for classifying weight categories. The research, led by Chiara Milanese from the University of Verona, utilized dual-energy X-ray absorptiometry (DXA) to measure actual body fat percentages, contrasting these findings with BMI classifications. The results indicated that BMI misclassified over one-third of participants, leading to an overestimation of the prevalence of underweight and overweight individuals.

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The study found that among those classified as obese by BMI, 34% were actually reclassified as overweight based on DXA measurements. Similarly, 53% of individuals labeled as overweight by BMI were found to have normal weight or obesity when assessed through DXA. The misclassification was particularly pronounced in the underweight category, where 68% were reclassified as having normal weight. Overall, the study highlighted that while BMI classified 41% of participants as overweight or obese, the DXA analysis indicated a combined prevalence of only 37%.

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The researchers emphasized the need for a revision of public health guidelines in Italy, advocating for the integration of direct body composition measurements, such as skinfold thickness or waist-to-height ratios, alongside BMI. They suggest that these additional metrics could provide a more accurate assessment of an individual's health status. The study's authors expressed concerns that similar misclassification issues may be prevalent in other regions, including Europe and the United States.

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In their conclusion, the researchers stated, “Public health guidelines in Italy need to be revised to consider combining direct body composition or their surrogate measures with BMI while assessing weight status in the general population.” They called for further studies to explore these discrepancies across diverse populations.

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While the study provides valuable insights, it is limited by its focus on a single ethnic group, which may restrict the applicability of its findings to other demographics. The authors acknowledged that the underweight group had a relatively small sample size, which could affect the robustness of the conclusions drawn.

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The findings of this study will be presented at the 33rd European Congress on Obesity in Istanbul, Turkey, from May 12-15, 2026. The researchers advocate for broader studies that include diverse populations to validate their findings and enhance the understanding of BMI's limitations in weight classification.

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• “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 relying on the traditional WHO BMI classification,” — Dr. Marwan El Ghoch, University of Modena and Reggio Emilia

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• “Public health guidelines in Italy need to be revised to consider combining direct body composition or their surrogate measures such as skinfold measurement or body circumference — such as the waist-to-height ratio —  with BMI while assessing weight status in the general population,” — Chiara Milanese, University of Verona

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