Matt Damon: I just ate everything I could see

Looking tanned and trim, Matt Damon declared his latest film challenge as "probably the funnest time I've had working."

He also enjoyed making the movie The Informant!

What PEOPLE's former Sexiest Man Alive was describing was adding 30 lbs. – not to mention the cheesy moustache, hairpiece and glasses – to become nearly unrecognizable for his role as Mark Whitacre, an agricultural company's vice president-turned-FBI informant.

"It was very, very easy to gain the weight," Damon told reporters at the Venice Film Festival on Monday. "It was very, very fun, probably the funnest time I had working because I didn't have to go to the gym after work and I just ate everything I could see."

Based on a true story, the comedy – which costars Two and A Half Men's Melanie Lynskey and Scott Bakula – is Damon's latest collaboration with Oceans director Steven Soderbergh.