While Charlize Theron is no stranger to changing her appearance for roles, including shaving her head for Mad Max: Fury Road and putting on weight for Monster, the actress’s most recent experience changing herself for a role came with an unexpected side effect.

In Tully, Theron plays Marlo, an exhausted mom to two young kids and a newborn, and for the role, the Academy Award-winning actress put on 50 pounds. But while the actress called the first few weeks of gaining weight for the role “fun,” she added that over time, the experience of having to push herself to gain weight began to take a toll on her mentally. She revealed to Entertainment Tonight that in order to keep up with the regimen needed to successfully gain the weight, she was eating at all hours, adding that she even set alarms in the middle of the night.

She explained, “I would literally wake up at two in the morning and I’d have a cup of cold macaroni and cheese just next to me. I would wake up and I would just eat it…I would just, like, shove it in my throat. It’s hard to maintain that weight.”

Adding that she wanted to gain the weight to really get into the reality of an exhausted woman with three young kids, the Atomic Blonde actress revealed that while putting on the weight and filming Tully, she began to feel depressed.

Catch a glimpse of Theron’s transformation in the Tully trailer:

Tully also stars Mackenzie Davis, Ron Livingston, and Mark Duplass and opens in theaters on May 4th.