http://portland.indymedia.org/en/2004/01/279198.shtml
The film is called Super Size Me: A Film of Epic Proportions and the director, Morgan Spurlock, at only McDonald's food (not the healthy stuff) for 3 meals a day for a month. If a server asked him if he'd like to supersize his meal he had to accept, and eat every bit of food on his plate. Within a few days of starting the experiment he was vomiting up his meals and battling headaches and depression.
After the monthlong experiment he had gained a ton of weight and his cholesterol had risen from 165-230. His liver was nearly ready to give out at the end of the month. Disgusting.