Biological Explanations for Anorexia Nervosa

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Introducing Anorexia Nervosa

Anorexia nervosa (AN) is an eating disorder. The NHS website indicates people with anorexia exercise excessively and/or eat too little in an attempt to keep their weight as low as possible. Anorexia nervosa is often driven by body-image distortion.

Prevalence of AN

According to the eating disorder charity BEAT, around 1.25 million people suffer from an eating disorder in the UK. Around 10% of those suffer from AN.
More women suffer from AN than men.
AN is usually developed between the ages of 16 and 17.
AN has the highest adolescent mortality rate of any psychological disorder.

Characteristics of AN

The DSM characterises AN with three main symptoms:
- Weight loss linked to strict restriction of calorie intake, to the point where weight is less than 85% of the expected.
- Fear of weight gain and becoming obese.
- Body dysmorphia: distorted perception of self-image.
Individuals with AN believe that they are fat even though they are very thin. They also deny that their low weight causes any serious risks to their health.

Explanations of AN

AN can be explained through biological mechanisms; genetic and neural.
Psychological explanations have also been suggested.

Genetic Explanations for Anorexia Nervosa

Genes may provide an explanation for the cause of anorexia nervosa (AN). Family, twin and adoption studies have been used to show this.

<b>Holland et al. (1988)</b> - twin study

Holland et al. (1988) - twin study

Holland et al. (1988) studied the concordance rates of AN in twins where at least one twin had a diagnosis.
They found that 56% of identical twins of individuals with AN developed AN themselves, while the rate was only 5% for non-identical twins did.
As identical twins share 100% of their genetic material, these findings suggest that AN has a strong genetic component.

Adoption studies (<b>Klump et al. (2009)</b>)

Adoption studies (Klump et al. (2009))

As identical twins also share a developmental environment, adoption studies are more reliable when trying to attribute a cause to genes.
Adoption studies of siblings have supported heritability of eating disorders, with rates of 59%-82% emerging in studies like Klump et al. (2009).

Issues with family, adoption and twin studies

Studies have not been reliably replicated and results have been inconsistent. So actual heritability rates are not known.
Many genetic models try to simplify causation and ignore the interaction of genes with the environment. It is far more likely that there are multiple contributing factors that differ between individuals.

Neural Explanations for Anorexia Nervosa

Anorexia nervosa (AN) may have a neural explanation. Both damage to the hypothalamus and irregular functioning of neurotransmitters dopamine and serotonin have been linked to AN.

Hypothalamus

AN may be caused by hypothalamic malfunctioning, particularly relating to the lateral hypothalamus (LH).
Animal studies show lesions to this area result in a lack of eating.
Recent research hypothesises that people with AN may have reduced blood flow to the LH. But no causal relationship had been found.

Serotonin

Some people with AN have elevated levels of serotonin, which are linked to anxiety.
Serotonin is produced when we eat food, which may explain why starvation sometimes makes people with AN feel better because it lessens their anxiety.
The metabolites produced by serotonin breakdown have been shown to exist at low levels in AN sufferers. This suggests the serotonin mechanisms are abnormal in these individuals.
But no causal relationship between serotonin mechanisms and AN has been discovered.

Dopamine

Some people with AN have been shown to have overactive dopamine receptors in the basal ganglia.
This may explain why some people with AN have indicated that they don't find eating food pleasurable because increased levels of dopamine in the basal ganglia are linked to abnormal interpretation of rewards.
Aversion to food, loss of weight and body dysmorphia have all been linked to increased dopaminergic activity.

Advantages of neural explanations

There is a lot of stigma surrounding AN and people blame certain factors such as parents, media or the individual.
Biological explanations can remove this blame and show that it is not 'their fault'.
Locating specific biological mechanisms that are disrupted in AN sufferers provides a good basis for treatment. But this can also shed doubt on biological explanations.
E.g. SSRIs - antidepressants that increase the brain’s serotonin uptake - are not effective in treating AN.