People being 'overdiagnosed' with obesity because BMI score not 'nuanced' enough, medics say

15 January 2025, 00:40

People are being "overdiagnosed" with obesity because the body mass index (BMI) is not "nuanced" enough, leading medics have warned.

A commission of more than 50 international experts said solely using BMI can lead to both overestimates and underestimates of the number of obese people.

For example, some people may be very active and their weight may cause no ill-effects but they are still classified as obese, while others may be suffering from significant harm because of obesity.

The Lancet commission said a "radical overhaul" is needed in the diagnosis of the condition.

They said: "BMI [is] useful but we need to go beyond BMI to determine excess body fat" and the measurement tool should be used only as a "surrogate measure of health risk", adding obesity should only be diagnosed using BMI when clinicians take other measurements such as waist to hip ratio or waist to height ratio.

The academics called for two new "diagnostic categories" of obesity:

• Clinical obesity, defined as a "chronic systematic illness" where excess fat can lead to organ damage and cause "life-altering and potentially life-threatening complications";
• Pre-clinical obesity, a "state of excess adiposity" where the person has a variable level of health risk but no ongoing illness.

They said there has been "polarised" debate about whether obesity should be classed as an illness and the new definitions should help provide some clarity.

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Professor Francesco Rubino, chair of the commission and of metabolic and bariatric surgery at King's College London, said: "No system - the NHS or others - have had these methods yet - I think everybody has been using the old classification for four decades, at least.

"But we are calling for a change, a radical change, because obviously, in the context of one billion people being classified as having obesity in the world today, and with a number that is projected to increase, no country is rich enough to be able to afford inaccuracy in the diagnosis of obesity."

He added: "The message remains that obesity can be a health risk. What we're proposing is to say that 'it's not only a health risk, for some it is actually an illness and that needs to be diagnosed'."