Charlize Theron reveals the one snack she ate 'everywhere' while gaining weight for 'Tully'

Charlize Theron is a fiend for a certain processed snack.

The 42-year-old actress opens up on Tuesday's episode of The Ellen DeGeneres Show about her go-to junk food when quickly gaining 50 lbs. for her role in Tully, a movie about an overworked, overtired mother of three.

"I ate a lot of everything, but my drug of choice is potato chips," she confesss. "[I ate them] everywhere. I had a bag in the car, a bag in the bathroom, a bag in the kitchen, a bag on the couch, a bag in my trailer. Everywhere I went, there was just a bag."

Theron admits she was a bit blindsided by the effects that excessive snacking would have on her mental state, adding that she felt "lethargic and tired all the time."

"The hardest thing for me was I wasn't prepared for how that amount of processed food will affect your mood, and I dealt with depression for the first time," she shares. "What they say about, you know, what you eat is kind of who you are is so true. I ate like a person who just didn't move, and I felt like that. That was a hard thing to break, because it's more mental than it is almost physical."

For her role as serial killer Aileen Wuornos in 2003's Monster, the star says she actually gained less weight -- and it was easier to lose.

"I was younger, I was 27, and I just didn't snack for a week and was back into shape," she recalls of the role that earned her a Best Actress Oscar win. "It was insane. That doesn't happen anymore."

As for losing the weight after shooting Tully, Theron recently told ET it "was hell."

"It took about a year and a half. It was a long journey, very long journey," she explained. "And it's hard because I had press junkets and movies around it and nobody knew that I had done it for this. And I think in the beginning everybody thought it was, like, prosthetics. And then I went on press junkets, and it was like nobody knew."

Theron did express to DeGeneres that she feels Tully -- in theaters May 4 -- is a pretty accurate portrayal of modern-day parenthood.

"The film deals with what parenthood looks like today. It's so insane to me that we live in a time where we share so much information. We share the medication that we take, whether it's through social media or whatever," she said. "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. It's strange, like, I did this, yes. But mothers go through this every single day, and 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."

She added that being both an actress and a parent herself, she felt a responsibility to be as authentic as possible for the role.

"I feel like I had to do it for the film if I was going to play a mother who was having her third child," Theron added. "I felt a responsibility to that, and for myself, as an actor, I wanted to feel as much as I possibly could."

As for her own kids -- 2-year-old daughter August and 6-year-old son Jackson -- the movie star says "it's like war" at home.

"The last time I was here, the little one was a year-and-a-half, and the oldest was five. I didn't grow up with siblings so this is all new to me. Then, the older one would say, 'Let's do this,' and the little one would be like, 'OK!' It was a peaceful, beautiful, loving relationship that made me cry every single day," she tells DeGeneres. "Now I cry, but not because it's peaceful and loving anymore. The 1-year-old is now almost three, and she's like, 'No.' The older one is like, 'What?! What do you mean no?' It's like war in our house every single day. 'Don't touch me! Don't look at me!' 'I wanna be alone!' I'm like, 'Are they 13 already?' And one that says all of that with a lisp."

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