Discovering the Biological Basis of Anorexia
By Hisaho Blair, NAMI Communications Intern
Back in the 1980s I wrote a research paper on anorexia nervosa. It focused on the causes of the illness as society’s preoccupation with thinness and the low self-esteem of those affected. Today, eating disorders still affect 70 million people worldwide and 20 to 25 percent of girls between the ages of 15 and 24. Anorexia nervosa has the highest mortality rate of any psychiatric illness, with some studies indicating that up to 20 percent of those affected will die prematurely from complications.
Many studies on anorexia have been conducted in the past 30 years. Although societal and psychological factors still play a role in the development of anorexia, much more is understood about the biological basis of the illness today. Technological advancements have allowed researchers to look at the brain as well as analyze genetic factors that may lead to anorexia.
The Brain and Biochemical Factors
Recent findings by German scientists at Ruhr University Bochum in the journal Behavioral Brain Research show that there are “connection errors” in the brains of people with anorexia nervosa. Using functional magnetic resonance imaging (fMRI), the researchers looked at brain activity in two regions of the brain important for processing body image in anorexic and healthy women.
Ten women with anorexia and 15 healthy women were shown silhouettes on a computer and asked to choose which one corresponded to their own body shape. The women in the anorexia group judged themselves to be fatter than they were, while the women in the healthy group thought they were thinner.
Researchers recorded the brain activity of the 25 test subjects as they looked at body images. In particular, they focused on the fusiform body area (FBA) and extrastriate body area (EBA) and measured the correlation of activity in the two areas. The women with anorexia showed a weaker connection between the two regions of the brain than the healthy women did. Furthermore, the weaker the connectivity, the fatter the women thought they were.
Previous studies by the group had shown that people with anorexia had a lower density of nerve cells in the EBA. This study shows that there is a functional alteration in addition to a structural one.
In September 2012, researchers at the Center for Brain Health at the University of Texas also used MRI to look at brain activation in individuals with anorexia versus those without. They asked subjects to evaluate their own characteristics compared to those of a friend. They found that self-identity is processed differently in women with anorexia. There were differences in activation in the brain’s precuneus, a region that is linked to self-consciousness. The scientists are now studying brains of recovered subjects to see if recovery restores normal brain activity.
Statistics have shown that a person is 10 times more likely to develop anorexia if a close relative also has experienced the illness. Researchers have been trying to find a genetic link to anorexia. In the 1990s, Dr. Collier and colleagues at the Maudsley Hospital in London found that people with anorexia were twice as likely to have variations in the gene for serotonin receptors. Serotonin is involved in regulating many body functions, including appetite.
Twin studies are a useful tool in determining if a trait is hereditary. In a study published in 1984 in the British Journal of Psychology, researchers found that the incidence of identical twins both suffering from eating disorders was as high as 52-56 percent, while the correlation in fraternal twins was only 5-11 percent.
In a study published in the International Journal of Eating Disorders in December 2012, researchers used twin studies to look at the effects of genetics and socio-cultural factors in thin-ideal internalization. They found significant genetic effects (44 percent correlation in identical twins vs. 24 percent in fraternal twins). In looking at environmental factors, they found that shared influences, such as similar family environment and exposure to media, were not significant in development of idealization of thinness. The non-shared factors, such as peer groups or traumatic events, were of more significance.
Epigenetics is a relatively new scientific field that looks at the interaction of the environment and genes. An epigenetic change is a change in gene expression (i.e., turning genes on or off) without changing the DNA sequence itself (not a mutation). Genes respond to the environment, and factors such as stress, diet, behavior or toxins can activate switches that control gene expression.
Where it was once thought that socio-cultural factors (e.g., media, parents, peers) and problems with self-esteem were the main causes, it is now understood that anorexia is more of a brain disorder. However, the environment does affect the brain and its function, and epigenetic changes can be inherited. An epigenetic model may help explain the complex changes that contribute to the illness.
So, like the nature vs. nurture debate, it’s not that simple. There’s genetic susceptibility, and there are environmental stressors. But it’s definitely not a matter of free willóno one chooses to become anorexic. Like any other illness, anorexia is biologically based. Hopefully continued research will lead to a better understanding and treatments for those affected by eating disorders.
National Eating Disorders Awareness Week begins this Sunday, Feb. 24. Check out the National Eating Disorders Association for more information.