Fitness may run in the family, but Katherine Schwarzenegger — the eldest First Daughter of California — isn’t pumping up iron. The 20-year-old University of Southern California junior just penned her first book, “Rock What You’ve Got: Secrets to Loving Your Inner and Outer Beauty“, a self-helper for tween and teen girls. Of course, it’d be hard not to notice that Katherine’s drop-dead gorgeous, but she readily admits her own struggles with insecurity. She chatted with Express about body image, Photoshop and those darned real-life Disney princesses.

Why did you choose to write about body image?
I got inspired when I did an internship at Dove when they came out with their Campaign for Real Beauty. I read a lot of really interesting statistics there, like that 70 percent of girls don’t engage in their normal activities when they feel badly about their body. I also took a class at school about the effects of the media on young women.

Our mothers didn’t have the same sort of body image pressure that we have. Why are things worse after just one generation?
I think it has a lot to do with the invention of Internet. Young girls have access to absolutely anything. The media changed so drastically from when our moms were our age. Every image of a celebrity is Photoshopped, and young girls think it’s real.

You’ve said you heard your tween cousins talking about wanting to be “thin and sexy.” Are pornography and oversexualization of women linked to low self-esteem?
I don’t know about pornography, but I definitely think that the oversexualization of young girls [is a factor]. Almost every young actress today has a sexual appearance. Young girls look to Miley Cyrus and other Disney actresses, and they see them as one person on television and another in public. Young girls want to be like them and that’s dangerous.

How did your father’s emphasis on fitness influence you?
I grew up with fitness being a large component of my life, more so than the average girl. But if anything, it definitely helps me because it made fitness and working out a routine thing in my life. But the fact that my dad was a bodybuilder didn’t have anything to do with the way I felt about my body. I looked at his and I could say, “Yeah, it’s a great body, but it’s not something that I want to look like.”

The fashion industry argues that clothes just hang better on stick-thin models. Thoughts?
I think most fashion designers view models as being a hanger for clothing. Having a curvy woman wear something gives it attitude. I get that designers don’t want the model to have personality because they want you to focus on the outfit, but that’s really ridiculous. You don’t want to applaud women who have eating disorders or tell them to “keep it up.” It’s a bad message.