Mark Kermode - Visual feast

An educational documentary with a car-crash-style allure. By Mark Kermode

Super Size Me (12A)

Back in the Seventies, I celebrated my 12th birthday with a bus ride to the Seven Sisters Road in north London, where I first experienced the much-hyped modern miracle of McDonald's. Having been raised on the drizzly delights of the Wimpy bar, I simply couldn't believe the orgasmic brilliance of a Big Mac meal: not one, but two burgers jammed between excitingly speckled baps; crisp'n'dry fries that made old-fashioned chips seem like ugly slabs of lardy spud; and a milk shake so firm you needed a suction pump to get it up the straw, not to mention strong teeth to chew it into swallowable gulps.

Any suspicions that something which tasted so good just had to be bad for you were quickly allayed by a catchy marketing jingle listing the Mac's wholesome ingredients ("two all-beef patties, special sauce, lettucecheesepickles and un-yuns . . ."), which soon became the refrain of playgrounds up and down the land. Little did we imagine that, nearly 30 years later, customers across the Atlantic would be suing McDonald's for making them fat, and that the British government would be predicting an obesity epidemic set to do more harm to the country's health than smoking, drinking or voting Labour.

Intrigued by one of the failed high- profile lawsuits against the fast-food industry, the sparky young film-maker Morgan Spurlock decided to find out just how bad a Big Mac and fries could be for your system by spending an entire month eating breakfast, lunch and dinner under the golden arches. There were a few ground rules: he could consume only products supplied by McDonald's; he could not exercise any more than the average American slob (which meant that he had to cut down drastically on his walking); and, when asked by a friendly assistant if he wanted to "supersize" his meal, he could not say no.

A team of physicians were on hand to monitor changes to Spurlock's body as he munched his way through a mountain of sugar and fat, piling on the pounds in predictable fashion. But it turned out that weight gain was the least of his problems. Along with the mood swings, irritability and loss of sexual appetite that were duly noted by his vegan-chef girlfriend, the possibility of irreparable liver damage soon began to loom so large that at least one doctor advised Spurlock to bail out. He wasn't just getting fat - he was getting sick.

If the power of a documentary film can be judged by its ability not only to reflect but also to affect the world in which we live, then Super Size Me may already be reckoned a bona fide success. Months after the film premiered at the Sundance Film Festival, McDonald's restaurants in the US dropped the "Supersize" option, unconvincingly claiming that the decision had nothing to do with the bad publicity generated by Super Size Me. In the UK, McDonald's celebrated the Edinburgh Film Festival premiere of Spurlock's movie last month by taking out full-page ads in the national press claim-ing that it agreed with some of his complaints, while gamely defending its changing policies towards customer eating habits (presumably, customers who drop dead prematurely are no good to anyone). Today, McDonald's menus include "healthy option" bags of fruit, low-fat salads and mineral water drinks. Its restaurants have even been handing out free "step counters" to encourage patrons not to fall foul of the bodily degeneration that Spurlock's film so brilliantly documents.

Health issues aside, what is most remarkable about Super Size Me is how much fun it is to watch. Eschewing the self-righteous pontificating that made Michael Moore's Fahrenheit 9/11 such a ponderous bore, Spurlock never forgets that the best way to educate an audience is to entertain. He provides an invigoratingly masochistic spectacle of human disintegration that has a car-crash-style allure. There is something genuinely creepy about the way in which his body responds to the onslaught of processed stodge. Early scenes of Spurlock puking a McDonald's meal out of his car window soon give way to an admission that he actually feels better after stuffing his face with burgers and fries - a feeling that will be familiar to addicts of a range of lethal substances, from Silk Cut to smack.

It remains to be seen whether or not the virtual volte-face that McDonald's has performed will convince the public that its products are wholesome fun for all the family (Spurlock seems especially exercised by the targeting of kids with fast-food marketing). As for Spurlock, his future as a hugely saleable screen comedian- cum-documentarian looks healthy and wealthy. Let's hope he doesn't go and bollocks it up in the manner of his celebrated, supersized predecessor.

12 issues for £12