Chris Hemsworth’s Shocking ‘Heart of the Sea’ Weight Loss

Chris Hemsworth posted a startling photo of himself on Instagram Sunday night in which the normally muscular actor appears gaunt and disheveled. (Getty Images)

“Just tried a new diet/training program called ‘Lost at Sea,’” he captioned the photo. “Wouldn’t recommend it.”

(Instagram/chrishemsworth)

The photo is from Hemsworth’s time filming the shipwreck movie, In the Heart of the Sea, which hits theaters mid-December. In the movie, the 32-year-old actor plays a 19^th-century sailor named Owen Chase who is marooned on a lifeboat-sized ship with his crew and forced to battle the elements.

The Thor star told Entertainment Weekly that he lost 15 pounds for the role, which was tough because he was already fit. “When I started, I was leaner than my Thor weight,” he said. “When you’re already starting off lean, it’s brutal to chew through that kind of weight. Every pound feels like a kilogram.”

To lose the weight, Hemsworth and his fellow cast members gradually ate less food, consuming just 500 calories a day at one point. (According to the USDA, an active male the same age as Hemsworth should eat 3,000 calories a day.)

“We kind of went insane, weighing ourselves every day,” Hemsworth said. “That’s all we spoke about. You’ve got 15 burly blokes on the sea and all we talked about was our diet, and who’d lost more weight, and who’s looking really skinny. It’s ridiculous!”

While Hemsworth had a sense of humor about the experience, experts say that kind of extreme calorie deprivation can be dangerous.

“A diet involving extreme calorie restriction will likely result in inadequate intake of key nutrients—protein, fat, carbs, fiber, vitamins, and minerals,” New York City registered dietitian Jessica Cording tells Yahoo Health. “Aside from being unpleasant to adhere to, it can cause digestive discomfort, mood problems, and low energy, among other things.”

It can also cause hair loss, brittle fingernails, and very low blood pressure, registered dietitian nutritionist Beth Warren, author of Living a Real Life with Real Food tells Yahoo Health.

Restricting your food intake can have a serious impact on your metabolism, Warren says. While you may mentally know that you’re restricting your calorie intake, your body simply thinks you’re starving and shifts your metabolism into a much slower, preservation mode. “You also break down muscle due to the lack of sufficient protein in the body, which also contribute to a slower metabolism,” Warren says.

It can also take a mental toll. “You have to think beyond the potential weight loss and understand that calories are your body’s fuel source to do what it needs to get done,” Warren says. “You cannot drive a car without enough gas and the same goes for your body without enough food.”

While severely restricting caloric intake for a short period of time may seem like an easy way to lose weight, Cording points out that it actually doesn’t work for any longer period of time. “Once you return to eating normally, you will likely see the weight pile back on,” she says. It can even make you gain more weight, she adds, because it can negatively impact your metabolism over time.

Take it from Chris Hemsworth: Severe calorie restriction is just a bad idea.

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