A few months back Pat accidentally tried on a pair of size 2 jeans at an outlet store and was astounded to discover that they fit. Of course, she bought them; she had never had a pair of size 2 pants in her closet—ever. But she couldn't resist asking the clerk why a woman who normally wears a size 8 would fit into a pair of size 2 jeans. The saleswoman laughed and said this clothing line's sizes seemed to fluctuate with the designer's own weight. "No matter how much she gains or loses," the saleswoman said, "we think she always wants to wear the same size."

That story came to mind as we were reading the results of a recent Cornell University study published in the journal Eating Behaviors, which examined how people's perceptions of their size and shape motivated them to lose weight. The authors assumed that the further someone was from a healthy weight, the more dissatisfied they would be with their body and the more pounds they would want to lose to achieve an ideal weight (as defined by a Body Mass Index between 18.5 and 24.9. The BMI is a ratio of height to weight. To check yours, click here). But the results didn't turn out quite as the researchers had expected, which always makes a study more interesting to us.

Although overweight and obese women expressed the greatest dissatisfaction with their bodies, the amount of weight they said they would "ideally" like to lose was so low that they would still be categorized as overweight, the researchers found. "We thought they would choose a weight that was within the 'normal' category," says Lori Neighbors, one of the study's authors who is now an assistant professor of nutrition at the University of Wisconsin. Meanwhile, "normal" weight women said they wanted to lose only a few pounds, rejecting the very thin images that we see glorified in fashion magazines, which also surprised the researchers. "We found that encouraging," says Neighbors, "because by not idealizing that extremely light-for-height weight, they are less likely to get into the kinds of weight-management behaviors that put women into a dieting tailspin and encourage them to use extreme methods."

The same might not be said for the underweight women, who told researchers they believed they were at their ideal weight. "They didn't seem to understand the health risks associated with being underweight," she says. "We think that maybe once you get to be a member of this very thin group you get the kind of social messages that keep you there."

Still, the larger health concern is with those who are overweight. Two-thirds of adult American women fall into the overweight or obese category, according to their BMIs. Just last week a report from the Centers for Disease Control found that the prevalence of obesity among U.S. adults doubled between 1980 and 2004 and has since stabilized at an alarmingly high level. Compared to women of a generation ago, we're 24 pounds heavier on average, and there's been an especially alarming increase in those at the upper end of the scale (not just obese, defined as a BMI of 30 or higher, but significantly obese, with a BMI above 35).

Because high BMIs are associated with increased risk of diabetes, high blood pressure, some cancers and heart problems, there's a lot of public health interest in turning this situation around. One way to do it may be to better understand the psychology of weight loss. Neighbors said it's possible that the overweight women in her study aimed for such modest diet goals because lower numbers on the scale seemed unattainable to them. "If you're five-foot-two and 200 pounds, maybe it seems like a pipe dream that your weight could be 120 pounds," she says. Still, that may just mean that women who are very overweight might need to achieve small weight loss goals before they can envision larger losses and change their eating and exercise behaviors accordingly.