During an appearance on "Jimmy Kimmel Live" last week, the actor, 49, revealed he needs to gain 30 pounds for his lead role in "Father Stu," a biopic about boxer-turned-priest Stuart Long.
"After we do the boxing scenes, I get to put on as much weight as possible over the course of the film, so I'm challenging myself to put on 30 pounds in the next six weeks," Mark explained.
"They want me to do it as healthy as possible," he added. "I'm like "Dude, I've been on such a regimen for so long, I just want to eat everything in sight," said the star, who often details his 4 a.m. workouts and bone broth fasts on social media.
"I want to go bakeries," he continued. "I want to go to Denny's. I want to get pancakes. I want to get everything I can possibly get my hands on!"
In "real life," the character's heavy years presumably came after the serious motorcycle accident that led him to have a spiritual, out-of-body experience in the hospital, according to The Hollywood Reporter.
From there, Stuart is said to have "rediscovered his faith" and studied to become a priest. But his once sculpted body would never quite recover, due to a rare, degenerative muscle disease.
Mark, on the other hand, will have to snap back to his usual, ripped form pretty quickly. The Daily Man reports his next project after "Father Stu" is the long-awaited "Six Billion Dollar Man," a reboot of the '70s series, "The Six Million Dollar Man," that features Mark as a bionic man with superhuman strength.