I think the movie was made more for entertainment rather than having a real scientific value, Mr Spurlock, of course, is a director, not a researcher.
What I see, nowadays, as a risk, along with the utter lack of exercise, is junk drinks more than junk food; now that, in general, the western society is more aware of the risks involved with eating junk food on a regular basis, we’re still struggling, though, with getting rid of junk drinks, like soda, soft drinks, industrial fruit juice and alcohol.
A documentary I liked, on the topic of food, was “Food Inc.”, during the documentary they interviewed a low-income family, and they said that going to Burger King and drinking Coca Cola, was cheaper than buying healthy groceries and water.
Or, at least, I think that part was in that documentary.