Cillian Murphy's 'sacrificial' diet to become Oppenheimer shared by co-star

24 July 2023 , 14:22

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Robert Downey Jr. was impressed by co-star Cillian Murphy's dedication to his role in Oppenheimer

While filming Oppenheimer, Cillian Murphy took on a very restrictive diet. The goal was to keep him looking frail and feeble to better resemble the physicist J. Robert Oppenheimer. Co-star Robert Downey Jr praised Cillian for the work he put into the role.

Robert told PEOPLE : "I have never witnessed a greater sacrifice by a lead actor in my career."

He described the role as a "behemoth". Robert was candid about how Cillian had to dedicate a lot of time into preparing for the role, even forgoing fun cast trips to instead learn 30,000 words of Dutch. He also praised Cillian's "humility" that was needed to "survive" the role.

Robert Downey Jr saw first hand the work it took for Cillian Murphy to succeed in the role (Melinda Sue Gordon)

Cillian's intense diet is not something that he advises, but it was definitely part of his process for getting into character and delivering this show-stopping performance. He admitted to the Guardian, though, that it certainly had its downsides.

He said: “It’s like you’re on this f***ing train that’s just bombing. It’s bang, bang, bang, bang. You sleep for a few hours, get up, bang it again. I was running on crazy energy; I went over a threshold to where I was not worrying about food or anything. I was so in it, a state of hyper... hyper something. But it was good because the character was like that. He never ate.”

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Oppenheimer died from cancer in 1967, so his poor diet and habit of "cigarettes and pipes" may have caught up to him. Thankfully, Cillian only had to live on this diet for a temporary time period.

Cillian Murphy barely ate during filming (AP)

Cillian also said: "I’ve smoked so many fake cigarettes for Peaky and this. My next character will not be a smoker. They can’t be good for you. Even herbal cigarettes have health warnings now."

Robert said that this work is "the nature of [ Christopher Nolan 's] ask" to play Oppenheimer. He isn't the only co-star who applauded Cillian's work ethic and devotion. Florence Pugh weighed in as well.

She told PEOPLE: “Working with [Cillian] was hugely impressive. Every single day he shows up knowing every single possible way, intonation, inflexion of how to bring this character to life. That was hugely impressive to me. There’s a reason why he is one of the greats.”

Oppenheimer opened in theaters on July 21.

Alex West