"I still have plenty of vices, but alcohol isn't one of them," Jared told British GQ. "It's probably just down to sleep and diet. If you travel long-haul a lot or don't sleep much, [your body's] not going to last very long, that's for sure."
For exercise, the boyishly handsome Leto does yoga workouts, hikes, and cycles. "I'm a pretty adventurous hiker, so I like to crawl through the brush," he said. "I like to be outdoors. I never use an iPod. I like to hear the sounds of nature."
Jared, the frontman for the band Thirty Seconds To Mars, fasted for a month to play a transsexual woman battling AIDs in the drama Dallas Buyers Club (which co-stars Matthew McConaughey).
But radical body transformations are nothing new for the dedicated actor. In 2007, the naturally lanky Jared gained 67 pounds to play John Lennon's assassin, Mark David Chapman, for the film Chapter 27.
Jared, who binge-ate to gain weight, says the unhealthy diet and sedentary lifestyle took its toll on him physically and psychologically.
"To get into character I just ate giant pizzas and everything you know you're not supposed to eat. That's what you eat to gain weight like that. If you're a young actor reading this, you should never do that. It's really stupid. It's a mental and physical challenge. Putting on the weight was very difficult and very weird. I started every meal completely stuffed."
After losing the weight in 2008, Leto said he would never again gain weight for a film role because carrying the excess weight on his slender frame damaged his health.
"I'd never do it [gain a lot of weight for a role] again. It definitely gave me some problems. I don't know if it was gout, but I had a definite problem with my feet. I couldn't walk for long distances, I had a wheelchair because it was so painful. My body was in shock from the amount of weight I gained. It took about a year to get back to a place that felt semi-normal."