Laura Prepon Reveals ‘My Mother Taught Me Bulimia’ in New Book: It Was Our 'Shared Secret’

When Laura Prepon began writing her new guide for moms, You & I, as Mothers, she wanted it to be completely honest.

“In order to have a real conversation about motherhood, we need to talk about what’s really going on, the stresses, the anxieties, how we were mothered,” the Orange Is the New Black actress, 40, says in an exclusive interview and book excerpt in this week’s issue of PEOPLE. “We need to share the truth.”

She felt something was missing in the books she turned to for advice after the birth of her daughter Ella in 2017. “I needed a voice to connect to,” she says.

Becoming that voice meant revealing a painful truth of her own. “My mother taught me bulimia. It started when I was 15 and lasted until my late twenties,” says Prepon.

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“I always thought of myself as this strong, confident woman,” she says, “but it became a compulsion that would completely debilitate me.”

At 15 years old, the 5’10” Prepon was, she says, “a healthy athletic kid.” But when she went to an open casting at a modeling agency, she was immediately told to lose 25 lbs.

She told her mom she wanted to give it a try, and her weight loss became “their shared project.”

“My mom started weighing me every morning and taking my measurements,” says Prepon, who dropped to 105 lbs. and remembers feeling how “proud” her mom was of her.

“That’s when she told me, ‘You can have your cake and eat it too,’ ” recalls Prepon. “I knew exactly what she was talking about.”

“It was a bonding thing we would do together,” she explains. “A shared secret.”

Looking back, she realizes that her mother, Marjorie, a Vassar graduate in the era of Twiggy, believed being thin would help her daughter. “She was bulimic in college,” says Prepon, “and after she lost weight, she met my father. So to her, being thin equaled success.”

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“I think she was trying to help me in her own way,” she says.

Some seven years ago, her mother was diagnosed with Alzheimer’s. “Seeing her lose her sense of self was shattering,” says Prepon. “It put me in confrontation with our past and began the path to recovery.”

With her mother now in the advanced stages of Alzheimer’s, she says of their relationship, “I don’t want to be angry with her, especially now, because I don’t know how much time we have left. I want those moments when she is present to be good.”

She began to focus on self acceptance and good health and nutrition, resolving to break the cycle of dysfunction so that someday she could be a healthy mom for her kids.

“Healing meant learning about my own body,” she says, “especially when I wanted to have children.”

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Today, she and her husband, actor Ben Foster, are the parents of 3-year-old Ella, and a baby boy, who was born at the end of February.

Her new book includes anecdotes from her own journey as a mother, as well as tips for moms of all ages, including stress reduction techniques, self care and healthy recipes she makes for her family.

She hopes by sharing her story, she can encourage other moms to be truthful about their struggles.

“I want to have an open conversation,” she says, “and help others feel less alone.”