Anorexia nervosa is typified by severe weight loss, due to the sufferer having an altered body image.

What this means in effect is that it is a psychological condition, where the sufferer truly believes themselves to be larger than they are. They reduce their food and calorie input, and often increase their exercise, until they lose significant amount of weight.

Of course the difficult thing to tell you whether someone is very slim, or whether they have anorexia nervosa. As it is almost always found in young females, one of the criteria is that the female will stop menstruating. This is caused by the fact that the body's energy reserves, the fat, have reduced to such a low level that the body would be unable to undergo reproduction and therefore the hormone system switches off the reproductive processes.

One of the other typical features from a behavioural point of view is that the sufferers of anorexia nervosa, although the have an altered body image when the viewing or considering themselves, know that their appearance would cause undue questioning and concern. Hence they tend to adopt behaviour that hides their severe weight loss, such as wearing very baggy clothes and also hide their lack of eating, by appearing to eat whilst actually sneaking food away to dispose of it later.

Anorexia nervosa is sometimes confused with bulimia nervosa, where in an attempt to lose weight, the sufferer eats food but then induces vomiting by one of several methods to rid themselves of the calories they have just ingested.

As anorexia nervosa is a complex psychological condition, there is no simple treatment. The first priority is to make a diagnosis and to persuade the sufferer to seek professional help. The usual first port of call for either the sufferer or family of the sufferer is the patient's general practitioner. Expert psychological or psychiatric help can then be recruited.