PICTURES: See Chris Pratt's Dramatic 60-Pound Weight Gain!

Chris Pratt is the anti-Matthew McConaughey.

To play a lawyer in the forthcoming comedy flick Starbuck, the 33-year-old actor was asked to put on a significant amount of weight. (The film centers around Vince Vaughn, whose character learns he's fathered 533 children through sperm donations.)

"I gained 60 pounds in about four and a half months. I just did it the old fashioned way: eating and drinking my face off," Pratt shared on The Tonight Show With Jay Leno Dec. 10. "I've lost a little bit of it, but it was hard. It was probably just as hard as losing weight. You wouldn't believe it, but it is. It's these same principle: It's all about pain."

Pratt continued to pack on the pounds while shooting season 5 of NBC's Parks and Recreation. "Our props department claimed that I ate 81 scoops of ice cream. It was really messed up," he laughed. "It's hard to have delicious ice cream around you and not eat it. When you're waiting around for everyone to get the scene set up, you're still eating ice cream."

"I've eaten weird things through the course of my life," added Pratt, who grew up in Lake Stevens, Washington. "I've eaten wild game, I've eaten possum -- possum's no good."

The actor also chatted about his new movie, Zero Dark Thirty, in which he plays a Navy SEAL who is tasked with capturing or killing Osama bin Laden.

"I got in good shape for that movie. I was able to go with [costar Joel Edgerton] to the BUD/s training facility in Coronado and got to meet real SEAL team guys," said Pratt, who welcomed firstborn son Jack (with wife Anna Faris) in late August. "I was very nervous to meet these guys because I didn't know how they were going to be. They're the kind of strong that they don' t have to tell you or prove to you that they're strong. You know!"

Chris Pratt and Anna Faris on December 10, 2012 in Hollywood, California.
Credit: Jason LaVeris/FilmMagic

Pratt even participated in some training drills. "They knew that I'm not the physical specimen that they are, and they were humble and kind about it," he recalled.

The actor filmed most of his scenes in the Middle East. "There have been terrorist attacks in Jordan . . . I didn't know a whole lot about where I was going, so I was nervous. But they're an ally to the U.S. and they treated us really well. . . Other than security measures at the hotel and metal detectors everywhere, it felt pretty safe."