You sit down at the fast-food restaurant, and there on your tray are a large soda and two brightly-coloured packages containing your meal.

On the french fries is a friendly health message: A BALANCED DIET SHOULD INCLUDE FRESH FRUIT AND VEGETABLES.

The cola has something a bit more scientific: CONTAINS HIGH-FRUCTOSE CORN SYRUP, A POTENTIAL SOURCE OF WEIGHT GAIN.

For your double cheeseburger, all subtlety is out. WARNING: A FATTY DIET IS A SILENT KILLER says the red sticker across the lid, adding for good measure, ENJOY YOUR MEAL!

Sounds far-fetched? Only slightly.

For an epidemic of obesity is unfolding across the world, and policymakers everywhere are finding themselves under pressure to get tough.

For decades, developed countries have offered their citizens advice on healthy eating.

But as waistlines expand relentlessly and childhood obesity soars, more and more governments are being tempted to take the same path with the food business as they did with tobacco.

That road started with voluntary measures by the cigarette industry, was followed by regulations that limited advertising, and finally by laws that restricted points of sale and demanded stern health warnings on packaging.

“At first glance the consumption of food is very different from tobacco,” say two nutrition experts, Ian Darnton-Hill of New York’s Columbia University and Mickey Chopra of South Africa’s University of the Western Cape, in the latest British Medical Journal (BMJ).

“After all, food is not a deadly product and people need to eat every day to satisfy basic physiological requirements.

“Perhaps this is why the public-health response to overnutrition has been largely based on the need for individuals to change their behaviour. But this approach is generally ineffective.”

At a European Congress on Obesity, held in Prague in May, several speakers warned the food business would be among the casualties if obesity were ignored.

“If we don’t do something soon we will pay a huge physical and financial cost from the medical complications of obesity, but the problem can be tackled by changing our lifestyles,” said Peter Kopelman, president of the European Association for the Study of Obesity.

He suggested industry voluntarily introduce a simple system of colour-coded warnings on food packages to advise on obesity and other health problems.

Britain’s House of Commons Health Committee last month slammed food advertisers and manufacturers, along with the government and National Health Service, for failing to tackle obesity.

It called for a voluntary withdrawal of TV advertising for junk food being pitched at children, and for an end to ad campaigns in which sports stars and other celebrities push crisps (US potato chips) and chocolate.

Another idea being kicked around among lawmakers in Britain, France and Germany is for a “fat tax” - foods that exceed certain limits in terms of calories or fat content would face a levy, whose proceeds would go into research or a national anti-obesity agency.

Such thinking is anathema in the United States, where many legislators, while sensitive to the obesity crisis, are hostile to a regulatory crackdown.

The House of Representatives in March approved the so-called Cheeseburger Bill (formally called the Personal Responsibility in Food Consumption Act), which would prevent consumers from sueing restaurants if they grow obese from their food.

The main case against the food industry is that consumers, especially children, are being ever more frantically plied with processed products that are replete with fats and sweeteners such as high-fructose corn syrup.

These ingredients are energy dense - they are crammed with calories, far more than are expended in the sedentary lifestyle of today, and so the surplus gets stored as fat.

The reply from the food business is quite naturally: Well, the product itself is not dangerous, and you don’t have to buy it.

Even so, sensitive to market demand and worried by the distant threat of a legislative counter-strike, some in the industry are changing their ways.

McDonalds, a favourite target for anti-obesity campaigners, won high marks this year when it scrapped the “supersizing” of fries and drinks and introduced healthy foods such as nuts and organic milk.

“Industry has to do something, otherwise the authorities will do it by law, which is exactly what we don’t want,” Nestor Carbonell-Cortina, vice president for international affairs at PepsiCo, said at a health conference in Warsaw last month staged by the World Economic Forum.