Firth bemused at interest in Zellweger's weight

The attention Renee Zellweger received over her up-and-down weight changes for the Bridget Jones movies has left co-star Colin Firth bemused.

"It's not that unusual for actors to alter their appearance to play a part. But I think if I did it, it wouldn't get anywhere near the amount of attention," he told the Boston Herald.

"It's absolutely fascinating to people that a woman would dare to do that - particularly someone who's very attractive and has a Hollywood-based career. They must sort of see her as reckless or something."

Zellweger, who stars in the new movie Bridget Jones: The Edge of Reason, once again piled on the kilos to portray the British heroine she first played in 2001's Bridget Jones's Diary.

Firth reprises his role as Bridget's lawyer-boyfriend, Mark Darcy.

Zellweger has said she would consider a third visit to the cult character.

Speaking at the London premiere for "Bridget Jones: The Edge of Reason" on Tuesday, Zellweger said that if author Helen Fielding were to write a third book, she would consider starring in the film.

"I guess you'd have to start by asking Helen Fielding if there's gonna be another book but sure, it'd be a lot of fun," she said in reply to questions from a Sky News reporter.

The movie opens in New Zealand on November 18.