Anorexia Nervosa. Anorexia nervosa is a highly distinctive serious mental disorder. the disorder is–years [2 Anorexia nervosa is an eating disorder defined by restriction of energy intake relative to requirements, leading to a significantly low body weight. Psychology. Restriction of energy intake relative to requirements, leading to a significantly low body weight in the context of age, sex Anorexia (an-o-REK-see-uh) nervosa — often simply called anorexia — is an eating disorder characterized b