FIRST IT WAS TOBACCO. NOW A LAWYER IS TAKING ON THE FAST-FOOD GIANTS FOR THEIR ROLE IN THE OBESITY EPIDEMIC.

 There is a challenge John Banzhaf likes to pose to students who enrol in his class on legal activism. Think of something that really irritates you or smacks of obvious civil injustice, he tells them. Then think of a way of using the law to right the wrong and seek redress. In other words, as Professor Banzhaf puts it with the candour we have come to expect from both heroes and villains in the legal system, let's sue the bastards. It's a unique approach to legal education that has had some astonishing results. Most famously, Banzhaf, who teaches at George Washington University, in the United States, pioneered the notion of suing tobacco companies for the deleterious health consequences of smoking.

 He started doing it in the mid-1960s, when everyone thought he was nuts, and he was still doing it in 1998 when certain states in the US successfully prised hundreds of millions of dollars out of the Big Five tobacco companies as compensation for their smoking-related health-care costs. If tobacco advertising is now banned on television and smoking no longer tolerated on planes or in shops and restaurants, it is largely due to Banzhaf's 35 years of campaigning and savvy application of public-interest law. And now he has a new target: the junk-food industry.

 America, as we all know, is the fattest nation on the planet and getting fatter all the time. A recent government report revealed that 61 per cent of Americans are overweight. Obesity generates $US117 billion in annual medical bills and triggers 300,000 premature deaths there each year. In Australia, the statistics are also grim. Studies show that the number of overweight children and teenagers has almost doubled in the past decade. The number of obese children has tripled and it is estimated that obesity costs Australia more than $2 billion a year in associated health problems.

 "It's really very serious," says nutritionist Dr Rosemary Stanton. "We're not as fat as the Americans, but we're fatter than the Brits and a lot fatter than the French. One third of the food dollar is now spent on food outside the home - restaurants, snacks, takeaway. It's clear that the Western diet, which is high in fat, salt and sugar, produces obesity and type-two diabetes. It's not good for our health and we need to do something."

 Is this a health problem on a par with the effects of smoking? Banzhaf and a growing number of health professionals think so, and US government figures bear them out.

 It's estimated that in Australia 45 per cent of men and 29 per cent of women are overweight. "Today's fast-food companies could become the tobacco industry defendants of tomorrow," says federal Liberal senator Guy Barnett. "Health warnings on junk-food packaging highlighting the medical and lifestyle risks will no doubt become a requirement in future years unless the industry acts now."

 In June, Barnett attended a health conference at the Harvard School of Public Health in Boston where the issue of litigation over health problems linked to obesity was discussed. "It's clear that the increasing cost of obesity, in terms of associated health problems, has to be addressed," he says. "It's time to take action. We have to change social behaviour and it's an issue for all three levels of government as well as families and individuals."

 Can fast-food companies, agribusiness giants, packagers and marketers be held responsible for the problem? Banzhaf argues that they are the ones stuffing consumers full of fat, sugar and chemical additives. With a little statistical analysis, he believes, it should be possible to assign specific shares of the blame to specific companies.

 Banzhaf, it must be said, is far from your stereotypical litigation lawyer, forever looking out for an opportunity to screw a corporation or public institution and make a fast buck. Not only does he not make a cent from the suits that he inspires, he would, in fact, much rather not bring them in the first place. He would love it if the government would overhaul the food industry to make people healthier, just as he would have preferred the government to take action on smoking unprompted.

 But America is a country in which recourse to the courts is frequently the only way to effect social change since Congress and the federal government are often beholden to powerful industry lobbies. As the mantra goes, "If you can't regulate, litigate", and that is exactly what Banzhaf has in mind.

 It's one thing to say that diet has a lot to do with the growing obesity problem, but quite another to prove in court that client A's heart attack was caused specifically by hamburgers or by bingeing on cola. Nobody sticks to one brand of food as they stick to one brand of cigarettes, so individual suits are out of the question and class actions would depend on highly complicated statistical analyses of food intake and medical cause and effect. Also, unlike smoking, there is nothing intrinsically unhealthy about eating.

 It invites the question: can food companies really be held responsible for the immoderate appetites of their customers? Clearly, if there is a legal case to be made, it is going to have to be fairly ingenious.

 Banzhaf's approach is to start with the relatively easy stuff. The first line of attack is to go after food companies that misrepresent their products by understating the fat content or omitting to mention ingredients. That is the basis of all the suits currently before the US courts. The second, slightly harder, line of attack is to accuse companies of making misleading health claims for their products - proclaiming pork to be "the other white meat", for example, when its fat and cholesterol content are in fact closer to beef than to chicken.

 The third approach would be to pick up on a failure to warn consumers of certain health risks. Is it wrong of a fast-food chain to fail to point out that its triple-bacon double cheeseburger super-size meal contains more fat than any sane human being should consume in a week? Arguably so. Is it grounds for a lawsuit? Maybe, if the plaintiffs can work with laws on "clear and conspicuous disclosure of material facts".

 And finally, the real zinger, if it can be made to work: an onslaught on the fast-food industry as a whole, in which it would be made to pay its share of responsibility for type-two diabetes, sclerotic arteries, heart attacks and strokes. Interestingly, McDonald's in France recently took the unusual step of telling its customers, through magazine ads, that it was not a good idea to eat there all the time, suggesting it should be only once a week.

 Legal analysts are sceptical as to whether Banzhaf's approach could ever work, and even the professor describes it as "a reach".

 But some promising avenues to explore include the possibility of describing fast food as something akin to an addiction deliberately fostered by manufacturers through their marketing, especially to children.

 This is one area of the debate that is gaining momentum in Australia. "Kids are vulnerable to clever marketing," says Professor Frank Oberklaid, director of the Centre for Community Child Health at Melbourne's Royal Children's Hospital. "The link between obesity in children and exposure to TV has been documented in recent studies. Not only is watching television a passive activity but exposure to advertising is another factor.

 You also tend to eat more when you watch TV." Both Oberklaid and Stanton would like to see television advertising for fast food banned during peak viewing times for children.

 Banzhaf has other strategies up his sleeve for exerting pressure on governments. One is to push for higher health insurance premiums for the overweight, a measure that would act as an incentive for people to shed kilos and would also shift more of the health-care costs towards the people who incur them. Another is to push for higher taxes. After all, if one of junk food's principle attractions is that it is cheap, taxation is a simple way for governments to ensure that it does not stay that way.

 Rosemary Stanton favours this approach over protracted legal action. "The amount in the budget spent on health education is minuscule. I would like to see a tax on some foods - soft drink, snacks, biscuits - and the money raised used on health education. We could run cooking classes, employ more dietitians to work with young people. There's a lot we could be doing and the money has to come from somewhere."

 Banzhaf does not pretend that successful lawsuits, on their own, would solve the problem of obesity. What he does believe is that intelligently mounted lawsuits can help change the climate of public opinion and pressure junk-food companies and government regulators into changing some of their ways. "None of the things I'm suggesting are panaceas," he says. "But even the threat of lawsuits might be enough to make some helpful changes."

 His is undoubtedly an idea whose time has come. Head to your nearest shopping centre and the evidence of our fast-food addiction is all too abundant. Under one roof there are McDonald's, Burger King, KFC, Taco Bell. With such excesses, not to mention the manifest effect on bellies, chins and thighs, have come the beginnings of a backlash. The junk-food merchants themselves have felt it, and have changed their strategies accordingly, with Coca-Cola and Pepsi diversifying into fruit juice and McDonald's going on a corporate buying spree to move into so-called family restaurants and fresh-sandwich chains.

 John Banzhaf's involvement began with a student of his, a vegan who had avoided fast-food fries for years because he knew they were dipped in beef tallow. The student was appalled by a McDonald's ad claiming its fries were cooked in 100 per cent pure vegetable oil - a statement that was literally true but omitted to mention that the fries were pre-cooked in beef fat. Class work on the issue evolved into a class action suit brought by Hindus who said the failure to disclose the beef content was an offence to their religion and constituted an "intentional tort". McDonald's has acknowledged the oversight and, according to Banzhaf, is on the verge of settling for around $US12.6 million. (McDonald's Australia has said it has never promoted its fries as being exclusively cooked in vegetable oil.) Hidden fat content is behind two other US actions, one against an ice-cream manufacturer in Florida, and another against a line of corn and rice puffs called Pirate's Booty that, according to a Good Housekeeping test, contains 340 per cent more fat than stated on the contents.

 Naturally, there are powerful interests anxious to stop an anti-obesity campaign. Food-industry lobbyists and laissez-faire economic thinkers have lambasted Banzhaf as a Food Nazi ("Grease Gestapo" and "Calorie Cop" have been hurled at him ) seeking to dictate what people should eat. In a bruising appearance on the Fox news channel, the presenters sought to trash Banzhaf as a hypocrite because he is somewhat overweight himself. Meanwhile, a burgeoning "fat power" movement argues that attempts to get people to lose weight is tantamount to discrimination. They say that it is perfectly possible for a woman of average height to have a "natural" body weight of 120kg or more, and that airlines, car manufacturers and restaurants should be obliged to provide larger seats.

 Talking to Banzhaf, one senses that it is going to take a lot more than a few gratuitous insults and fat-is-good activists to undermine his determination. Unlike many consumer advocates, he is no pious moralist trying to tell people what is good for them. He is a legal thinker first and foremost, and his primary motivation is his belief that the law can be used as an activist tool for the public good.

 "Somebody needs to push the envelope," says Frank Oberklaid. "There is a sense of urgency. We're faced with the same problems as the US and although not to the same extent, it [obesity] is considered one of the major epidemics of our time."

 "As a lawyer," says Banzhaf, "I have two choices. I can litigate on behalf of whoever brings the buck into my office. Or I can look around and ask what kinds of problems I can attack through legal action. I find the latter much more interesting. We are seeing groups that might not previously have had much in common coming together - vegans, Muslims, Hindus, conservative Jews, scientists, physicians, animal-rights groups, children's rights groups, sports organisations," he says. "Once they join forces, lawyers are going to smell the money, and legal action will gain its own momentum."

 It could take years, or even, like the tobacco campaign, several decades, but Banzhaf is lucid about what he can and can't achieve: "Are suits possible? Yuh. Are some already successful? Yuh. Can we predict which ones will go and which ones will not? No, we can't," he says. "But we'll soon find out."