Matt Damon plays a pathological liar in Steven Soderbergh's "The Informant!" — the true-life story of an agribusiness executive who blows the whistle on his company's price fixing schemes with international competitors.

Soderbergh said Monday at the Venice Film Festival, where his comedy is showing out of competition, that lying plays an important function in life — as long as the lies don't get out of hand.

"I think lying is very important and necessary. It does take a lot of energy. It is one of the ways I stay thin," Soderbergh told reporters.

Damon didn't have that luxury for the role of Mark Whitacre, an Archer Daniels Midland executive who exposed the price fixing-scandal while covering up his own million-dollar path of extortion. He had to both lie, a lot, and put on 30 pounds (14 kilograms) for the role.

"It was very, very easy to gain the weight. Very, very fun," Damon said. "I just basically ate everything I could see for a few months."

Soderbergh first talked to Damon about doing the role seven years ago. They did three other movies in the meantime.

In Soderbergh's words: "Seven years of foreplay and then a quickie."

"Steven's theory on comedy is you make sure the screenplay is perfect, and then you shoot the actual production really, really fast," Damon said. "So that is what we did. We stewed on the script for seven years, and then shot this film in 30-something days."

At up to eight pages a day, Damon said the pace was close to a television schedule.

Soderbergh said he purposely did not meet the real Mark Whitacre before filming — in contrast to "Erin Brockovich" and his two films about revolutionary Che Guevara, for which he tried to meet everyone involved in the real story that he could.

"The strange thing is, that Whitacre has seen the film and has said it was very accurate," Soderbergh said. "Maybe on 'Che' and 'Erin,' I was wasting my time."

Source: AP