The star had packed on 30 pounds (13.6 kilograms) because he thought action scenes of toned Ward were complete, and he was caught out when producers wanted more ring drama.
The actor's longtime trainer, Brian Nguyen, who once worked as the fitness coach for the Jacksonville Jaguars football team, admits he and Wahlberg really struggled to get back the shape Wahlberg was in for The Fighter reshoots.
He tells Men's Fitness magazine, "He (Wahlberg) was having a whole bottle of wine at night and doughnuts at the craft table (to fatten up).
"They had to do reshoots for some fight scenes and were like, 'How long do you need, three weeks?' I was like, 'Three weeks? We've been doing nothing!'"
Miraculously, Nguyen managed to get Wahlberg back into tip-top shape in just five weeks.