The 43-year-old actor was on a liquid diet for a month and said he kept losing weight during the film's shoot, reported News.Com.Au.
"I was on a liquid diet for about a month under the watchful eye of doctors," the actor said.
Wahlberg plays the role of a literary professor whose gambling addiction sees him run afoul of gangsters.
"I continued to lose weight during the shoot but I was relieved when it was over and I could start eating again," he said.
When asked about his rapid transition to his normal size, the actor said, "It's a lot easier to gain it than it is to lose it.