Actor Chris Hemsworth had a "pretty moody existence" while losing a drastic amount of weight for his new movie.

The 32-year-old hunk had to drop 33 pounds (14.9 kilograms) on a diet of 500 calories a day in just four weeks for his role in Ron Howard's new drama In the Heart of the Sea.

The star has made no secret of how much of an effort it was to shift the weight from his frame, and admits he finds it so much easier to put on the same amount of weight to play Marvel superhero Thor.

"The gaining is fine, you just eat a lot and you lift weights but that was underfed, which led to a pretty moody existence and inconsistent emotions," he said during an appearance on Good Morning America. "You play all sorts of games: 'If I eat this maybe I don't eat that'. The insanity is nuts."

However, Chris found the restricted diet helped him better capture his character Owen Chase, one of a group of men stranded at sea for 90 days after a massive whale destroys their ship.

"In order to do it justice, the story, we had to suffer in some way and we did," he said. "In other words, not a whole lot of acting was required. We were desperate."

Chris has previously revealed how his diet consisted of "a boiled egg, a couple of crackers and a celery stick".

In comparison, his diet for Thor includes a wider variety of foods.

"To get back to looking like Thor is simple: I get in the gym and work out," he told Men's Health. "I enjoy it. It keeps me fit and healthy. I've got to eat more calories - certain types and all clean - and it can get boring eating chicken breast and rice and so on. But at least you're fed properly."