When he hears that two girls are suing McDonald's because they're obese, New York filmmaker Spurlock decides to eat an all-McDonald's diet for a month--with a few key rules, including the exclusion of any other food and a limit on his exercise so he's more in line with the average American. Starting as an exceptionally healthy young man, we watch him turn into a pasty, pudgy, mopey mess ... after only five days! A team of doctors (Isaacs, Hanjhu, Siegel), a nutritionist (Bennett), a physiologist (Rowley) and his vegan-chef girlfriend (Jamieson) all keep an eye on him, and along the way each urges him to abandon the experiment. They're all shocked at how devastating the diet is on his body--as destructive as going on a month-long drinking binge!

Spurlock constructs the film brilliantly, maintaining a darkly hilarious tone while continually jolting us with images of fat Americans, greasy fast food and, most tellingly, children who are programmed to overeat from an early age. During his diet he traverses America, examining the issue with an offhandedness that belies the strong material. We learn a lot about how the American food industry works, how it's drifted into such a dangerously unhealthy system and how difficult it will be to change.

Besides Spurlock's personal odyssey, which is funny and scary in equal measure, the film's strongest message centres on school food programmes that ignore health and nutrition in the name of efficiency and economy. Spurlock effortlessly shows how spurious each of their arguments are, how strongly in the grip of corporate greed we really are, and how the current system merely feeds into a system of obesity, hyperactivity and illness. That he can entertain us so much while teaching us something this important is a real achievement.