Super Size Me smacks viewers early on with a money shot. Morgan Spurlock, the star and director of the documentary, is jawing through a Super Size meal with naughty elation. It's his first Super Size ever! Five minutes later, and the grin is fading. Some minutes more, and the director is complaining of a McStomachache. Then McGas. And then before we know it, he's got his head out the car window. Whoop, there it is. The McVomit.

With that, it becomes clear that Spurlock, 33, has made something akin to a porno flick, one that memorializes his sordid, sadomasochistic affair with McDonald's.

Spurlock's main focus is actually the tricky line between corporate and personal responsibility, the societal costs of obesity and America's fast-food culture. But he's also written himself into the script in a way that's too entertaining to ignore. His role? A human guinea pig who eats nothing but McDonald's for a month.

Intrigued by lawsuits alleging that McDonald's was guilty of making its customers fat -- and by the restaurant's claims that its food was nutritious -- Spurlock sets up an experiment, monitored by three doctors, a physical therapist, a nutritionist, and his concerned vegan-chef girlfriend. He'll eat three meals at McDonald's a day. If McDonald's doesn't make it, he doesn't eat it. He must be asked to Super Size before he can Super Size his meals. He also restricts the amount he walks to just a mile a day.

Watching the sick, sad joys of Spurlock's life with the Ronald feels delicious and dirty from the beginning -- those shovelfuls of fries, the squishy McGriddles, barrel-sized Cokes. Then things get even uglier. His boyish Ron Howard looks grown slack and bloated, Spurlock grabs his palpitating ticker in the middle of the night, and for a few, teetering moments, the documentary borders on becoming the first fast-food snuff film. Spurlock is literally eating himself to death, and so, he's saying, is the vast majority of the U.S. public.

As its larger-than-life title would indicate, Super Size Me is no stranger to hyperbole and exaggeration -- it's a social satire, after all. But some of these techniques seem ill-suited to the scientific part of Super Size's equation. Three Golden Arches meals a day? The experiment is hardly representative, despite Spurlock's efforts to make it seem less far-fetched through a barrage of statistics on American obesity, and his visual editorializing. The camera gazes on human Shamus washed up on a beach, their cellulite-riddled rumps happily munching away at their shorts. Lookit that! My diet's not so far off! Spurlock seems to be saying -- but even if one was already inclined to agree, one feels bullied into going along with him. Spurlock has clearly taken a page from that plump provocateur Michael Moore in learning how to cattle-prod his audience.

For those who won't have their arms twisted, the spectre of "personal responsibility" raises its head. Faced with the Shamus and a rapidly swelling Spurlock, a viewer can channel schoolmarm-dominatrix Dr. Laura: Anyone who eats that much McDonald's deserves a smack. Everyone knows McDonald's is bad for you. But therein lies the unexpected strength of Spurlock's gimmick -- no one knows how bad the stuff is. Spurlock's Unhappy Meal adventure is the secret sauce that holds his movie together -- at times suspect, and at other times just the thing that gives the film its indefinable staying power.

As Spurlock dodders into one of his doctor's offices, ashen, burping like an impacted bullock, the physician can't help but register his alarm. The filmmaker's weight and cholesterol levels have skyrocketed, he's gained ten pounds in a week, his heartbeat is sludgy. And as for the liver? It seems that the good physician has never had a nice piece of foie gras, or else he'd know what force-feeding an animal with high-fat foods will do -- produce a liver that would be perfect with some fava beans and a nice Chianti.

"Your liver is sick," the doctor pauses, aghast. "It is now like pate."

The doctors, along with Spurlock, had thought he'd gain just a few pounds and suffer no real harm. But now, they say, they're armed with real data indicating just how damaging an all-McDonald's diet can be. In some ways, Spurlock's no different from a laboratory animal dosed with unrealistic amounts of cosmetic products -- that is, after all, how a product's toxicity level is measured.

In answering the how bad question, Spurlock's documentary makes an excellent case for why McDonald's must provide accessible nutritional information for its foods. When faced with such a highly processed product, the hypothetical "reasonable person" who forms the basis of product liability law rulings probably can't guess at the majority of the food's ingredients or their potential hazards. But not surprisingly, when Spurlock goes hunting for nutritional information in McDonald's after McDonald's, he finds the info sheet in the basement or behind a display -- or, more often than not, he doesn't find it at all.

Spurlock implies that his film may have had something to do with McDonald's recent decision to stop offering Super Size meals, and to institute a new Adult Happy Meal, which will feature apple slices, bottled water, a pedometer, and an exercise guide. Perhaps it's true. Even as the fast-food industry successfully pushed the "Cheeseburger bill" -- which would ban any obesity-related lawsuits of the food industry -- through the House, they seem to recognize that they might be losing the hearts and minds of their consumers, thanks to Spurlock. The Q&A with Spurlock that followed my viewing of the film was hijacked by a food lobbyist who was booed down from the microphone; outside the theater stood "protesters" (i.e., representatives of the pro-free-market Competitive Enterprise Institute advertising their counter-documentary -- a filmmaker ate at McDonald's for 30 days, exercised, and lost 10 pounds! )

Then a celery-pusher attacked me with a pamphlet for the vegan lifestyle.

The squall outside the cinema was a regular food fight, all right, and testament to Super Size's ability to provoke, to enrage, and to threaten those on all sides of the food and politics spectrum. It was a heartening sight, especially in light of what Subway's weight-loss poster boy Jared Fogle says to an overweight teenager in one scene from the film. "The world's not going to change," he says. "You have to change." Familiar and depressing words to people who find themselves outside the norm. Spurlock seems to have subverted Fogle's words with his half-insane, half-heroic documentary, the creation of a true crusader. Spurlock certainly changed his life, nearly killing himself to make his point. And he may have changed more than himself -- it looks as if the rest of the world, and even Ronald himself, is taking notice.

A Prospect senior correspondent, Noy Thrupkaew has eaten only one Big Mac in her life. She will probably never eat another. Her next column will appear on Friday.