BMI may have misclassified millions of people, researchers find

Summarised from 4 outlets · Updated 11 Nov, 16:09 · Archive

Research suggests body mass index has wrongly classified over 2 million people in the UK alone.

A study led by King's College London, involving researchers from around the world, has found that body mass index alone misclassifies obesity in substantial numbers of people. The research suggests that in the UK, some 2.4 million people have dangerous levels of body fat that BMI fails to identify, whilst an estimated 1.3 million people classified as obese actually have no excess fat and no excess health risk.

The analysis included data from 844,108 adults across the UK, China, the US and Spain, with more than 430,000 from the UK Biobank study. The team tested an alternative approach that combines standard BMI with other measurements including waist-to-hip ratio and waist-to-height ratio, as well as organ function tests.

When these additional measurements were added to BMI assessments, the researchers found significant misclassification. Up to 8.6 per cent of people in the study had 'hidden obesity', classified as overweight by BMI alone but showing obesity-level body fat when other measurements were used. Meanwhile, up to 3.1 per cent were wrongly diagnosed as obese by BMI but showed no excess fat on closer examination.

Professor Francesco Rubino, chair of metabolic and bariatric surgery at King's College London, said BMI alone cannot determine whether someone is already ill or at risk of illness. The researchers argued that the 'uniform' BMI tool prevents 'personalised, proportionate care'. The new diagnostic approach was proposed by a Lancet Commission comprising more than 50 international experts in January 2025.

How it is being reported

• More than two million Brits have ‘hidden obesity’ due to problems with body mass index measureTwo thirds of Brits are officially overweight or obese but new study casts doubt on the body mass index (BMI) measure suggesting that may be all wrong, research saysThe Mirror · 11 Nov, 16:15
• BMI alternative for identifying obesity ‘could prevent misdiagnosis in millions’Combining body mass index with other measurements and tests would lead to better care and outcomes, experts say An alternative to BMI for diagnosing obesity could prevent misdiagnosis in millions of people worldwide, according to doctors who found it more accurately distinguished healthy people from those with harmful excess body fat. Medical experts have long considered body mass index a blunt instrument for defining obesity, leading to concerns that substantial numbers of people with excess body fat are missed while others who are healthy are wrongly diagnosed. Continue reading...The Guardian · 11 Nov, 16:00
• More than 1 million Brits 'wrongly classified as obese under flawed BMI'The framework both overestimates and underestimates how excess body fat affects health, researchers sayThe Independent · 11 Nov, 16:00
• Body mass index may have misclassified millions of people in UK, researchers sayMillions of people may have been misclassified on the body mass index (BMI) scale, research has suggested.Sky News · 11 Nov, 09:36

In this story: King's College London · Francesco Rubino · UK · China · United States · Spain · UK Biobank · Lancet Commission

This summary was written by AI from the headlines and standfirsts above, and states as fact only what at least two outlets report. How we use AI · Report a problem · Corrections log