Most of the public response to eating disorders has focused on culture — see for instance the recent teen protests against airbrushing in Teen Vogue and Seventeen. While girls banding together to change the norms of media aimed at them are doing something impressive and valuable (and, in Seventeen's case, successful), a growing body of research shows eating disorders have a major genetic component as well. And a new study shows that even the desire to look like thin models — short of an actual eating disorder — has a major genetic component.
For their study, Michigan State psychology researcher Jessica Suisman looked at 343 female adolescent twins. They gave each twin a 9-item standardized survey designed to measure "thin-ideal internalization" — that is, how much the girls felt cultural and social pressure to be thin. The survey asked them about how much they wanted to look like thin women in magazines and on TV. Then they compared each girl's responses to those of her twin.
They found that identical twins, who share all their genetic material, had much closer scores on the survey than fraternal twins, who share only about half. That is, twins who were genetically closer were much more likely to be similar in terms of how much pressure they felt to be thin. Given that most of the twins, identical and fraternal, were raised in the same house, the results show genetics had a much bigger effect than shared environmental factors like how parents treated kids or what magazines or TV they were exposed to at home.
The study authors do note that non-shared environmental factors, like one twin reading a lot more of a certain magazine than the other, could have had an effect — the identical twins didn't all have the same scores on the survey. But their findings indicate that genes play a bigger role in wanting to be thin than anything twins experience together at home. They also show that like eating disorders themselves, the feeling that you need to be as thin as a model — which can itself be a risk factor for eating disorders — has a big genetic component.
Suisman says it's unlikely we'll see a genetic test for either eating disorders or thin-ideal internalization any time soon: "the type of genetic influence we are seeing is probably based on small effects of numerous genes, making it particularly difficult to isolate any particular gene that may be a marker for increased risk." However, the knowledge that both these things have a genetic component could still be useful to people dealing with body image issues, and their families. She explains, "Just like a doctor may recommend that a person who has a family history of heart disease or cancer take extra health precautions, individuals with a family history of problems related to thin-ideal internalization, body image, or eating disorders may benefit from being cognizant of their own increased risk."
So while this study may not allow doctors to perform a simple blood test to see who will feel pressure to be thin, it might give people whose siblings or parents felt that way some useful information. And it might help them choose their media consumption more carefully. Even if shared environment doesn't play as big a role as genetics, cultural forces do have an effect — after all, the thin-ideal survey is based on people's feelings about models and actresses. Maybe people with a family history of body image problems could surround themselves — or their kids — with TV, magazines, websites, and movies that show a wide range of bodies, as a way of counteracting the influence of their genes. And of course, it would probably help if more material like that was out there.