Though it was Tuesday when news broke that Mary-Kate Olsen was seeking help for an eating disorder, she'd actually entered a treatment program last week, according to a source close to the actress. She's expected to remain there for about a month.

According to experts who specialize in teen girls and eating disorders, anorexia and bulimia are complicated diseases that affect both the mind and body and take a long time to fully recover from. It's not simply a case of girls who are literally dying to be thin, although that can be one of the victim's goals.

"There's more to this than just the hype about the thinness," said Lynn Grefe, CEO of the National Eating Disorder Association. "Society will just tell [an anorexic girl] to eat, like she's doing it on purpose. And she wishes she could eat."

A clinical program could help Olsen re-learn how to eat -- possibly via a feeding tube at first, later under the supervision of a nutritionist. This should help her return to her normal weight. Counselors will also try to help her understand why she developed an eating disorder, and doctors may prescribe an anti-depressant.

"This can be about the child's wish not to grow up," said Michelle Ascher Dunn, a New York psychoanalyst. "In getting thinner, you lose your breasts, you lose your period, and you become pre-adolescent. You lose your adult physical status, and you get to turn time backwards."

The seeds of an eating disorder can be sown as early as age 8, Dunn said -- as soon as a child realizes their body is changing -- but the onset generally occurs in adolescence. Ten million women and 1 million men suffer from eating disorders in the United States, and 15- to 19-year-olds account for 40 percent of identified cases, according to NEDA statistics.

Girls who are high achievers -- perfectionists who get great grades, excel in sports and are considered leaders -- are most susceptible to eating disorders, Dunn said, because they offer a goal to strive for.

Plus, disorders can be aggravated when the victim is famous and her career depends on how she looks. "One patient told me that her life was so out of control that this was the one thing she felt she could control: her weight," Grefe said. "We hear this a lot."

"Part of the control issue," Dunn said, "is about feeling empty, in a physical sense. Anorexics get to love feeling empty. It makes them feel full of power and self-control. The danger is that they stop feeling hungry, and if girls are just playing at it, if they practice being empty and lose their appetite, they can fall into it and become a functioning anorexic."

The body's under-nourishment affects how the mind works, Grefe said. This can prevent people with eating disorders from visualizing themselves properly. This "dysmorphia" can prevent an anorexic from seeing that they are wasting away. Getting help usually requires an intervention by family or friends, who can see the warning signs: dramatic mood shifts, emotional withdrawal, unnecessary dieting, food avoidance, food rituals and frequent trips to the bathroom after meals.

Denial can also be a warning sign. "That denial is like Novocain," Dunn said. "You're in pain, but you don't know it, you won't let yourself feel it. You don't want to admit it."

"Anorexia is a quiet disease," Grefe said. "They feel ashamed, and so only a third [of them] receive mental treatment. It's got the highest mortality rate of any mental illness. It's no joking matter."

But it is treatable. As with overcoming an addiction, overcoming eating disorders can be a long process -- for some, it takes four to seven years. Once Olsen finishes her stint in the treatment facility (see [article id="1488598"]"Mary-Kate Olsen Seeks Treatment For Eating Disorder"[/article]), she should expect outpatient therapy to be part of her healing process.

"You can't walk out [of the clinic] and think everything's fine," Grefe said. "You have to be aware, and you have to work at it."

Part of the problem may be the social pressure that's put on women to be thin in order to be fashionable and desirable. "We need more Bridget Jones types," Grefe said. "We need to love our different shapes and sizes, as long as they're in healthy proportions. And we need to wake up, because women are dying."