- Actor Chris Hemsworth built huge muscles to play Thor with the help of his personal trainer Luke Zocchi.
- But one of his most challenging roles required him to lose a lot of weight quickly, Zocchi told Insider.
- Intermittent fasting was crucial for hitting the weight loss goal and the results were "crazy" he said.
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Actor Chris Hemsworth is best known for sporting a god-like physique as Thor, and building and maintaining Marvel muscles takes a lot of hard work and strategy.
But his trainer's proudest moment was getting Hemsworth to drop a lot of weight to play a shipwrecked sailor 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 only during a certain window of time during the day.
Zocchi said intermittent fasting is 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 was 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 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 the other 16 hours of the day.
"We implemented intermittent fasting along with lower calories and it was crazy how much that worked," said Zocchi.
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 co-stars stuck to a diet of just 500 calories a day).
-Chris Hemsworth (@chrishemsworth) November 22, 2015
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 and definitely not without professional supervision. Major weight loss can also lead to side effects like muscle loss, which impairs strength and slows metabolism.
However, actors often have to gain and lose weight for their roles, sometimes drastically, so trainers rely on all the techniques they know for 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.
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 "The Huntsman: Winter's War," and maintained a bulkier physique for his role as himbo Kevin in the 2016 "Ghostbusters" remake.
By the time "Thor: Ragnarok" begain 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 bulk up again for "Thor: Love And Thunder," which comes out in 2022.
He has published his 10-week diet and training program - with adaptations for different levels of strength and experience - on Centr Power.
