Being fat has suddenly become politically unacceptable. According to the Health Secretary, Alan Johnson, obesity is a "potential crisis on the scale of climate change", while the US Surgeon General has described it as "a greater threat than weapons of mass destruction".
Professor Philip James, chair of the International Obesity Task Force, raised the alarm in the UK two years ago, when he warned that an "unprecedented epidemic of life-threatening obesity" had taken off in the Eighties. And last week, the Prime Minister earmarked funding for "a long-term action plan to fight obesity" – after the Government-commissioned Foresight report found that half the population will be clinically obese within 25 years, and that, by 2050, obesity will cost the country £45bn a year.
Such a response might make sense if there really was an epidemic rise in obesity. In fact, the claims about the UK and US obesity "epidemics" are wildly exaggerated and – more seriously – deliberately skewed.
Politicians have been taken in by a cottage industry that has developed around the obesity crusade; an industry that consists of a wide range of groups, from public-health bureaucrats to big business, including the pharmaceutical industry.
These organisations and individuals, with their need for ever-greater empires and funding, know only too well that warning of impending disaster captures the Government's attention. Yet in this classic case of spin, there are real victims: those people condemned by wrong-headed policies to a lifetime of yo-yo dieting and an unhealthy obsession with food and weight.
An analysis of the science behind the headlines reveals a very different picture. For a start, the claim that half of the British population will be clinically obese in 25 years assumes, without any empirical foundation, that every overweight child will become an overweight adult and that every overweight adult will progress to obesity.
It is true that Body Mass Index (a figure consisting of height squared divided by weight squared) statistics show a significant increase in overweight adults over the past decade. But this is an extraordinary case of moving the methodological goalposts: in 1997, the BMI classification of being overweight was changed from 27 to 25. At a stroke, millions of people previously classed as normal suddenly became overweight, with no good reason to explain the change. This obscures the fact that the average adult weighs only a pound or two more than those of a generation ago. The increase in obesity applies only to the morbidly obese (with a BMI greater than 40), who make up less than 5 per cent of the obese.
Further, there is not a shred of evidence to suggest that childhood obesity is on the increase, let alone accelerating. The Department of Health's own survey, published in December 2004, shows that for all children aged two to 15 there was actually a slight decline in obesity prevalence from 2004-2005. And in children aged 11-15, there was a 17.5 per cent decline. So, it is difficult to see from the Government's own data just where this talk of an obesity "epidemic" is coming from.
What's more, the latest UK National Diet and Nutrition Survey (2000) found that caloric intake in both boys and girls aged four to 18 declined since the previous survey in 1983. There is similar data in the States: a study published in the Journal of the American Medical Association in 2004 found no statistically significant increase in the prevalence of overweight or obese children between 1999 and 2002.
Behind the medical profession's goal of identifying overweight people is the claim that it is unhealthy to be above normal weight. I am no obesity apologist: morbidly obese people are so fat that they are putting their lives at risk. But the claim that being overweight or modestly obese is associated with an increased risk of premature death has been discredited by a series of studies. For example, the 2004 US Centers for Disease Control and Prevention (CDC) study claimed that there were nearly 400,000 annual deaths attributable to diet and physical inactivity. Yet this was discredited the following year by a study from researchers at the CDC and the National Institutes of Health, which put the figure of annual deaths from overweight and obesity at just 25,814.
Even the alleged link between excessive food intake and childhood obesity has no scientific basis. A 2002 cross-cultural review of obesity in the US, France, Australia, Britain and Spain found little evidence that overweight or obese children and adolescents consumed more calories than others. At least one study has found that overweight children consume fewer calories than their thinner peers do.
Indeed, the whole idea of "good" food and "bad" food is increasingly open to question. It has long been known that consuming a high-fat diet does not necessarily raise blood cholesterol or reduce longevity – as can be seen by the fat-loving Dutch and East Africa's Masai. A recent series of studies has also shown that a low-fat diet has little effect on reducing the risk of breast cancer, colorectal cancer or cardiovascular disease in postmenopausal women.
There is also strong evidence that blaming childhood obesity on advertising is fatally flawed – and that banning advertising of junk food will have little or no effect on our children's weight. And research into the connection between food advertising and the size of the food market, both in Europe and the US, has found that advertising influences brand selection, but not diet.
I am an independent academic and not a junk-food industry lobbyist. I am a passionate combatant in this debate, because I believe that the obesity crusade is dangerous. Virtually all the literature on dieting has concluded that attempts at weight loss are largely unsuccessful and, more worryingly, that there are health risks in such behaviour.
There are similar doubts over the efficacy of policies to counter childhood obesity, whether through changing school food, removing vending machines with "bad" food or increasing physical education.
In the States, an obesity prevention programme in 50 schools known as Catch (Child Adolescent Trial for Cardiovascular Health) found no statistically significant changes in the children's blood pressure, BMI or cholesterol levels. Such results are hardly surprising: several recent studies have shown that adult attempts to control children's eating patterns lead to children eating more – as well as raising the risk of body-image problems and eating disorders. It's this unintended, and uninvestigated, outcome of a weight-obsessed society that should be the cause for concern.
If we take into account the relatively few lives lost prematurely due to obesity, and compare them to the very significant health costs associated with both dieting and eating disorders, there is surely a compelling case that the damage to health from attempting to lose weight is far greater than the health consequences of overweight and obesity. Indeed, perhaps rather than a campaign against obesity, it is a war on thinness that is required.
Professor Basham is co-author with Dr John Luik of 'Diet Nation' and is the Democracy Institute's founding director. 'Diet Nation: the obesity debate' takes place at Battle of Ideas 2007 festival, Royal College of Art, London SW7 on Saturday 27 October (020-7269 9224; www.battleofideas.org.uk)Reuse content