They are deluded into thinking that they are much fatter than they really are and because of this are prepared not only to starve themselves but, if necessary, also to purge themselves or to make themselves sick after food.

In addition to weight loss, this chronic starvation results in a wide variety of other signs and symptoms related to their upset metabolism.

Men have low levels of testosterone and so become impotent and lose their libido. Women cease to ovulate and lose their periods.

Amenorrhoea — the long-term absence of menstrual periods — is almost inevitable if women fall 15 per cent below the accepted body weight. Other important changes in the endocrine system affect the levels of the growth hormone and the levels of natural steroids produced by the supra-renal glands. The insulin levels are also grossly disturbed and there are usually changes in thyroid production.

These hormonal changes are the body’s defence mechanism against starvation for although the mind of a patient with anorexia leads the person to believe that they are fat, their endocrine controlled by the hypothalamic pituitary axis knows that they are starving and adjusts the hormonal and metabolic systems accordingly.

Although the diagnosis of anorexia is made as a result of a triad of symptoms — a distorted body image, extreme weight loss, and in women loss of periods — the conundrum is not the diagnosis but the reason for the trouble.

Without an understanding of the patient’s family background, heredity, personality and current environment it is impossible to devise a successful regime that may overcome these problems. Without treatment the anorexia may become chronic and the patient may, in about 5 per cent of cases, succumb to the effects of chronic starvation.

Anorexia affects about 1 per cent of the population. Girls are involved more often than boys, women more often than men. Although it is usually said that it can affect any age group and both sexes, in more than 90 per cent of cases it affects adolescent girls or women in their early 20s. Among the older women who are more likely to develop anorexia are those with an adolescent daughter, who emphasises their own loss of youth.

There are characteristics in a patient’s personality that constitute risk factors. Although anorexia is not hereditary in the strict sense of the word, it is more common in certain families.

Anorexia — which means loss of appetite — is not a true description of how the patient feels because even when starving themselves slowly they do not feel hungry.

Anorexic patients are frequently obsessive about food; they fuss interminably about its purity, its organic make-up and about their diet. They share all those anxieties about too many fats, calorie-rich foods and about the way the food is cooked (many are excellent cooks).

Many are obsessive about exercise. I have known patients who have got up early in order to put in four hours’ exercise before they bicycle to work. Others suffer from one of the forms of clinical depression that needs treatment. This is one reason why so many attempt suicide.

Another cause for high suicide rates is the frequency with which these patients are prone to other personality disorders.

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