Epidemiological studies provide information about the occurrence of disorders and trends in the frequency of disorders over time. For epidemiological studies on eating disorders there are some methodological issues. Eating disorders are relatively rare among the general population and patients tend to deny or conceal their illness and avoid professional help. This makes community studies costly and ineffective. Therefore, many epidemiological studies use psychiatric case registers or medical records from hospitals in a circumscribed area. This type of study will underestimate the occurrence of eating disorders in the general population, because not all patients will be detected by their general practitioner or referred to the hospital or mental health care. Furthermore, differences in rates over time could be due to improved case detection, increased public awareness leading to earlier detection and wider availability of treatment services, instead of a true increase in occurrence [
1,
2].
Anorexia nervosa (AN) and bulimia nervosa (BN) are the two specified eating disorders according to the
Diagnostic and Statistical Manual of Mental Disorders Fourth Edition (DSM-IV). However, the most common eating disorder diagnosis in either clinical and community samples is the rest category ‘eating disorder not otherwise specified’ (EDNOS) [
3–
7]
. EDNOS is a heterogeneous, not well defined group of eating disorders and includes partial syndromes of AN and BN, purging disorder and binge eating disorder (BED). A comprehensive meta-analysis of 125 studies suggests that EDNOS is associated with substantial psychological and physiological morbidity, comparable with the specified eating disorders [
8]. In 2013 the fifth edition of the DSM is scheduled to appear, including a thoroughly revised eating disorder section. A major goal is to reduce the size of the EDNOS-category. To achieve this goal the criteria for AN and BN will be broadened [
9,
10] and BED will be added as a specific eating disorder. The decision to make BED a separate diagnosis is partly informed by epidemiological data supporting the construct validity of BED. BED differs from AN and BN in terms of age at onset, gender and racial distribution, psychiatric comorbidity and association with obesity. BED is often seen in obese individuals, but is distinct from obesity per se regarding levels of psychopathology, weight- and shape concerns and quality of life [
11]. BED aggregates strongly in families independently of obesity, which may reflect genetic influences [
12,
13].
In this review we will describe the epidemiology of AN, BN, EDNOS and BED according to DSM-IV and – if available – to the proposed DSM-5-criteria. The proposed changes in DSM-5 diagnostic criteria will alter the coverage of the diagnostic categories and thus their disease frequencies as well. Some studies used both a narrow and a broad or partial definition of AN, including DSM-IV AN with or without amenorrhea and ICD-10 atypical AN [
14–
16]. These broad or partial definitions of AN are in line with the proposed DSM-5-criteria for AN and will be referred to as ‘broad AN’ throughout this review [
9]. In a Finnish study of female twins, the 5-year clinical recovery rates of AN and broad AN were almost the same; i.e. 66.8 % and 69.1 % respectively, providing evidence for the validity of broad AN [
14]. Definitions of each epidemiological measure are provided at the respective paragraphs.
This article is based on research publications on the epidemiology of eating disorders and updates our previous reviews, with special emphasis on studies published in the last three years [
2,
17–
19].