Kate Middleton: Is slim bride-to-be sending girls wrong message?

BELFAST, NORTHERN IRELAND - MARCH 08: Kate Middleton arrives at City Hall on March 8, 2011 in Belfast, Northern Ireland. The Royal Couple are visiting Northern Ireland as part of a tour of the country that a couple of weeks ago took them to St Andrews University in Scotland and Anglesey in North Wales to launch a lifeboat. This day-long trip to Ireland has been kept top secret due to security issues. They will marry on the 29th April at Westminster Abbey in a much anticipated ceremony. (Photo by Chris Jackson/Getty Images) *** Local Caption *** Kate Middleton
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Kate Middleton in Belfast, Northern Ireland on March 8, 2011.
Getty Images

(CBS/AP) It's no secret that Kate Middleton is thin. But the even slimmer frame the princess-to-be has been sporting in recent days has some wondering if she's joined the ranks of women who are too thin.

The subject even became a topic on Twitter, with one tweet saying she shouldn't lose any more weight - and should serve as a healthy role model to young girls.

Palace officials Wednesday refused to say whether Prince William's fiancee is trying to lose weight before the big day, which is set for April 29. They also declined to specify her height or weight.

Nutritionists who deal with eating disorders - like the bulimia that plagued William's mother, the late Princess Diana - say it is usually fine for prospective brides to diet before their weddings as long as they don't try to lose too much weight, which can create an unhealthy "yo-yo effect" when the pounds are put back on before the honeymoon is over.

But nutritionist Amanda Hamilton said Middleton should be careful.

"She's already slim enough so I would have concerns over that," Hamilton said. "Anyone would look at her picture and ask why does she have to lose weight. She looks fantastic. She's on the very slim end of what would be considered healthy. She's not in the danger zone, I don't think ... but she doesn't have any weight to lose."

In the U.S., an estimated 10 million females and one million males are affected by eating disorders like anorexia and bulimia, according to the National Eating Disorders Association. The conditions, which can be life-threatening, are treated with psychotherapy, along with careful attention to nutrition and care for any medical problems associated with the disorder.

What causes eating disorders in the first place? Experts believe it's a complicated mix of factors, including family dynamics and heredity. And "media messages" seem to play a key role.

According to the association, "To the extent that media messages like advertising and celebrity spotlights help our culture define what is beautiful and what is 'good,' the media's power over our development of self-esteem and body image can be incredibly strong."