"Brothers" is all about transformation: Tobey Maguire's from doting father to scarred former prisoner of war; Natalie Portman's from loving wife to grieving widow and back again; and Jake Gyllenhaal's from familial black sheep to man on whom everyone begins to rely.

The transformations, though, weren't solely the territory of these fictional characters. As [article id="1627460"]Portman and Maguire[/article] told MTV News recently, their decisions to take on the roles required significant changes in their own lives.

"As I'm getting older, it's becoming more and more difficult to rest on the patterns of being sort of cute and girly," said Portman, a vet of fare like "Closer" and "Garden State."

While she's played a mother in past films, "Brothers" -- out Friday (December 4) -- offered the 28-year-old actress her first chance to play a significantly more mature character. Grace Cahill is the wife of a Marine named Sam (Maguire) seemingly killed in action, only to be rescued after months of Taliban captivity in Afghanistan. "It's definitely an exciting opportunity to get to play a more womanly character," she said.

Maguire, meanwhile, had to undergo a serious physical transformation to represent accurately the toll captivity took on Sam. "I dropped a bunch of weight," he said. "Through shooting and a break, I had five weeks, and I lost about 20 pounds, which is a lot of weight considering where I started out at."

It wasn't easy work for the 34-year-old, but through strict diet and exercise -- plus the knowledge that he'd be able to pig out once filming ended -- he was able to endure the ordeal. "It was very intense," he explained. "I just didn't eat a lot and worked out a ton. I got into a real focused mind-set. I knew what was necessary, I knew how long it was going to take, and I just had to do it."

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