Christopher Snowdon

Obesity isn’t a ‘disease’, whatever the American Medical Association may think

Obesity isn't a 'disease', whatever the American Medical Association may think
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This week, The Guardian informed us, a study revealed the ‘scale of the British public’s denial about weight problems’. Data collected by the Association for the Study of Obesity found that ‘more than a fifth of Britons who think their size is healthy or normal were in fact overweight’. This apparent delusion has been attributed to the normalisation of obesity in modern society. ‘We’ve almost become accustomed to people being bigger',  Prof David Kerrigan told The Guardian, ‘because they don’t stand out.’

Dare we offer an alternative explanation for why a minority of overweight people see themselves as normal and healthy? Could it be that they are normal and healthy?

In terms of health, there is a great deal of evidence showing that overweight (but not obese) people live as long as ‘normal’ people and possibly slightly longer. In terms of normality, if most people are overweight then being overweight is normal by definition, but that is not what the Association for the Study of Obesity means. They use the body mass index (BMI) measure, which is all well and good so long as you treat it as a rule of thumb rather than a law of nature. Alas, they do the latter.

BMI, which was invented in the 1840s, is calculated by dividing a person’s height by their weight. That’s it. The science starts and ends there. The number that results is then classified as ‘underweight’, ‘overweight’ or ‘obese’. Any BMI between 25 and 30 is currently classified as ‘overweight’, but this has never been more than a rough approximation and these cut offs have been selected largely because they are round numbers. I have no problem with the metric system but it would be truly remarkable if human beings evolved in such a way to make health risks kick in when their height in centimetres divided by their weight in kilograms exceeded exactly 25.

The flaws of BMI are well known are well known. It is a simplistic two-dimensional formula which takes no account of body shape and is guaranteed to deliver false positives (and, indeed, false negatives). It is not a great measure of health at the best of times and as a measure of corpulence it is particularly unreliable for people who are short, tall, shrivelled, athletic, muscular or still growing (the latter explains why so many parents receive letters from school telling them that their perfectly healthy children are borderline obese).

A more useful measure is fat as a percentage of body weight, but measuring that requires more money and effort so BMI is used instead. BMI is far from useless, particularly at the higher readings, but it cannot be assumed that everybody who denies that they are overweight despite having a BMI of 26 is deluded. If you saw them in their bathing suit you might even agree with them, and even the medical profession would have agreed with them until the 1990s when the threshold for ‘overweight’ was dropped from 27 to 25.

It is churlish to complain too much about BMI. It’s a measure that serves a purpose. Whilst any definition of ‘overweight’ is bound to be somewhat arbitrary, it has to be defined somehow. Nevertheless, a little humility would not go amiss when obesity researchers use crude mathematical formulae to answer subjective questions.

And the question of whether somebody is overweight is a subjective one. The dictionary defines overweight as ‘above a weight considered normal or desirable’. By whom? Surely the individual should have some say in the matter.

This lack of humility on the part of these particular researchers morphs into something approaching arrogance in the study itself, such as it is (it remains unpublished by any journal and is more a series of infographics than a study).

The authors note with dismay that ‘only’ 18 per cent of Britons ‘recognised obesity as a disease’. Good for them. It isn’t a disease. It’s a risk factor for disease, it might even be a condition, but a disease in itself? The authors note that the American Medical Association voted last year to classify obesity as a disease, but expert opinion remains divided.

It is the kind of thing about which reasonable, well-informed people can disagree, in the same way that reasonable, well-informed people in the 1960s could disagree with the ‘scientific fact’ that homosexuality is a mental disorder, despite the American Psychiatric Association classifying it as such until 1973. Are 82 per cent of Britons ignorant and ill-informed just because a trade union in a different continent recently decided to change a definition? Apparently so. The authors lament that ‘obesity as a disease is not widely recognised’.

The authors even complain that ‘obesity is not recognised as being as dangerous as smoking’. Once again the word ‘recognised’ signals that the debate is over and the science has spoken. But has it? It’s a contentious claim and the anti-smoking lobby, for one, would take issue with it.

Even if it were a verifiable fact, it seems unfair to berate the great unwashed for not ‘recognising’ it when we are repeatedly told that ‘smoking harms nearly every organ of the body’, that ‘stopping smoking is the single, most important thing you can do to improve your health’ and that tobacco smoke is so deadly that the mere whiff of it on someone’s clothes could strike us dead.

A newspaper-reading public that is assaulted on a near-daily basis with such claims as ‘sitting is the new smoking’, ‘loneliness is more dangerous than obesity’ and ‘sugar is the new tobacco’ may feel inclined to ignore the experts altogether and get on with their lives. In doing so, they display more wisdom than researchers who despair at the public’s ‘denial’ of their bald assertions.