BMI: The great red herring for heart health

Body mass index (BMI) is a clumsy and imprecise measure of obesity.  It’s arrived at through a complicated computation, which involves dividing your weight by your height, and the result is a number.  If you’re slightly over the ‘ideal’ number for your weight and height, you’re overweight.  If you’re way over, you’re obese.

Despite its imperfections, the BMI remains the standard by which we assess obesity in our weight-obsessed times.  After all, obese people will die younger and are much more likely to suffer from heart conditions, or so we’re told.

But that’s not what researchers found when they analysed 40 studies that involved more than 250,000 people.  When they looked at the figures, researchers found that obese people, as defined by the BMI, had far fewer cardiovascular problems or were living longer than their leaner counterparts.

In fact, it was only the people at the far end of the BMI spectrums who had health problems.  Only those who were underweight or seriously obese, according to the BMI measure, were more likely to suffer a heart condition.
So what’s gone wrong?  According to the researchers, it’s the BMI measure itself.  It doesn’t differentiate between fat and lean mass, and so fit people with muscles would be classified as overweight according to the BMI.

(Source: Lancet, 2006; 368: 666-78).


E-news broadcast 31 August 2006 No.288 [Subscribe]