It’s the start of another year and the body mass index (BMI) is being criticised again. This time a Lancet-commissioned group of experts is denouncing it as a diagnostic tool for obesity. They say that doctors should look at the overall health of a patient when diagnosing obesity, not just rely on this one flawed metric.
BMI is calculated by measuring a person’s mass in kilograms and then dividing that by the square of their height in metres. For recording and diagnostic purposes, anyone with a BMI below 18.5 is classified as “underweight”. The “normal weight” range extends from 18.5 to 24.5 and the “overweight” classification spans 24.5 to 30. “Obesity” is defined as having a BMI above 30.
Given the health implications related to a diagnosis of obesity, or even of being overweight, you might have assumed that the metric used to diagnose these conditions, the BMI, would have a strong theoretical and experimental basis. Sadly this is far from the truth.
