Night eating syndrome: Should it be included in DSM-V?

by Joye C. Anestis

It seems to me that the public has a fascination with eating disorders, and not only the ones that are formally recognized as pathological constructs (e.g., anorexia nervosa, bulimia nervosa).  In newspapers and magazines and on shows like Today and Good Morning America, I've seen reference to "pregorexia," "manorexia," "tweenorexia," "drunkorexia," and "tanorexia," to name a few.  Our willingness to just add -orexia to the end of a phrase or word is odd to me, especially when really these "disorders" appear to simply be eating disorder symptoms in specific populations (in this case, pregnant women, men, and pre-teens).  Just in case you hear someone use the terms, drunkorexia is restricting food intake in order to drink more alcohol and tanorexia is a presumed addition to tanning, so they actually seem very different from the other -orexias out there.  But there are some "new" eating disorders that are being considered for inclusion in the upcoming DSM-V.  Binge eating disorder, for example, is certainly a shoo-in.  Other potential inclusions are purging disorder and night eating syndrome (NES), the focus of the current post.  In general, NES involves the consumption of large amounts of food in the evening.  It is presumed to only occur in obese individuals.

A recent review article by Striegel-Moore, Franko, & Garcia (2009) examined the state of the empirical evidence for NES.  Their review builds upon two previous reviews (Striegel-Moore et al., 2006; Stunkard et al., in press) and used the same guidelines utilized by these studies to evaluate the scientific evidence, namely 1) ample literature, 2) a common set of diagnostic criteria, 3) at least 2 empirical studies by independent groups indicating high inter-rater reliability of the diagnosis among clinicians, 4) evidence of syndrome validity, and 5) reliable differentiation of the syndrome from others (these criteria were originally articulated by Blashfield et al., 1990).  General findings of their literature review are as follows, and I will address each of the Blashfield criteria in turn:

Defining NES 

In an earlier review, Striegel-Moore and colleagues (2006) arrived at 3 conclusions about the definition of NES, observations that had been noted in reviews that both preceded and followed Striegel-Moore et al. (2006).  First of all, most studies defined it as evening hyperphagia (an abnormally increased appetite for & consumption of food, occurring after the evening meal, in which a significant portion of the day's calories are consumed), insomnia, and morning anorexia.  This indicated considerable consistency across studies in determining the presence of NES based on these 3 criteria.  The authors 2nd conclusion, however, noted that studies were highly inconsistent in the way each of these 3 symptoms were operationalized (or defined within each study).  For example, the studies almost always lacked a frequency or duration criteria.  For most conditions currently considered mental illnesses, the symptoms have to have been present for a set amount of time before we can consider them to be disordered (for example, binge eating and inappropriate compensatory behaviors must occur twice a week for at least 3 months in order to warrant a diagnosis of bulimia nervosa). 

The updated review did not note many changes in the status of the literature.  They found  considerable variability in the operationalization of evening hyperphagia.  One change that was noted in this criteria was the addition of "nocturnal eating episodes" - waking up in the  night and eating before going back to sleep - to many studies of evening hyperphagia; however, data is inconclusive on its role in NES.  The operationalization of morning anorexia is also inconsistent, and some NES experts have concluded that it is not central to the definition of the syndrome.  Finally, the treatment of insomnia in the current literature is also inconsistent, with many studies no longer requiring it for a diagnosis of NES.

Syndrome vs. Symptom?

Striegel-Moore et al. note that researchers generally use one of two distinct definitions of NES.  One is the syndrome we have been discussing with symptoms of evening hyperphagia and/or nocturnal eating episodes, morning anorexia, and insomnia along with the exclusion of bulimia and binge eating disorder (anorexia is generally not included in exclusionary criteria because NES is thought to occur exclusively in obese individuals, thus systematically excluding those with anorexia).  The alternate definition requires the presence of just one symptom: evening hyperphagia and/or morning anorexia.  The syndrome definition is generally more restrictive than the symptom definition, and no studies have compared individuals who meet syndrome criteria versus the less restrictive syndrome definition.

Diagnostic reliability and assessment of NES 

Striegel-Moore included 27 papers in their review, and only one these reported inter-rater reliability.  Although inter-rater reliability was adequate in this one study, we still have insufficient information on the reliability of the definition.  Likewise, reliability data on the Night Eating Questionnaire, a 14-item self-report questionnaire, is lacking.

Syndrome validity

Blashfield et al. requires at least 2 independent studies demonstrating that, if an individual exhibits one symptom, then the same patient has at least a .50 probability of exhibiting another.  At the time of the present review, only one study included data that could answer this question.  While this study did indicate that, at least for morning anorexia and evening hyperphagia, the same patient with one symptom would have at least a 50% chance of exhibiting another symptom, additional studies are needed to confirm syndrome validity.

Can NES be distinguished from "normal" and from other disorders?

An important consideration when examining new mental disorders is whether they are distinct entities from already established disorders.  This is a question that has not been adequately answered regarding NES.  At the time of the present review, no taxometric analyses have been conducted on NES.  When examining prevalence, clinical significance, and correlates of NES, the comorbidty between NES and other eating disorders, and course and treatment outcome, several methodological problems emerge which limit the conclusions that can be drawn (problems beyond the ones already mentioned above).  One such problem is the recruitment strategies used by the studies, which have not allowed for pure epidemiological studies that would give information on prevalence.  The studies have also had difficulty recruiting appropriate control subjects.  Sample sizes are quite small (14 of the studies had 20 or fewer participants), and few studies report effect sizes.  In sum:

• • No conclusive evidence exists on the prevalence of NES at this time. 
  • We can tentatively suggest that obesity or higher BMI scores may be clinical correlates of NES, depression may be more common in individuals with NES, and there may be considerable comorbidity between NES and binge eating disorder.  Studies examining the difference between NES and binge eating disorder are inconclusive. 
  • In terms of examining the clinical course and outcome of NES, no prospective studies have examined the natural course of NES.  A few retrospective studies have been done, but all except one used only bariatric surgery patients making it impossible to differentiate the effects of surgery from the course of NES. 
  • Only a handful of treatment studies have been conducted on NES, but there is some initial support for the use of sertraline in its treatment.

So the overall conclusion we can draw is that we simply do not know enough about this phenomenon.  It is apparent that there are people who engage in this behavior, but it has not yet been determined at what point the behavior might become disordered or even if it is distinct from other disorders (e.g., binge eating disorder).   Striegel-Moore et al. offer up 5 options for how to deal with NES in the upcoming DSM-V:

1. Introduce NES as a new eating disorder - Doing so would stimulate a great deal of research on the phenomenon.  On the other hand, diagnostic criteria have not been delineated well enough to take this step.
2. Introduce NES as an example of Eating Disorder Not Otherwise Specified (EDNOS) - This was done for binge eating disorder in DSM-IV ,and it prompted a significant amount of research on the disorder.
3. Introduce evening hyperphagia and nocturnal eating as symptom dimensions to be rated for each eating disorder - This would force clinicians and researchers to consider these symptoms without adding a new syndrome to the list of eating disorders.  Although this option may overlook the potential complexity of NES.
4. Introduce NES as a provisional diagnosis in need of further study - Again, this was done for binge eating disorder in DSM-IV.
5. Note evening hyperphagia and nocturnal eating as symptoms that can worsen medical conditions - As there is no research studying this question, no argument can be made either way.

What do you think?  Anyone on the DSM-V Eating Disorder task force that could illuminate the status of this phenomenon?  Anyone have clinical experience with NES?

If you would like to learn more about eating disorders, we recommend the following items, all of which are available through our online store of science-based psychological resources:

• Overcoming Binge Eating by Christopher Fairburn

• Cognitive Behavior Therapy and Eating Disorders by Christopher Fairburn
  

• Cognitive-Behavioral Treatment of Obesity: A Clinician's Guide by Zafra Cooper, Christopher Fairburn, and Deborah Hawker

• Dialectical Behavior Therapy for Binge Eating and Bulimia by Debra Safer, Christy Telch, and Eunice Chen
  

• Treatment Manual for Anorexia Nervosa: A Family-Based Approach by James Lock, Daniel le Grange, and Stewart Agras

• Crave: Why You Binge Eat and How to Stop by Cynthia Bulik

Joye Anestis is a doctoral candidate in the clinical psychology department at Florida State University