The Green Mile star swore off meat three years ago (09) and has been so impressed with the health benefits of his new eating regime, he's signed up to try to convince others to ditch animals from their diet.
He shows off his toned physique and rippling muscles in a new PETA billboard ad and is shown alongside the slogan, "I Am Michael Clarke Duncan, and I Am a Vegetarian".
The Oscar-nominated actor tells the campaign group, "The best thing about being a vegetarian for me, number one is I know I'm not harming any animals. The number two thing is increased strength. I'm a lot stronger than I was when I was eating meat.
"Most of your most powerful animals in the wild are vegetarian, so I'm trying to get my strength to that level. I don't know if I'll make it or not, but elephants are vegetarians. They're pretty big, so..."