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Monday 26th August 2019

Mathematician finds flaw in BMI

21st January 2013

An Oxford mathematician has come up with a new way of calculating a person's body mass index which means shorter people may be overweight without realising it.


Professor Nick Trefethen said he believed the current BMI system was not accurate and he had created his own using a new formula which takes into account a person's height.

The traditional way of calculating BMI is to divide a person's weight in kilos by their height in metres squared. 

A normal BMI result is between 18.5 and 24.9, an overweight result is between 25 and 29.9, an obese result is 30 or over and an underweight result is below 18.5.

Professor Trefethen's new formula multiplies a person's weight in kilos by 1.3 and divides the result by their height in metres to the power of 2.5.

Using the new formula, a person who was 1.83m (6 feet) would drop a point from their current BMI reading, while someone who was 1.52m (5 feet) would add a point. 

Professor Trefethen said the health service should explain why they use the traditional formula.

He said: "The NHS relies on the BMI pervasively in all of its public discussions of obesity. We deserve an explanation of what justification they have for using this formula."


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