One Tree Hill star and FitCeleb Sophia Bush is only 26, but for her good health is a lifelong mission.

“I’ve 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.

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. Sophia recently spoke with Health magazine about all this and more, and here is a part of the interview: 

Let’s talk fitness. You work out with a trainer, right?
With the long hours on the show, it’s 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. They’re the best trainers in L.A., and they share a similar attitude of “We don’t want you to be skinny, we want you to be in the best shape for you.” I’m not a waify girl and never will be. I think it’s healthy when fitness experts encourage fitness rather than getting a certain body shape. And I’m Italian—I love food. I’m not going to cut out bread and pasta and wine to be thinner.

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

You’re into boxing as well, right?
I looove 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. It’s 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 I’m so excited about it. You can work out on it, but I use mine after a workout to shake out my muscles. And what’s neat is that it helps you build bone density. I’m 26 now, and thinking about the fact that women are developing osteoporosis in their 40s.

You’re passionate about health-care reform. How did you get involved?
It’s easy to be in your 20s and feel like you’re 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. I’ve 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?
It’s the reason I’m not a smoker or a big drinker, and it’s why I’m getting more active. For me, fitness isn’t 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 don’t want to go through what I watched my grandparents go through.

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.

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 I’m 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, I’m like, “Can I have my jeans a size up, please?” But I feel you should treat yourself in moderation.