Charlize Theron isn't a stranger to dramatic transformations for film roles; it's what won her an Academy Award back in 2004; but she's taken that aesthetic even further with her latest film 'Tully' which sees her star as an overwhelmed and, indeed, overweight mother of three.

Charlize Theron at the premiere of 'Tully'Charlize Theron at the premiere of 'Tully'

The 42-year-old made the brave decision to gain almost fifty pounds to portray protagonist Marlo in the movie, because she wanted to be accurate when it came to the struggles real mothers go through when they don't have the money for a private chef and personal trainer.

'The film deals with what parenting looks like today', she said on 'The Ellen Show'. 'It's so insane to me that we live in a time where we share so much information... but for some reason when it comes to parenting, there's still so much stigma around it and we just don't talk about a lot of stuff that parents go through.'

'Mothers do this every single day', she continued. 'They get pregnant and they gain all that weight and it takes them a year and a half to lose it and if they don't they get judged. I feel like I had to do it for the film if I was gonna go and play a mother who's having her third child. I felt a responsibility to that and I think for myself as an actor I wanted to feel as much as I possibly could.'

In the end, she found herself snacking on multiple bags of potato chips, her 'drug of choice', each day to gain weight, but eating so much junk food really took a toll on Charlize's mental health by the end of it.

'I wasn't prepared for how that amount of processed food will affect your mood', she said. 'And I dealt with depression for the first time. What they say about what you eat is kind of who you are is so true. Because I ate like a person who just didn't move and I felt like that and I was lethargic and tired all the time.'

It's not the first time Charlize has gained weight for a role. She played serial killer Aileen Wuornos in 2004's 'Monster', where she wanted to accurately portray the life of a street hooker who would eat and drink whenever she got a chance because there was no guarantee of a next meal.

More: Charlize Theron says weight gain made her depressed

She gained less for 'Monster', though it was much easier to lose it all when Charlize was just 27-years-old. 'I just didn't snack for a week and I was back into shape', she recalled.