Colin Farrell says it wasn’t hard to gain 40 lbs. in just two months for his new role as a father of two in the satirical comedy The Lobster– it just meant he had zero portion control.

“I just ate and didn’t move for a while,” Farrell, 39, tells PEOPLE of how he packed on the pounds. “It was stuff I normally eat, but just a lot more of it. People talk about portion control – there was no control!”

As soon as the film wrapped, Farrell dedicated himself to losing the extra weight. "I dropped the weight so quickly just by starving and working out," he explained.