A pilot study released on Monday of U.S. eating disorder patients aged between 10 and 22 showed that up to a third learn new weight loss or purging methods from Web sites that promote eating disorders by enabling users to share tips, such as what drugs induce vomiting and what Internet sites sell them.

But the study -- published in the American Academy of Pediatrics' journal Pediatrics -- found that eating disorder sufferers were also learning new high-risk ways to lose weight from each other on Web sites aimed at helping them recover.

The survey by researchers from Stanford University School of Medicine and Lucile Packard Children's Hospital at Stanford showed a third of patients also visited pro-recovery sites and half of them learned new weight loss and purging methods.

"Parents and physicians need to realize that the Internet is essentially an unmonitored media forum," said Rebecka Peebles, Packard Children's adolescent medicine and eating disorder specialist and an author of the study.

"It's just not possible to completely control the content of an interactive site," she said in a telephone interview.

A wave of pro-eating disorder sites showed up on the Internet between 2001 and 2003, prompting operators of several Internet hosts to try to remove such sites. But the study showed many pro-anorexia and bulimia sites remain accessible, with most patients finding them and pro-recovery sites through chance searches.

"I feel so sick eating as much as 800 calories," a teen-age girl, who called herself "berlinium," wrote in a pro-anorexia chat room on Monday.

"And then for some reason now when I try to purge, I can't get anything up. I mean I am literally shoving my fingers past my tonsils, but nothing," she said, adding that she had just bought a drug off the Internet to induce vomiting.

Eating disorders returned to the global spotlight recently when two models suffering anorexia died in Brazil and Uruguay.

The fashion industry has long been blamed for encouraging anorexia and bulimia among teen-agers with its use of excessively thin catwalk models. In September, the city of Madrid banned models below a certain weight from its fashion week shows.

The U.S. study was based on an anonymous survey of 76 patients who were diagnosed with an eating disorder at Packard Children's Hospital between 1997 and 2004, as well as 106 parents of patients.

While half of the parents surveyed said they were aware of Web sites promoting eating disorders, only 28 percent had ever discussed these sites with their child and only 20 percent said they placed limits on their child's Internet use.