Leto has previously put his youthful appearance down to living a vege-based lifestyle.
"It's probably just down to sleep and diet," he told Rolling Stone in 2016. "If you travel long haul a lot or don't sleep much, it's not going to last very long, that's for sure.
"I don't eat meat ever," he said. "But if someone's mum made a cookie and handed it to me, I'd probably take a bite, or if I'm in Alaska and there's wild salmon out of the river, I'd probably eat it."
The 50-year-old star plays former vice president and managing director of Gucci in the new film House of Gucci, starring alongside Lady Gaga and Adam Driver. The movie tells the true story of Patrizia Reggiani who served 16 years for plotting the murder of her husband, Maurizio Gucci.
