Moving beyond BMI in obesity diagnosis

For decades, BMI (body mass index) has been the gold standard for diagnosing obesity, a simple calculation of height and weight used to estimate excess body fat. But what if this long-standing measure is doing more harm than good?

According to a report published in The Lancet Diabetes and Endocrinology, doctors and researchers are calling for a radical overhaul of how obesity is diagnosed. They warn that BMI alone is an unreliable metric that may lead to widespread misdiagnosis, causing significant consequences for individuals and health systems globally.

More than 1 billion people are estimated to live with obesity. However, experts argue that BMI fails to capture the complexity of the condition. It doesn’t account for fat distribution, doesn’t measure actual fat levels, and, crucially, doesn’t reflect a person’s overall health. This can result in both under diagnosis, leaving health problems undetected, and over diagnosis, potentially leading to unnecessary treatments.

The commission of global experts has proposed a more nuanced approach. By incorporating additional measures, such as waist-to-hip and waist-to-height ratios, alongside clinical signs of ill health, they hope to redefine obesity diagnosis. These changes have been endorsed by over 75 medical organisations worldwide.

Central to the proposal is the introduction of two new categories, Clinical Obesity and Pre-Clinical Obesity.

Clinical Obesity is defined by excess body fat that impairs organ function or significantly affects daily activities. This is considered a chronic disease requiring medical intervention, such as weight-loss medications or surgery. Pre-Clinical Obesity refers to individuals with excess body fat who maintain normal organ function and overall health but are at higher risk of future health issues like type 2 diabetes or cardiovascular disease.

Professor Francesco Rubino, chair of the Lancet commission, explains: “Obesity is not a one-size-fits-all condition. This reframing allows us to deliver more personalised care, ensuring those who need urgent treatment receive it while supporting others in reducing future health risks.”

While the Royal College of Physicians has welcomed this shift, some voices caution against focusing solely on diagnostic methods.