In trying to understand the causes of eating disorders, scientists have studied the personalities, genetics, environments, and biochemistry of people with these illnesses. As is often the case, the more that is learned, the more complex the roots of eating disorders appear.
Most people with eating disorders share certain personality traits: low self-esteem, feelings of helplessness, and a fear of becoming fat. In anorexia, bulimia, and binge eating disorder, eating behaviors seem to develop as a way of handling stress and anxieties.
People with anorexia tend to be "too good to be true." They rarely disobey, keep their feelings to themselves, and tend to be perfectionists, good students, and excellent athletes.
Some researchers believe that people with anorexia restrict food -- particularly carbohydrates -- to gain a sense of control in some area of their lives. Having followed the wishes of others for the most part, they have not learned how to cope with the problems typical of adolescence, growing up, and becoming independent.
Controlling their weight appears to offer two advantages, at least initially: they can take control of their bodies and gain approval from others. However, it eventually becomes clear to other that they are out-of-control and dangerously thin.
People who develop bulimia and binge eating disorder typically consume huge amounts of food -- often junk food -- to reduce stress and relieve anxiety. With binge eating, however, comes guilt and depression. Purging can bring relief, but it is only temporary. Individuals with bulimia are also impulsive and more likely to engage in risky behavior such as abuse of alcohol and drugs.
Genetic and environmental factors
Eating disorders appear to run in families -- with female relatives most often affected. This finding suggests that genetic factors may predispose some people to eating disorders; however, other influences -- both behavioral and environmental -- may also play a role. One recent study found that mothers who are overly concerned about their daughters' weight and physical attractiveness may put the girls at increased risk of developing an eating disorder. In addition, girls with eating disorders often have father and brothers who are overly critical of their weight.
Although most victims of anorexia and bulimia are adolescent and young adult women, these illnesses can also strike men and older women. Anorexia and bulimia are found most often in Caucasians, but these illnesses also affect African Americans and other racial ethnic groups. People pursuing professions or activities that emphasize thinness -- like modeling, dancing, gymnastics, wrestling, and long-distance running -- are more susceptible to the problem. In contrast to other eating disorders, one-third to one-fourth of all patients with binge eating disorder are men. Preliminary studies also show that the condition occurs equally among African Americans and Caucasians.
In an attempt to understand eating disorders, scientists have studied the biochemical on the neuroendocrine system -- a combination of the central nervous and hormonal systems. Through complex but carefully balanced feedback mechanisms, the neuroendocrine system regulates sexual function, physical growth and development, appetite and digestion, sleep, heart and kidney function, emotions, thinking, and memory--in other words, multiple functions of the mind and body. Many of these regulatory mechanisms are seriously disturbed in people with eating disorders.
In the central nervous system -- particularly the brain -- key chemical messengers known as neurotransmitters control hormone production. Scientists have found that the neurotransmitters serotonin and norepinephrine function abnormally in people affected by depression. Recently, researchers funded by NIMH have learned that these neurotransmitters are also decreased in acutely ill anorexia and bulimia patients and long-term recovered anorexia patients. Because many people with eating disorders also appear to suffer from depression, some scientists believe that there may be a link between these two disorders. In fact, new research has suggested that some patients with anorexia may respond well to the antidepressant medication fluoxetine which affects serotonin function in the body.
People with either anorexia or certain forms of depression also tend to have higher than normal levels of cortisol, a brain hormone released in response to stress. Scientists have been able to show that the excess levels of cortisol in both anorexia and depression are caused by a problem that occurs in or near a region of the brain called the hypothalamus.
In addition to connections between depression and eating disorders, scientists have found biochemical similarities between people with eating disorders and obsessive-compulsive disorder (OCD). Just as serotonin levels are known to be abnormal in people with depression and eating disorders, they are also abnormal in patients with OCD.
Recently, NIMH researchers have found that many patients with bulimia have obsessive-compulsive behavior as severe as that seen in patients actually diagnosed with OCD. Conversely, patients with OCD frequently have abnormal eating behaviors.
The hormone vasopressin is another brain chemical found to be abnormal in people with eating disorders and OCD. NIMH researchers have shown that levels of this hormone are elevated in patients with OCD, anorexia, and bulimia. Normally released in response to physical and possibly emotional stress, vasopressin may contribute to the obsessive behavior seen in some patients with eating disorders.
NIMH-supported investigators are also exploring the role of other brain chemicals in eating behavior. Many are conducting studies in animals to shed some light on human disorders. For example, scientists have found that levels of neuropeptide Y and peptide YY, recently shown to be elevated in patients with anorexia and bulimia, stimulate eating behavior in laboratory animals. Other investigators have found that cholecystokinin (CCK), a hormone known to be low in some women with bulimia, causes laboratory animals to feel full and stop eating. This finding may possibly explain why women with bulimia do not feel satisfied after eating and continue to binge.
Written by Lee Hoffman, Office of Scientific Information (OSI), National Institute of Mental Health (NIMH).