Biological explanations of anorexia (AN)

Theories of how chemicals in the body can cause anorexia and evolutionary explinations.

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Clinical characteristics

Anxiety - Anorexics not only fear being fat and obsess about food intake, but actually have a phobia of food.

Weight loss - The person will have less than 85% of the average weight (for their age and height). They may also avoid meals, carefully plan meals, do excessive exercise and hide food. 

Amenarilien - Missing 3 consecutive periods, caused by lack of nutrition

Body image distortion - See themselves as fat (when in fact they are very thin) and deny the seriousness of their condition. 

All 4 are needed for a diagnosis of anorexia

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Pet scans were taken of 10 recovering anorexics and 12 healthy people. It was found that the women with anorexia had overactive dopamine receptors in the Basal Ganglia, where dopamine help interpret harm and infection. The increased levels of dopamine activity seems to alter the perception of reward. They do not associate food as pleasurable. 


Research into young girls with AN has found that they have high levels of homovillic acid, a waste product of dopamine compared to non-anorexics. This supports the link between dopamine and weight fluctuation. Obese people have been found to have the complete opposite, this supports this theory. However, the cause and effects are unknown. 

AO3 - Freewill and Determinism

American insurance companies only pay out to illnesses that have a biological cause. However, since there is no clear biological cause, anorexia is seen to be voluntary. Research has suggested it is biologically based like schizophrenia.

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Neurodevelopment (AO1)

Obstetric (birth) complications - There is a positive correlation between premature birth and the development on AN. It has been suggested that hypoxia (lack of oxygen) impares the neural development. 

Bulik et al (2005) suggests that AN mothers put their children at a higher risk of AN, a 'double disadvantage' due to nutritional vunerability and inadequate nutrition during pregnancy. 

Season of birth hypothesis - It has also been found AN people are more likely to b born in the spring months. The reason being that the child will be in the second trimester of the pregnancy, when the brain undergoes lots of development. The winter months mean there are more viruses and infections around.

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Neuro development


A study of births (that followed the development from birth to adulthood) supported the obstetric complication theory. It was found that complications before and after birth. Things such as placental infarction (obstruction to the blood supply to the baby), early feeding difficulties and low birth weight.

It has been found that people with AN tend to have been born in the spring, this supports the season of birth hypothesis. It is also reasonable to predict that when the brain is undergoing the most development, at the time of the year when infections are most abundant, that damage could occur to the brain.


Bulik suggests that people need to realise anorexia is due to dysfunctional biology, not a dysfunctional family. This also means it is harder to treat. These theories also blame the parents for the development of AN

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Evolutionary explinations

Reproduction suppression hypothesis (Surrey 1987)

It is suggested that young girls self starve to delay puberty, in order to increase the chance of the chances of survival for their offspring. The theory suggests that women can then have children when they are biologically, emotionally and socially ready for the responsibilities.

By delaying having a child until after the teenage years and early 20s it allows the girl to go university, get a secure job, etc. This allows the woman to build resources (babies are expensive to raise) and the right level of maturity. 


However, Singh argues men prefer the 'hour glass' figure, not thinness. The 'hour glass' figure signals fertility and that the woman is not already pregnant. 

The lack of periods can also lean women to become infertile, which contradicts the evolutionary explanation. The evolutionary theory is also seen to be reductionist, as it blames emotions and family conflicts. 

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There is also a problem as many research focuses on women. However, 25% of people with eating disorders are male. It is unclear if men have just been ignored in the past or if there is a growing number of male's with eating disorders, but it is clear there is little studies into men.

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You could also talk about the role of serotonin and real world applications, otherwise, the information is useful and concise

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