Super Size Me was ridiculous, I bought into it too, but he was going out of his way to eat unhealthy at McDonald's. Even McDonald's puts nutritional information out there and doesn't recommend the daily intake of calories that guy was making.
The point is that they do recommend it, just not in the tiny print. 99% of what they say is "eat more", 1% is "with care".
The advertising shows combinations of items, the staff offer upsizing for a deal, etc. Their business model clearly takes advantage of upselling and impulse buys.
SSM is a story about what happens to someone who doesn't know any better and just goes to the convenient restaurant, eating the standard portions they sell. It's best viewed with that other documentary, about the guy who got skinny eating at McDs (and exercising!). It's not (strictly) the food that does it, but the portions and lifestyle it encourages.
