Can We Rely On BMI?

For Years, It's Been the Official Way of Calculating a Healthy Body Weight, but Is It Actually Less Accurate Than They Claim?

- Natalia Lubomirski

Whatever your body shape or size, chances are you’ve heard of the most popular way to monitor it: body mass index (or BMI). This calculation – which divides a person’s weight in kilograms by the square of their height in metres – has been used for decades to track weight and health. But can we trust this 180-year-old equation to accurately calculate fat levels and keep us healthy?

»The fat formula

With obesity rates rising, keeping track of our population’s health is more important than ever.

BMI has been popular with medical professionals and the general public since mathematician Adolphe Quetelet created the clever formula in the 1840s. His calculation uses two simple body measurements to estimate body-fat content. The results then determine which of the four categories we fit into: underweight (readings under 18.5), normal weight (18.5–24.9), overweight (25–29.9) and obese (30+). “It’s used as a rough measure to help decide if a patient’s weight is healthy,” says GP Dr Jeff Foster. “We regularly use it in monitoring chronic diseases, such as diabetes or heart disease.”

»Can we rely on it?