In image-conscious France, it may soon be a crime to glamorise the ultra-thin. New legislation aims crack down on websites that advise anorexics how to starve - and could be used to hit fashion industry heavyweights, too.

The French parliament's lower house has adopted the groundbreaking bill that would make it illegal to incite extreme thinness.

It recommends fines of up to 45,000 euros ($A76,805) and three-year prison sentences for offenders. It next goes to the Senate in the coming weeks.

Fashion industry experts have said that, if passed, the law would be the strongest of its kind anywhere. And given France's longtime status as a fashion capital, it could send shock waves through the industry worldwide.

The anorexia-linked death of a Brazilian model in 2006 prompted efforts throughout the international fashion industry to address the health repercussions of using ultra-thin models.

The bill is short on specifics. Critics noted that it does not spell out who it is targeting or even define "extreme thinness". Doctors and psychologists welcomed the move, but said anorexia's link with media images remains hazy.

French politicians and fashion industry members signed a non-binding charter last week on promoting healthier body images. But the bill's author, conservative MP Valery Boyer, said this did not go far enough.

Her bill has focused attention on pro-anorexia websites that, for instance, give advice on how to eat an apple a day - and nothing else.

Health Minister Roselyne Bachelot said websites that encourage young girls to starve should not be protected by freedom of expression.

Ms Boyer said her proposed law would also enable a judge to sanction those responsible for a magazine photo of a model whose "thinness altered her health".

"That is the objective of this text," she said without specifying who might be prosecuted.