A new large-scale study published in Nature suggests that body mass index (BMI) is insufficient for diagnosing obesity and assessing health risks. An analysis of data from more than 800,000 people shows that a new approach, which considers waist circumference and excess fat distribution alongside body weight, predicts the risk of health complications much more accurately.
For years, clinicians have debated whether BMI, which is based on height and weight, is the best tool for classifying obesity. According to Katja Martins, a researcher at the University of Alabama, BMI does not reflect a person’s actual body composition. For example, a muscular person may have a high BMI despite having very little body fat.
Clinical and preclinical obesity
The new system, known as the Combined Anthropometric Definition of Obesity (CAD-obesity), uses waist circumference alongside standard measurements. It is well established that fat tissue accumulated in the abdominal area poses significantly greater health risks.
Under the new model, an individual with excess weight who has at least one of 18 specific medical conditions, including heart failure and sleep apnoea, is diagnosed with “clinical obesity”. This indicates that excess fat is already damaging tissues and organs. Patients who have excess body fat but retain normal organ function and have no associated diseases are classified as having “preclinical obesity”.
Diagnostic inaccuracies
The study’s authors, led by Professor Francesco Rubino of King’s College London, examined databases from the United States, the United Kingdom, Spain and China. An analysis of more than 50,000 deaths recorded during a 15-year follow-up period showed that the previous approach often provided a misleading picture.
Specifically, the CAD-obesity system identified 5–9% of patients who had high-risk obesity but were classified as merely “overweight” under standard BMI criteria. Conversely, 1–3% of patients diagnosed with obesity using the previous method showed no increased health risks under the new model.
The study confirmed that people classified as having obesity under the new definition had a 6–7% higher risk of mortality than individuals with normal weight. The risk was particularly high among those in the “clinical obesity” group.
As Francesco Rubino points out, obesity affects one billion people worldwide. Consequently, inaccuracies in BMI classification could prevent millions of patients from receiving appropriate treatment, including bariatric surgery, simply because their BMI does not meet the established threshold.
Despite the clear clinical advantages of the new model, some specialists have raised concerns about practical barriers. According to Jennifer Kuk, a researcher at York University in Toronto, measuring waist circumference during routine appointments may cause discomfort or stress for some patients. Therefore, it is important not to make the diagnostic process unnecessarily complicated. Nevertheless, the findings published in Nature clearly indicate that relying solely on the relationship between weight and height is no longer sufficient to assess patients’ actual physiological risks.
