William Skidelsky learns that Brad Pitt is fat

Did you know that Brad Pitt is overweight, and George Clooney obese?

As if the wars on terror, drugs, crime and Iraq weren't enough to be getting on with, it seems that there is a new demon in our midst. According to a report by a committee of MPs, Britain is in the grip of an obesity crisis. The figures appear to speak for themselves: more than 50 per cent of UK adults are overweight and, of those, 22 per cent are obese.

Without wishing to deny that British people are getting larger, I very much doubt that the problem is as severe as it sounds. Increasingly, our politicians seem to be going in for the American tactic of presenting complex, many-sided issues as potentially overwhelming threats. Whenever those responsible for public policy adopt a bunker mentality, it is worth asking who the beneficiaries are. In the case of obesity, they include the government, which can present itself as acting quickly to counter a potent new danger, and the diet industry, which must be rubbing its hands at the prospect of vastly increased sales.

Most people accept the obesity figures unquestioningly, without pausing to consider how they were arrived at. Yet the method by which obesity is measured - the body mass index (BMI) - has changed during the past few years. As several commentators have pointed out, the new method classes Brad Pitt as overweight and George Clooney as obese.

Not least among the repercussions of all this are the implications for language. The word "obese" used to denote someone who was not merely overweight, but disgustingly so. As the category of obesity has expanded, the word has retained this strongly negative connotation As a result, people who once would have been considered merely "plump" or "large" are increasingly looked on with the disgust that the word "obese" implies.

Another side of this process is an increased tendency to treat obesity as if it were an illness, rather than a relationship between body weight and height. Being overweight is associated with increased incidence of various illnesses, but this in no way means that obesity is itself an illness. In any case, it is not clear whether fatness is the real risk factor, or the things that tend to go with it (such as lack of fitness). There is plenty of evidence to suggest that being fat is not dangerous if you are fit.

The current obesity "crisis" is just the latest stage in our culture's demonisation of fatness. We expect everyone to conform to an ideal body shape while ignoring both how unreasonable that expectation is, and the untold misery it causes. The results of the "obesity crisis" are all too easy to predict: ever more diets and health fads, and ever more fretting about weight. Will any of this result in British people eating better? Will it heck.