Redefining Obesity: The Push to Move Beyond BMI

Body mass index (BMI) has been the primary tool for diagnosing obesity, with a BMI of 25 to less than 30 classified as overweight and a BMI of 30 or higher indicating obesity. However, the American Medical Association recently advised against relying solely on BMI, citing data that it often fails to accurately reflect actual body fat. Clinicians now face a choice: continue using BMI or adopt new frameworks that consider fat distribution and organ dysfunction.

Brian Lee, a hepatologist at Keck Medicine of USC, notes that while clinicians understand BMI's limitations, it remains prevalent due to its ease of calculation. The main obstacle to adopting new frameworks is time, as waist circumference and waist-to-height ratio require manual measurement.

A global commission proposed a more nuanced approach in 2023, suggesting that clinicians verify obesity status using additional measures like waist circumference, waist-to-hip ratio, or direct fat mass assessment. These methods could lead to a significant reclassification of patients. For instance, a study found that 26.1% of adults with a normal BMI would be diagnosed with clinical obesity under these guidelines, and 50.3% of those in the overweight category would qualify.

The European Association for the Study of Obesity also endorsed a similar framework, combining BMI, waist-to-height ratio, and clinical comorbidities. While these new approaches aim to link obesity diagnosis to actual health consequences, they also pose challenges. The expanded label of obesity could lead to delays in care, and waist measurements are more variable than height and weight.

Insurance coverage for obesity treatment may also be affected, as eligibility could drop by nearly 20% if only the clinical obesity definition is considered.

Despite these challenges, the goal is not to discard BMI, which remains useful and cost-free. Instead, the aim is to supplement it with additional measures to ensure that patients with obesity-related organ dysfunction receive the care they need, even if they don't meet traditional BMI thresholds.