The Biological Explanation
· Your brain requires a healthy, nutritious diet to function normally. It uses a fifth of all the calories you eat. So extreme dieting can disrupt normal functions of the brain
· Malnutrition can also change the balance of hormones in the body, which can affect how the brain functions
· The change in hormones causes the brain to become sensitive to the effects of an amino acid called tryptophan, found in almost all types of food
· This sensitivity can cause feelings of anxiety in people with anorexia when they eat. At the same time, starving themselves and excessive exercise lowers levels of tryptophan, which may make the person feel calmer and more relaxed
· Appetite is controlled by a part of the brain called the hypothalamus. When your body needs more food, your hypothalamus releases chemicals to stimulate your appetite.
· Once you have eaten enough food, hormones signal to your hypothalamus. Your hypothalamus will then release a different set of chemicals that essentially reward you for eating, and make you feel satisfied.
· It is thought that this ‘appetite-reward pathway’ becomes scrambled in people with anorexia. The feeling of fullness after a meal does not produce a sense of reward, but a sense of anxiety, guilt or self-loathing. In turn, feeling hungry may help reduce these negative feelings.
Genetic Explanation
· Disorders with a genetic component tend to run in families
· Stober and Humphrey 1987 – relatives of eating disorder patients were 4-5 times more likely than members of the general population to develop and eating disorder themselves
· Collier et al 1999 – women with eating disorders were twice as likely as a control group to have an abnormal version of the gene that controls serotonin brain systems
· Hook et al 2000 – examined medical records of 144,000 people on the island of Curacao, where it is considered attractive to be fat – the prevalence of eating disorders was the same as in Europe and USA
Twin Studies
· If one half of the MZ twin (identical) gets the genetic disorder, then the other half will
· If on half of the DZ twin (non-identical) gets the genetic disorder, then the other half has a 50% chance of getting it
· If MZ concordance is higher than DZ concordance = genetic influence
· If MZ and DZ concordance are similar = environment
· If MZ concordance is less than 100% = genes and environment
· If MZ is 100% and DZ is 50% = genetic
· Holland et al 1984 – MZ twins = 56% DZ twins = 5%
· Kortegaard et al 200 – MZ twins = 25% DZ twins = 13%
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