Visionary yo-yo dieting in which you sometimes appear very buff to your friends, and sometimes you appear very fat.
"What's going on with Steve? He had a beer belly last week, and now he has abs."
"I don't know man, I think he's having a Matt Damon Effect"
"I don't know man, I think he's having a Matt Damon Effect"
by superawesomeguy1496 October 6, 2011
Get the Matt Damon Effectmug.