The metaphysical clown, Kurt Vallentin, once enacted the following scene: the curtain goes up and reveals darkness, apart from a circle of light cast by a street lamp. Vallentin is desperately searching for something. "What have you lost?" asks a passing policeman. "The key to my house." The policeman joins him in his search. They find nothing and after a while the policeman inquires, "Are you sure you lost it here?" "No" says Vallentin pointing to a dark corner of the stage: "Over there." "Then why are you looking for it here?" "There's no light over there," says Vallentin.
Could the recent media hysteria about food advertising and obesity in children be a good example of looking in the wrong place; of being attracted by the light rather than guided by reason? Not according to the journalists, campaigners and politicians who have been rushing to condemn the food industry and seem certain they've found the bogeyman.
Even the Lancet couldn't resist a vitriolic editorial attacking sports celebrities and food manufacturers for promoting junk food. The journal was responding to a review of the impact of food promotion on children commissioned by the Food Standards Agency (FSA), which it described as "harrowing reading". Though the findings were heavily qualified, the review authors concluded that advertising has a negative impact on children's food choices.
As a consequence of this intense media scrutiny, some big brand companies, including Coca-Cola and Heinz, have announced a ban on advertising their products to children; and the culture secretary Tessa Jowell has asked the new television regulator, Ofcom, to review its advertising code for children. Last week, the Consumers' Association called for the government to ban the advertising of high-fat foods on children's TV and in cinemas, and the Wanless report on public health points towards the need for a broader debate about the health of the nation and the rising tide of obesity.
A major difficulty for the authors of the FSA report is the lack of quality scientific evidence on the relationship between food advertising and food choices in children. Most of the articles cited in the critical areas of the study were North American in origin, from selected social and ethnic groups and were 20-30 years old. In fact, the dominant influence on children's eating habits was parental behaviour, which was 15 times greater than TV advertising. Moreover, in Quebec where food advertising to children has been banned since 1980, obesity rates are no different from those in other Canadian provinces.
A similar decade-long ban in Sweden has not resulted in any significant reduction in obesity rates. Put bluntly, there is no credible scientific evidence to support the assertion that food advertising is causally related to childhood obesity, a conclusion apparently accepted by the authors of the FSA report, which states: "There is no prima facie reason to assume that food promotion will undermine children's dietary health; it can influence it, but this influence could just as easily be positive as negative."
If children over-consume they will become fat, but there are reasons for regarding the fundamental problem of childhood obesity as being the rapid decline in physical activity levels during the past few decades.
Evidence shows that children today expend about 600 kcal less than their counterparts 50 years ago and contemporary British children, even in the pre-school years - spend much of their time seated. Another example is that of car use, which has grown considerably faster for children than for the rest of the population. In 1964, around 37% of travel by children was in a car; it was more than 70% in 2002.
This decline in physical activity has been exacerbated by the failure of successive governments to provide an environment in which physical activity can be incorporated into everyday life. If parents have concerns about their children's safety, either because of traffic or possible abuse by strangers, they will opt for the car over the pavement - and who can blame them?
Many schools in Britain do not have sufficient resources to purchase basic sports equipment, while politicians propose spending £2.4bn on trying to secure the Olympic Games for 2012. The constant emphasis on competitive sport alienates those children who are less physically gifted and diminishes the importance of lifelong physical activity for health.
Health policy makers and those controlling the public purse should reflect that active children are more likely to become physically active adults, with lower rates of heart disease, diabetes and cancer. Even those who are obese but physically active have better long-term health outcomes than their sedentary, lean but unfit counterparts.
For every complex problem there is a simple solution - and it is always wrong. Blaming food advertising for childhood obesity may attract popular support, but it misses the point. The real scandal is the decline in physical activity among children, which is more important than any marginal effects of food advertising.
· Dr David Ashton is honorary senior lecturer in clinical epidemiology/cardiac medicine at the Imperial College School of Medicine and group medical director of BMI Healthcare.
