Medical experts are calling for a shift away from using body mass index as the sole metric for diagnosing obesity. A new approach that combines BMI with additional body measurements and organ function tests could prevent misdiagnosis in millions of people, according to a study published in Nature.
Body mass index has long been criticized as a blunt instrument. It calculates weight relative to height but does not account for where fat is stored or how it affects internal organs. This limitation leads to significant errors, with the new analysis suggesting that BMI alone misses obesity in 5 to 9 percent of adults and wrongly diagnoses the condition in up to 3 percent.
Combining Metrics for Accuracy
The proposed method addresses these gaps by adding waist circumference and waist-to-height ratio to the standard BMI calculation. Under this framework, a person with a BMI over 40 is automatically classified as obese. However, individuals with a lower BMI must be evaluated using waist measurements to determine if they carry harmful excess body fat.
A BMI of 30 or higher combined with a raised waist measurement counts as obesity. Similarly, a BMI between 25 and 29.9 is considered obese if the waist measurement and waist-to-height ratio are high. In most countries, a raised waist measurement is defined as more than 102 centimeters for men and 88 centimeters for women. The threshold for a high waist-to-height ratio is approximately 0.57.
Researchers analyzed health records from more than 800,000 people in the United Kingdom, the United States, China, and Spain. They tracked the health outcomes of these participants for up to 15 years to validate the new diagnostic criteria.
Distinguishing Clinical from Pre-Clinical Obesity
A critical component of the new system is the distinction between clinical obesity and pre-clinical obesity. Clinical obesity indicates an active disease state where excess body fat is already impairing organ function. Pre-clinical obesity identifies individuals who carry excess fat and face health risks, but whose organs are not yet damaged.
This distinction allows doctors to tailor interventions more effectively. The study found that only a quarter to a third of people classified as obese under the new definition had clinical obesity. This group represents 5 to 10 percent of the wider population and carries a substantially higher risk of death.
Conversely, 80 to 90 percent of people with pre-clinical obesity did not progress to clinical obesity or active disease within the next 10 years. The data also showed that some individuals with a high BMI were not obese under the new definition and actually had a lower mortality risk than others considered healthy by traditional standards.
Francisco Rubino, a professor of metabolic and bariatric surgery at King’s College London, emphasized the scale of the problem. He noted that misclassification can account for tens of millions of people, making the inaccuracy of BMI a major issue for both public health and individual care.
The new approach allows clinicians to differentiate between healthy individuals and those who are sick despite having the same BMI. For example, three people with a BMI of 32 could receive very different diagnoses. One might have no excess body fat and be healthy. Another could have excess fat but no organ dysfunction, resulting in a pre-clinical obesity diagnosis. The third might have excess fat and organ dysfunction, leading to a clinical obesity diagnosis.
Rubino stated that while the process is more complex for clinicians, it ensures better healthcare outcomes. He argued that diagnosing obesity at the individual level allows for optimized interventions, whether that involves lifestyle advice, GLP-1 weight loss drugs, or surgery. He confirmed that he believes this method should be employed in clinical settings to improve safety and efficacy.
Source: The Guardian
