Chris Hemsworth, is that you?
"Just tried a new diet/training program called 'Lost at Sea,'" he wrote in the caption. "Wouldn't recommend it."
The former People's Sexiest Man honoree lost a crazy amount of weight and muscle for his role in "In the Heart of the Sea," a story about a group of sailors stuck out at sea for 90 days after having their ship destroyed by a massive sperm whale.
Based on a real-life event from 1820, the film is an adaptation from the book, "In the Heart of the Sea: The Tragedy of the Whaleship Essex" by Nathaniel Philbrick.
"We have to shoot the really skinny stuff where we drop down to five, six, 700 calories a day, [for] a good three or four weeks and it's going to be pretty uncomfortable, but we'll be together in our misery," Chris told ET (via Us) this summer.
"I spend more time thinking about food than anything else," he added.
"In the Heart of the Sea" hits theaters Dec. 11.
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