A new study from Italian researchers challenges the reliability of Body Mass Index as a tool for assessing body weight and health. The findings, to be presented at the European Congress on Obesity 2026 and published in Nutrients, show that BMI may incorrectly classify more than one-third of adults when compared with more precise body fat measurements.
BMI, widely used in clinical and public health settings, estimates weight status based on height and weight but does not directly measure body fat or its distribution. This limitation has raised concerns about its accuracy.
To investigate further, researchers compared BMI classifications with results from Dual-energy X-ray absorptiometry, considered the gold standard for measuring body fat percentage.
The study analyzed 1,351 adults aged 18 to 98. Based on BMI, about 41% were categorized as overweight or obese. However, DXA-based assessments showed a lower prevalence of 37%, revealing significant discrepancies.
Among those labeled obese by BMI, 34% were actually overweight according to DXA. Misclassification was even higher in the overweight category, where 53% were placed incorrectly, many of whom were found to have normal body fat levels.
Even individuals considered “normal weight” were not always accurately classified. While BMI and DXA agreed in 78% of such cases, 22% were reassigned to different categories when body fat was directly measured.
The greatest mismatch occurred in the underweight group, where more than two-thirds were reclassified as normal weight using DXA.
These findings suggest that BMI may overestimate both obesity and underweight prevalence, potentially leading to misleading health assessments. Experts recommend combining BMI with additional tools such as waist-to-height ratio, skinfold measurements, or direct body composition analysis for a more accurate evaluation.
Overall, the study highlights the need to update current guidelines and adopt more comprehensive approaches to assessing body health.
REFERENCE: Chiara Milanese, Leila Itani, Valentina Cavedon, Marwan El Ghoch. The WHO BMI System Misclassifies Weight Status in Adults from the General Population in North Italy: A DXA-Based Assessment Study (18–98 Years). Nutrients, 2025; 17 (13): 2162 DOI: 10.3390/nu17132162
Researchers Warn BMI Fails to Accurately Assess Health in Many Adults
