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.
The new approach, which combines BMI with other body measurements and organ function tests, suggests BMI alone misses obesity in 5-9% of adults, while wrongly diagnosing the condition in as many as 3%.
“This misclassification can account for tens of millions of people, so the inaccuracy of BMI is a big problem at scale and also for individuals,” said Francisco Rubino, a professor of metabolic and bariatric surgery at King’s College London.
Under the new definition, someone with a BMI over 40 is considered obese, but doctors check people with a lower BMI for excess body fat by looking at their waist measurement.
A BMI of 30-plus with a raised waist measurement or waist-to-height ratio counts as obese, as does a BMI from 25 to 29.9 if waist measurement and waist-to-height ratio are high. In most countries, a raised waist measurement means more than 102cm (40in) for men and 88cm for women, while thresholds for a high waist-to-height ratio are about 0.57.
In a second step of the diagnosis, doctors distinguish between clinical obesity, meaning an active disease where excess body fat is already impairing organ function, and pre-clinical obesity, where the extra fat is a health risk but has yet to cause problems.
Source: The Guardian, 11 November 2026
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