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Oct 3, 2012

Desire to Be Thin Is in the Genes

  • How deeply women become preoccupied with staying thin in order to meet the "ideal body standards" set by media images of super-skinny fashion models and styled-to-perfection film stars may be partly down to their genetic makeup, researchers claim. The results of a study comparing hundreds of monozygotic (identical) and dizygotic (nonidentical) twins indicate that thin-ideal internalization (i.e., buckling to perceived outside pressure to stay thin) may be 40% "heritable". Interestingly, this is about the same level of heritability that prior studies have assigned to some of the potential outcomes of thin ideal internalization; i.e., disordered eating and eating disorders.

    Girls and women are bombarded with images of the ideal body through advertising, television, magazines, and the movies. But not all women will bow to the pressure such imagery exerts and become preoccupied with trying to mirror that perceived perfection. While current research on the etiology of thin-ideal internalization focuses on psychosocial influences, investigators at Michigan State University decided to carry out a study that would, for the first time they claim, look at the impact of genes on thin-ideal internalization.

    Kelly L. Klump, Ph.D., and colleagues talked to 343 (205 monozygotic; 138 dizygotic) female twins between the ages of 12 and 22 years, from the Michigan State University Twin Registry (MUSTR). The participants’ body mass index was recorded, and they were asked to rate how much they agreed with statements about the degree to which they want to look like women from media sources such as magazines, television, and movies. These questions allowed the researchers to assess how far the participants were affected by this thin-ideal body image, using a nine-item, general thin-ideal internalization subscale from the Sociocultural Attitudes Towards Appearance Questionnaire-3 (SATAQ-3), which has been validated in prior research.

    Comparing data from the monozygotic (genetically identical) twins with that from the dizygotic twins (who share 50% of their genes) indicated that the heritability of thin idealization is just over 40%. In other words, genetic makeup is responsible for nearly half of the reason why some women will become preoccupied with matching an ideal body image and others won’t.

    Interestingly, while environmental factors were also important, shared factors such as exposure to the same media didn’t have as big an impact as expected, comments Jessica L. Suisman, lead author of the team’s published paper in the International Journal of Eating Disorders. “Instead, nonshared factors that make co-twins different from each other had the greatest impact.” In fact, Suisman adds, “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.”

    The researchers say more research is needed to investigate the possible interplay between genetic and nonshared environmental factors in the development of thin-ideal internalization. “Similarly, future twin and molecular studies should more closely examine genetic risk for the construct by investigating overlap in the genetic architecture of thin-ideal internalization and the disordered eating symptoms it predicts as well as exploring specific genes that may confer risk for the development of thin-ideal internalization.”

    The Michigan State University team, working with academic collaborators in Florida and Virginia, report their findings in a paper titled “Genetic and Environmental Influences on Thin-Ideal Internalization.”


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