This is a topic I’ve been interested in for some time, and would love to do more research on. Here is an overview of the two restrictive types of eating disorders: anorexia nervosa and bulimia nervosa.
Anorexia is thought to be a relatively modern disorder, however it has been recognised as an eating disorder since the 19th Century, whereas bulimia has only been recognised since 1980. Anorexia is categorised by significantly restricted food intake coupled with a distorted body image. This eating disorder affects 1 in 200 adolescents, with 90% of the sufferers female. Sufferers of bulimia nervosa consume large amounts of food and then purge, either by forcefully vomiting or laxative abuse. This eating disorder is rare in men, and affects up to 3% of young women.
There are several different biological theories about the cause of eating disorders. If eating disorders have a genetic link, then abnormal relationships with food should be found amongst the close relatives of a sufferer of an eating disorder. A recent study found that the female relatives of an anorexia nervosa sufferer have an 11.4 times higher chance of having an eating disorder compared to the female relatives of someone who does not have the disorder.
One of the possible biological causes of eating disorders could a biochemical imbalance in the brain. The hypothalamus is a small cone shaped structure in the brain which connects to the pituitary gland via the pituitary stalk (see picture below).
The hypothalamus is the area of the brain responsible for maintaining homeostasis – part of which involves regulating appetite and thirst (Damage to the ventromedial hypothalamus has been linked to overeating, while damage to the lateral hypothalamus has been shown to cause starvation).
However, not every sufferer of an eating disorder has damage to their hypothalamus. The hypothalamus also regulates the secretion of neurotransmitters in the brain, and there is evidence to show that abnormally low or high levels of these neurotransmitters, in particular serotonin could be a contributing factor to eating disorders. Serotonin is involved in regulating hunger and satiety, and serotonergic disfunction has been found to increase susceptibility of eating disorders (Kaye et al).
One of the treatments for bulimia involves patients taking drugs called SSRIs which increase the amount of serotonin at synapses (like the one shown in the cartoon below). Taking these drugs has been shown to lessen the binging and purging symptoms of the disorder, although it is likely that other therapy is needed for a sufferer to completely recover.
However, although there are biological factors which can cause an individual to develop an eating disorder, there must be other factors which can also play a part. This is shown by the fact that there isn’t a 100% correlation between identical twins who have the disorder. There is also evidence that cases of eating disorders are rising, which has been blamed on the shift in culture towards favouring skinny models and celebrities.
Ogden (1992) analysed the physical features of female fashion models over a 20 year period, and found that models became taller, with a decrease in hip and bust size relative to waist size, giving a more androgynous body shape. These findings correlate with an increase in eating disorders, suggesting that there could be a causal relationship between them.
This was just a brief overview of the causes of eating disorders, although a single cause has yet to be identified. It is likely that an interaction of biological and social factors can cause someone to develop anorexia or bulimia. As eating disorders have the highest mortality rate of any mental illness, it is vital that more research is done in order to develop effective treatments and help more people overcome these conditions.