Nick Jonas can't seem to keep his shirt on these days. But with a body like that, who's complaining?

The 22-year-old singer recently posed shirtless for Details magazine and discussed how he got his body into stellar shape for his new DirecTV series "Kingdom."

"I had about six weeks to put on 12 to 15 pounds of muscle before filming started on Kingdom-my character is a fighter whose strong suits are wrestling and grappling," Jonas told the magazine. "Diet had a lot to do with it. I went from consuming about 3,000 calories a day to 4,200! Plaeta, food-delivery service, sent me three meals a day and snacks. It was an incredible way to know that I was getting what I need to build muscle and not have to think about it. Breakfast was usually an omelet with veggies and cashew cheese, a turkey-meat patty, and some fruit; lunch and dinner would be lean protein, veggies, and nuts; snacks consisted of things like snap peas with peanut sauce."

The former "Jonas Brother" is no stranger to watching what he eats. Nick has been very vocal over the years about living with type 1 diabetes.

"I don't have the luxury of eating whatever I want whenever I want anyway, because of my type 1 diabetes, so I have been conscientious about food for a long time," said Jonas, adding, "I do have guilty pleasures, though. I wasn't drinking at all while I was training for the show, but now that we're done, I keep it classy with Coors Light."

So where does the busy celeb go to get back to get back on track after he splurges?

"If I've had an indulgent night, I try to make up for it as soon as possible the next day," said Jonas. "First thing I do if I'm in Los Angeles is go to Voda Spa and sit in the steam room, sauna, all of it-try to sweat out as much as I can. Then I'll go work it out. I have a trainer in West Hollywood, Gregg Miele at Heart and Hustle gym. When I was getting in shape for the show, I was doing three sessions a day: one fight-training with Kingdom's coach, Joe "Daddy" Stephenson, and two strength-building with Gregg. Each workout focused on a different region of the body-upper body, core, or legs-and we'd do a circuit of six different moves for one area. Lifting a lot of weights, really trying to break the muscles down.

Nick also reveals that he and girlfriend Olivia Culpo has a favorite Los Angeles workout spot that has helped him switch up his fitness routine.

"I got pretty Hulk-ish. Now that I'm on tour for my album, I've leaned out about 10 pounds from what I'd gained. It's been fun to change my physicality. My meal plan came down to about 2,500 calories, and the portions got really small. I exercise only three or four times a week. I've been working on stretching and lengthening my muscles with hot yoga-my girlfriend introduced me to Modo Yoga on La Brea-and I'm trying to incorporate more cardio. But I hate going to the gym. I think everybody hates cardio to some degree. I'm not the kind of person who wakes up in the morning and can't wait to work out. I kind of dread it, actually. I see it as a necessary evil."