What are Eating Disorders?
Eating disorders are classified as:
- Anorexia Nervosa (AN)
- Bulimia Nervosa (BN)
- Eating disorder not otherwise specified (EDNOS or atypical eating disorders).
- Obesity – Please see separate guidance on Obesity.
Often the disorders are mixed and the symptoms of one disorder may be present in another disorder, for example vomiting in Anorexia Nervosa or weight loss in Bulimia Nervosa.
If there is co-morbidity with diabetes, medical risks are exponentially increased.
What is Anorexia Nervosa (AN)?
AN is characterised by:
- A morbid fear of fatness.
- A distorted body image. The person believes that they are too fat even when they are seriously underweight.
- Weight loss to a severe degree with a Body Mass Index (BMI) of 17.5 kg/m2 or less.
- Amenorrhoea (cessation of periods) in females.
What is Bulimia Nervosa (BN)?
The core feature of Bulimia Nervosa (BN) is binge eating associated with sense of loss of control and compensatory vomiting and/or purging. Laxatives and diuretics (water tablets) are commonly used. There are associated overvalued ideas concerning body shape and weight of the type seen in Anorexia Nervosa (AN).
Presentation is usually several years later than AN and diagnosis is usually in the late teens or twenties. It commonly follows a period of dietary restriction and 25% of people have a history of AN. As the overeating becomes more frequent the body weight returns to a more normal level. At some stage, self induced vomiting and laxative abuse are adopted to compensate for over eating.
BN appears to be the result of exposure to general risk factors for psychological disorders combined with risk factors for dieting. They include a family history of psychiatric disorder; adverse childhood experience; depression; alcohol or substance abuse; low self esteem; perfectionism.
The risk of BN is increased in those who were overweight in childhood and were teased or criticised about their eating or their weight.
It is thought that a region on chromosome 10 is linked with BN.
Overall there is a considerable overlap in the causal factors for AN and BN.
Eating disorder not otherwise specified (EDNOS or atypical eating disorders)
These are eating disorders that do not meet the criteria for AN or BN, for example, a person who does not binge but purges regularly and is normal weight does not meet the criteria for bulimia nervosa or a normal weight anorexic (due to beginning anorexic behaviour from a heavier weight).
They are common and the impairment they cause may be comparable to that of AN and BN.
A subgroup within EDNOS is “binge eating disorder” (compulsive overeating) which is characterised by recurrent binge eating episodes in the absence of other diagnostic features of Bulimia Nervosa.
Binge eating disorder (compulsive overeating) is characterised by recurrent binge eating episodes during which a person feels a loss of control over his or her eating. It differs from BN in that binge eating episodes are not followed by purging (vomiting or laxative abuse), excessive exercise or fasting, and as a result people with binge eating disorder are often overweight or obese. They also experience shame, guilt and distress about their eating which can further exacerbate their binge eating. People with binge eating disorder often have coexisting psychological illness including anxiety, depression and personality disorders.
Amended June 2008
