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What causes bulimia nervosa?

Researchers have several theories about the causes of bulimia nervosa; yet no single theory accounts for all possible causes and symptoms. Most of the current theories about the disorder relate to self-perceptions about body image (size, shape, and weight), mood and depression, and genetics, but researchers and clinicians do not know why one particular person develops the disorder while another person with a very similar profile does not. Researchers are studying possible cause-and-effect relationships between bulimia nervosa and other mental disorders commonly associated with it. Pinpointing the causes of bulimia nervosa has proven difficult because the disorder has both mental and physical components, and it develops in many age groups, races, socioeconomic classes, and both sexes.

Types of Theories

One popular theory for the development of bulimia nervosa, the "cognitive behavior model" theory, presumes that the affected person is unhappy with his or her body size and shape and associates feeling full with being fat. This perception triggers emotions of anxiety, depression, anger, and self-loathing. To the person with bulimia nervosa, purging or excessive exercise becomes a way of removing the "fat feeling" and undesirable feelings and emotions that go with it. The affected person feels better emotionally after the purging or exercising, and the feeling of improved well-being positively reinforces the behavior. Some psychological risk factors, according to this model, are an individual's concern with his or her body size, shape, a propensity for perfectionism, and obsessive traits.

Several other theories can be grouped under "interpersonal and sociocultural models." These theories stem from the observation that bulimia nervosa often co-exists with another mental disorder, such as depression and that an individual feels pressure from society to be thin. This pressure, along with other interpersonal problems and depression, may trigger the bulimia nervosa behavior.

The "pathophysiologic model" suggests that brain chemistry causes the disorder. Levels of chemicals such as serotonin, some types of opioids, endorphins, estrogen, and a peptide called cholecystokinin, or CCK, have been found to be abnormal in individuals with bulimia nervosa. Abnormal levels of some of these chemicals are also found in people with other mental disorders. Eating can also cause changes in the levels of these chemicals. However, researchers have yet to show that these imbalances cause bulimia nervosa—the abnormal levels could be a result, rather than cause, of the behavior.

Models for the biologic basis of eating disorders are being explored through family, twin, and molecular genetic studies. Family and twin studies have consistently shown that bulimia nervosa runs in families (as do other eating disorders). Many recent molecular genetic studies have identified several possible genes, but no consistent association between a particular gene and bulimia nervosa has been conclusively proven. For example, a Japanese study published in late 2005 identified a particular gene (a type of growth hormone secretagogue receptor, GHSR) that occurred much more often in bulimia nervosa patients than in the study's control group of individuals without an eating disorder or in the study's other two groups individuals with other types of eating disorders. The researchers concluded that this gene was a risk factor for bulimia nervosa, but not for the other eating disorders. These findings require confirmation by additional studies. Other studies from Japan and Europe published in 2005 suggested brain-derived neurotrophic factor (BDNF) as a susceptibility gene for eating disorders, and researchers have found lower than usual levels of BDNF in patients with bulimia nervosa.

  
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Bulimia nervosa is an eating disorder in which a person engages in binge eating (eating a lot of food in a short time) followed by some type of behavior to prevent weight gain from the food that was eaten. This behavior can take two forms: self-induced vomiting, misuse of enemas, laxatives, diet pills (called purging) and excessive exercise, fasting, or diabetic omission of insulin (called non-purging). Some people with bulimia nervosa may also starve themselves for periods of time before binge eating again. Bulimia nervosa has important mental, emotional, and physical aspects that require consideration during treatment.

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