Causes of Eating Disorders - Biological Factors
Research provides strong evidence for an inherited predisposition (tendency) toward developing an eating disorder. In other words, eating disorders are often biologically inherited and tend to run in families. Recent research suggests that inherited biological and genetic factors contribute approximately 56% of the risk for developing an eating disorder. Individuals who have a mother or a sister with anorexia nervosa are approximately twelve times more likely to develop anorexia and four times more likely to develop bulimia than other individuals without a family history of these disorders. Studies of twins have shown a higher rate of eating disorders when they are identical (compared to fraternal twins or other siblings). Samples of DNA, the substance inside cells that carries genetic information, from pairs of siblings with eating disorders are now being analyzed to determine if they share genetic characteristics that are different from pairs of siblings without these disorders.
Research has also focused on abnormalities in the structure or activity of the hypothalamus, a brain structure responsible for regulating eating behaviors. Studies suggest that the hypothalamus of bulimics may not trigger a normal satiation (feeling full or finished) response. So, even after a meal, these individuals do not feel full. A wealth of research suggests that several different neurotransmitters are involved in eating disorders. Before discussing the contributions of specific neurotransmitters to different disorders, it is important to provide a bit of background about the functioning of these chemicals.
Neurotransmitters carry messages from cell to cell throughout the brain and nervous system. Neurotransmitters released from one cell travel across a cellular space (called a synapse) and attach to another cell's receptors. These receptors are specifically designed to receive certain neurotransmitters. In our brain and nervous system, multiple neurotransmitters are working simultaneously to control all sorts of functions such as mood, appetite, energy level, memory, etc. The effect of the neurotransmitter depends on the type of receptor being stimulated (i.e., whether it slows down or speeds up the receiving cell) as well as the part of the brain or nervous system that receives it. For example, serotonin (discussed below) can affect sleep, eating, temperature regulation, muscle movement, memory, and host of other behaviors depending on the specific receptors stimulated, and where in the body or brain those receptors are located.
The neurotransmitter serotonin affects binging behavior in bulimics. These individuals often crave (and gorge) on foods rich in carbohydrates. The body converts sugars from carbohydrates, through a multi-step process, into tryptophan. Tryptophan is then used to create serotonin, which is partially responsible for the regulation of appetite, creating a sense of satiation, and regulating emotions and judgment. Thus, the binge behavior of bulimics 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, although other brain chemicals, such as dopamine and norephinephrine, were normal in comparison to individuals with no history of eating disorders. The successful treatment of bulimia with Prozac (a medication typically used for depression), which acts to increase the amount of serotonin in the brain, is additional evidence of the importance of this brain chemical.