Eating disorders comprise a range of syndromes encompassing physical, psychological, and social features [National Collaborating Centre for Mental Health, 2004].

• An eating disorder involves [Fairburn and Harrison, 2003]:
• A definite disturbance of eating habits, or weight-control behaviour.
• A disturbance of eating and/or associated over-evaluation of body shape or weight resulting in a clinically significant impairment of physical health or psychosocial functioning.
• A behavioural disturbance that is not secondary to any general medical disorder, or any psychiatric condition.
• The main types of eating disorders are:
• Clinical features of anorexia nervosa — a syndrome in which the person maintains a low body weight as a result of a preoccupation with weight, construed as either a fear of fatness or a pursuit of thinness.
• Clinical features of bulimia nervosa — characterized by recurrent episodes of binge eating and compensatory behaviour (any one or a combination of vomiting, fasting, or excessive exercise) in order to prevent weight gain.
• Clinical features of atypical eating disorders — closely resemble anorexia nervosa or bulimia nervosa, but do not meet the precise diagnostic criteria for them, for example binge eating disorder where individuals engage in uncontrollable episodes of binge eating, but do not use compensatory purging behaviours.

[National Collaborating Centre for Mental Health, 2004]

• These different types of eating disorders have many features in common and the person can move between the different diagnostic categories [Fairburn and Harrison, 2003].
• Obesity may also fulfil some of the criteria of an eating disorder, but is not usually managed by eating disorder services and is not discussed further in this topic. For more information, see the CKS topic on Obesity.