The formula used to calculate body mass index (BMI) has erroneously made tall people seem fatter than they are and shorter people seem thinner, according to mathematicians who say that it didn't take into account that a person's weight grows with their height. So an Oxford mathematician has come up with a new formula that he says more accurately determines whether a person is overweight or obese.

BMI—which doctors use to gauge patients' risk for heart disease, high blood pressure, and other ailments—has traditionally been calculated by dividing a person's weight by his or her height squared. A score between 18.5 and 25 is considered average weight. Anything lower is underweight, and higher is overweight, with scores over 30 considered obese. Under the new formula, developed by Professor Nick Trefethen, the weight is multiplied by 1.3, and then divided by the height to the power of 2.5 instead of squared. However, like the old formula, the new formula fails to distinguish between muscle and fat, meaning that athletes or people who weight train could have a BMI that indicates that they are overweight, when they are perfectly healthy.

Essentially, this new formula means that taller people lose a BMI point, while shorter people gain a BMI point. People of average height have no change. So what does this mean for you? Well, if you're under 5 ft. 7, some math nerd might consider you to be overweight.


Image via SAJE/Shutterstock

Short people 'fatter than they think' under new BMI [Telegraph]