TUESDAY, Oct. 2, 2012 — A size-zero model in a magazine or an airbrushed actress on a movie poster can look like the most beautiful person in the world.

Idealizing that model can lead to eating disorder symptoms shared by millions of men and women. Yet, only some women appear to "buy in" to this ideal. The reason why, researchers at Michigan State University say, comes down to your genes.

To explore the influence of genes on idealization of thinness, researchers asked 300 female twins between 12 and 22 how much they desired to look like thin movie stars and models. Once the level of "thin idealization" was assessed, identical twins, who share 100 percent of their genes, were compared to fraternal twins, who share 50 percent of their genes with each other.

Researchers found identical twins' level of idealization to be more similar than fraternal twins, suggesting that genes may play a role. They estimate that 43 percent of thin idealization is inherited, meaning almost half of women can point to their genes as the reason they idealize thinness.

What researchers called "non-shared factors" also had a profound impact on a twin's thin idealization. (These factors could include a single twin's involvement in a weight-focused activity like cheerleading, or one of the twins being exposed to more media that promotes thinness than the other.)

"The broad cultural risk factors that we thought were most influential in the development of thin-ideal internalization are not as important as genetic risk and environmental risk factors that are specific and unique to each twin," explained Jessica Suisman, lead author on the study, in a release.

Study co-author Kelly Klump, PhD, said this underscores the likelihood that many things contribute to dangerous eating disorders, and that eating disorder experts should consider both the genetic and environmental factors when treating patients.

This is not the first twin study to find a genetic component to eating disorders — siblings of patients with eating disorders are more likely to have eating disorders themselves, numerous studies have found.

Family can affect eating disorder risk in other ways, too. Teens with eating disorders are more likely to have conflicted relationships with their parents or other family members, perhaps because of familial pressure to be thin.

TELL US: Do you think pressure to be thin runs in families? Share your experiences in the comments below. (Note: Mobile users won't be able to comment.)