Anorexia is an illness that occurs mainly in teenage girls, although increasingly boys suffer from it too. People with anorexia are obsessed with being thin and are terrified of gaining weight. As a result, they starve themselves (especially avoiding high-calorie foods), and exercise obsessively until they become extremely thin and well below the normal weight for their age and height.
Bulimia usually affects women in their early to mid-twenties. People with bulimia are also terrified of gaining weight, but they can usually keep within a normal weight. This is because they eat very large amounts of fattening food (called 'bingeing'), but then get rid of that food by vomiting or by taking laxatives.