Jennifer Aniston spoke with Jason Bateman about how she transformed for her Oscar-buzzy role in Cake, explaining that she "stopped working out" to gain weight and even lowered "the cadence of her voice" Credit: Pixplus/Bauer-Griffin/GC Images

Jennifer Aniston really threw her weight behind her role in Cake. In order to play Claire Simmons, a woman who suffers chronic pain after a debilitating car accident, the Friends alum had to completely transform herself -- and that meant, among other things, adding a few pounds to her famously fit frame.

Aniston, 45, spoke about her make-under at an American Cinematheque screening of the film in L.A. on Nov. 19, telling her host (and Horrible Bosses costar) Jason Bateman about the lengths to which she went to get into character. At one point during the audience Q&A portion of their chat, she was asked by a fan how she gained weight for the part.

"I knew that was coming," she replied. "I basically just didn't work out for two-and-a-half months. I stopped working out and I stopped being as careful about my diet as I normally am. I was still healthy, but I'd allow more."

Another part of her transformation required the Life of Crime actress to go completely without makeup on camera, save for some shadowing to enhance the dark circles under her eyes. "That's a byproduct of the character," she told Bateman of the bare-faced look. "I've said it before: It's very refreshing."

She added, "There's a level of fearlessness. I think that you have to be able to sort of go, 'F--k it, I'm ready to just disappear.'" Read all the Oscar buzz for Aniston.

To do that, she said, she had to dig deep and access another part of herself. "First it was just understanding the logistics of what the accident was -- where did the pain exist, what was the injury," Aniston explained. After that, it was about mastering "the cadence of [the character's] voice, lowering the voice into her body," the Aveeno skincare spokeswoman continued. "Because I can tend to be up here." 

Fake scars helped to complete the make-under. "There was a big concern with the scars...We did a lot of experimenting and we had an extraordinary makeup artist make these scars for us," she explained. "We did some trials, some scar test days. Oh, if you could have seen some of the pictures, it looked like Chainsaw Massacre kind of stuff, you know? Like Freddy Kruger."

Ultimately, she told Bateman, they figured out just the right look "And by the end, I didn't even notice they were there," she said. "And I also thought they were...I don't know, I thought they were kind of beautiful."