This time the Bourne star says that gaining around 30 pounds to play whistle-blower Mark Whitacre in The Informant was slightly more enjoyable.
"I felt terrific, I really did love it," he reveals, before adding: "The gaining weight was alarmingly easy - just drinking beer, a lot of beer, even dark beer, and eating pizza and burgers, all the stuff you would normally tell yourself not to eat - and it came right on.
"I was always eating. If I wasn't eating a normal meal, I was eating Doritos and junk food, to pack it on."
Yet the Boston native now shows no sign of the extra weight.
"With the lack of exercise, it was probably two months before [the movie that] I started to put it on, and the movie was a couple of months. I think that was enough time for me," he laughs.
In his new movie The Informant, Damon moves away from his traditional 'Bourne Identity' and joins the more sedentary figures behind the world of American business.
Surprisingly, Matt's wife of three years, Luciana, gave the thumbs up to his new chubbier look.
"There was just more of me to love," he says, laughing.
"She was a good sport about it, and we had fun. I love parading around with my belly and my stepdaughter thought it was really funny too that I got all squishy."
Not only did the father-of-three put on weight for the Steven Soderbergh-directed movie, he also donned a dodgy barnet and moustache.
"The hair was spectacular, the wig," he recalls, grinning.
"His face is also rounder than mine so I had little things stuck in my gums to push my cheeks out. And I wore a fake moustache."
"Every day, people would come and watch us shoot, and invariably, somebody would say, 'Wow, you are so much better-looking in person'. I would say, 'Thank you' but would wonder if it was the wig, the moustache, the 30 pounds, the fake nose or the wardrobe. I don't know what this says about the mid-west but the people are extraordinarily polite."
The dark comedy, which is based on a true story, is set in Illinois, home to the original informant in the mid-Nineties.
"It's weird to make a period piece about a time I remember well," says Matt. "I remember walking into the first wardrobe fitting, going, 'What are they going to do with the clothes? I mean, the clothes are just like they are now'. I walked in and went, 'Oh my God, I forgot'. So that was kind of an eye-opener for me."
Matt, who won an Academy Award for his joint screenplay of Good Will Hunting with best mate Ben Affleck, jokes that the reason behind him saying, 'Yes' to playing Mark is to nab himself further Oscar glory.
"That's why we did this movie," he quipped.
"I tallied up all the things that seemed to gain awards and we basically made an algorithm and then wrote the movie around that. That's why I did it."
The multi-talented actor, who has branched out into producing, hasn't always been on such a winning streak. When director Steven Soderbergh rang him almost ten years ago, regarding Ocean's Eleven, Damon initially thought that he was being offered a writing job.
"I had just done two movies, which really tanked," he says.
"I was thinking that I was going to have to go back to writing because nobody had offered me a job in about nine months. It was in that climate I got a phone call from Steven and he said, 'I've found something for us to work on'. I thought he was giving me a job as a writer, and he told me, 'No, I want you to star in the movie'. It was the most unlikely phone call I felt like I could get."
The Informant! marks Damon's fifth reunion with the renowned director, whom he credits for improving his acting.
"There was one scene we talked about with this regressive interior monologue. I thought a lot about how to play that and then when I got to the scene, it turned out weird. Steven stepped in and gave me a little direction, and saved me from myself."
Matt, who became a household name after 1997's Good Will Hunting, has taken on a wide range of roles, from charming murderer Tom Ripley in The Talented Mr Ripley to amnesiac assassin Jason Bourne in the Bourne series.
Next up is the Clint Eastwood-directed Invictus with Morgan Freeman, which already has Oscar buzz around it, and thriller Green Zone. He's also lined up to star in the Coen Brothers remake of Sixties western, True Grit, which will also star Josh Brolin and Jeff Bridges.
Away from Hollywood blockbusters, Matt is known for his ongoing playful relationship with US comedians Jimmy Kimmel and Sarah Silverman, and is also featured on Team America: World Police as a puppet voiced by South Park's Trey Parker.
"I loved that. I was really happy to be in that, I really like that movie," he says.
"I still get people come up with pictures of the puppet and ask me to sign it, but they say: 'Can you just write Maaaaatt Damon?'"
Extra time - Matt Damon
Matthew Paige Damon was born in October 8, 1970, in Cambridge, Massachusetts.
He lived near best friend and future writing partner Ben Affleck while growing up.
His debut film role was in Mystic Pizza, in which he delivered one line of dialogue.
He met his Argentinian wife in Miami, where she worked as a bartender, and the couple tied the knot in December 2005. They now have three children - stepdaughter Alexia, and daughters Isabella and Gia.
He's not fussed about being a celebrity. "I found myself getting more publicly shy when the gala events and big crowds started. Some people embrace it. To me, it's not worth enough to risk my private life being public."
