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Causes of Eating Disorders - Biological Factors

Bridget Engel, Psy.D., edited by Kathryn Patricelli, MA

image by Victor Svensson (lic)Eating disorders are often biologically inherited and tend to run in families. Research suggests that inherited these genetic factors contribute approximately 56% of the risk for developing an eating disorder. People who have a mother or a sister with anorexia are approximately twelve times more likely to develop anorexia than those without a family history. They are also four times more likely to develop bulimia than those without a family history. Studies of twins have shown a higher rate of eating disorders when they are identical (compared to fraternal twins or other siblings). Research has also focused on abnormalities in the structure or activity of the hypothalamus. The hypothalamus is a brain structure responsible for regulating eating behaviors. Studies suggest that the hypothalamus of those with bulimia may not trigger a response feeling of being full or finished eating. Because of this, even after a meal, they do not feel full.

Research suggests that several different neurotransmitters in the brain are involved in eating disorders. The brain uses a number of chemicals as messengers to communicate with other parts of the brain and nervous system. These chemical messengers, known as neurotransmitters, are essential to all of the brain's functions. Since they are messengers, they typically come from one place and go to another to deliver their messages. Where one neuron or nerve cell ends, another one begins.

In between two linked neurons is a tiny space or gap called a synapse. In a simple example, one cell sends a neurotransmitter message across this gap and the next cell receives the signal by catching the messenger chemical as it floats across the gap. The receiving neuron's capture of the neurotransmitter chemicals alerts it that a message has been sent, and this neuron in turn sends a new message off to additional neurons that it is connected to, and so on down the line.

In our brain and nervous system, multiple messengers are working at the same time to control all sorts of functions. These include mood, appetite, energy level, memory, etc.

The neurotransmitter serotonin affects binging behavior in those with bulimia. These individuals often crave and eat a lot of foods rich in carbohydrates. The body converts sugars from carbohydrates, through a multi-step process, into tryptophan. Tryptophan is then used to create serotonin. Serotonin is partially responsible for the control of appetite, creating a sense of being full, and regulating emotions and judgment. Because of this, the binge behavior of those with bulimia may also be a response to low serotonin levels in the brain.

A research team at the University of Pittsburgh found that individuals successfully treated for bulimia still had abnormally low serotonin levels. Other brain chemicals, such as dopamine and norephinephrine, were normal when compared to people with no history of eating disorders. Bulimia was shown to be successfully treated with a medication typically used for depression. This medication acts to increase the amount of serotonin in the brain. Because this was a successful treatment, it provides additional evidence of the importance of serotonin as a possible cause of bulimia.

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