The Brain Mechanisms of an Eating Disorder

Eating disorders are a taboo subject in our society today, but according to The Alliance for Eating Disorder Awareness, 1 in 5 women have an eating disorder or have distorted perceptions of food and eating habits; in addition to this statistic, The Alliance reports that eating disorders affect over 24 million Americans [1]. These statistics are surprisingly overwhelming considering how infrequently the subject is discussed. Yet with the massive number of people that are affected by eating disorders, there are still many uncertainties about the causes of such an aberrant disease. We understand many of the psychological elements, like poor body image and a sense of control, but what exactly causes these thoughts to surface? Many attribute these to the media and the environment, and while those are two plausible targets, a significant amount of behavior can be attributed to abnormalities in neurotransmitter levels in the brain, which can perpetuate many of the irrational thoughts about food and eating habits. There are various mechanisms that could potentially sustain the symptoms of anorexia nervosa or bulimia nervosa, such as hormones and neurotransmitter irregularities.

There are two hormones that seem to be found at high levels in patients with anorexia nervosa and bulimia nervosa: neuropeptide Y and ghrelin. Neuropeptide Y is secreted by the arcuate nucleus of the hypothalamus and is meant to produce intense eating; high levels of neuropeptide Y are found in the cerebrospinal fluid of extremely underweight anorexics [2]. Ghrelin is produced by the stomach and are found that “blood levels of this hormone increase while fasting and are reduced after a meal [2].” Considering the intended purpose of neuropeptide Y and ghrelin, their presence is not surprising to see high levels of this hormone because the patient would have intense hunger, and considering in normal patients it would produce ravenous eating, the body would over produce neuropeptide Y in hopes of producing eating to combat the self-starvation.

Another hormone that is believed to be linked to eating disorders is estrogen; considering the higher incidence of anorexia and bulimia in women, almost 95% of patients, and its increased onset during adolescence, it is not surprising that estrogen could have a potential link to the development of these disorders [3]. At puberty, the body experiences changes in hormone levels, that result in the growth of secondary sex characteristics. Many girls and boys welcome these changes as they are ready and prepared to progress into the next stage; however, some, mainly young girls, perceive themselves to be getting fat and want to counteract this, and begin to develop eating disorders. Many would expect that boys would also experience the same kind of alarm, yet the changes that boys experience are to become more muscular, which are changes that are perceived as positive changes. In this case of estrogen, the social and psychological implications are important to consider, yet a study by Söderstein et al. reveals that more than the development of secondary sex characteristics could be the cause of the increased incidence of eating disorders in women.

Söderstein et al. investigated the metabolic responses in short-term food deprivation comparing to a standard of the subjects eating on a non-deprived food schedule. The subjects were divided into men and women and were then allowed to eat as much food as possible; seven days later the subjects were asked to omit dinner from the previous night and breakfast from that morning, and the food intake from both groups were both investigated. The results recorded the men eating more food than the women at both eating sessions. While this finding is not that surprising, a shocking statistic recorded was that the women ate 20% less after being deprived food then when on a regular eating schedule [3]. The rationale reported by Söderstein et al. is that women have a harder time compensating once deprived of food, which explains why there is a higher incidence in women of eating disorders than in men.

Once treated for an eating disorder, the rate of relapse is high and could be related to the neurotransmitter, serotonin. Patients diagnosed with bulimia have a 30-60% chance of relapse after 6 months of being free of the disorder, and anorexia nervosa patients have an even higher chance of relapsing [4]. The role of serotonin is well understood in regards to depression, and depression has a high comorbidity with eating disorders [5]. A patient suffering from depression feels as though they have no control over their happiness or their life, and one of the ways that people respond to the feeling of no control is to take control of their eating habits, generally by severely limiting the amount of food that they intake daily.

Many of the symptoms of eating disorders are also associated with other psychological disorders like depression and anxiety, which serotonin has a significant influence in, but what exactly can cause an eating disorder? Many experts still maintain that it is the influence of the media and personal desire to be perfect as the cause for the eating disorder, and although these forces continue to be a factor throughout the tenure of an eating disorder, the biological influences like hormones and neurotransmitters only maintain the disease. It is important to remember that in a patient without the thoughts and desires of an eating disorder, that the mechanisms described help to maintain a healthy lifestyle. The benefit of understanding the biological mechanisms of disorders like anorexia and bulimia nervosa is that it provides an opportunity to do a drug treatment along with the common therapy, and provides a promising future for the further discussion, understanding, and treatment of eating disorders.

[1] Alliance for Eating Disorders Awareness, The (2005). “Eating Disorder Statistics.” Retrieved February 25, 2008, from The Alliance for Eating Disorders Awareness Web site: http://www.eatingdisorderinfo.org/18.html

[2] Carlson, Neil (2007). Physiology of Behavior. Boston, MA: Pearson Education, Inc. 410-428.

[3] Södersten, Per et al. (2006). “Understanding Eating Disorders.” Hormones and Behaviors. 50, 572-578.

[4] Deshmukh, Rashmi, MD and Kathleen Franco, MD (2003, Dec 22). Cleveland Clinic. Retrieved February 25, 2008, from Eating Disorders Web site: http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/psychiatry/eating/eating.htm

[5] Nolen-Hoeksema, Susan (2007). Abnormal Psychology (4rd edition). NY: McGraw-Hill.