Mark Wahlbergwent all in on his transformation for his upcoming movieStu.

“It’s the mustache,” Wahlberg joked, before admitting the truth.

“It was fun for about an hour.

Mark Wahlberg

Mark Whalberg on Fallon.NBC

And then it’s such a hard, physical thing to do.

Losing weight, you just kind of tough it out, you just don’t eat, and exercise.

And this, even when you’re full, you’d wake up after a meal.

I was eating every three hours.”

So what kept Wahlberg motivated?

The drive for making (and producing) a film he was passionate about.

“Once the metabolism starts to slow down, it gets really difficult.

“And I was also crazy to have financed a lot of it myself.