Film anoraks may recall Renee Zellweger starring in films such as Return of the Texas Chainsaw Massacre (alongside the then unknown Matthew McConaughey), but it was not until hit film Jerry Maguire, where as the young woman who wins over the heart of a self-absorbed Tom Cruise, that she was thrown into the limelight.

Now she's back as the slightly plump, eponymous character of the eagerly awaited Bridget Jones Diary, a romantic comedy with Hugh Grant and Colin Firth. Adapted from the best-selling book by Helen Fielding, it humourously chronicles the small daily triumphs and tribulations of a woman in her early thirties, as she tries to kick her tobacco and alcohol addictions and searches for a more satisfying love life.

Meeting Renee Zellweger in Los Angeles she doesn't sound like a woman who had been talking enthusiastically to the press for the past four days. "It's the athlete in me that prepares me for this", the Texan native says with her slight Southern drawl in evidence.

It is precisely her Texan heritage that had Brit tabloids frothing when it was announced she would play the lead.

The actress - who is far from plump and far from British - laughs at the mention of controversy. "What controversy? I'm VERY excited about talking about that." The actress merely shrugs it off. After all, there are more important concerns she has, anyway.

"You know what? I put so much pressure on myself for everything ELSE that I do, that it could not possibly exceed what was already there.

In THIS case, I felt a responsibility to both Helen Fielding, [the author of the novel] because she created it, not me, and I did not want to blasphemise this beautiful character that she created."

As well as the voice coaching to fine-tune her English accent, part of Zellweger's preparations involved spending three weeks working undercover in a "job experience placement" for British publishing firm Picador in Victoria in London

It was an acting challenge, she says, little more. "The only thing hard about it was being away from home and loved ones and leaving the dog behind." But the characterisation, itself, she insists, was NOT hard. "It was a process, and so exciting to watch happen, because some of the stuff was slow in coming, but it was WORKING."

Zellweger also had to gain weight for the role, because that "was an important part to me, because I wanted it to be legitimate." She remained consistently coy about what she did in order to gain the weight for the role, merely referring to that part of her preparation as "boringly technical." This despite the media's growing obsession with the actress's gaining and then loss of weight.

Zellweger insists that both novel and film - that revolve around a young, insecure woman dealing with her life, work, eating habits and love - goes beyond the simplicity of a weight issue.

"It's about a woman who has a self-image issue and it's a big part of the theme of the film" which includes weeding through society's "definitions of what beauty and success are, for this generation of women, and finding your OWN happiness, defining it for yourself and determining your OWN self-worth. Hers is a struggle that is inclusive of those things and not specific to her, alone in the world. It's about the theme of self-acceptance."

Perhaps another magnet to this character was that it enabled this actress to re-evaluate her own self-worth in the Hollywood scheme of things. "I think it depends on how you define yourself and how you define your job as an actor. That's the fun part of it. It's fun to be a girl and play with that, dress up and become pretty sometimes. But I don't want to ever rely on that, I don't want that to be the core of what I depend on, in terms of my work experience. It frankly doesn't interest me.

My experiences with physicality revolve pretty much more around lifestyle. Like any girl I want to take care of myself and in every respect. But physicality for me is more about a reflection of lifestyle and trying to maintain a particular energy level when you have to sit in a room and talk for three days."

No wonder she played Bridget Jones with singular vision. Renee Zellweger has come a long way since Jerry Maguire. Those sceptical about her ability to portray Ms Jones may well be surprised at what they see.