I remember this documentary, and it was honestly one of the dumbest things I'd ever seen. There was, even before this came out, virtually no one who thought eating a shit ton of fast food was healthy for you.

A Guy who ate largely healthy, one day, suddenly started eating nothing but McDonalds. Even if the result wasn't obvious to pretty much everyone before this started, as an experiment it fails horrible because it comes as such a sudden shock to his system that bad effects happening to him would be inevitable.

Penn and Teller had a show back in the day called 'Bullshit' that talked a lot about this, and did far more to give out details about fast food than this documentary, all without the terribly conceived premise of stuffing yourself with nothing but fast food.