Acting is undoubtedly an art form and there are many ways of approaching it.
Some people learn their lines, turn it on when the director calls action, then knock off and go home. Others immerse themselves in the character for months on end, adopting an entirely new accent and way of life for the part.
The 49-year-old plays the part of Paolo Gucci, who was once chief designer and vice president of luxury fashion label Gucci, and it sounds like Leto really went the extra mile to accurately portray him.
Asked about how he captured the legacy of the character, he told i-D: "I did it all. I was snorting lines of arrabbiata sauce by the middle of this movie. I had olive oil for blood.
"This was a deep dive I did. If you took a biopsy of my skin, it would come back as parmesan cheese! This is my love letter to Italy.
"There was a lot of work and preparation, and yes, I had an Italian accent and I enjoyed and embraced that, and lived in that space as much as I could, and for as long as I possibly could.
"I climbed into that creative cave and came out through the bowels and intestines into the oesophagus of the one and only Paolo Gucci."
Wow. That is one hell of an answer right there.
Leto - who is also the lead vocalist for Thirty Seconds to Mars, a band he formed with his older brother Shannon - went on to explain that fully immersing himself in such a way made it easier for him to tackle such a daunting project.
He continued: "It goes back to Paolo's ass: Al Pacino (Aldo Gucci) feels bigger than me; Ridley feels bigger than me; it all feels bigger than me.
"It feels impossible when you look at it from the outside to stand toe-to-toe with your heroes. It all seems daunting.
"But that's the great thing about working immersively. You're so entrenched in your character that it's like going to war. You've been training for the battle and there's nothing that can stop you."
Leto stars alongside Adam Driver (Maurizio Gucci) and Lady Gaga (Patrizia Reggiani) in the movie, which comes out tomorrow (Friday 26 November).
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