The result? Twenty-five extra pounds (12kg), higher cholesterol and an award-winning documentary of his fast-food journey, Super Size Me: A Film of Epic Portions.
Morgan Spurlock hit the morning TV shows on Thursday to promote his film on surviving on a McDonald's diet, little more than a day after the company said it would stop oversized portions by the end of the year.
His tongue-in-cheek look at America's obesity crisis illustrates the effects of gorging on fast-food fare for breakfast, lunch and dinner.
"I felt terrible. You eat this food and you feel great immediately, but right after you get the McStomach aches, the McHeadaches - you get depressed," the New York-based director said on NBC's Today show.
Spurlock, 33, said he first got the idea after stuffing himself with a Thanksgiving dinner in 2002. He was lounging on the sofa at his childhood home in West Virginia when he saw a story about a lawsuit filed on behalf of two girls who claimed McDonald's caused their obesity. The suit was dismissed.
When McDonald's defended itself by saying its food was nutritious, Spurlock decided to test that claim.
"I thought if it's that good for me, I should eat it for breakfast lunch and dinner," he told ABC's Good Morning America show.
"You eat this food and you feel great immediately, but right after you get the McStomach aches, the McHeadaches"
When he began his McDonald's binge, he weighed 185lb (84kg). He ballooned to 210lb (95kg) by the end. His cholesterol rose by 60 points.
McDonald's Super Size option, which includes a 7oz carton of fries and a 42oz fountain soda, has been targeted by critics as contributing to America's obesity problem.
McDonald's, the world's biggest fast-food outlet, has given a cool reception to the documentary, which won an award at the Sundance Film Festival in January and is to be distributed across the US later this year.
McDonald's said changes in its menu did not happen because of the movie, but were rather to "support a balanced lifestyle".
"This film had a tremendous impact on their decision to eliminate super-size portions and it is really going to have an impact on people who see the movie on how they see their own diet," he said.
Since going off McDonald's, Spurlock has lost about 20lb (9 g), but says the last few are proving hard to shed.