Eating disorders involve abnormal patterns of behaviour where people consistently eat too much or too little, and other behaviours such as bingeing and vomiting. There is a spectrum of eating disorders ranging from mildly abnormal attitudes about eating to severe anorexia nervosa. Examples of eating disorders are anorexia nervosa, bulimia nervosa and arguably obesity. The principal psychological problem is a morbid fear of fatness. In order to keep his or her body mass down, the anorexic patient will diet excessively, combining this technique with strenuous exercise, the abuse of laxatives and diuretics and self-induced vomiting. Although the sufferer may be almost cachexic he or she may see themselves as overweight. Sometimes such skeletal patients may draw self-portraits which are really caricatures of themselves showing themselves as obese. One of the criteria used for the diagnosis of anorexia nervosa is a body mass 15" or more below the expected mass for a person of that age, sex and height.