Filmmaker Adam McKay encouraged the Despicable Me star to plump up a little to portray money manager Mark Baum, based on real-life financier Steve Eisman, so he took advantage of the opportunity to pig out on junk food.

"I gained like, 25 pounds," he reveals to U.S. breakfast show Good Morning America. "Adam MCKay, the director, asked me to put on some weight because the character, the guy dresses well, but doesn't necessarily look good in clothes and is always a little bit 'schlubby' (sic), so I ate a lot of deep dish pizza."

Steve had no problem gaining the extra weight and he felt a strange pride when Adam applauded his chubbiness at the start of the shoot.

"I showed up the first day and Adam said, 'Wow, you're really fat!'," he recalls. "And it was a compliment, it was great! It think it's the only way that that's acceptable."

The Big Short is based on the 2010 book of the same name by Michael Lewis, about the real-life financial problems which led to the worldwide economic downturn of 2007-2008.

Brad Pitt, Christian Bale, and Ryan Gosling also star in the movie, and Steve claims he wasn't the only one looking less than his best in the film.

"Ryan walked out of his trailer for the first time in his look and I said, 'Never look like that again, don't ever do that!'," Steve laughs. "He's such a good-looking guy and it's a bad, bad (style)... it's a creepy look. I don't know what it is, but it works for him (in the film)."