Jonathan Prime/Warner Bros.

  • Chris Hemsworth built huge muscles to play Thor with the help of Luke Zocchi, his personal trainer.

  • But one of his most challenging roles required him to lose a lot of weight quickly, Zocchi said.

  • Intermittent fasting was crucial for hitting the goal weight and the results were “crazy,” he said. 

  • Visit Insider’s homepage for more stories.

The actor Chris Hemsworth is best known for sporting a godlike physique as Thor, and building and maintaining Marvel muscles takes a lot of hard work and strategy.

But his trainer said his proudest moment was getting Hemsworth to drop a lot of weight to play a sailor after a shipwreck for 2015’s “In the Heart of the Sea.”

“Everyone thinks of him in Thor, being big and muscly, but this was the big accomplishment for me. It was a huge challenge for us,” Luke Zocchi, Hemsworth’s longtime personal trainer and friend, told Insider in an interview coordinated by Centr, Hemsworth’s wellness app.

He said a key component of the body transformation was intermittent fasting, a popular diet technique that involves eating during only a certain window of time each day.

Zocchi said intermittent fasting was now his preferred strategy for boosting weight loss, for celebrities and everyday dieters alike.

Intermittent fasting can boost weight loss when exercise fails, Zocchi said

For the role, Hemsworth had to lose as much weight as possible and get progressively skinnier throughout the film. Zocchi said it was particularly challenging because the actor was already lean after losing weight for a previous role and used to working out intensely.

Hemsworth stuck to a rigorous workout schedule to burn calories during filming, but exercise alone wasn’t enough to keep him shedding pounds, Zocchi said.

“He was so tired from all the training we couldn’t add any more workouts, so nutrition was a big deal,” Zocchi said. 

To change things up, Hemsworth began eating all his meals within an eight-hour window each day, fasting for the other 16 hours.

“We implemented intermittent fasting, along with lower calories, and it was crazy how much that worked,” Zocchi said.

Intermittent fasting isn’t for everyone, and research on its effectiveness is mixed.

But Zocchi said it gave Hemsworth an edge in hitting his goals when they had tried everything else, including severe calorie cutting (at one point, Hemsworth and his costars stuck to a diet of just 500 calories a day, Entertainment Weekly reported).

Actors have to lose weight quickly, but it can be risky

Rapid, extreme weight loss can be incredibly risky, even for actors with plenty of resources and support such as Hemsworth, George Clooney, and Joaquin Phoenix.

You shouldn’t attempt severe calorie restriction at home or without professional supervision. Major weight loss can also lead to side effects like muscle loss, which impairs strength and slows the metabolism.

Actors often have to gain and lose weight for their roles, sometimes drastically, so trainers rely on all the techniques they know for the best results.

For Zocchi, intermittent fasting is the one.

“It’s a really good system to help lose weight. I always go back to that,” he said.

Video: What 8 Marvel movies looked like behind the scenes

Bulking up again

Shortly after “In the Heart of the Sea” hit theaters in December 2015, Hemsworth had filled out again for his next role in “The Huntsman: Winter’s War” and maintained a bulkier physique for his role as Kevin in the 2016 “Ghostbusters” remake.

By the time “Thor: Ragnarok” began filming in summer 2016, Hemsworth was back to his divine proportions to play the god of thunder again. 

Most recently, Zocchi worked with Hemsworth to help him bulk up again for “Thor: Love And Thunder,” which comes out next year.

He has published his 10-week diet and training program – with adaptations for different levels of strength and experience – on Centr Power.

Read the original article on Insider