An Italian research team comparing standard BMI categories with dual-energy X-ray absorptiometry (DXA) body-fat measurements found that more than one-third of adults were placed in the wrong weight category, and that BMI slightly overestimated the combined prevalence of overweight and obesity in the sample.
A study led by Professor Marwan El Ghoch of the University of Modena and Reggio Emilia found that body mass index (BMI) frequently misclassified adults’ weight status when compared with body fat percentage measured by dual-energy X-ray absorptiometry (DXA), a technique widely regarded as a gold-standard tool for assessing body composition.
Researchers examined 1,351 White Caucasian adults aged 18 to 98 years, about 60% of whom were women. All participants had been referred to the Department of Neurosciences, Biomedicine and Movement Sciences at the University of Verona in Italy.
Using World Health Organization (WHO) BMI cutoffs, 1.4% of participants were categorized as underweight (BMI 30). That equated to a combined overweight-and-obesity prevalence of about 41%, which the researchers said was consistent with available data from Italy’s Veneto region.
When the same participants were reclassified using DXA-derived body fat percentage, the combined prevalence of overweight and obesity was about 37% (23.4% overweight and 13.2% obesity), compared with 41% under BMI.
The study reported substantial category-level disagreement between the two methods. Among people labeled obese by BMI, 34% were categorized as overweight based on DXA. Among those labeled overweight by BMI, 53% were placed in a different category using DXA; of those misclassified, about three-quarters fell into the normal-weight range and the remaining quarter met criteria for obesity.
Agreement was stronger in the normal-weight BMI range, with BMI and DXA aligning in 78% of cases, according to the researchers. The underweight BMI group showed the largest mismatch: 13 of 19 people (68.4%) categorized as underweight by BMI were reassigned to normal weight based on DXA.
“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,” El Ghoch said in a statement distributed by the European Association for the Study of Obesity.
Co-author Professor Chiara Milanese of the University of Verona said that even when BMI and DXA produce a similar overall prevalence of overweight and obesity, they do not necessarily identify the same individuals. “Even though both systems identify a similar overall prevalence of overweight and obesity, we are talking in some cases about different people,” she said.
The findings are due to be presented at the European Congress on Obesity (ECO 2026), scheduled for May 12–15 in Istanbul, Turkey, and are published in the journal Nutrients. The researchers argued that BMI-based public health assessments could be improved by incorporating additional measures of body composition or simpler proxies such as skinfold measurements or waist-to-height ratio, and they suggested similar misclassification patterns may occur in other White Caucasian populations beyond Italy.
