For years, the conventional wisdom about adolescent body image has been that we have a nation of youngsters obsessing about their bodies, panicked that they might be toting a couple extra pounds.

And we've blamed advertising and media images for feeding teens unrealistic, unattainable ideas of body beauty, making them want a body they don't have, making them believe they're too fat when they're not.

That may be true in some cases, but it turns out that somehow, most teens actually seem to believe they're not overweight even when they are.

That's right. Contrary to popular belief, most kids don't think they're overweight, and if they're off-base about their body weight at all, they're wrong in the other direction, actually thinking they're underweight when they're nothing of the kind.

In a study of more than 2,000 students in grades 9 through 12, the students completed what's called the Youth Risk Behavior Survey, a research tool created by the Centers for Disease Control to examine all sorts of youth habits. Part of the YRBS questionnaire asked about the students' beliefs about their body weights. These students were later weighed and measured by researchers.

In this large group, 51.2% of the teens were normal weight, 47.4% were overweight and only 1.5% were underweight, based on health standards set for weight, height and gender by the Centers for Disease Control.

The purpose of the study was to look at how the youths' actual body weight related to their perceptions of their body weight. Previous studies have shown that kids' perceptions of their weight were the best indicator of whether or not they'd diet. Their perceptions were a better indicator than even whether or not they actually needed to lose weight.

And that seems to jibe with the claim that normal-weight kids, who are influenced by unrealistic body images in the media, will needlessly diet to try to attain those supposedly desirable bodies.

But look at the perception numbers in this recent study. Of those high schoolers, 34.8% believed they were underweight; 42.9% believed they were normal weight, and only 22.3% believed they were overweight even though more than half of them actually were!

Could it be that this is some kind of accidental backlash, an unintended consequence of all the time and effort that has gone into trying to counter unrealistic images and get teens to accept more normal, healthy bodies without actually being clear about what normal and healthy is?

There's no doubt that more teens are overweight than ever before. And maybe kids are looking at all the skinny models they can't be and defiantly taking another bite. But it's likely that the increase in overweight among teens has more to do with the same environmental influences that are contributing to American's weight problems across all ages: less activity, bigger portions, fattier foods.

One way or another, it looks like kids aren't getting the message about what a healthy weight is, and for many, it turns out that their ideas are oddly skewed. Of the youths who were actually overweight, only about half (53.8%) accurately perceived themselves as overweight. Some 20% thought they were about the right weight, but the rest of those teens more than a quarter of them actually believed that they were underweight.

Why is this a problem? Because it's likely that those heavy kids who don't recognize themselves as overweight won't try to control or reduce their weight, which makes their weight excess more likely to persist and worsen, leading to very real health problems diabetes, high cholesterol, heart disease, etc. you know the list.

It's worth noting that this study included a huge sample, with more than 2,000 teens participating, and a pretty ethnically diverse sample including black, white and Hispanic youth. Few others have been this extensive.

And most previous studies on teens and body image have not come from a medical inquiry, but from a psychosocial perspective, examining the way cultural influences affect teens' attitudes and behaviors.

Much has been made of the effects of advertising, for instance. Marketing is about creating desire for something. When children and teens (not to mention adults) are barraged with imagery of a certain beauty standard, they understandably want to achieve that standard. That creates a consumer market for various products: the clothes, cosmetics, toiletries and health products that promise to help the consumer achieve that standard.

Some say it also creates pressures that lead teens to unhealthy behaviors. Smoking, substance abuse and eating disorders in particular have been cited as consequences of these pressures and a lot of effort has gone into raising awareness about these potentially lethal problems.

It's a little odd, then, that there hasn't been more interest in the far more common and often equally dangerous problems associated with overweight.

In the YRBS study, only 1.5% of students were actually underweight or at risk for underweight not what you'd call a prevalent condition. Compare that to the 47.4% of students who were actually overweight or at risk for overweight.

And among the skinny kids in the study, none of them characterized themselves as overweight, whereas at the heavy end of the range, again, more than a quarter of the heavy students thought of themselves as underweight. It's pretty clear where there's a bigger misconception problem.

To be fair, this study doesn't exactly contradict the conventional wisdom, because it examined teens' thinking about their body weights compared to the reality of their body weights it did not examine their feelings about their bodies or any self-esteem issues they may have had. It's quite possible that some of those kids regardless of their actual or perceived size still felt unhappy with their bodies.

But it does seem to indicate that, even as youth have grown progressively heavier and more overweight, they've somehow developed very serious misconceptions about what appropriate and normal body weights should be, to the extent that many are overweight and don't even know it.

And that seems to indicate that as any effort to help kids' reject unhealthy, unrealistic stereotypes ought to also include helping them accept what realistic, healthy bodies actually are.

Caroline J. Cederquist, M.D. is a board certified Family Physician and a board certified Bariatric Physician. She specializes in lifetime weight management at the Cederquist Medical Wellness Center. She is also the author of "Helping Your Overweight Child A Family Guide," which is available at DrCederquist.com, Amazon.com or by calling 1-800-431-1579. For more information about Dr Cederquist and her weight management plan, visit http://www.diettoyourdoor.com/