Katherine Schwarzenegger felt something was amiss one day last summer when she overheard her young cousins chatting with each other about their bodies.

“They’re 8 years old and were talking about how they don’t want to be fat and how they want to be ‘sexy,’ ” she said.

It wasn’t the first time the USC Annenberg School for Communication & Journalism junior had heard the girls and her other young friends divulge body image issues.

The 20-year-old daughter of parents Arnold Schwarzenegger and Maria Shriver, she is familiar with the struggle to maintain self-esteem. As a teen, her own battle to appreciate her self-worth was magnified under the scrutiny of the public eye.

In time, Schwarzenegger tackled her body image issues and earned self-confidence. To encourage other young women – and their mothers – she began writing about her struggle in Rock What You’ve Got: Secrets to Loving Your Inner and Outer Beauty.

The new book came out of her drive to counsel her cousins and other girls struggling with anxiety about their bodies.

“I want girls to read this and feel that it’s OK to be themselves and to understand that every girl can be beautiful no matter what size and shape she is,” she said. “You don’t have to look like you’re on a billboard to feel beautiful. I really wanted to correct girls’ perception of that.”

Throughout the book, Schwarzenegger weaves in interviews with experts, research (much of it derived from the Dove Campaign for Real Beauty, which she worked for as an intern) and statistics on eating disorders, body image issues, plastic surgery, birth control and other topics. Her “moms only” sections give advice to mothers aiming to raise healthy teen and pre-teen girls.

She tells her own story of growing up as the daughter of a famous bodybuilder-turned-governor and a mother who also built a successful career in front of the camera. Schwarzenegger’s mother faced her own pressures growing up under the strict food rules of mother Eunice Kennedy Shriver, who never weighed more than 100 pounds during most of her adult life.

As a result, “Mom never forced us to eat or stop eating,” Schwarzenegger writes. “She never policed us.”

Her father, on the other hand, was much more of a food watchdog and more prone to ask, “Are you sure you need that second helping?” And it was no fun for the children in the house when he was gearing up to film a movie and would tear through the house, trashing all the ice cream and junk food.

Schwarzenegger pulls back the curtain on the Kennedys as well – or at least how she felt growing up as a Kennedy. In the book, she reveals how she felt like a misfit during summers at her family’s compound on Cape Cod. The hairstyle, multiple earrings and dark nail polish she wore to express herself in Los Angeles made her feel “a little like the black sheep in my conservative extended family,” she writes. The questions and criticism from her cousins made her feel “insecure and lost.”

She credits her parents with the strict yet supportive upbringing that made her feel secure and ultimately steered her toward mature decisions. Her mother, she said, was reassuring and non-judgmental, but she was never a pushover.

“I think that throughout the book, you get a sense of how real they really are and how they’re really like every other parent,” Schwarzenegger said. “They deal with the exact same issues every other parent deals with.”

An open relationship with her mother also motivated her to write the book, said Schwarzenegger, who encourages readers to strengthen their ties and seek advice from their own mothers as they struggle with self-doubts.

“I never thought I would write a book,” she said. “But my fuel came from research and information on the growing number of girls who feel so much pressure to be thin – and how young all of this is starting. My goal is to let girls know they’re not alone when they’re going through this and to spread the word about what young girls are going through today.

“Society needs to know about the kind of pressure that is put on girls. We have to change it in some way.”

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