Matt Damon says it was hard to get in shape for Elysium because he's "become more of a glutton" as he's gotten older Credit: Jon Kopaloff/FilmMagic

All work and no food makes Matt Damon a crabby man. The actor had to stick to a strict diet and exercise plan to get in shape for his new movie, Elysium, and though he's done it before with no problem, he says this time was more difficult.

"I was grumpy on this set, because I was on a diet for the whole movie," he told Us Weekly at the film's L.A. premiere on Wednesday, Aug. 7, noting that he gets "quiet" when he's feeling cross. "I think I shut up a little bit and keep to myself."

Damon, 42, blames the mood swings on getting older. "It's not even that it was as extreme as diets I've done before, but it's like, at my age, I want to eat everything in my path, you know what I mean?" he quipped. "I think I've become more of a glutton."

Indeed, the married father of four told reporters at a New York screening of the sci-fi action flick that he struggled to stay motivated while filming. "It was really hard because I love to eat and I love to drink," he confessed. "I'm at the point in my life where somebody was silly enough to marry me and won't leave me if I put on a few pounds."

"I think [my wife, Luciana Barroso] likes the variety," he added. "When I did The Informant, I put on 40 pounds. I was like, 'You like this guy, too, don't you?' I'm trying to talk her into that guy. That's the guy I'm most comfortable being."