Matt Damon was always grumpy on the set of 'Elysium'.

The 42-year-old actor underwent a tough fitness regime and had a strict diet to get in shape for the movie and admitted giving up treats left him angry and unapproachable.

He told Us Weekly: ''I was grumpy on this set, because I was on a diet for the whole movie. I think I shut up a little bit and keep to myself.

''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? I think I've become more of a glutton.

''It was really hard because I love to eat and I love to drink.''

Matt - who raises four daughters Alexia, 14 , Isabella, six, Gia, four and Stella, two, with wife Luciana Barroso - previously revealed his wife doesn't mind when he changes shape for movies because she ''likes the variety''.

He said: ''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 likes the variety. 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.''