Whatever you believe about the best diet to control diabetes, this new documentary "Fat Head" is bound to shake up those beliefs. I have been studying and trying to practice good nutrition for years, and even so, some parts of it disturbed me. Still, most of it delighted me. This is a funny movie.

About half way through I almost stopped watching. "Fat Head" was beginning to look like a movie in praise of fast food.

A guy named Tom Naughton wrote, directed, and starred in this 104 minute film. Like Morgan Spurlock in his 2004 documentary "Super Size Me," Naughton lived on fast food for a month. But unlike Spurlock, Naughton lost weight.

For one thing, Naughton didn't eat anywhere the 5,000 daily calories that Spurlock claimed to consume. But neither did Spurlock, according to Naughton, who says that it doesn't jibe with the record. For another thing, Naughton ate a lot more wisely, limiting himself to 100 grams of carbohydrate per day.

That's how the new documentary starts off. Since I never eat at fast food restaurants -- except one that specializes in great salads -- I was disturbed. Then, I heard Naughton say in the movie, "A fast food diet is not a good diet."

And the movie moved on. It turns out that Naughton wasn't making an apologia for fast food. The fast food industry, he says, is not at fault for what he calls the "so-called obesity epidemic," which he argues is really a high blood glucose epidemic. Instead, he argues for personal responsibility and against government intervention and interventionists like Michael Jacobson of the Center for Science in the Public Interest, who he calls "a tireless propagator of junk science."

But Naughton reserves his greatest contempt for Ancel Keys, who got so famous that Time magazine featured him on its cover for his manipulating the "lipid hypothesis" statistics in the "Seven Countries Study." Data from those seven countries seemed to show a relationship between a diet high in saturated fat and heart disease, but Keys conveniently ignored data from even more countries that didn't fit his hypothesis, which then became -- and still is -- the accepted wisdom of our medical establishment.

This makes "Fat Head" sound like a serious, dull movie. It is anything but that. In fact, it's closer to being a comedy than anything else. Naughton is a professional comedian who is also a former health writer. Consequently, "Fat Head" both funny and exceedingly thought-provoking.

Naughton just didn't eat in fast food restaurants, mostly McDonald's. He also went around interviewing real people. The people he talked with were men and women in the street as well as experts like Michael Eades, M.D., and his wife Mary Dan Eades, M.D., the authors of Protein Power; Mary Enig, Ph.D., and Sally Fallon, the authors of The Skinny on Fat; Al Sears, M.D., the founder and director of The Wellness Research Foundation and the author of The Doctor's Heart Cure; J. Eric Oliver, Ph.D., of the University of Chicago and the author of Fat Politics; and Reason magazine editor Jacob Sullum.