I hate Super Size Me. It's a terrible movie, a terrible documentary, and makes an example of what's fundamentally the wrong way to tell a true story.
To begin with, Morgan Spurlock sensationalizes his decision to eat McDonald's food as an experiment. It isn't. Any valid experiment follows the scientific process. Any valid experiment can be duplicated. His, I guarantee, can not, because he leaves out much of the truth throughout the movie. Morgan Spurlock is a journalist, not a scientist or a nutritionist of any sort, and the movie shows it.
He starts out on what's nearly a vegan diet, because he eats with his girlfriend, who is a vegan, often. Whether that diet is balanced or not, honestly, we don't know. It wasn't well documented, though it would need to be for us to actually perceive anything Spurlock does as meaningful. I'm not going to claim I'm a nutritionist, either, but I will say that with a little research, you'll find drastic, sudden changes to one's diet can have a severely debilitating effect.
Anyway, moving beyond the basic scientific issues with the film, I have to mention that Spurlock decided to leave out a few nice facts. Most specifically? A major portion of his calories came from milk shakes. Milk shakes are single-handedly the worst menu item at a variety of places. Milk, itself, is unhealthy, contains high volumes of fat and calories. Add in the sugar, and it's a bit worse. Had Spurlock wanted to take an honest approach, he would have at least divulged that he favored milkshakes enough that his nutritionist would site them as being the most debilitating part of his diet. In fact, at least according to wikipedia, his nutritionist said 1/3 of his calories were from soft drinks and shakes.
That's not normal, and clearly that's not healthy. That's also not an aspect of normal McDonald's food, either. Oh, also, he's refused to publish food logs of what he ate during his "experiment." Why, if this thing actual was an experiment, would documentation like that not be released?
Spurlock's goal was to create a piece of sensational media. What you see in the movie isn't based on scientific fact. It's there to elicit a sudden, knee-jerk response. Without the documentation of a food log, it's impossible to duplicate the actions Spurlock took. He's withheld information to elicit a false moral high ground, and people jumped to react to it. Take a look at the movie Super Size Me to see a lot of lies and misleading of the truth.
I'm not saying that a McDonald's diet or a fast-food diet is good for you, I'm not saying it's bad. I'm saying that using Super Size Me as a source for anything is just a poor decision, and I encourage you to invest some time into looking into the facts and realities of the movie, as well as the facts and realities of nutrition in general.