A new approach to diagnosing obesity provides a more accurate picture of who faces serious health risks, and who may benefit from treatment, than body mass index (BMI) alone, according to an international study published in Nature.
The research, led by King’s College London and involving 844,108 adults from China, Spain, the United Kingdom and the United States, validates a new diagnostic framework that distinguishes between clinical obesity, in which excess body fat impairs organ function or daily activities, and preclinical obesity, in which excess body fat poses health risks but organ function remains intact.
Robert H. Eckel, MD, of the division of endocrinology, metabolism, diabetes and cardiology at the University of Colorado Anschutz, was one of two U.S.-based researchers involved in the international study.
The findings highlight limitations of relying on BMI alone to diagnose obesity. By incorporating additional measurements, including waist circumference and waist-to-height ratio, researchers found that BMI alone both overestimated and underestimated obesity across all four study populations. The combined approach identified obesity in an additional 3.3% to 7.4% of participants, depending on the population.
Importantly, the researchers found that the new classification better distinguished differences in health outcomes. Over 10 years, clinical obesity was associated with a substantially higher risk of death, while preclinical obesity carried only a modest increase in risk. Between 77% and 91% of people classified as having preclinical obesity did not progress to clinical obesity over a decade.
“These findings reinforce that obesity is not a one-size-fits-all diagnosis,” said Eckel. “BMI can be a useful starting point, but it doesn't tell us enough about whether body fat is increased, where it is distributed or whether it is affecting a person's health. Looking at additional measures alongside organ function gives clinicians a more complete picture of an individual's health and potential risks.”
The researchers say the findings support broader adoption of the diagnostic framework proposed by a 2025 Lancet Diabetes & Endocrinology Commission, which aims to move obesity diagnosis beyond a single measurement and toward a more individualized understanding of disease.
“An important takeaway is that we need to distinguish between having excess body fat and having an active disease attributed to excess body fat that is already affecting the body,” said Eckel. “That distinction can help guide more appropriate prevention and treatment strategies, rather than assuming everyone with the same BMI has the same health risks.”
In addition to CU Anschutz, participating institutions included Huazhong University of Science and Technology, North China University of Science and Technology, Pennington Biomedical Research Center at Louisiana State University, the University of Girona and Università Cattolica del Sacro Cuore.
Key Points:
- BMI alone is insufficient. Additional measurements provide a more accurate picture of obesity and health risks.
- Obesity isn't one-size-fits-all. The study distinguishes between clinical and preclinical obesity.
- The distinction matters. Clinical obesity carries a substantially higher risk of death than preclinical obesity.
- Progression isn't inevitable. 77%–91% of people with preclinical obesity did not develop clinical obesity over 10 years.
- CU Anschutz played a role in the international research. Robert H. Eckel, MD, was one of only two U.S.-based researchers involved in the study of more than 844,000 adults.