While the first three weeks for Theron were “fun” with regular trips to In-N-Out for breakfast (including two milkshakes), the 12 weeks after were tough.
"All of a sudden you're just done eating that amount and then it becomes a job," she told the publication. "I remember having to set my alarm in the middle of the night in order to just maintain [the weight]."
Theron added: "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."
Losing the weight was "hell", too. "It took about a year and a half," the Atomic Blonde star said. "It was a long journey, very long journey."
Tully marks the third time Juno and Young Adult director Jason Reitman has collaborated with writer Diablo Cody.
Tully is released in cinemas in Australia on May 10.