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By Ree Hines

On Friday, filmgoers can see Chris Hemsworth hit the big screen in "Thor: The Dark World," but that might be the last they see of his muscle-bound physique for a while. The actor is currently on a low-cal crash diet for his next on-screen adventure.

In "Heart of the Sea," which is based on the real-life events that inspired Herman Melville's "Moby Dick," the 30-year-old star will show off his svelte, shipwreck look.

“A bunch of sailors in a whaling ship get struck by a whale, the ship sinks and they jump onto the small rafts and drift for 90 days," Hemsworth said of the setup during a recent visit to "Jimmy Kimmel Live."

He joked that the story, in which the sailors have to "eat each other" was basically "a romantic comedy." Alas, it's not. It's serious business, and Hemsworth is currently in the process of shedding serious pounds.

"We have to get rather skinny," he said. "So we’re on 500 or 600 calories a day. ... It's funny; you've never heard 15 ... big, burly guys playing sailors talk about their calorie count, what they should and shouldn't eat, what their cheat meal is going to be."

Hemsworth admitted that a weekly cheat meal is a must given his sparse daily intake.

"I mean, you can consume (600 calories) in a milkshake," he explained. "So it ends up being a couple of small salads, a couple of small pieces of protein and that's kind of it and you go to bed hungry. And then you have like a fasting period of 15 hours, like, you stop eating completely, and then you have little meals through the day."

And his cheats? The one he had before paying Kimmel a visit consisted of around 10 pieces of pizza, and that, he added, left him feeling "really guilty."