Biological explanations for anorexia nervosa

Reproduction suppression 

Females in the acestral enviroment had a delayed onset of sexual maturation when conditions were not conducive to their offsprings survival - adaptive. 

AN may be a variation of this adaption, causing females to alter the timing of their reproduction when they feel unable to cope with the biological, social and emotional responsibilities of womanhood. 

There is research support for this...

This explanation is supported by the observation that the onset of puberty is delayed in prepubertal girls with AN. Additionally because amenorrhoea is a typical characteristic of AN, this means that reproduction is suspended in AN females.

Gender bias...

This does not explain why AN would develop in men, 25% of adults with eating disorders are men, suggesting that AN is not soley a female disorder and therefore cannot be explained in terms of reproduction suppression.

Serotonin

Disruption of serotonin levels leads to increased anxiety, which may then trigger AN. 

Bailer et al found high levels of serotonin in women with binge eating/purging AN, with highest levels in those with the most anxiety. 

A problem for the serotonin explanations...

SSRI's, which alter levels of serotonin in the brain, are ineffective when used with AN patients. However some studies e.g. Tannenhaus report that SSRI's may help to elevate mood which therefore reduce some of the obsessive symptoms of AN.

'Adapted to flee' famine hypothesis 

Typical AN symptoms of food restriction, hyperactivity, and denial of starvation reflect evolved adaption in reponse to local famine conditions. 

When individuals lose weight, adaptive mechanisms usually cause conservation of energy and an increase in desire for food.

This adaption must be 'turned off' so that individuals increase their chances of survival by moving to a more favourable environment in terms of food resources. 

Season of birth

Individuals with AN are more likely to be born during spring months. (Eagles et al, 2001)

Explanations for this association include intrauterine infections during pregnancy and temperature at time of contraception.

Willoughby et al, 2005, found that among patients with AN in equatorial regions of the world there was no seasonal effect in the development of AN. 

There is research support for this...

Eagles et al, found that AN individuals tend to be later in birth order than healthy individuals. They may be at greater risk of being exposed to common infections from their siblings during the critical period of brain development in the second trimester of pregnancy.

There are limitations of evolutionary explanations of AN...

We might question how the symptoms of AN would have been passed on through our geenerations by natural selection, especially as AN decreases fertility and makes reproduction more difficult and may even kill the individual with this condition.

Ultimate versus proximate factors...

Although AN may have been an effective adaption in the harsh conditions (ultimate factors) outside these conditions the development of AN would not be favourable to the individual, suggesting that its development now is a consequence of factors that have very little to do with evolution, (i.e. proximate factors such as birth complications.)

Dopamine

Increased dopamine activity in the basal ganglia alters the way people interpret rewards, so individuals with AN find it difficult to associate good feelings with things that are usually pleasurable e.g. food.

There is research support for this...

Castro-Fornieles et al found that adolescent girls with AN had higher levels of waste product of dopamine. However Wang et al found that obese individuals had lower levels of dopamine, suggesting an inverse relationship between levels of dopamine and body weight.

Pregnancy and birth complications 

Lindberg and Hjern found a significant association between premature birth and development of AN. Birth complications may lead to braind damage caused by lack of oxygen, impairing the neurodevelopment of the child. 

Nutritional factors may be implicated if mothers have an eating disorder. Bulik et al suggest that motjers with AN expose their offspring to a double disadvanage - transmission of a genetic vunerablity to AN and inadequate nutrition during pregnancy. 

There is research support for this...

Favaro et al found that the perinatal complications associated with risk of developing AN were placental infarcation (obstructed blood supply in the placenta) early eating difficulties and a low birth weight. 

Biological explanations can reduce parental feeligs of guilt...

An advantage of these explanations of AN is that people realise they are dealing with dysfunctional biology, rather that dysfunctiona family which isn't treatable. This reduces the guilt felt by many parents that they caused the development of AN in their child.

IDA - Biological determinism 

Research in this area has implications for insurance payouts for psychiatric conditions which do not regard AN as biologically based and therefore not liable for a payout.