To paraphrase a comment in the guide book, if you don't care what you look like, feel free to eat as much junk food as you want! You'll still get in great physical shape, you just won't look like it
That being said, if you haven't seen the movie "Super Size Me", I would go watch it, and then consider whether you really want to keep eating that stuff. (Though I must add that when my fiance and I watched that movie about a year ago, we picked up some KFC on our way back from renting the movie

) If you're set on eating fast food though, for whatever reason, try to stick to the menu items in the back of the nutrition guide, and try not to eat out more than once or twice a week.