Mark Wahlberg has revealed his regret at the extreme diet regime he followed to gain weight for his role in new boxing movie Stu.
The 50-year-old action movie stalwart told Jimmy Fallon on The Tonight Show that his three-week weight gain was a physically demanding and unpleasant experience.
He had to pile on the pounds over a short period to play Father Stuart Long, who was a boxer before becoming a priest in his later life.
Wahlberg said: "Unfortunately, I had to consume, for two weeks 7,000 calories, and then for another two weeks, 11,000 calories. And it was fun for about an hour.
Watch: Mark Wahlberg shows off body transformation
"It's such a hard, physical thing to do. Losing weight, you just kind of tough it out. You just don't eat, and exercise.
"And this, even when you're full, I would wake up after a meal and have another meal. I was eating every three hours. It was not fun."
Wahlberg admitted that gaining and losing weight for movies has become increasingly difficult as he has got older.
He said his devotion to the process in this case was partially driven by the fact the movie was a passion project which he had partially financed himself and had just 30 days to shoot.
"I knew I was on a ticking clock on my own dime, and you get things done pretty quickly when that's the case," said Wahlberg.
Boxing-based movies have often driven actors to extraordinary physical transformations, with stars including Miles Teller and Jake Gyllenhaal getting ripped in order to step into the ring.
Most famously, though, Robert De Niro gained around 60 pounds to play Jake LaMotta in some of the later scenes of Martin Scorsese's 1980 classic Raging Bull.
Read more: Marking the 40th anniversary of Raging Bull
Wahlberg's latest film — sci-fi action tale Infinite — recently debuted in the USA via the new streaming service Paramount+.
He will be seen next in the video game adaptation Uncharted, in which he portrays Sully — a father figure to Tom Holland's protagonist Nathan Drake.
Watch: Mark Wahlberg shaves head for new role