Devised almost 200 years ago, body mass index is used as a marker of health by many, yet called useless by others. What’s the truth?
If I were writing about 200 years ago, the title of this column would be Should I worry about my Quetelet Index?. That’s what BMI, the body mass index, was known as when the statistician and sociologist Adolphe Quetelet devised it in the 1830s. But Quetelet never intended the measure as a means of medical assessment. Two centuries later, plenty of experts will tell you that it doesn’t exactly work as advertised either. So is it time to throw it out altogether, or can it still tell us something useful about our health?
To get the basics out of the way, your BMI is simply your mass (in kilos) divided by the square of your height (in metres), expressed in the units kg/m2. According to the NHS, a calculation in the healthy weight range is between 18.5 and 24.9 – though this can differ slightly among ethnic groups. Obviously, this doesn’t work as well as a measure for children, old people or pregnant women, but where things get trickier is among groups with higher muscle mass and bone density, who can often be classed as “obese” or “overweight”, even when they are sporting a well-defined six pack.
