Fifty eight researchers are challenging the way obesity is defined and diagnosed, calling for a more nuanced approach than measuring body mass index (BMI).

A new publication by the The Lancet Diabetes and Endocrinology Commission on Clinical Obesity proposes two categories: pre-clinical obesity, when a person has extra body fat but their organs work normally and clinical obesity when the excess fat harms the body’s organs and tissues.

The commission is calling for obesity to be diagnosed by direct measurements of body fat, along with waist size and other measurements, as well as using treatment plans based on solid evidence.

Because it is easy to measure and compare, BMI has long been used as a tool to diagnose obesity but it is a flawed measure as it doesn’t account for differences in body composition, such as muscle versus fat, which means a muscular athlete could be labelled obese.

The proposal is endorsed by the Royal College of Physicians. Special advisor on obesity, Dr Kath McCullough, says obesity needs a more clinically sound framework: “For too long we’ve relied on BMI as a simple measure of obesity, which has often misrepresented the condition and fails to full reflect how excess body fat impacts a person’s health.

“The commission’s distinction between pre-clinical and clincial obesity represents a vital step forward, highlighting the need to indentify and intervene early while providing appropriate care to those already experiencing severe health impacts.”