Italian research to be presented at this year’s European Congress on Obesity (ECO 2026, Istanbul, Turkey, May 12-15) and published in a journal nutrients When the gold standard technique of dual-energy X-ray absorptiometry (DXA) is used to measure body fat in the general population, the traditional WHO body mass index (BMI) classification system has been shown to misidentify a significant number of people as overweight or obese.
Marwan El Gogh, a professor at the Department of Biomedical, Metabolic and Neurosciences at the University of Modena Reggio Emilia in Modena, Italy, explains that in recent years the BMI system has received a lot of criticism because it does not accurately capture body fat percentage and distribution, and therefore cannot correctly classify weight status based on obesity. Despite these concerns, BMI as a weight classification system continues to be used by the general public in primary care (i.e. general practitioners) and non-clinical (i.e. insurance and health insurance) settings, he added.
In this new study, Professor El Gogh and researchers from the University of Verona in Italy and the University of Beirut in Lebanon set out to determine the effectiveness of the BMI classification system, particularly in terms of its ability to accurately identify overweight and obese people, in a sample of the general population whose body fat was measured using DXA. DXA uses a person’s age and body fat percentage to determine weight status categories based on obesity level*.
The study included 1,351 mixed-sex adults (60% female) aged 18 to 98 years, all referred to the Department of Neuroscience, Biomedicine and Exercise Science at the University of Verona in Verona, Italy. All participants in this study were Caucasian (because BMI varies by ethnicity).
According to the WHO BMI system, 19 (1.4%) of these participants were underweight (BMI <18.5), 787 (58.3%) were normal weight (BMI 18.5-25), 354 (26.2%) were overweight (BMI 25-30), and 191 (14.1%) were obese (BMI ≥30). The overall prevalence of overweight and obesity combined was approximately 41%, consistent with the regional population of Veneto, Italy. Participants were then reclassified according to obesity degree based on body fat percentage (BF%) measured by DXA.
DXA revealed that more than a third (34%) of obese people defined by BMI were misclassified and should be placed in the overweight category. DXA showed that over half (53%) of people with BMI were misclassified as overweight. Three-quarters of the misclassified people were placed in the normal weight category, while the remaining one-quarter should have been classified as obese.
BMI and DXA agreed better when considering people with normal weight BMI (18.5–25), with DXA concordant in 78% of cases. However, 22% of normal-weight individuals were classified into a different category on DXA (9.7% underweight, 11.4% overweight, and 0.8% obese). Finally, the BMI-DXA discrepancy was greatest in the underweight group, although the absolute numbers were small. Two-thirds (13 of 19, 68.4%) of the underweight category (<18.5) defined by BMI were in the wrong category when analyzed by DXA. Originally, it should have been classified as normal weight.
Combining all correct and incorrect classifications, DXA analysis revealed an overall prevalence of overweight and obesity of approximately 37% for the entire cohort (23.4% overweight and 13.2% obesity, compared to 26.2% and 14.1% for BMI).
Professor El Gogh, who led the study, said: “Our main findings highlight the fact that relying on the traditional WHO BMI classification misclassifies a large proportion of the Italian general population, more than a third of adults, into the wrong weight status category. As a result, the prevalence of underweight, overweight and obesity is overestimated when compared to classification based on body fat percentage measured with the gold standard technique of dual-energy X-ray absorptiometry.” (DXA). ”
Another important finding of our study is that although both systems identify similar overall prevalence of overweight and obesity, in some cases we are talking about different populations. This means that individuals identified by DXA are not all the same as individuals by BMI classification. This is due to discrepancies between the WHO BMI and DXA-derived BF% classification systems in determining the weight status of the general population in weight ranges and age groups for men and women. ”
Professor Chiara Milanese, study co-author, University of Verona
Therefore, the authors conclude: “Italian public health guidelines need to be revised to take into account the combination of direct body composition or alternative measurements such as BMI with body circumference, such as measurements of subcutaneous fat or waist circumference (e.g. waist-to-height ratio), while assessing the weight status of the general population.” Misclassification is also expected to occur in white Caucasian populations in Europe and other countries around the world. However, to confirm this, and if similar effects exist in other ethnic groups, future research should extend the analysis to other countries in Europe and the world to see if such misclassification also occurs in people of other ethnicities. ”
sauce:
European Obesity Research Association
Reference magazines:
Milanese, C. Others. (2025). The WHO’s BMI system misclassifies the weight status of adults from the general population in Northern Italy: A DXA-based assessment study (18–98 years). nutrients. DOI: 10.3390/nu17132162. https://www.mdpi.com/2072-6643/17/13/2162
