The Etiology of Anorexia Nervosa and Bulimia Nervosa By ...
[Pages:34]The Etiology of Anorexia Nervosa and Bulimia Nervosa By Ryn Lister Fall 2005
A Critical Literature Review submitted in partial fulfillment of the requirements of the Senior Thesis Class
Abstract
Proper nutrition is an important concept that is enforced over and over by parents, teachers, coaches and the government. Nutrition effects every system in the body and can dramatically alter someone's personal state of health. However, society presents a picture of bodily perfection that combined with genetic predisposition can result in the manifestation of an eating disorder. Eating disorders occur on a continuum, ranging from extreme obesity to anorexia. Of the many eating disorders, anorexia and bulimia have been most extensively studied. They both occur predominately in females and the onset is usually during teenage years, and in both, the defining symptom is an intense sense of fear to gain weight.
This paper reviews some of the major recent research on the etiology of anorexia and bulimia. Both disorders are examined from a physiological, genetic and behavioral/social aspect in an attempt to clarify the influence that each has on etiology of anorexia and bulimia. The knowledge of these disorders is growing in the field of science as well as in society. With the advancements, anorexia and bulimia have become more treatable, but remain incurable. A deeper knowledge of the etiology of these eating disorders is necessary in order to get closer to finding improving treatment.
Introduction
In today's society, eating disorders are becoming more uniformly accepted as serious psychological disorders. Initially thought to be social disorders, the improvement in knowledge of genetics is beginning to suggest that there is also a physiological basis that contributes to the etiology of eating disorders. It is commonly accepted that eating disorders occur on a continuum, with intense restriction of food at one end and extreme overeating at the other end. Currently, there is an obesity epidemic occurring in America. Easily accessible food that is high in fat and hectic daily routines that do not allow time for exercise are effecting this country's health. As obesity is receiving more attention from the media and researchers, the opposite end of the spectrum is also peaking the interest of the medical society. Although eating disorders are not as prevalent as obesity, they are very dangerous disorders. Eating disorders are threatening for many reasons. Firstly, eating disorders are complex. They derive from environmental and genetic factors, and are often accompanied by one or more psychological disorders. The prevalence rate for both anorexia and bulimia is low, 0.1%-1% for anorexia and 1%-2% for bulimia.. These numbers are good, however, the rate of relapse after treatment is between 8% and 62% within the first 5 years of recovery (Bulick, 2005). The prevalence rates for anorexia and bulimia must be approached cautiously. The data is based on those patients who have been diagnosed, meaning those who have sought the help of a doctor or psychologist. Partial cases of anorexia and bulimia may go unnoticed and untreated, while others may refuse to seek medical help. Lastly, research has shows that the mortality rate for patients with eating disorders is much higher. As compared to a healthy population, the mortality rate for patients with eating disorders is 6.0 to 12.82 times higher. The seriousness of eating disorders is very evident. Despite the low
prevalence rate, the high relapse rate, high mortality rate and the complexity of the disorder have prompted an increase of research in this field .
Both disorders largely affect young females age 12-22, however the diagnosis in males is becoming more common. Currently it occurs in males 10% as often as it occurs in females. Researchers are running a wide range of experiment that explore the possible physiological, genetic and environmental causes of eating disorders. Presently, the treatment of an eating disorder requires an expansive medical team. The various causes, symptoms, side effects and treatment of eating disorders often require a dietitian, psychologist, psychiatrist, and other medical specialists to properly treat the disorder. Whether inpatient or outpatient the overall therapeutic goal is to have the patient gain weight and maintain it by removing the fear of weight gain and terminating the behavior that resulted from that fear. Appetitive behavior is influenced by neurotransmitters, hormones, genes, personality, mood, environment, and so much more. Each of these different aspects must be explored in an attempt to learn as much as possible about these disorders.
As research in this field progresses, so does the hope that a more effective form of treatment and preventative measures will soon be found. This paper reviews the current literature on the physiology, genetic and behavioral/social component that contribute to anorexia and bulimia. Research specific to both disorders will be cited in order to gain understanding about each disorder individually. Though the two disorders are very similar in appearance, their etiology is slightly different. The similarities and differences of these two disorders as well as the possible implications of each will be discussed.
The Etiology of Anorexia Nervosa
Since the recognition of anorexia nervosa as a psychological disorder, the medically accepted definition of the disorder has changed. The currently accepted DSM-IV definition of a full syndrome anorexic patient will display all of the following symptoms: A refusal to maintain normal body weight, so that their body weight is less than 85% of that which is expected; an intense fear of gaining weight despite being underweight; abnormalities in the way one perceives his/her own body, extreme influence of body weight on self perception and/or denial of the seriousness of low body weight. In postmenstral females, amenorrhea is often apparent and males show a severe decrease in circulating hormones. Younger patients who experience an earlier onset of the disorder may not reach their full potential height due to nutritional deficiencies. A patient who meets some but not all of the requirements, or does not meet the requirements to the point that they are preventing him/her from leading a normal lifestyle, often receive a partial diagnosis. In addition to the physical symptoms and side effects of the disorder, many patients also deal with mood disorders such as depression, bi-polar disorder, and anxiety disorders such as obsessive-compulsive disorder. One disorder does not cause the other, however there is a strong correlation between the presence of one with the other.
There are two forms of anorexia. The first is the restricting type, defined as a period when the patient severely restricts his/her caloric intake and does not engage in binging or purging behavior. In this state patients classify types of foods as either good or bad, allowing themselves to eat none of the bad and very little of the good. Once emaciated, an anorexic patient may become satisfied with his/her body, but will continue to not eat in order to prevent weight gain. An anorexic patient is most dangerous, however, when he/she does not become
satisfied with his/her body and continues to try to lose weight. Instead of maintaining a low unhealthy body weight, they continue to allow their weight to drop even lower, resulting in hospitalization and forced feeding. The second form of anorexia is the binging/purging type. This occurs when a patient suffering from anorexia binges on food and then purges in order to lose the calories. Purging can be defined as over-exercising, misuse of laxatives and diuretics, vomiting, or fasting. This cycle can occur one day a week or up to several times a day. Binging/purging cycles are seen as phases that restrictive anorexics go through when at a very low point and are very desperate to lose weight. Not all anorexics experience binging/purging cycles, however it is very common for recovering anorexics to relapse into stages of binging and purging.
This section of the paper examines the research that is being done in many different fields in an attempt to learn more about anorexia nervosa. Physiological aspects, genetic components and social and environmental factors all contribute negative components that result in the manifestation of an anorexia. Research is working to determine the magnitude of effect that each factor has and how it creates that effect.
Physiology of Anorexia Nervosa
The physiological research being done on anorexia nervosa has focused mainly on neurological abnormalities and their effects on emotion and behavior. As knowledge of the brain grows, researchers are looking to neurotransmitter and hormonal deficiencies as the cause of eating disorders. Serotonin, dopamine, ghrelin, leptin, and brain derived neurotrophic factor have all been individually researched. Each of these possibilities will be explored using
evidence from some of the most recent studies. Serotonin has been a neurotransmitter targeted in the research on eating disorders for
multiple reasons. Firstly, patients with anorexia tend to demonstrate abnormal serotonin processes involving receptors and transporters. Secondly, many comorbid personality and affective disorders that accompany anorexia, such as anxiety, harm avoidance, and depression are known to be negatively effected by abnormalities in 5-HT as well as 5-HT transmitters. And thirdly, symptoms of anorexia have been slightly ameliorated by treatment with medications known to affect 5-HT pathways (Kaye et al, 2005; Kaye et al,2005). Research has shown that 5HT is involved in moderating appetitive behavior. Studies conducted by Takimoto and his colleagues showed that 5-HT distributes some control over postprandiasl satiety. A decrease in hypothalamic 5-HT leads to an increase in carbohydrate intake and impairment of the normal levels of satiety. Other research on anorexia has shown through the use of PET scans that there is reduced 5-HT2A receptor activity in parts of the cingulate cortex and temporal and parietal cortical areas of the brain in anorexia (Bailer et al, 2004). Both of these studies were conducted on recovered anorexic patients, and despite no longer being ill, they sill showed these discrepancies in 5-HT2a receptor activity. In addition to th abnormal function of the 5-HT2a receptor, it has also been found that discrepancies from the norm also occur in the 5-HT1a receptor and the 5-HT transporter. Even though there have been a couple of studies to show no significant effect in symptoms with the administration of SSRI's, other research has shown a significant improvement in inpatient anorexics after the administration of fluoxetine and other antidepressants (Kaye et al, 2005: Attia et al, 1988; Strober et al, 1999; Kaye et al, 2001).
Researchers such as Kaye et al, and Uher use both PET and SPECT scans in order to determine the activity level of 5-HT in the different areas of the brain (Kaye et al, 2005; Uheret
al, 2005). In a study by Uher et al, brain activity was monitored using functional magnetic resonance imaging. Healthy women and women with eating disorders were shown pictures of underweight, normal weight, and overweight women. The subject also rated their level of fear and disgust on a scale of 1-7 when presented with the drawings. The subjects ratings and recorded brain activity were analyzed and compared. Healthy women and female anorexic patients both showed activation in the later fusiform gyrus, inferior parietal cortex and lateral prefrontal cortex. The difference was found in the strength of the responses. This effect and/or cause of this difference is unclear. It is possible that the decreased 5-HT response was present pre-diagnosis and contributed to the development of the disorder. Or, the disorder could have resulted in the damage of brain tissue, causing the decreased response. Overall, the anorexic patients rated all of the images as more aversive on the both the scale of fear and disgust. They were unable to find any body image to be satisfactory. The researchers were able to find a correlation between the ratings of aversiveness to activity in the right medial apical prefrontal cortex. Previous studies (Bailer et al, 2005) have also, through the use of MRI and PET scans, identified potential alterations in temporal lobe. The temporal lobe functions in abstract behavior, problem solving, movement and others. This study by Bailer et al was also able to show that the altered 5-HT activity in the temporal and frontal lobe of the brain was present while suffering from anorexia and after recovery from anorexia. The fact that this abnormality persists after recovery insinuates that the low 5-HT activity is making the subject vulnerable to anorexia.
More evasive research is being conduced using animal models. In a study by Hillebrand et al (2005), research was conducted on rats with activity-based anorexia. Activity-based anorexia is accepted as the animal model of anorexia. It can be inflicted on an animal with the
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