Introduction to biological explanations of anorexia

Eating disorders are not caused by any known physical disease, but they may involve biochemical imbalances in the body. Biological explanations focus on how internal physiological factors, such as hormone levels and brain chemistry, might contribute to the development of these disorders.

The role of the hypothalamus in hunger regulation

Research has highlighted the hypothalamus's role as a kind of 'weight thermostat' that helps maintain a stable body weight.

Key parts of the hypothalamus involved

• Lateral hypothalamus (LH) - This area triggers feelings of hunger when activated. It prompts the body to seek food if body weight drops below a certain set point.
• Ventromedial hypothalamus (VMH) - This section suppresses hunger when activated. It signals the body to stop eating if weight rises above the set point.

How the hypothalamus functions as a weight thermostat

The LH and VMH work together to regulate eating behaviours. If body weight falls below a set point, the LH activates, sending signals to brain areas responsible for thinking and behaviours related to eating. Conversely, if weight exceeds the set point, the VMH activates to reduce hunger. This system helps maintain balance.

Hypothalamus dysfunction and endocrine imbalances

Amenorrhoea can occur before significant weight loss, suggesting a primary disorder of low endocrine levels, which is associated with hypothalamus dysfunction. This indicates that anorexic symptoms may be caused by low hormone levels.

Link to amenorrhoea and hormone levels

Amenorrhoea, often seen in females with anorexia, can appear even before substantial weight loss, pointing to low levels of endocrine hormones. Such low hormone levels are associated with hypothalamus malfunction. Studies show that individuals with anorexia around 19 years of age have endocrine hormone levels similar to those of a healthy nine-year-old.

Neurotransmitter imbalances in anorexia

An imbalance in neurotransmitters in particular parts of the brain may contribute to anorexia.

Key neurotransmitters involved

• Noradrenaline - Changes in its levels can be present when anorexia develops.
• Serotonin - This neurotransmitter is involved in behavioural functions, including depression and obsessive-compulsive disorder.

How imbalances affect brain function

When anorexia develops, levels of noradrenaline and serotonin in the brain can change, and this might be a cause of the problem. Early studies found a reduction in levels of the serotonin metabolite 5-HIAA in people with eating disorders, suggesting that brain serotonin pathways were underactive. A reduction in receptors also suggests a dysfunction of the serotonin system. The brain serotonin system has been implicated in personality traits associated with eating disorders, such as obsessionality, perfectionism, anxiety, and depression. It is also part of the neurotransmitter system of the hypothalamus that controls feeding behaviour, and therefore is likely to be involved in the causes of eating disorders.

Key research on neurotransmitter imbalances

Research studies provide evidence for the role of neurotransmitters in anorexia, highlighting how chemical changes in the brain might initiate or maintain the condition.

Fava et al. (1989)

• Results - They found changes in the amount of noradrenaline and serotonin present in the brain when anorexia develops. Early studies also noted reduced 5-HIAA in those with eating disorders, suggesting underactive serotonin pathways and a reduction in serotonin receptors.
• Conclusions - These changes were suggested to be a cause of the problem.