NEWS FEATURE
11 October 2023

Why BMI is flawed — and how to redefine obesity

The main diagnostic test for obesity — the body mass index — accounts for only height and weight, leaving out a slew of factors that influence body fat and health.

McKenzie Prillaman

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BMI, which is calculated by dividing weight by height squared, has been used for several decades as an international standard to determine healthy weights. It serves as a proxy for body fat, and higher numbers can indicate increased risk for metabolic disease and death.

But BMI does not measure body fat, and it also ignores factors that affect how healthy someone is at a given weight, including age, sex and race. Not everyone with a high BMI has poor health or a raised risk of death1–3.

That’s why there is a small but growing movement to go beyond BMI when diagnosing and treating obesity, which the World Health Organization (WHO) recognizes as a chronic disease. In June, the American Medical Association (AMA) called for more weight-related metrics to be used in conjunction with BMI owing to its imperfections and questionable history.

But, with global rates of obesity having tripled over the past 50 years, and a wave of cutting-edge weight-loss drugs now hitting the market, a high BMI still reigns as the main criterion for obesity treatment. Specialists worry that the surging demand for the drugs will exacerbate reliance on BMI as a solo diagnostic tool.

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