• By Kevin Mount
  • Posted on Tuesday 01st April, 2008

Are wiry girls just strung that way?

We tend to think of genetic traits as qualities that manifest themselves almost as soon as we emerge into the world: brown hair, a gentle disposition, poor eyesight, and such. But it seems that some patterning lies dormant until something around us or inside us changes and, by doing so, releases the genetic trigger. In this vein, a group of researchers from Michigan State University and the University of Minnesota in the US believe they have identified a trigger associated with the development of eating disorders. Girls become more prone to eating disorders when they enter adolescence. Some studies have suggested that the pressure to be thin increases as girls go through puberty and want to be sexually attractive. However, this explanation doesn’t fit with the university teams' findings.Kelly Klump and her colleagues looked at data tracking the development of 772 female twins from the ages of 11, 14, and 18 years. Specifically, they considered the girls’ responses to survey questions about body dissatisfaction, weight preoccupation, binge eating and so forth. Then they compared identical twins (who are genetic duplicates of one another) to fraternal twins (who share, on average, only 50 percent of their genes).They found that the identical twins generally provided similar answers to one another when asked about their eating patterns over the seven-year period. But the answers given by fraternal twins became much less similar after they went through puberty. Since all the twins resided in a western culture, the difference between identical and fraternal twins could not be explained by broad cultural effects.The researchers argue instead that their findings suggest that puberty triggers a genetic tendency towards eating disorders. Before puberty, genes don’t appear to influence girls in this way. Parents and friends might foster an equivalent problem at younger ages but eating disorders are less common among prepubescent girls. After puberty, the most significant factors appear to be genetic make-up and a young woman’s experiences outside the home. Parents don’t seem to contribute to the problem among these older adolescents. So it seems we can’t lay all of the blame on parents nor on a cultural obsession with thinness. Instead, the findings suggest that research should identify girls with a genetic predisposition for eating disorders and examine the post-puberty experiences that might aggravate the problem.• Summary of “Changes in Genetic and Environmental Influences on Disordered Eating Across Adolescence: A Longitudinal Twin Study” by Kelly L. Klump, S. Alexandra Burt, Matt McGue, and William G. Iacono in Archives of General Psychiatry, Volume 64, Issue 12, December 2007, pp 1409–1415.

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