Laura Prepon on Hiding Her Bulimia from That '70s Show Cast: 'I Was Very, Very Private'

In her new guidebook to motherhood, You & I, as Mothers, actress Laura Prepon bravely reveals that her mother taught her how to be bulimic when she was 15 years old, a cycle of dysfunction that lasted until her late twenties.

“I think she was trying to help me in her own way,” she tells PEOPLE of their complicated history. “To her, being thin equaled success.”

The Orange Is the New Black actress, 40, is sharing her story with the hope that being honest about her own struggles with her body, as well as the emotions and stress that come with being a new mom, will let others know they are not alone.

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“In order to have a real conversation about motherhood, we need to drop our defenses and share truth,” she says. “We need to talk about what is really going on.”

The bulimia, which began when Prepon was a young model, continued through her early acting career, including her seven years on That ’70s Show. “My weight fluctuated a lot on that show,” she says. “I had to have two wardrobes. I used my period as an excuse. I get really bloated.”

“When I see an episode of the show, I can tell by the way I looked whether I was doing it or not,” she notes.

“Craft services was new then, too,” she adds. “It was freshly baked everything. It wasn’t just M&Ms in a bowl, so there were triggers all the time.”

Her costars on the show were not aware of her eating disorder. “I was very, very private,” says Prepon. “I’d have spurts where I would get a handle on it and wouldn’t do it for a while. Then something would happen and I would get triggered and the cycle would begin again, just like with any compulsion.”

“There were days that were a constant cycle of binging and purging and self loathing,” she recalls. “As someone who always felt I was a strong independent person, this compulsion would completely debilitate me.”

Prepon’s path towards health and self acceptance began after her mom was diagnosed with Alzheimer’s some seven years ago and her mother continued with her bulimia. “It was so scary,” she says. “I didn’t want that to be me.”

Getting cast in Orange Is the New Black in 2012 only strengthened her resolve to find peace with herself.

“When Orange came along, I wasn’t at my thinnest by any means, so in my mind, I thought, ‘I don’t know if I’m going to get this because I don’t have the ideal body size my mother put into my head,’ ” she remembers.

But of course, she did become a part of the groundbreaking series.

“I’m so happy in my career that I see the change happening and being a part of a show like Orange is so wonderful for many reasons,” notes Prepon. “One is that there are so many women of different ethnicities and shapes that are celebrated. I’m so thankful to have been a part of that.”

If you or someone you know is battling an eating disorder, please contact the National Eating Disorders Association (NEDA) at 1-800-931-2237 or go to NationalEatingDisorders.org.