Chris Hemsworth 'Going To Bed Hungry' On 500 Calories A Day For 'Thor' Slimdown

Actor Chris Hemsworth packed on the pounds to play super-buff superhero "Thor" in the film's "The Dark World" sequel, hitting theaters today.

But his next role, a shipwrecked sailor in Ron Howard's "Heart of the Sea," requires Hemsworth to shed his "Thor" weight and more.

The film, which tells the story of the true events that inspired Herman Melville to write "Moby Dick," has its cast of "15 big, burly guys talking about their calorie count, what they should and shouldn't eat, what their cheat meal is going to be," Hemsworth told Jimmy Kimmel while appearing on his show this week.

"A bunch of sailors in a ship get struck by a whale. The ship sinks and they jump onto the small rafts and drift for 90 days and basically begin to die and eat each other," Hemsworth explains of the plot line.

"A romantic comedy," Kimmel joked, to which Hemsworth further explained, "we have to get rather skinny, so we're on about 500 or 600 calories a day."

So what exactly is the actor eating to shrink his body size?

"500 calories, you can drink that in one milkshake," Hemsworth laments, "So it ends up being a couple of small salads, a couple of small pieces of protein, and that's it, you go to bed hungry and have a fasting period of about 15 hours where you stop eating completely and then you have smaller meals throughout the day."

But, he admitted to the late night host, "I had a cheat meal a couple minutes ago, a bit of pizza."

"How many slices?" questions Kimmel, to which Hemsworth responds, "Like 10, I had most of it. But that's just once a week and then you feel really guilty."

"That sounds like the worst thing ever," jokes Kimmel. "You should be skinny for the next 'Thor' movie, like a really scrawny and starved Thor."

Watch Hemsworth discuss his diet on "Kimmel" below:

Here's Hemsworth with his extra 20 pounds of muscle as "Thor":

And here's Hemsworth at the film's premiere earlier this week, already noticeably slimmer in the midst of crazy crash diet: