Charlize Theron was gripped by depression when making ‘Tully’.

The 43-year-old actress – who has adopted children Jackson, six, and three-year-old August – gained 35lbs to play a struggling new parent in the movie and she thinks the change in her diet caused problems with her mental health.

She said: “It was about how hard it is to be a mom, no matter how that baby came to you. Whether you adopted or had children through a surrogate, it doesn’t matter – once that child is in your home there’s a challenge that comes with that. 

“When I got the script, my little one was four months old and I was delirious.

“I was like, ‘Yeah, I can completely relate to that’.

“I didn’t have any experience of depression, but weirdly as I was gaining the weight for the role, I actually became depressed for the first time in my life – I think because of the huge intake of sugar.”

(c) Instagram

And the lack of exercise also took its toll on Charlize, and she only felt herself again some time after the shoot had ended and her body had “equalised”.

She explained to the Sunday Telegraph magazine: “Fitness is something that I enjoy.

“I’ve never been a couch potato – I love to go and do yoga for an hour and a half. Not moving is not good for my head. 

“I dealt with depression for the whole shoot and afterwards, until my body kind of equalised itself. I have friends who have gone through post-partum depression, and in a weird way, my diet and how I changed physically for this role helped me feel, on a minute percentage, what it’s like for your body not to feel like it’s yours, to not feel like your head is yours.”

The Oscar-winning star’s friends thought ‘Tully’ was a “vanity project” – so they thought it was funny when they saw her appearance in the film.

She said: “When I was [first] telling him about it, he said, ‘That sounds like a real vanity project.’

“And then when he saw it, he texted me and said, ‘I love that a vanity project for you is getting fat and wearing sweatpants.’ “

Bang Showbiz