Biological explanations for Anorexia Nervosa

Disturbances in levels of serotonin appear to be a characteristic of individuals with eating disorders.

For example, Bailer et al compared serotonin activity in women recovering from restrictive type and binge eating/purging type anorexia with healthy controls. It was found that high levels of serotonin activity was in the binge eating/purging type. Additionally, the highest serotonin levels were in women who showed the most anxiety, suggesting that persistent disruption of serotonin levels may lead to increased anxiety triggering AN.

A problem with this explanation is that SSRI's which alter levels of brain serotonin, are ineffective when used with AN patients.

However, Kaye et al found that when used with recovering AN patients, these drugs were effective in preventing relapse.

Therefore, malnutrition-related changes in serotonin function may make the action of SSRI's ineffective, which only become effective when weight loss turns to a more normal level.

Recent studies suggest a role for dopamine in AN.

Kaye et al used a PET scan to compare dopamine activity in the brains of 10 women recovering from AN.

In AN women they found overactivity in dopamine receptors, in a part of the brain called the basal ganglia,where dopamine plays a part in the interpretation of harm and pleasure.

Increased activity in this area appears to alter the way people interpret rewards. Individuals with AN found it difficult to associate good feelings with the things that people find most pleasurable.

Supportive evidence comes form Castro-Fornieles et al who found that adolescent girls with AN had higher levels of a waste product of dopamine than a control group. Improvement in weight levels was assosiated with normalistation of the waste product of dopamine.

Research has also shown lower than normal levels of dopamine receptors in the brains of obese individuals.

Levels of dopamine appear to be inversely related to body weight, although whether this is a cause or a consequnce is not yet clear.

Lindberg and Hjern found a significant assciation between premature birth and development of AN.

Birth implicatins may lead to brain damage caused by lack of oxygen, impairing the neurodevelopment of the child. Nutritional factors maybe implicated if mothers have an eating disorder.

Bulik et al suggests hat mothers with AN expose thier offspring to a 'double disadvantage' -transmission of their genertic vulnrability to AN, and inadequate nutrition during preganacy.

Supporting evidence comes from Favaro et al who found that immediatlely after or before birth complications, significantly associated with AN were placental infarction, early eating difficulties and a low birth weight.

This is a prospctive birth study which is a powerful research approach because it provides support for the contibution of obstetric complications.

The AFFH proposes that the typical symptoms for AN are food restriction, hyperactivity and denial of starvation.

This reflects the operation of adaptive mechanisms that once caused migration in response to local famine conditions.

In pre-historic times, when there is no source of food, starvation begins, where most animals and humans feel intense hunger and begin to search for food.

However, starved individuals with a genetic tendancy towards anorexia say they feel full, are not fazed by starvation and have a new lease of energy.

In the EEA those starving foragers who decieved themselves about their physical condition would have been more confident about moving on to a more favourable environment in terms of food avaliablility, and so would have been more likely to survive.

Therefore, for modern day individuals, among those who are genetically vulnerable to AN, losing too much weight may trigger these ancestral mechanisms.

Support

Anoreixa symptoms have been recorded through out history e.g St Catherine of Siena.

If this behaviour existed a long time ago, this makes socio cultural explanations such as pressure to be thin less likely and supports a biological-based account.

However, records are scarce and are esentially case studies which may explain a very rare behaviour.

Most studies of eating disorders have concentrated on the study of women but, according to recent statistics 25% of adults with eating disorders are men. Whether this figure indicates that more men nowadays suffer from disordered eating compared to ten years ago or whether previously boys and men escaped attention is not yet clear.

However, what this does show is that eating disorders such as AN are not exclusively a female problem.