The 'Informant!' actor – who plays overweight Mark Whitacre, an agricultural businessman who becomes an FBI informer, in the film – piled on 30lbs for the role, and delighted in gorging on calorific treats.
He said: "It was very, very easy to gain the weight. It was very, very fun, probably the most fun time I’ve had working because I didn't have to go to the gym after work and I just ate everything I could see."
Matt, 38, feasted on fast food and crisps to put on the weight, making sure he snacked throughout the day.
He explained: "I definitely got doughy. I started eating like crazy and drinking dark beer. Between meals on set, I'd eat a Value Meal at McDonald's and then Doritos on top of it. It was absolute heaven."
Matt – who was voted People magazine's Sexiest Man Alive in 2007 – has had less fun trying to regain his toned physique, but is hopeful a stringent exercise regime will help him buff up his body.
He revealed: "If you put it on, it's easier to get it back off. I'm just boxing. I figure if you get hit enough times, it will fall off! Now I'm the Sexiest Man Alive's chunky cousin."
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