Certain stipulations that Spurlock had to adhere to while filming...notice that exercise is nowhere on the Wiki for it?
Spurlock has specific rules governing his eating habits:
He must fully eat three McDonald's meals per day: breakfast, lunch, and dinner.
He must consume every item on the McDonald's menu at least once over the course of the 30 days (he managed this in nine days).
He must only ingest items that are offered on the McDonald's menu, including bottled water. All outside consumption of food is prohibited.
He must Super Size the meal when offered, but only when offered (i.e., he is not able to Super Size by his own accord).
He will attempt to walk about as much as a typical U.S citizen, based on a suggested figure of 5,000 standardized distance steps per day,[8] but he did not closely adhere to this, as he walked more while in New York than Houston.
Like a mathematical equation, or a good public speaker, the result can be elicited with a little know how and being clever. It's not always what you say, but what you do not say.