Obesity is typically assessed by measuring someone’s body mass index, but now researchers are calling for a more nuanced approach that could help with treatment
By Carissa Wong
14 January 2025
Measuring body fat more carefully could help treat obesity
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Rethinking the way we define obesity could help millions of people worldwide, argue a team of researchers who want to introduce a new category of “preclinical” obesity.
The current definition of obesity, as set by the World Health Organization (WHO), is having excess body fat that poses a risk to health. The WHO recommends that healthcare workers assess whether people have obesity by calculating their body mass index (BMI), a measure of weight relative to height. A BMI between 18.5 and 24.9 is considered healthy, while below or above indicates someone is under or overweight. A BMI above 30 indicates that someone is obese.
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It is true that high levels of body fat can cause it to infiltrate organs such as the liver and pancreas, impairing their function. It can also ramp up inflammation, raising the risk of conditions such as cancer, liver disease and heart problems.
But BMI poorly reflects a person’s body fat levels. “With BMI, we don’t know if that ‘excess’ weight is due to excess body fat or stronger muscle mass or bone mass,” says Francesco Rubino at King’s College London, who led the review on obesity.
Even when assessed correctly, through measurement of the waist or, more rarely, X-ray scans, body fat levels don’t fully dictate someone’s health. “No two people respond the same way to excess body fat. This is impacted by a person’s race and ethnicity, their age, what foods they eat, and genetics plays a tremendous role,” says Steven Heymsfield at Louisiana State University.