The cause of anorexia nervosa is not fully understood. It is thought to develop from a mix of physical, emotional, and social triggers.

Extreme dieting changes how the brain and metabolism work, and it stresses the body. These changes may make you more likely to develop an eating disorder. 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.

Your brain requires a healthy, nutritious diet to function normally. It uses a fifth of all the calories you eat. So the extreme dieting associated with anorexia can disrupt the normal functions of the brain, possibly making anorexia symptoms worse.

Malnutrition can also change the balance of hormones in the body, which can disrupt the normal functioning of the brain.

There are a number of theories on how the brain may be affected by anorexia. One theory is that the changes mentioned above cause the brain to become very sensitive to the effects of an amino acid called tryptophan, found in almost all types of food.

This sensitivity may then cause feelings of anxiety in people with anorexia when they eat. At the same time, starving themselves and excessive exercise is known to lower 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, known as neurotransmitters and neuropeptides, which stimulate your appetite.

Once you have eaten enough food, your body will release a hormone called leptin, which signals to your hypothalamus that you have eaten enough food. Your hypothalamus will release a different set of chemicals that essentially reward you for eating, and make you feel satisfied.

It is thought that due to changes in the brain, the ‘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 to reduce these negative feelings.

In addition, people with anorexia nervosa tend to not experience pleasure or live “in the moment.” They often have exaggerated and obsessive worry about the consequences of their behaviors, looking for rules when there are none, and are overly concerned about making mistakes. Co-author Julie L. Fudge of the Department of Psychiatry & Neurobiology and Anatomy at the University of Rochester Medical Center, notes that imaging studies suggest that individuals with anorexia have an imbalance between circuits in the brain that regulate reward and emotion (the ventral or limbic circuit) and circuits that are associated with consequences and planning ahead (the dorsal or cognitive circuit.)

“Brain-imaging studies also show that individuals with anorexia have alterations in those parts of the brain involved with bodily sensations, such as sensing the rewarding aspects of pleasurable foods,” said co-author Martin Paulus, UC San Diego professor of psychiatry, who heads UC San Diego’s Laboratory of Biological Dynamics and Theoretical Medicine. “Anorexics may literally not recognize when they are hungry.”

One such brain region is the anterior insula, which is critically important for interoception, or the self-awareness of internal body signals. In addition to a failure to respond appropriately to signals of hunger, symptoms of anorexia – such as distorted body image and diminished motivation to change – could be related to disturbed interoceptive awareness.

“Anorexia is very complicated, and there needs to be a paradigm shift in understanding its underlying cause,” said Kaye. “We’re just beginning to understand how the brain is working in people with this disorder.”

Genetics play a big part in anorexia and bulimia. Compared with people who don’t have these disorders, people who have eating disorders are more likely to have a family history of an eating disorder, obesity, or a mood disorder (such as anxiety or depression). Research has found that most people who develop anorexia share certain psychological factors that help to 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.

A combination of certain personality traits (such as low self-confidence along with perfectionism) and cultural and social pressures can play a part in anorexia. Environmental factors, such as going through puberty or living in a culture where thinness is an ideal, then causes the person to begin a pattern of long-term dieting and weight loss. At the same time, magazines and newspapers focus on celebrities’ minor physical imperfections, such as gaining a few pounds or having cellulite.

For some teens, anorexia may be a way of coping with stress and the challenges of the teen years. Stressful life events, such as moving, divorce, or the death of a loved one, can trigger anorexia.