The BBC – Britain’s politically-correct state broadcaster – got in on the act too, heralding the movie with its own ‘Healthier Britain Week’ and commissioning opinion polls claiming that the Brits are desperate for government to save them from their bad eating habits.

But this movie is in the worst tradition of that other ‘documentary’ producer of Bowling for Columbine and Fahrenheit 9/11, the (even plumper) Michael Moore. These movies are all pieces of advocacy, rather than an objective analysis of a key social issue. Certainly, they deal with important issues – America’s gun culture, events leading up to 9/11, and obesity. But they are all a clever, cynical and misleading use of film by partisans of the anti-conservative, anti-business cause. They pose as objective, but use the most misleading tricks of spin to promote a particular case, artfully deploying humour and emotional tricks to make us believe it.

The trouble for corporations like McDonalds and conservative politicians like George Bush, is that when these movies are done well, they make oodles of money, so their creators just go on and do more. Bowling for Columbine set the trend as the biggest grossing ‘documentary’ of all time, and now you cannot escape Moore in any cinema, bookshop, or even party convention. Spurlock’s effort cost $65,000 to make and had soon grossed over $10 million.

But it’s power without responsibility. However outrageous the spin, those attacked have no right of reply: websites like moorelies.com are hardly up to the job. Nor can these ‘social critics’ be voted out of office. And if they can convince other media like the BBC that there is truth in their claims (or even that it is just good entertainment), pretty soon the entire chatterati is peddling the same nonsense. It’s a perfect system for enthusiasts who can’t win an argument on the facts.

Superficially – and certainly in the headlines that herald it – Spurlock’s film suggests that eating at McDonalds all the time ruins your health and makes you fat. But it ain’t necessarily so. Certainly, eating three meals a day at the same burger joint is nobody-s idea of a balanced diet. But – if, after all the anti-fast-food hype you can believe this – it doesn’t have to make you fat.

You need to cram in 3500 extra calories a day over your natural metabolism (about 2500 a day for Spurlock, he tells us) to gain a pound. That’s a lot of eating. So Spurlock gorges at each meal, has hash browns alongside his breakfast, and drinks lots of fizzy sweet drinks and milkshakes. And just to make certain of it, he eats desserts with lunch and dinner, snacks throughout the day, and gives up any exercise at all.

This is eating absurdly – and for a purpose: the purpose of giving one of those nasty multinationals a poke in the belly. But, says Aaron Walker on the technology and business website techcentralstation.com, if Spurlock had reduced his intake to extra-value meals and had one less soft drink, he could easily have maintained his intake at 2500 calories. It’s not the restaurant that leads people to gain weight, it’s their choices.

That’s the problem. Movies like this send out a powerful message – the wrong one. The message that we’re not responsible for what we do, it’s all the fault of the wicked corporations. And that mind-set makes things perfect for the lawyers to move in and target these companies’ cash. Having bankrupted tobacco, now they’re working over fast food. What’s next? Booze, with Spurlock giving up water and drinking only spirits for a month? Snack foods?

But why should law-abiding businesses be castigated if we abuse their products? Like all businesses, McDonalds offers choice. You don’t have to force down ice-cream desserts. You can eat salads and drink water. Or go somewhere else.

We have become convinced us that only government save us from business, and from ourselves. Sadly, it does the opposite: why act responsibly when there’s a free state health service to patch you up afterwards?

MacDonalds have tried to fight back, saying how nutritious their food is. But this isn’t about rational argument. The ‘comedy-documentary’ genre has already taken things out of the realm of rationality. Hitler’s propaganda minister, Joseph Goebbels, knew that it was no good blaring out party slogans. Get people into the cinema with a good romantic movie, entertain them, and you can slip in the message underneath: subtle, emotional, powerful.

Corporations have been inventive at creating positive messages through their advertising. But there is no point in trying to argue facts against a movie like Super Size Me. They now have to learn to use some of the same techniques to defend themselves against the unfair, misleading, negative messages that the ‘comedy-documentary’ producers are popularizing. They’d better start getting good at it soon. Because now the anti-capitalists have learnt how to make a political point and clean up at the box office at the same time, they certainly aren’t going to go stop now.

Dr Eamonn Butler is Director of the Adam Smith Institute. This article was originally published in The Business newspaper.