Matt Damon returned to his high school weight to portray Odysseus in Christopher Nolan's The Odyssey.

The Oscar-winning actor, 55, stars as King Odysseus in Christopher's adaptation of Homer's ancient Greek epic, which follows the legendary warrior's 20-year journey home after the Trojan War, and Matt has now described the physically demanding production as the most challenging film of his career.

To prepare for the role, Matt reduced his weight to 167 lbs - his high school weight - while adopting a strict diet and undergoing an intensive fitness regime before filming across Iceland, Scotland, Greece, Italy and Morocco.

The Odyssey, which opens in cinemas on 17 July, also stars Anne Hathaway as Odysseus' wife, Tom Holland as his son, alongside Robert Pattinson, Zendaya, Charlize Theron, Lupita Nyong'o, Jon Bernthal, Mia Goth, Benny Safdie, Himesh Patel, Elliot Page and Samantha Morton.

The project follows Christopher's Oscar-winning success with Oppenheimer, while Matt remains best known for films including Good Will Hunting, The Bourne franchise, The Martian, Saving Private Ryan and The Talented Mr. Ripley.

Discussing the physical preparation for the role, Matt was quoted by People saying: "I didn't change it in an unhealthy way."

He continued: "I think if I had done the opposite and put weight on, that would have been dangerous and it's not something I'll do anymore. I was happy to do it earlier in my life."

To portray the battle-weary Greek king, Matt explained changing his diet became central to the process.

He said he eliminated gluten, "among other things."

The actor added: "It was more about just getting really, really physically fit, which just really involves changing your diet, just a whole lifestyle change.

"You have to just be very, very intentional about everything you're putting in your body."

Filming took the cast and crew across several countries as they recreated Homer's mythical world using large-scale practical locations alongside visual effects designed for IMAX presentation.

Looking back on the experience, Matt said: "This movie was by far the hardest movie to the most challenging movie I've ever been a part of."

He explained everyone involved had been "completely maxing out and straining against what they thought was possible".

Matt compared the production to a real-life expedition rather than a conventional film shoot.

He said: "It really felt more like an expedition than a movie."

Matt added: "And if you were cold and wet, you just turned and you looked and Chris was just as cold and just as wet and going through it."

By the end of each filming week, exhaustion had become routine.

Matt said: "People were just running on fumes."

He added: "But that feeling of elation when we would get to the end of a week and we'd look around and it was a real sense of pride like, 'Okay, that's another week.'

"And I would go home like everyone else and just kind of sleep, get my rest and be ready for Monday. I loved every minute of it."

For Matt, however, the most meaningful reaction came after sharing the completed film with one of his daughters.

He said: "I have one daughter who's really not reverential at all about (my movies) and loves to give me s***."

Recalling her response to his latest effort, Matt said: "She saw The Odyssey, and at the end she actually turned to me and she said, 'Dad, I'm proud of you'."

He added with a laugh: "She's never said anything like that, because we joke around a lot. At that point I was kind of like, 'I'm good. It was all worth it'."

Christopher's adaptation of The Odyssey follows Odysseus as he battles storms, mythical creatures and impossible odds in an attempt to return home to Ithaca.