I think the film makes a very strong case! One can't deny that there's something going on with the guy's heart by the end (not to mention that fun scene where he throws up out the door of his SUV). Ironically, the evidence that made the strongest case for me isn't in all of the versions. One part of his experiment involved obtaining fries from many different restaurants (including local ones). During the experiment, he let them all sit under glass basically rotting, ... just to see what happened to them. The fries from "fresher" sources all produced mold in a few days. The fries from other fast food restaurants were definitely showing their age in a week or two. However, the McDonalds fries looked exactly the same from beginning to end. There's something wrong with food that doesn't decay. Period.
Interestingly, a local news anchorman recently did what he called a "Drive Through Diet" where he only ate fast food for a month. After seeing Supersize Me, I thought, come on, this has been done. Ironically, this anchorman ended up losing 12 pounds. Unlike Supersize Me, he always chose water or diet Coke instead of regular soda. He didn't Big Mac's every day, and watched his calorie intake.
While Supersize Me likely showed a more realistic version of what fast food can do to the average consumer, I agree that it did not necessarily prove that McDonald's food is wholly unhealthy.
I think this movie makes its audience more aware of the facts about what they are eating. We may inherently know that there are "a lot" of fat grams in a large fry, but when confronted with the cooking method, actual amount of salt in and on the fries, and the fat and calorie counts, it is a different story. The fallacy of the movie, in my opinion, is that fast food is the problem. All restaurants are guilty of portion size and cooking methods that are not as healthy as they may be, but at the end of the conversation, a restaurant doesn't put the food in the mouth -- the consumer does. Films like this may help us think about the choices we make, but the obesity problem is WAY bigger than fast food menus.
I do not think that the movie proves this at all. It is possible to gain weight and become unhealthy eating more or less any kind of food. The weight gain came not from the inherent evils of McDonald's food, but from the abusive way in which Spurlock was consuming the food.
I do not believe McDonald's food is healthy, but I do not believe that it is so unhealthy that it would cause health problems when eaten in moderation. Spurlock may have proved that McDonald's pushes excessive portions on its customers, but that is not the same as proving that simply eating their food (in a more disciplined way) would cause a significant level of damage to one's health.
I think that Spurlock's film did prove that consuming McDonalds can cause health problems. Granted, Spurlock's investigation is a fixed context, in that there was nothing consumed only McDonalds' food for a month, but the effects noted over small periods of time were quite staggering. Consider that Spurlock gained about ten pounds in under a week and by the three week mark, Spurlock had suffered heart palpitations. I think that these end up compelling the viewer to fully grasp that there was, and to a significant extent, still is a health challenge in consuming McDonald's food on an uncontrolled basis. The film is not indicating that McDonalds consumption is on the same level as Spurlock's. Yet, rather the large level of McDonalds consumption has to be seen on a larger scale, the scale at which the company engineers profits as well as targeting sales to younger kids. This consumption has to be seen in the context of Spurlock's film, causing a great deal of reflection and thought. In this light, the film was successful in its attempts. McDonalds stopped advocating the concept of "super sizing" meals and became more responsive to offering up salads and other "health conscious" means on their menus.