One of the subtler sleights of hand used by obesity crusaders is to talk about obesity while using figures that refer to people who are obese or overweight. Health reporters do it all the time and subeditors frequently put the word ‘obesity’ in the headline when the story is actually about people who are overweight (see here and here, to pick two examples at random).
Since there are more overweight people than there are obese people, the effect — and probably the intention — of this blurring of the lines is to inflate the number of supposed victims of the obesity ‘epidemic’. A quarter of Britons are obese, but if you add in people who are merely overweight this rises to 60 per cent.
If overweight people are part of an ‘epidemic’, what are their health risks? The answer, it seems, is not very much. A study published this week in the Journal of the American Medical Association looked at health outcomes among a group of Danes and found that the lowest rates of both cardiovascular mortality and overall mortality were among those who were overweight. In earlier cohorts, the longest living Danes had been those with a BMI at the upper end of the ‘healthy weight’ category (18.5 to 25), but for the 21st-century cohort, the optimal BMI was 27.
If this was just one study it could be treated with scepticism, but it is actually the tip of a substantial iceberg of research showing the same thing. A meta-analysis published in the same journal in 2013 looked at 97 studies with a total sample size of nearly three million people and concluded that ‘overweight was associated with significantly lower all-cause mortality’. It didn’t put a figure on the healthiest BMI, but since overweight begins at 25, it was clearly more than that.
Some ‘public health’ campaigners hated the findings of the 2013 meta-analysis. The researchers were accused of ‘sending the wrong message’ and the study sparked a debate about whether it was ever acceptable to lie to the public for their own good. Sending the right message and telling the truth are not always compatible in this politically charged corner of academia.
And yet the facts speak for themselves: being overweight is associated with the lowest rates of mortality. In the 2013 study, even those who were mildly obese did not have a higher mortality risk than those who were of ‘healthy weight’.
None of this should be particularly surprising. Body mass index is nothing more than a person’s weight divided by the square of their height. There was never any reason to think that health outcomes would be dictated by a crude mathematical formula based on the metric system.
The Danish study found that people with a BMI of 27 had the lowest rate of mortality. By coincidence, ‘overweight’ used to be defined as a BMI of 27 or more, but in an early act of problem inflation this was reduced to 25 in the 1980s. Naturally, this shifting of the goalposts led to a rise in the number of people who were overweight and since those who have a BMI between 18.5 and 25 are officially defined as having a ‘healthy weight’ there is a clear implication that anything over 25 is unhealthy.
But that is not what the evidence says. The classifications of ‘overweight’ and ‘obese’ have never been based on empirical data about health outcomes. The figures of 25 and 30 seem to have been picked for no other reason than that there are round numbers. And although obesity is an undoubted risk factor for several serious diseases, overweight remains more of an issue of aesthetics than health.