THE ACTRESS JAMIE-LYNN SIGLER WANTS to be clear about something: It was not the pressures of her career–playing Meadow, the feisty daughter of mob boss Tony Soprano (James Gandolfini) on the HBO Mafia drama The Sopranos–that drove her to develop an eating disorder in the year between shooting the pilot and shooting the show's first season. "Actually, the producers threatened to replace me because I was so thin," she says. "They said, 'We want Meadow to be healthy."'

In November 1997, after she had finished the pilot, Jamie-Lynn, then a 16-year-old high-school junior, was in the car with her mother, Connie, in her hometown of Jericho, New York. "My mom was picking me up from rehearsal for the school play and taking me to dance class, and I was changing into my leotard in the backseat," recalls Jamie-Lynn, now 20. "And she said, 'Jamie, I'm going to stop at McDonald's to get you something to eat.' I said, 'No, no, no, I'm not hungry."'

Jamie-Lynn vividly remembers what her mother said next: "You're going to develop an eating disorder." Jamie-Lynn thought this was ridiculous. "What are you talking about?" she told her mother, "I'd never have one." But just five months later, the 5-foot-7 teenager had gone from a slender 120 pounds to a skeletal 90 pounds. "I was basically unrecognizable," she says.

From the age of eight, Jamie-Lynn was a classic overachiever. Dancing, singing, acting and earning straight A's, she was a talented, bright girl who did a lot, and all of it well. "I was known to some people as 'Miss Perfect,'" she says. "l had always done a million and one things, but I loved it. I never felt like anything was out of control." By 11th grade, in addition to her acting pursuits and her studies, Jamie-Lynn was also serving on the student council, teaching a drama class to five-year-olds and preparing for her SATs, with thoughts of college. "I kept adding to what I was doing," she says. "I never wanted to give up on anything."

It was the typical setup for food and weight problems. "The majority of women with eating disorders are perfectionist and goal-oriented," says Ira M. Sacker, M.D., author of Dying to Be Thin: Understanding and Defeating Anorexia Nervosa and Bulimia– A Practical, Lifesaving Guide (Warner Books). "And no matter what they accomplish, they never feel good enough. Low self-esteem is key."

There were other factors for Jamie-Lynn. During her junior year, her first serious boyfriend, whom she had been dating for a year, broke up with her. Meanwhile, everyone around her seemed to be incessantly discussing calories. Common triggers for eating disorders include peer pressure and a boyfriend or girlfriend's reaction to one's appearance, explains Sacker, who is also founder and director of the nonprofit foundation Helping to End Eating Disorders (HEED).

Jamie-Lynn had always been active–dancing, playing softball–and had never thought of her pastimes as exercise. "I just thought they were fun," she says. "But now, all of a sudden, I felt like everything in my life was getting out of control, and here was one thing I could control."

She developed a punishing diet and exercise regimen that quickly took over her life. Each day began at 4 A.M. in the basement, with two and a half hours of exercise–running on the treadmill, followed by a workout video. Then a shower and breakfast–maybe three egg whites and two tomatoes. She might have a scooped-out bagel with mustard for lunch, a Diet Coke before dance class (more exercise) in the afternoon, a fat-free yogurt for dinner. "I ate ridiculous meals, and eventually eliminated fat from my diet. I found out later I was consuming only 400 or 500 calories a day, when someone as active as I was should have had about 2,200 calories a day," says Jamie-Lynn.

Her frenetic activity didn't stop at the treadmill or the ballet barre. She extended each task–squatting deeply when she made her bed, walking back and forth repeatedly in the kitchen as she cooked her breakfast, even taking her dirty clothes down to the laundry room one piece at a time. "Sitting at my desk at school, I'd constantly have to be lifting a leg or shaking, because I read somewhere that fidgeting burns calories," she says. "I'd take the long way to the bathroom, because a friend told me it burned calories. I would never stop."

Her friends expressed their concern. To avoid their worried looks, and because she didn't want to eat out and not know exactly how many calories she was consuming, she stopped socializing. She hung around at home instead. " That was not like me at all. I was a social butterfly before," says Jamie-Lynn. "But now I'd say, 'Hey, Dad, let's go skating. Let's have a catch in the park.' What 16-year-old girl wants to hang out with her dad every weekend? She should be at the mall, looking at boys and shopping."

Jamie-Lynn's parents–Connie is a homemaker and Steve is the founder of the 44,000-member national Men's Senior Baseball League–were growing increasingly worried about their daughter's obsessive activities. "One day my mom hugged me and started crying because she could feel every bone in my body," Jamie-Lynn says. But they felt helpless against her state of denial. "We were gently suggestive," says Steve. "We'd ask, 'Why don't you try to sleep till 5:30?' Or, 'How about half a slice of bread?' We were concerned that if we were too aggressive, she would only react that much more adversely. We had to try to work within her situation." He and Connie were able to be so patient only by maintaining faith in their daughter's eventual recovery. But, Steve admits, "it was very emotionally straining."

Jamie-Lynn's social isolation grew, because of her own defensiveness and her classmates' insensitivity. "Some people I knew would say, 'Yuck, she looks disgusting,'" she says. "They're almost happy to see something wrong with you when you're Miss Perfect. But I'm sure half the time they said that, unfortunately, it was out of jealousy, because they wanted to be that thin too." Later, working with a therapist, Jamie-Lynn found the courage to confront those people who were judging her behind her back. "I'd say, 'If you really want to know what's going on in my life, come talk to me and I'll tell you.'"

Jamie-Lynn avoided mirrors just as she avoided discussing or even admitting she had a problem. She did step on the scale every morning to watch her weight plummet. Her particular disorder, Sacker explains, is called exercise bulimia–excessive exercise, at least two to four hours a day, with a direct correlation between the number of calories consumed and the amount of exercise required to "purge" them. "It was like obsessive-compulsive disorder," Jamie-Lynn says. "I had to do this ritual. You feel like your life will end if you don't."

But the ritual itself was becoming life-threatening. According to Sacker, eating disorders may have the highest mortality rate of all mental illnesses– he fears as high as 20 percent. "Few people realize that," says Sacker, "because the cause of death is listed as heart failure, kidney failure, liver failure"–not an eating disorder.

The lowest point came on a Saturday morning in April 1998.Jamie-Lynn and her parents had planned to leave at 10 A.M. to drive into New York City, in-line skate, have lunch and return home. Jamie-Lynn even let herself sleep in, thinking she'd exercise when she came back. But when they hit the road a half hour late, she began to panic. "I was in the backseat, crying, worrying about when I would eat–because part of my ritual was to write down everything I was going to eat and when I would eat it and when I would exercise, and that I had to be asleep by 10:30 that night because I had to wake up at 4 the next morning," Jamie-Lynn says. "At the same time, I was thinking, 'How did I get to this point? Why can't I be 16 and happy?' Finally, I told my parents, 'l can't do this anymore. I don't want to live anymore.'" Steve pulled over, and Jamie Lynn at last confessed that she had a problem. "Literally, the second I said, 'l have an eating disorder,' it felt like a ton of bricks had been lifted off my shoulders."

Once Jamie-Lynn had faced her problem, she was eager to be well. Over the next five months, with the help of a psychotherapist and a nutritionist, she worked toward achieving a more moderate, healthy lifestyle–eating more, exercising less, thinking less about both, and most important, regaining confidence in herself.

But recovery–both physical and psychological–came gradually. In May she and her parents went to her brother Brian's graduation from the University of Michigan. (Brian, now 25, is at St. John's University School of Law, while Jamie-Lynn's other brother, Adam, 28, is a stockbroker.) When they arrived at the Detroit airport, Brian, who hadn't seen his sister in six months, didn't recognize her. That weekend, Jamie-Lynn made an effort to eat–a slice of cake at the reception, chips and soda that night at Brian's fraternity house. "But the next morning when I woke up, I was convinced I was not going to be able to fit into any of my clothes," she says. She hurried off to exercise, leaving her mother in tears.

When Jamie-Lynn, at about 95 pounds, returned to The Sopranos that fall to shoot the first season, she was so scared about losing her job that she started eating everything in sight–not difficult on a set where baked ziti and chicken cacciatore are omnipresent. "l gained weight too fast, because my metabolism had literally shut down," she says. The warm, family-like atmosphere on the set did help ground Jamie-Lynn, her father remembers. "Being surrounded on a daily basis by such supportive people accelerated Jamie-Lynn's recovery process," he says.

Today Jamie-Lynn is back to a healthy weight and a healthy attitude about it–that is, she doesn't know exactly what her weight is. Whether she's playing Meadow, touring in the title role of Cinderella (as she did this past summer), promoting her debut album (Here to Heaven, released in October) or modeling with the Wilhelmina agency, Jamie-Lynn is determined not to let the pressures of celebrity get to her. "I'm not going to follow any kind of Hollywood model," she says.

She's become a spokesperson for Sacker's organization, HEED, and for the Alliance for Eating Disorders Awareness. She still likes to in-line skate, play sports and dance, but her life no longer revolves around exercise. She tries to maintain a balanced diet, eating when she's hungry and not counting calories. And she gives in to her sweet tooth. "l love any kind of fruity dessert. That's my downfall. Well, not downfall," she quickly corrects. "It's just what I like."

Jamie-Lynn is also back to her social-butterfly ways–which, it turns out, often involve eating. "l love going out with my friends for dinner," she says. "It's the best way to feel like a normal kid. Friends and I recently went out to celebrate finishing my album, and we had lots of great food–bruschetta, steak, and for dessert, my favorite–apple pie!" she says. "It was a time I can remember with a smile, and not an instance when I was too wrapped up in counting calories to enjoy it."

Of course there are still tough days now and then. "You're depressed, and everybody is getting on your nerves and you feel like everything's wrong in your life. Sometimes I look in the mirror and go, 'Ugh, my ass looks fat,' Jamie-Lynn says. "The truth of the matter is, the eating disorder is always going to be with me. But what I went through was traumatic enough and enough of a learning experience that I would never fall so deeply again. I'm so much happier now."