There is no single cause of anorexia nervosa. Several different factors are usually involved in producing this disorder.
Psychological causes for anorexia
People with anorexia are often perfectionists and overachievers. They’re the “good” daughters and sons who do what they’re told, excel in everything they do, and focus on pleasing others. But while they may appear to have it all together, inside they feel helpless, inadequate, and worthless. Through their harshly critical lens, if they’re not perfect, they’re a total failure.
In addition to the cultural pressure to be thin, there are other family and social pressures that can contribute to anorexia. This includes participation in an activity that demands slenderness, such as ballet, gymnastics, or modeling. It also includes having parents who are overly controlling, put a lot of emphasis on looks, diet themselves, or criticize their children’s bodies and appearance. Stressful life events—such as the onset of puberty, a breakup, or going away to school—can also trigger anorexia.
Neurochemical or biological factor
Research suggests that a genetic predisposition to anorexia may run in families. If a girl has a sibling with anorexia, she is 10 to 20 times more likely than the general population to develop anorexia herself. Brain chemistry also plays a significant role. People with anorexia tend to have high levels of cortisol, the brain hormone most related to stress, and decreased levels of serotonin and norepinephrine, which are associated with feelings of well-being.
Useful link about anorexia nervosa: