updated 11/30/2010 AT 11:00 AM ET
•originally published 12/05/2010 AT 10:00 AM ET
“She ended up winning. She gained about 15, 16 pounds. He gained 14,” the film’s director, Derek Cianfrance, told PEOPLE at Monday’s Gotham Independent Film Awards sponsored by Euphoria Calvin Klein.
“Michelle was eating a pint of ice cream for breakfast and dinner and avocado sandwiches all day. She wanted to do it. She talked about her character having a certain self-hatred.”