A GONZO documentary in the Michael Moore mold -- but without Moore's grating presence -- "Super Size Me" is an anti-junk-food screed that manages to entertain even as it informs and alarms. Oh, yes, and sickens. To paraphrase the old line, I laughed, I cried, I threw up.

Okay, I didn't, but filmmaker Morgan Spurlock does, and on camera. That charming little scene takes place within one week of Spurlock's embarking on the unusual odyssey that forms the essential structure (but not necessarily the sole subject) of his film. It concerns Spurlock's eating three meals a day at McDonald's for 30 days.

That's right. Spurlock, who was in excellent physical shape at the beginning of his film -- at least according to the three doctors he consulted with early on and then again regularly throughout the film's making -- set out to investigate the direct effects on his health of an all-Mickey D's diet after becoming curious about a lawsuit that had been filed by two people who accused McDonald's of making them fat. One phrase that caught his eye in the legal documentation was the issue of whether habitually eating at McDonald's was "unreasonably dangerous." He set up certain rules for himself: Among other requirements, such as limiting his exercise, every menu item had to be consumed at least once; and whenever he was offered the restaurant chain's "Super Size" option, he had to accept.

Over the course of the month, he gained 25 pounds; his cholesterol and triglycerides shot up; his liver turned to fat; his libido waned; and he experienced chest pains, mood disorders, interrupted sleep and energy levels that fluctuated like the tides. It's a wonder his girlfriend, a vegan chef, didn't leave him. It's scary, yes, but Spurlock's light touch as a filmmaker, his eye and ear for irony as delicious as an Egg McMuffin, and his easy good humor (on display in his use of animated barnyard animals, wry musical choices, man-on-the-street interviews and deadpan running commentary) leaven the script, which is rich with disturbing statistics.

Such as the fact that one in four Americans eats fast food at least once a day.

I guarantee you, that percentage is about to drop, at least among those of us who have the sense and good fortune to watch this cautionary tale. Its effect is like one of those photos of a 750-pound man that you clip from the National Enquirer and stick on your refrigerator. Talk about negative reinforcement. I'm no granola-cruncher, and I like my Big Macs as much as the next guy, but watching Spurlock boof up a gut full of fries on the sidewalks of Manhattan -- and listening to all three of Spurlock's doctors and a professional nutritionist tell him to stop before he kills himself -- put me off my next Happy Meal.

Does "Super Size Me" have an ax to grind? Yes. Is it fair and balanced? Hardly, although Spurlock is shown making several vain attempts to get an on-camera interview with a McDonald's spokesman. What's more, who eats at McDonald's all the time?

Nevertheless, Spurlock has a point, only part of which has to do with whether Chicken McNuggets are bad or good for you. What he's really exploring -- economics, choice, education, advertising and the abuses of corporate power -- has larger cultural resonance. His point is at the end of a very sharp stick. If nothing else, it's meant to wake you up.

SUPER SIZE ME (Unrated, 98 minutes) -- Contains obscenity, vomiting, a glimpse of a rectal exam, discussion of sex and sexual dysfunction, shots of gastric bypass surgery and other unappetizing things. Area theaters.

"Super Size Me's" Morgan Spurlock celebrates the end of his all-McDonald's diet with a party at McDonald's.