A new definition of obesity could help treat millions of people

Rethinking the way we define obesity could have a significant impact on global health, according to a group of researchers proposing the introduction of a new category called “preclinical” obesity.

The current definition of obesity, as outlined by the World Health Organization (WHO), is based on excess body fat that poses a health risk. The standard method for assessing obesity is by calculating the body mass index (BMI), which compares weight to height. A BMI of 18.5 to 24.9 is considered healthy, while values below or above this range indicate underweight or overweight. A BMI above 30 signifies obesity.

While high levels of body fat can lead to health issues such as organ dysfunction and inflammation, BMI is not always an accurate reflection of body fat levels. According to Francesco Rubino from King’s College London, BMI does not differentiate between excess body fat, muscle mass, or bone mass.

Even when body fat levels are measured directly through waist circumference or X-rays, the relationship between body fat and health is complex and varies among individuals based on factors like race, age, diet, and genetics, explains Steven Heymsfield from Louisiana State University.

Proposed by Rubino and his team, the new classification of obesity would distinguish between preclinical and clinical forms. Both categories would involve excess body fat, but only clinical obesity would present symptoms related to excess fat, such as heart issues or breathing difficulties. Preclinical obesity, on the other hand, would indicate a higher risk of developing such symptoms in the future.

This approach is similar to prediabetes, where blood sugar levels are elevated but not high enough for a diabetes diagnosis, Rubino points out.

Under the proposed changes, healthcare professionals would assess body fat levels directly using waist measurements or X-rays in addition to BMI calculations. Blood tests would be used to evaluate organ health and symptoms experienced by individuals. While blood tests are already a standard practice, direct body fat measurements may increase workload for clinicians, notes Heymsfield.

If widely adopted, the new classifications could lead to more personalized advice and treatment for individuals with obesity. Those with preclinical obesity may benefit from lifestyle changes and monitoring, while clinical obesity may require medical interventions such as medication or surgery, Rubino suggests.

“It would enable us to better allocate resources and provide appropriate care to individuals,” says Adrian Brown from University College London.

Laura Gray from the University of Sheffield supports the proposed revisions, emphasizing the need for aligning clinical guidelines with current research findings. “Not everyone classified as obese by BMI is unwell, and conversely, not everyone with a lower BMI is healthy,” Gray adds.

By endorsing the updated definitions, which have gained support from 76 health organizations globally, there is potential to reduce the stigma associated with obesity. “The goal is to redefine obesity as a disease in its own right, highlighting the various risk factors beyond just behavior and emphasizing the role of genetics, environment, and psychology,” Gray concludes.