The term 'eating disorders' refers to a group of psychiatric disorders in which disturbances of eating are a prominent feature. The most well-known of these disorders are anorexia nervosa and bulimia nervosa, and most other eating disorders are variants of one or other of these conditions.
Anorexia nervosa has been recognized for at least the last 100 years. It is characterized by a severe and persistent restriction of food intake and an abnormally low body weight. The dietary restriction is driven by an intense desire to control body weight and avoid 'fatness'.

It is primarily a disorder of young women, the majority of sufferers being female (about 80 per cent) and in their teens, and it is largely confined to societies where slimness is viewed as attractive and dieting is therefore common.

In addition to restricting their food intake, sufferers from anorexia nervosa often engage in other methods of weight control, including extreme exercising, self-induced vomiting and the misuse of laxatives and diuretics. Accompanying the behavioural disturbance is a preoccupation with food and eating, and an extreme concern about body shape and weight. Mood may be depressed, obsessional behaviour is common and typically the sufferer is socially withdrawn.

Not surprisingly given the low body weight, physical health is affected. Indeed, there is a wide range of physical problems all of which are secondary to the disturbed eating and low body weight. They include hormonal abnormalities which prevent menstruation, and changes in intestinal function which make the sufferers feel full even after eating small quantities of food. Some of the physical problems are life-threatening.

Bulimia Nervosa
Some of the physical problems are life-threatening. In contrast to anorexia nervosa, bulimia nervosa was first delineated as recently as 1979, yet it is much more common than anorexia nervosa. It is thought to have emerged in the I970s as a variant of anorexia nervosa and it now affects at least 1 per cent of young adult women, the majority of sufferers being in their 20s.
Bulimia nervosa is primarily characterized by a loss of control over eating. Whereas most people with anorexia nervosa successfully maintain strict control over their food intake, those with bulimia nervosa are unable to do so: instead, their attempts to diet are punctuated by repeated 'binges' in which very large amounts of food are eaten. Typically these binges occur in secret and are followed by self- induced vomiting or the taking of laxatives in an attempt to minimize the amount of food absorbed. As in anorexia nervosa there is an intense concern about body shape and weight. Depressed mood is also common but these people are less likely to withdraw socially. An important feature is the shame and guilt that accompanies the binges and results in the disorder being kept secret for many years.

This secrecy is helped by the fact that body weight is generally unremarkable. Physical health may be impaired in bulimia nervosa, most abnormalities being milder versions 0f those seen in anorexia nervosa. Anorexia nervosa generally starts with what appears to be normal adolescent dieting.

However, this dieting is more extreme and persistent than that of their peers, with the result that body weight rapidly falls. Driving the intense restriction of food intake is a general need to be in control, one expression of which is dieting. In bulimia nervosa the onset tends to be similar but control over eating breaks down at some point and once this happens it is rarely regained.
As a result, body weight rises to near normal levels. Our understanding of background to the development of anorexia nervosa and bulimia nervosa is limited. It seems that there are two classes of risk factor - one that increases the risk of psychiatric disturbance in general and one that increases the risk of dieting. Among the former is a family history of depression and alcoholism, and exposure to a range of adverse childhood experiences.

Certain childhood traits also appear to increase risk, most especially low self-esteem, perfectionism and extreme compliance. Among the factors that increase the risk of dieting are family concerns about shape, weight and eating, including eating disorders, and obesity in childhood. The course of these disorders varies widely. Anorexia nervosa can be short-lived and self-remitting; alternatively, it can be a life-long affliction. The same applies to bulimia nervosa. As a result treatment needs vary.

Treatments
The treatment of bulimia nervosa has been much studied. It is now established that the treatment of choice is a short-term psychological treatment. This treatment generally involves about 20 appointments with a psychiatrist or clinical psychologist over four to five months.

The focus is on identifying and modifying the mechanisms that maintain the problem, most especially the concerns about shape and weight and the disturbed pattern of eating. Between half and two-thirds of patients make a full and seemingly lasting response to this form of treatment.

The only other treatment to have shown promise is the use of antidepressant drugs, but their effect is often short-lived. It has recently been shown that self-help versions of cognitive behaviour therapy can be effective and these have the advantage of ease of dissemination.

There has been much less research on the treatment of anorexia nervosa largely because treatment may take a long time and the disorder is much less common. Some patients respond rapidly with barely any outside intervention whereas others can be very difficult to treat. Generally treatment involves a combination of dietary advice and psychotherapy, the latter often involving the patient's family.

Most patients are treated as outpatients, but some require more intensive treatment as a day patient or in-patient. Drugs rarely have a major role. If you suspect that someone has an eating disorder, it is best to be open with them. Discuss your concerns with them. Often it is helpful to suggest that they read about such problems (see below) since doing so can help them evaluate their own difficulties and assess their need for outside help.

‘Normal’ Body Weight
What constitutes an 'abnormally low' body weight? In people over the age of 14 years the body mass index is used to classify body weight. It is body weight in kilograms divided by height in metres squared (i.e. weight/height).
The healthy range is 20-25, overweight is 25-30, and obesity is above 30. At the other extreme, the weight threshold for anorexia nervosa is a body mass index below 17.5.

Below the age of 14 years reference is made to standard height-weight (or BMI) tables, the requirement for anorexia nervosa being that weight is below 85 per cent of that expected for the person's age, height and sex.