The bunkum of Body Mass Index

The claim that we face an epidemic of obesity is based on the changing distribution of body mass index (BMI) in society. BMI is a fairly crude way of assessing fatness first proposed by a Belgian mathematician, Adolphe Quetelet, in 1832. It is defined as a person’s weight in kilograms divided by their height in metres, squared (kg/m2). As a recent piece in Slate magazine notes, BMI only gained popularity after the well-known American researcher, Ancel Keys, proposed it as the best way of quickly assessing fatness in an article in 1972.   The other major development was the establishment of cut-off points for weight and health, based on BMI, by the US National Institutes for Health (NIH) in 1985. Now BMI had the force of official backing. As a means of giving health authorities a rough idea of how our bodies are changing, BMI is crude but has the merit of simplicity. However, when applied to individuals, it has the potential to be downright distorting. Firstly, it makes no distinction between fat and muscle mass. Secondly, it is blind to where fat is stored on the body, which some researchers and doctors believe may be crucial to whether it is a health problem or not. Thirdly, it gives a pseudo-scientific precision to the notion that carrying a bit of extra weight is going to kill you.   BMI is actually a poor indicator of future health prospects. There is little difference in mortality rates between people who are of ‘normal’ weight (BMIs of 20-25), ‘overweight’ (BMIs greater than 25 but under 30) and ‘obese’ (greater than 30 but less than 40). Only those who are ‘morbidly obese’ (BMI over 40) and those who are underweight (BMI below 18) have markedly worse health outcomes than those in the middle. Yet on this shaky foundation, a whole industry of weight-watching, health-obsessing, parent-berating government intervention has been built.   Full article at Spiked Online   http://twitter.com/spikedonline

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