'The weight gain was worth it'

"Every time a boxer goes into the ring they are risking their life," she says. "For me, it was a movie, but my trainer, Hector Roca, thought that I should know what it's like to get hit. In movies you see a lot of people get hit and they come back like this." And she does a big dramatic move, flaying her neck back.

"But if you really get hit you come back like this." She tucks in her chin and lights some kind of fire in her eyes.

"They wanted me to put on 10lb of muscle, but I didn't think that was enough, so I put on 19lb." For those 19lb she had to sleep for nine hours, because that's when muscles grow. "But I couldn't go that long without eating, so I had these protein shakes in the middle of the night."

So was it like having a baby, getting up in the middle of the night for feeds?

"Yeah, but the baby was myself. The million-dollar baby, right."

I wonder how her husband, Chad Lowe (brother of Rob, an actor and director) dealt with the change in sleep pattern.

"I was eating 210 grams of protein a day, and for that you have to drink an incredible amount of water. So I would wake up to go to the bathroom two or three times a night anyway."

Did she ever think, this is too tough, I can't do this?

"Well, there were moments, but my trainer's belief in me would push me through, so I would just plug my nose and drink 12 egg whites in one sitting and punch and study my form for almost half the day. Now I have so many friends who are boxers, I go to matches all the time and it will always be one of my preferred workouts. I've lost 13lb, but the extra six I'd like to keep on. I like the idea that you can look really feminine and really strong."

She is wearing jeans and a pink long-sleeved T-shirt with the word Love embroidered in it. "I bought this two days after we wrapped and my arms wouldn't fit into it. I almost got the next size up, but Chad said, 'No, no, no, you'll fit into it.'" She is very couply with Chad. Couply enough to go shopping together.

Does she worry that these roles with such huge transformations will have a serious effect on her mental state and physique? I remember reading that, a couple of weeks after playing Brandon, Swank had felt lost somewhere between being a man and a woman.

"Well, there was a moment where I thought I wouldn't want to have a broken nose for the rest of my life. But, you know, I'm not a worrier. People say to me that I don't play feminine characters. To me, Maggie is really feminine. I would say feminism comes from strength. It comes from being comfortable in your own body. I think that's beautiful. My mother had that. She's so strong and self-made."

Hilary did get acting work when she hit LA. Fortunately, she was sacked from the teen TV series Beverly Hills 90210 and landed the part of Brandon only weeks later. Chad was the more famous soap actor when they met. Is there professional jealousy now she is so successful? "Never. We've always supported each other. It's not like Chad is going to get my roles. If you're not comfortable with someone's success, you shouldn't be with them.

"Look, we've been happy for 12 years," she adds. "But I wouldn't want people to look at our relationship and think it's easy, because it's not. We met, that was luck. But relationships take work."

What has changed since her first trip up to the podium to collect the Oscar six years ago?

"I've become a woman. My relationship has deepened with my husband. I'm still not quite ready for children," she says. "They'd have to come first. It would be strange to have someone else raise your child.

"But there's nothing in my life I would change because I'm really content."

Million Dollar Baby is out now.