The Biology of Anorexia Nervosa

             In order to be diagnosed with anorexia nervosa, a person must meet the DSM-IV criteria for the disorder. This includes a body weight less than 85% of that expected, a preoccupation with food or feelings of becoming fat, a disturbance in self-image, and the absence of a menstrual cycle in females.  An estimated .5-3.7% of females will meet these criteria—will suffer from anorexia nervosa—in their lifetime (6). Though these prevalence numbers are not as high as many other disorders, anorexia nervosa (AN) remains a serious concern; it has one of the highest mortality rates of any psychiatric disorder (5). But what causes AN? Many studies, and much media attention, have focused on environmental and cultural factors that play a role in the development of AN. But in addition to these factors, newer research suggests that there is also a biological basis that makes certain individuals more vulnerable to the disorder.

            Research has persuasively demonstrated that environment plays a large role in the development of AN. A correlation has been found between parents who make negative comments, especially about weight and food, and the development of anorexia (7). Moreover, the children with obsessive thoughts about food and weight are found to positively correlate with parents who also have obsessive thoughts about food and weight (7). Some researchers have also suggested that families who avoid emotional issues and value perfectionism may create an increased likelihood of development of AN (8). But these correlations are not necessarily causations; some children may be more vulnerable to parental criticisms than other children.

            The media may also create an unhealthy atmosphere for young women. A majority of people in the US are overweight, but only 6% of characters on television shows are overweight. Moreover, the weight gap between models and the general public has continued increasing. Some researchers have also claimed that the gender gap in the prevalence of AN suggests a cultural role—that the fact that our society places less emphasis on men looking slim explains why they are less likely to develop AN (2). But this scrutiny of the cultural atmosphere, though warranted, does not explain why eating disorders have existed throughout history. It also does not explain why not every young woman develops anorexia.

            The other day, while getting ready for Neurobiology and Behavior, I was watching Rachel Ray. She had on a woman who, though not anorexic or (presumably, since it was not mentioned) bulimic, clearly had an above-normal obsession with weight and food. They brought out another woman who talked about how the atmosphere in this country creates these feelings of insufficiently and need to diet. But, what they failed to mention, at least before I left for class, was why this woman in particular was so affected by the environment. Perhaps that is too much to ask of Rachel Ray, but the question remains—what makes certain people more vulnerable to their environment?

            One interesting theory of the development of AN comes from evolutionary psychology. Some researchers posit that AN is an adaptation gone awry (3). Thousands of years ago, our ancestors were a nomadic people who relied on gathering to eat. In times of famine, people who could go for a long time without eating had a higher likelihood of continuing on and finding a new food source. The ability to feel satiated when not eating was once an advantageous adaptation. Therefore, individuals with a genetic tendency towards anorexia feel sated and unfazed by starvation. A few weeks ago, someone made a forum post about how she did not see how anorexia could be chosen by natural selection. But it actually does make sense—that the ability to go for long periods of time without eating and remain full of energy is advantageous. Unfortunately, it is fairly impossible to prove this theory because you cannot really experiment on evolutionary psychology. But the theory does point towards a biological susceptibility to anorexia.

            Therefore, many researchers have focused on a possible biological basis for the development of anorexia. Some women may simply be more vulnerable to environmental factors. For instance, people with a mother or sister who had AN are twelve times more likely than those with no family history to develop AN themselves (1). While this may also be an issue of family environments, twin studies have demonstrated that monozygotic twins show higher concordance rates of AN than DZ twins (2). It would seem, therefore, that genetics plays a role in the development of AN. Research also suggests that people suffering from anorexia have higher levels of serotonin and higher levels of dopamine receptor activity. The latter could explain why, though compelled to lose weight, anorexics feel no enjoyment in the process (4).

            One question that remains is when these brain chemistry changes take place. Though they could exist prior to anorexia, neurotransmitter level alterations may instead be brought on by the disease itself. One study using rats found that anorexia induced a change in several neurotransmitter systems (Gietzen and Magrum, 2001). However, other researchers point to findings of neurochemical alterations in recovered anorexics as evidence that these changes most likely existed before the onset of the disorder (4).

            Clearly, more research is needed to work out what and when neurological changes occur in anorexics because it seems that the environment cannot be the only factor in who develops anorexia nervosa. If that were the case, many more people would starve themselves. Instead, it seems that genetics, biology and the environment all play central roles in the development of AN. Genetics, and some biological factors, load the gun, and then the environment pulls the trigger. Keeping with the gun analogy, other biological factors likely keep the bullet moving.

References

      1.  Anred: Causes of Anorexia Nervosa

2. Culture and Eating Disorders: A Review

3. An evolutionary explanation for anorexia?

4. Neurochemical Abnormalities of Anorexia Nervosa and Bulimia Nervosa

      5. Anorexia Nervosa @ U. Maryland Medical Center

      6. Prevalence of Anorexia

      7. Negative Comments from Family affect weight concerns in women at high risk for eating disorders

      8. Perfectionism in Anorexia Nervosa