Your Body Mass Index (BMI) can help you to work out your weight loss wellbeing, as it tells you whether you are ‘normal’, ‘underweight’, ‘overweight’ or ‘obese’ for your size. However, mathematician Nick Trefethen, Professor of Numerical Analysis at Oxford University, believes that the way BMI is calculated is wrong, and has proposed a new method.
Adolphe Quetelet devised the BMI methods over 150 years ago, which consists of taking your weight (in kilograms) and dividing it by your height squared (in metres), yet according to Trefethen, people have put too much trust in it in part because it looks so precise. Einstein’s E=MC2 is ‘an equation of physics and it’s really right, says Trefethen. ‘The BMI formula looks similar. It seems to have the same character but it doesn’t reflect a precise truth about our world, it’s an approximation to a very complicated reality.’
Therefore, the mathematician proposes that, instead, BMI should be worked out via: 1.3 x weight, divided by height to the power 2.5. However, Trefethen admits that he doesn’t have a medical background and that his work isn’t based on real life observations of people’s weight and height, and according to Tim Cole, Professor of Medical Statistics at University College London, this new equation is just one of many that has questioned the equation, and he’s not convinced it will change anything.
Cole says, ‘I think he’s aware of the deficiencies of BMI but I don’t think his index goes anywhere to addressing those shortcomings. BMI is an imperfect index and you can tinker about with the power of height as much as you like but [the equation] shouldn’t be expected to do what it can’t do which is to measure fatness, because it doesn’t include fatness.’
He adds that though BMI is useful to apply to populations, when it comes to fat and wellness ‘BMI can’t do better than make a guess as to how much fat there is. If your weight is excessive then the implication is that the excess is fat and, of course, people’s body composition varies enormously and BMI doesn’t know anything about that so it’s a very imprecise index when applied to individuals.’
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