For Mark Wahlberg, gaining weight to play a boxer-turned-priest packed a major punch.

On Tuesday, the actor appeared on "The Kyle and Jackie O Show" in Australia where he detailed how he physically prepared for the upcoming film "Father Stu."

"I would say it’s easier to stay in shape than it is to get in shape," the former Calvin Klein model admitted. "I put on 30 pounds… that was really difficult. I’m not getting younger."

The 50-year-old chronicled his transformation for his 18.1 million followers on Instagram.

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According to the outlet, the star put on the pounds in six weeks for the role.

Back in July, Wahlberg revealed on "The Tonight Show" that stepping away from his no-nonsense fitness routine wasn’t easy.

"Unfortunately, I had to consume, for two weeks, 7,000 calories, and then for another two weeks, 11,000 calories," Wahlberg said at the time. "Even when you’re full, I would wake up after a meal to have another meal. I was eating every three hours. It was not fun."

The father of four remarked that gaining and losing weight for a role has become harder with age.

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Mark Wahlberg

Mark Wahlberg said that gaining and losing weight for a role has become harder with age. (Reuters)

"Once the metabolism starts to slow down, it gets really difficult," Wahlberg explained. "I was trying to get this movie made for six years, we only had 30 days to shoot it, and so I wanted to really make it happen."

"And [I] was also crazy to have financed a lot of it myself," he shared. "So I knew I was on a ticking clock on my own dime, and you get things done pretty quickly when that's the case."

In May, Wahlberg told Jimmy Kimmel he planned to gain 30 pounds in six weeks by eating a "20-piece chicken nugget and 20-piece hot wings from Kentucky Fried Chicken with a six-pack of beer," as quoted by Men’s Health.

The assignment seemed fun for the actor – at first.

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Mark Wahlberg

Mark Wahlberg hosts the opening of F45 Training at Miramar MCAs, the first fitness franchise on a US military base on June 11, 2021, in San Diego, California. (Photo by Phillip Faraone/Getty Images for F45 Training)

"I’m like, ‘Dude, I’ve been on such a regimen for so long, I just want to eat everything in sight,’" said Wahlberg. "I want to go to bakeries, I want to go to Denny’s, I want to get pancakes. I want to get everything that I could possibly get my hands on."

Wahlberg has since returned to hitting the gym. In January, he posted a video of himself baring his toned torso and biceps.

"Had to whisper to not upset my wife for not wearing a shirt," Wahlberg joked in the caption.