Last updated: Sep 26, 2008

One Tree Hill star Sophia Bush is only 26, but for her, good health is a lifelong mission. “Ive started to treat my health like a science project,” says Bush, who can rattle off lists of bone-density-building exercises and antioxidant-rich foods with aplomb. Bright and refreshingly levelheaded, the Pasadena, Calif., native is the only child of father Charles, a photographer, and mom Maureen, who runs a photo studio. And Bush has done her parents proud: You wont find her spilling half-naked out of a limo. (In fact, the only time she made tabloid news was when she and her Hill co-star Chad Michael Murray divorced in 2005 after five months of marriage.)

Bush spends most of the year commuting from her Los Angeles home to the Wilmington, N.C., set of One Tree Hill, which has just started its sixth season. (Shes also in two upcoming films: The Narrows and Table For Three.) In her limited spare time, Bush is a passionate advocate for health-care reform, a role she took on after witnessing loved ones who have fallen ill. Here, she holds forth on that cause and much more.

Any scoop on the new season of One Tree Hill?
The show is going to be really exciting this year, because its taken a dark turn—everyones struggling with hard issues.

Lets talk fitness. You work out with a trainer, right?

With the long hours on the show, its hard to get in the gym. But when I was home in L.A. for the summer, I spent four days a week with my trainer, Jason Walsh, who is just…the dude. And I spend a lot of time with Harley Pasternak too. Theyre the best trainers in L.A., and they share a similar attitude of “We dont want you to be skinny, we want you to be in the best shape for you.” Im not a waif–y girl and never will be. I think its healthy when fitness experts encourage fitness rather than getting a certain body shape. And Im Italian—I love food. Im not going to cut out bread and pasta and wine to be thinner.

Plus, youre more fun. We all have friends who wont touch any bread.
Im not going to dinner with somebody who eats like a bird, nor do I want to eat like a bird. But its weird: In our business, Im a size 2 and considered curvy. Its important to remind young women, “Listen, even skinny girls have cellulite, even Halle Berry has cellulite, and what you see in photos isnt totally real.”

Youre into boxing as well, right?
I love to box. I once took a kickboxing class in college and got totally hooked. One of the things Jason and I do is heavy-bag training. He puts on the padded gloves, and we do combinations. Its a good thing as a woman to feel powerful, and boxing is a great way to work out all your aggression.

Any other workout obsessions?
I just got a vibrating plate called a VibraSlim and Im so excited about it. You can work out on it, but I use mine after a workout to shake out my muscles. And whats neat is that it helps you build bone density. Im 26 now, and thinking about the fact that women are developing osteoporosis in their 40s.

Youre passionate about health-care reform. How did you get involved?
Its easy to be in your 20s and feel like youre invincible. But I had a friend who at 23 went through two rounds of lymphoma, beat cancer, and then had to beat it again. And my grandfather died of lung cancer last year, which was really hard. Ive had many family members go through the health-care system, and it just shocks me that we leave so many people by the wayside in this country.

So are you more vigilant with your own health?
Its the reason Im not a smoker or a big drinker, and its why Im getting more active. For me, fitness isnt about wanting to be rated with Jessica Alba on the “Hot 100” list. I want to be able to hike the mountains of California with my grandkids. And I dont want to go through what I watched my grandparents go through.

You seem so grounded.
To be honest, Im amazed that other people arent! I think the weird “Im fabulous, Im entitled to everything” attitude that pervades parts of Hollywood is nauseating.

How do you combat stress?
Calling my mom or my best friends to say hi, because hearing their voices makes me feel better. Or, I go to the gym. (Read about Sophia's typical Saturday night.)

Ever had trouble with your weight?
I think we all have. You can look up old episodes of my show and see when I was being far too friendly with the craft-services table. Because Im 5-foot-4 and athletically built, if I gain 5 pounds it looks like a lot. And when that lovely female time of the month rolls around, Im like, “Can I have my jeans a size up, please?” But I feel you should treat yourself in moderation.

Youre very focused. Whats next for you?
Of course, I have a set of things I want to achieve. But I also dont like to think too far ahead because then you stop paying attention to your life. Its more important to me to make sure Im being a good friend, a good coworker, a good daughter. The important thing is to be happy every day.