"I think [I've lost] probably a little over 20 pounds, something like that," the actor, 32, told PEOPLE Monday on the red carpet at the Hollywood Film Awards, where he looked noticeably thinner as he was honored for his role in Prisoners.
While he may look different, his approach hasn't changed as he prepares for Nightcrawler, Gyllenhaal said.
"It's not different than getting into character for anything. It's more about believing where you are and being present where you are," he said. "Who's to say what the process is? I have a strange one … but I love what I do."
Meanwhile, fellow honoree Matthew McConaughey continues to put the weight back on after his memorable transformation for Dallas Buyers Club. The actor, 43, told PEOPLE that the five pillars of his life – career, parenting, love, friendship and health – are all nicely in sync at the moment.
"I've got a great wife and family who support what I go do," he said. "Everything's at a good level right now, and I've been trying to keep it that way."
Sandra Bullock, Julia Roberts and Harrison Ford also stopped to chat with PEOPLE, and to reflect on their good fortune in Hollywood.
Asked how her Hollywood experience has changed since becoming a mother, Bullock, 49, replied, "I don't know if the roles have changed, but the person in the roles has. You know, I don't look at anything the same anymore. I can't imagine what it was like before, because I don't remember. I don't know if the roles have changed, but I have. A lot."
Roberts, 45, gushed about working with Meryl Streep in August: Osage County, calling it "a lifelong dream" and saying Streep was "more than I could have ever wished for as a castmate and a friend."
And Ford, 71, said he was looking forward to more modest yet rewarding roles going forward. "I lucked into this leading-man business," he said. "And look, it's been very, very good to me. But I've always wanted to be a character actor. And I'm looking forward to those opportunities as my career, such as it is, progresses."