The original Super Size Me has been criticized by a lot of people for being fraudulent. A couple of other people went through Spurlock's claimed method and rules, and ended up with much less damning results. Check out the links in the Wikipedia article.
It is depressing how many documentaries are full of crap. From unrelated stock footage to distorted facts easy check able in the internet era to glaring omissions, it is almost as infuriating as TV shows' general habit of bloating 10 minutes of content into 22 minutes+commercials.