‘He’s a maniac’, says Zac Efron’s Iron Claw co-star as Hollywood star undergoes insane body transformation for new movie

ZAC Efron has revealed the secrets behind his epic body transformation for wrestling movie The Iron Claw – liver and onions.

The Hollywood heartthrob, 36, has shown off his incredible muscular frame for his role as Kevin Von Erich in the indy film about the 'cursed' Von Erich wrestling family.

It is the High School Musical star's most dramatic body transformation to date after he also went to severe lengths to get into shape for the 2017 movie Baywatch.

As well as undergoing an intense training regime, Efron ditched his vegan diet for intermittent fasting which involves eating two meat-heavy meals a day.

"I started intermittent fasting just after I stopped being vegan," Efron told Men's Health.

"My body wasn't processing the vegetables in the right way.

"So, I decided to stop it and try something new. 

"Intermittent fasting has been really helpful with that."

After doing some morning cardio work, Efron breaks his fast around 11am with some bone broth soup and vegetables along with "clean proteins" like elk and chicken. 

In the evening, he has his second meal of the day, which comprises another serving of meat and "a healthy carbohydrate like sweet potatoes or quinoa."

The diet change means Efron can now eat organ meats once again.

"This is kind of weird, but I really like organ meats. I love liver and onions," he said.

Efron has gained the praise of Iron Claw co-star Jeremy Allen White about his dedication to his craft.

"Zac's a maniac," White told Esquire.

"He's so focused and knowledgeable on training, diet, all that.

"In terms of a physical transformation, I think he kind of blew us all out of the water. 

"He looks really amazing in this thing."

When White signed up for The Iron Claw to play Kerry Von Erich, Efron sent him a note which read: “Get training, eat, keep doing what you’re doing, stay hard.”

Efron has changed his habits since undergoing a dramatic body transformation for Baywatch, which he says was a challenge both physically and mentally. 

“I started to develop insomnia, and I fell into a pretty bad depression, for a long time,” he told Men’s Health US. 

“That Baywatch look, I don’t know if that’s really attainable."

As well as taking diuretics, Efron was overtraining and eating the same three meals every day. 

He also did not sleep enough – if filming stopped at midnight, he would still wake up at 4am to train. 

"Something about that experience burned me out. I had a really hard time recentering," he said. 

"Ultimately they chalked it up to taking way too many diuretics for way too long, and it messed something up.”

After filming wrapped, Efron took a break from acting and decided to get out of shape for the first time in his life. 

"At one point, that was a dream of mine – what it would be like to not have to be in shape all the time,” Efron said. 

“What if I just say, ‘F**k it and let myself go?’ So I tried it, and I was successful. 

"And for all the reasons I thought it would be incredible, I was just miserable. 

"My body would not feel healthy; I just didn’t feel alive. I felt bogged down and slow."

The Iron Claw is released to theaters on December 22.