Zellweger gained weight not once, but twice, to play the title role in "Bridget Jones's Diary" and the sequel, and has referred to her preparation for the part as "boringly technical."
According to the Daily Mail, Zellweger, who is a slim size six normally, added enough pounds to her frame to play an average size-14 woman. At the time she was filming the second installment, "Bridget Jones: The Edge of Reason," she told About.com that she felt the role called for the extra weight.
"It had to be authentic to me," she said. "It had to be. And if you're not going to become the character and be the character, then I don't really see the point in undertaking the experience. I wanted to have that experience and people were suggesting to me, 'Oh, it might not be necessary.' Or, 'You shouldn't do as much as you did last time because it's probably not healthy.' For me, then it would render the experience pointless from a creative perspective. I wanted to revisit this character in every respect."
But whether she will revisit the character a third time seems less certain – especially if it means gaining and losing weight a third time.
"Can I just tell you my body is whacked by the time we finish one of those," she told a reporter at the Daily Mail last December. "I had a panic attack with all the specialists talking about how bad this is for you, long term, putting on that much weight in short periods of time, and they're all saying, 'You must stop this now or you're going to die'."
For the film "Chapter 27," in which Jared Leto plays John Lennon assassin Mark David Chapman, the normally thin young actor gained 62 pounds. Packing on the pounds wasn't easy.
Leto, who was a vegetarian at the time, would down a large Dominoes pizza every night for dinner, he told an interviewer on Sirius satellite radio. "It actually wasn't any fun. Some people think, 'Oh it was enjoyable,' but I was force feeding myself to such an extent that I would throw up in the back of my throat every day. My body was falling apart, and it was just really bad."
He also got treated differently. "There [were] some funny situations where a very powerful person ran into me, and they looked at me, and they were like, 'Oh, you've just grown up, haven't you?'" he said.
When filming wrapped, Leto couldn't wait to take off the weight. "Eight days after I was done with the film, I fasted for 10 days, and I got right back on the road with [rock band] 30 Seconds to Mars."
He told about.com that gaining weight was harder on his body than losing was. "I felt absolutely fine in losing the weight," he said. "It was putting the weight on too fast that I felt that I was pushing things too far."
To play the super-svelte Deena Jones -- modeled on naturally thin Diana Ross – for the film "Dreamgirls," Knowles lost 20 pounds, an idea that, she told reporters at the Cannes Film Festival premiere, was her own.
"The director [Bill Condon] actually kept telling me to 'eat, eat, eat' for continuity, but I really wanted to go all the way," Knowles said. "I was inspired by Tom Hanks. He did it all the way [for "Castaway"], so I said, I can do it all the way!"
"At the beginning [of filming], I was my normal weight," she said. "I actually gained a little bit, but then I lost 20 pounds when I went from young Deena to old Deena. I wanted it to be something more than just make-up and hair. I wanted to see the change."