Images of waif-like models and size zero actresses aren't entirely to blame for the relentless drive many women feel to be thin. According to a new University of Michigan study, women possess "skinny genes" that control their desire for a svelte figure.
The study, published in the current issue of the International Journal of Eating Disorders, quizzed 300 sets of twin sisters on how they'd compare their bodies to the slim, gorgeous women they see every day in magazines, movies and TV, and also asked them how much they wished they looked like those women. Researchers call such aspirations, "thin idealization."
Identical twins, who have all their genes in common, tended to have similar levels of thin idealization, even when their life experiences were vastly different. For example, if one identical twin was a dancer -- an activity where thinness is prized -- and her sister wasn't, they still felt a similar level of pressure to appear skinny, whether they felt a little pressure or a lot.
There was much more disparity in the level of thin idealization among the sets of fraternal twins, who on average share only about half their genes. And this was true even if they lived similar lives and had similar experiences.
"This doesn't mean environmental factors don't influence how women feel about their bodies, but surprisingly, external factors like media had a much smaller impact on how much women wanted to be thin than we expected," said the study's lead researcher Jessica L. Suisman.
The study estimated that about half of the reason women differ in their opinions of ideal weight can be chalked up to genetics.
Cynthia Bulik, director of the University of North Carolina eating disorders program and author of "The Woman in the Mirror," said this is an important finding because women and girls who have high thin idealization scores tend to be at greater risk for developing poor body image and eating disorders.
"Studies like this might explain why some women can easily ignore the barrage of information admonishing them to be rail thin, lose weight and banish cellulite, whereas other women are exquisitely sensitive to those same messages," she said. "It suggests this sensitivity might be influenced by genetic factors."
The Michigan researchers acknowledged that a woman's body image is complex and influenced by numerous factors. They didn't try to pinpoint the precise genes responsible for a woman's focus on her figure and weight.
Suisman said that simply understanding that women are born with some innate, preset urge to feel thin might help experts target women susceptible to eating disorders and improve treatment program designs.
And for now, Suisman said, the results of this study can only be generalized for women who live in a Western society at this particular point in history.
"In another culture, in another era, someone might have those same genes and express them quite differently," she said. "We won't know until there is more work done in this area."