
Cillian Murphy has revealed the toll that starving himself took on his mental health during filming of In the Heart of the Sea.
The 39-year-old star lost 20lbs in just six weeks to play a naval officer of the Essex, a 19th century whaling ship which was attacked by an aggressive bull whale, leaving the crew stranded.
Based on the true story that inspired Moby Dick, it required Murphy and co-star Chris Hemsworth lose weight rapidly.
"It was done in stages," Cillian told the Sunday World magazine. "First, we were all in the gym and having steak for breakfast, getting very fit but lean, working on about 3,500 calories.
"But by the time we got to [the set at] the Canaries, it was sorely reduced. Our food intake was maybe 500 calories, which is an egg, some salad leaves, very little."
The movie, directed by Ron Howard, did not have a budget to allow the actors to go away and lose weight gradually so they were forced to do so on set as they filmed.
Cillian was relieved he was not around his family (wife Yvonne McGuinness and sons Carrick (10) and Aran (8) as he said he went "slightly mad".
"I actually think I went mad during it," he revealed.
"There was a slight form of madness. Your brain isn't getting enough sustenance and you go through all these emotions; you're hysterical, you're lucid and then you're weeping all the time. It was just a very strange, odd experience."
In the Heart of the Sea is out now.