There is no single cause for anorexia. Most experts believe the condition is caused by a combination of psychological, environmental and biological factors, which lead to a destructive cycle of behaviour.
It is widely accepted some people have distinct personality traits, making them more vulnerable to anorexia.
Environmental factors, such as going through puberty or living in a culture where being thin is an ideal, then causes the person to begin a pattern of long-term dieting and weight loss.
The lack of a normal diet has a biological effect on the brain, which helps reinforce the obsessive thinking and behaviour associated with anorexia.
A cycle then begins. The more the person diets, the greater its effect on the brain and the greater the desire to lose weight. This means that symptoms gradually, and then rapidly, get worse.
Each of these factors is explained in more detail below.
Most people who develop anorexia share certain psychological factors that help define their personality and, to some extent, their behaviour. These include:
- a tendency towards depression and anxiety
- poor reaction to stress
- excessive worrying and feeling scared or doubtful about the future
- perfectionism - setting strict, demanding goals or standards
- inhibition - where a person restrains or controls their behaviour and expression
- feelings of obsession and compulsion (though not necessary 'full-blown' obsessive compulsive disorder) - an obsession is an unwanted thought, image or urge that repeatedly enters a person's mind. A compulsion is a repetitive behaviour or mental act that a person feels compelled to perform.
Puberty seems to be an important environmental factor contributing to anorexia.
It may be the combination of hormonal changes and feelings of stress, anxiety and low self-esteem during puberty that triggers anorexia.
Western culture and society also play a part. Girls (and, to a lesser extent, boys) are exposed to a wide range of different media which constantly reinforce the message that being thin is beautiful.
At the same time, magazines and newspapers focus on celebrities' minor physical imperfections, such as gaining a few pounds or having cellulite.
Other environmental factors that may contribute towards anorexia include:
Your brain requires a healthy, nutritious diet to function normally. It uses a fifth of all the calories you eat. So extreme dieting can disrupt normal functions of the brain, possibly making anorexia symptoms worse.
Malnutrition can also change the balance of hormones in the body, which can affect how the brain functions.
It is thought the change in hormones causes the brain to become sensitive to the effects of an amino acid called tryptophan, found in almost all types of food.
This sensitivity can cause feelings of anxiety in people with anorexia when they eat. At the same time, starving themselves and excessive exercise lowers levels of tryptophan, which may make the person feel calmer and more relaxed.
Another theory is that the system controlling a person's sense of appetite becomes disrupted.
Appetite is controlled by a part of the brain called the hypothalamus. When your body needs more food, your hypothalamus releases chemicals to stimulate your appetite.
Once you have eaten enough food, hormones signal to your hypothalamus. Your hypothalamus will then release a different set of chemicals that essentially reward you for eating, and make you feel satisfied.
It is thought that this 'appetite-reward pathway' becomes scrambled in people with anorexia. The feeling of fullness after a meal does not produce a sense of reward, but a sense of anxiety, guilt or self-loathing. In turn, feeling hungry may help reduce these negative feelings.