From PEOPLE Magazine Click to enlarge
When Maureen McCormick showed up for the first day of taping Celebrity Fit Club, the show's nutritionist, Dr. Ian Smith, admits he was shocked to see her petite 5'3" frame carrying 150 lbs. "All of us remember beautiful, skinny Marcia Brady," says Smith. "So it was a jolt."

What may come as a greater shock to viewers of the show (which premieres April 22) are her revelations that shortly after The Brady Bunch ended in 1974, the impossibly perfect oldest Brady girl began her 10-year battle with bulimia—and a cocaine addiction that would last six years. "It was sickening," says McCormick, now 50, of the destructive behaviors she has put behind her.

"It came from being a teenager, not from being on the show at all," she says, careful not to tarnish Marcia's reputation—nor paint herself as a stereotypically troubled child star. The eating disorder, she says, started after she reentered a public high school at 17 (she had been tutored on-set). She remembers the very day. "I was with some girls, we had a gallon of ice cream, and someone mentioned how we could eat it all and not gain weight. It seemed ideal. Once I started [purging], it was hard to stop."

It didn't help that her post-Brady career options included guest spots on The Love Boat and Fantasy Island for which "I had to be in a bathing suit. That made me so self-conscious." She would recover briefly, she says, "then gain weight and revert back."

By then she had begun using cocaine. "I got into it through a boyfriend, who was friends with people who did drugs," she recalls. "I have a very addictive personality. I know that now." Through therapy and, she says, her faith, after several relapses McCormick kicked both problems without a formal rehab program. "Being able to quit drugs and finding belief in a higher power gave me the tools to end the bulimia."

A few years later, while attending a church concert, she met printer salesman Michael Cummings. Remarkably, Cummings, now 54, had never seen an episode of The Brady Bunch ("a total blessing," she says). They wed in 1985 and have one child, Natalie, 17.

Aware that her daughter has reached the age when her own troubles began, McCormick says, "I worry about it every day. But I'm honest with her, and she knows what I've been through. I hope that keeps her from making those same mistakes."

Though McCormick's weight had fluctuated after ending her bulimia, she stayed fairly slender for most of her adult life. But she put on a fast 30 lbs. following the death of her mother, Irene, from kidney cancer in 2004. "My mom was my best friend," says McCormick. "After that I wasn't exercising, just eating and sleeping a lot. It's amazing how quickly weight can come on!"

Her sorrow was compounded as her mom's death meant McCormick and her father faced the responsibility of putting her brother Denny, 55, who is mentally disabled, in a group home. "I cried every day, I had so much guilt. He needs full-time care. Now I can see he has more of a life, but everything was happening at once. I was eating to cope."

It was Natalie who suggested going on Fit Club. "To admit that you are overweight is very hard," says McCormick. But after a chat with producers, she was in. "It came at the right time in her life," says her husband. "She reached a point where enough was enough." The show's producers were thrilled to have her in a line-up that includes '80s teen pop star Tiffany and rapper Warren G. But there remained the question of McCormick's past eating disorder. "There was a concern that the competition may drive her into her old behaviors of bulimia," says Ian Smith. But it didn't become an issue, because "she knew what her warning signs were." He can't yet reveal how many pounds she dropped, but Smith does say she followed the diet to the letter: "She did everything right. She was the hero of this season."

The show, says McCormick, "helped me emotionally, physically. I have much more energy now." Since leaving Fit Club thinner and happier, she says, "this whole new world has opened up. Now I like to walk around naked. And it makes sex much, much better!" If that declaration doesn't put Marcia Brady in the past for good, it's possible nothing will.