Anorexia nervosa is an eating disorder characterised by excess control - a morbid fear of obesity leads the sufferer to try and limit or reduce their weight by excessive dieting, exercising, vomiting, purging and use of diuretics. Sufferers are typically more than 15% below the average weight for their height/sex/age. Typically they have amenorrhoea (if female) or low libido (if male). 1-2% of female teenagers are anorexic.