Understanding anorexia nervosa

Anorexia nervosa is an eating disorder characterised by an intense fear of gaining weight, leading to severe restrictions in food intake and often resulting in significant weight loss. This condition stems from the term "anorectic," which refers to a nervous loss of appetite, but it involves more than just reduced eating - it is an emotional disorder where individuals develop an obsessive desire to lose weight, sometimes through refusing food entirely or having a strong aversion to it.

Although dieting might seem like a way to control weight, anorexia nervosa often represents an attempt to gain control over one's life and emotions, particularly in response to traumatic events or chaotic environments. The effects of these extreme behaviours are far more severe than those from typical dieting, potentially leading to life-threatening complications.

Who is affected by anorexia nervosa

• Anorexia most commonly develops around the ages of 16 to 17.
• It primarily affects girls and women, with estimates showing that 1.0 to 4.2 per cent of women experience it in their lifetime, though it has become more common in boys and men recently.
• In the UK, approximately 1.6 million people are affected by eating disorders overall, with around 11 per cent being male; of those with eating disorders, approximately 10 per cent have anorexia.
• Anorexia has the highest fatality rate among mental illnesses, with around 4 per cent of individuals dying from complications.

Key symptoms of anorexia nervosa

• Chronic dieting despite being underweight - Continuing to restrict food intake even when already at a dangerously low weight.
• Obsession with food details - Fixating on calories and fat content of meals.
• Ritualistic eating habits - Engaging in patterns like cutting food into tiny pieces, eating alone, or hiding food to avoid consumption.
• Amenorrhoea - The abnormal absence or loss of menstrual cycles, defined as missing three consecutive periods.

These symptoms highlight how anorexia nervosa disrupts both physical health and daily functioning, often requiring medical intervention.

Biological explanations: Hypothalamus dysfunction

Biological factors may contribute to anorexia nervosa by affecting brain structures involved in hunger and satiety (the feeling of fullness). One key area of research focuses on the hypothalamus, a small region in the brain that regulates various bodily functions, including appetite and weight control.

The hypothalamus acts like a "weight thermostat" through two main parts: the lateral hypothalamus (LH), which triggers hunger (acting as an "on switch"), and the ventromedial hypothalamus (VMH), which signals fullness (acting as an "off switch"). In anorexia, a biochemical imbalance might cause the VMH to remain stuck in the "off" position, leading individuals to feel constantly full and not hungry, even when they need nourishment. This dysfunction could explain the persistent aversion to food.

Connection to hormone changes and amenorrhoea

Amenorrhoea, the loss of menstrual cycles, can occur before significant weight loss in anorexia, suggesting it stems from a primary disorder rather than just malnutrition. This points to issues with endocrine levels - the hormones produced by the body's endocrine system, which regulates processes like metabolism and reproduction.

Research shows that endocrine levels in individuals around 19 years of age with anorexia resemble those of a healthy nine-year-old, indicating a hypothalamus dysfunction that disrupts normal hormone production. As a result, changes in hormone levels may cause or exacerbate anorexic symptoms, such as reduced appetite and reproductive issues.

The role of neurotransmitter imbalances

Another biological perspective on anorexia nervosa involves imbalances in neurotransmitters, which are chemical messengers in the brain that transmit signals between nerve cells. These imbalances can affect mood, appetite, and behaviour, potentially contributing to the disorder.

Noradrenaline and serotonin are two key neurotransmitters implicated in anorexia. Noradrenaline promotes eating by acting on parts of the hypothalamus, while serotonin suppresses appetite (as observed in studies with non-human animals). When anorexia develops, levels of these neurotransmitters change, which might trigger or maintain the condition.

Research study: Fava et al. (1989)

• Method - Researchers analysed brain chemistry in people developing anorexia, focusing on noradrenaline and serotonin levels.
• Results - They found alterations in the amounts of noradrenaline and serotonin present in the brain during the onset of anorexia.
• Conclusions - These changes could cause the appetite suppression seen in anorexia, with serotonin potentially playing a role in reducing hunger signals.
• Evaluation - The study supports a biological basis but does not prove causation, as neurotransmitter changes might result from anorexia rather than causing it; further research is needed to clarify the direction of influence.

Genetic factors in anorexia nervosa

Genetics may also play a role in anorexia nervosa, suggesting that some individuals inherit a predisposition to the disorder. This is explored through twin studies, which compare identical (monozygotic or MZ) twins, who share 100 per cent of their genes, with fraternal (dizygotic or DZ) twins, who share about 50 per cent.

Higher concordance rates (where both twins have the disorder if one does) in MZ twins compared to DZ twins indicate a genetic influence, as environmental factors are often similar for both types of twins.

Research study: Scott (1986)

• Method - Scott examined existing twin studies to compare concordance rates between MZ and DZ twins.
• Results - Concordance rates were higher for MZ twins than for DZ twins.
• Conclusions - The difference suggests a genetic component to anorexia, as MZ twins share more genetic material.
• Limitations - Twin studies assume equal environments for MZ and DZ pairs, which may not always hold true; small sample sizes can also affect reliability.

Research study: Holland, Sicotte, and Treasure (1988)

• Method - Researchers studied pairs of MZ and DZ twins where at least one had anorexia.
• Results - Around 56 per cent of MZ twins were concordant for anorexia, compared to about 5 per cent of DZ twins.
• Conclusions - The much higher rate in MZ twins supports a strong genetic factor in the development of anorexia.
• Evaluation - The findings strengthen the genetic argument but cannot rule out environmental influences; the study highlights the need for larger samples to confirm results.

The diathesis-stress model for anorexia

While biological factors like genetics and brain chemistry are important, they may not cause anorexia nervosa on their own. Instead, the diathesis-stress model proposes an interaction between biological predispositions (diathesis) and environmental triggers (stress).

In this model, individuals may have a genetic vulnerability to anorexia that remains dormant until activated by stressful events, such as the death of a close relative or other traumatic experiences. This combination explains why not everyone with a genetic risk develops the disorder - environmental factors are needed to "trigger" it.

Key components of the diathesis-stress model

• Diathesis - A biological predisposition, such as a genetic vulnerability or neurotransmitter imbalance, that increases susceptibility.
• Stress - Environmental events, like trauma or chaos, that activate the dormant vulnerability.
• Outcome - The development of anorexia when both elements are present, suggesting that neither biology nor environment alone is sufficient.

This model provides a comprehensive view, integrating research on genetics, brain function, and life experiences to explain the causes of anorexia nervosa.