Fans of actress Jennifer Aniston know that she's a huge fitness buff and loves to work out; the former 'Friends' star is known for her slender physique and pleasant nature. However, when Jennifer Aniston prepared for her lead role in 'Cake', a story about an emotionally broken woman seeking respite in painkillers, she reported how cranky and unhealthy she needed to be.

"It's interesting when you stop exercising," Aniston tells the Daily Mail, "My stamina was shot. I was cranky. I was irritable... I'm really not any of those things."

Not taking care of her body didn't only change her physically; it took a toll mentally as well. As Aniston continued to gain weight for the film she realized the importance of exercising for her state of mind, and her soul. She began to grow depressed throughout the filming despite her usual positive nature. Plus, Aniston began to develop insomnia, she had problems sleeping regularly.

About her depression and insomnia, Aniston says, "I surrendered into it. I actually didn't fight it..." Even with the hard work, Jennifer says that she loved the role, and loved the character.

"This woman going through the most unimaginable drama... I also found her layered and complicated and funny." Jennifer describes her mental transformation as painful as her physical change. "To go that deep into someone's psyche was hard to even imagine," Jennifer admits. She often had trouble getting up and moving because her character, Claire, was so dark and unfortunate.

Jennifer Aniston's sacrifice seems to have paid off. She has been nominated for a Golden Globe award and is rumored to be a serious contender for an Oscar nomination.