Night eating syndrome (NES) is a clinical phenomenon combining facets of both sleeping disorders and eating disorders (EDs). NES was first described by Stunkard in 1955 in a sample of obese patients 2. Core characteristics included morning anorexia nervosa (AN), Evening Hyperphagia (25% of daily food eaten after 7 p.m.), insomnia, deteriorating mood (worsening in the evening), and emotional distress 2. Diagnostic criteria for NES have been modified many times over the years, generating almost 20 different sets of criteria to date.

In an attempt to clarify this syndrome's diagnostic criteria, an international NES Working Group comprising sleep and ED experts convened in Minneapolis in 2008 and two years later published their consensual set of criteria 1. These diagnostic criteria were proposed and primarily accepted for inclusion in the American Psychiatric Association (APA) DSM-5 edition 3, under "Other specified feeding and eating disorders."

For the current study, we used all proposed criteria published in 2010 1, which include: significantly increased food intake in the evening (Evening Hyperphagia) and/or at night time (night ingestion) of at least 25% of daily food intake; at least two episodes like this per week; and awareness and recall of evening and nocturnal eating episodes. In addition, the daily pattern is manifested by at least three of the following features: morning anorexia; a strong urge to eat between dinner and sleep onset and/or during the night; insomnia; a belief that one must eat in order to sleep; and depressed or worsening mood in the evening. This syndrome is associated with significant distress, is maintained for at least 3 months, and is not secondary to any other medical or psychiatric disorder. These new criteria currently represent the most updated instrument for diagnosing NES.

Although few significant studies have investigated the prevalence of NES, all reports show that the syndrome is common among individuals who are overweight and/or obese. In the general population, approximately 1.5% of adults are affected by NES 45, but among individuals seeking weight loss treatment, the syndrome is significantly more prevalent (e.g., 8.9% in an obesity clinic) 45. Among patients seeking treatment for EDs, such as bulimia nervosa (BN), binge eating disorders (BED), and AN, the prevalence rates for NES were 9%, 16%, and 0%, respectively 6. In a psychiatric population, the prevalence rate is 12.3% for NES 7.

Only a few studies have examined NES among patients diagnosed with EDs 68, primarily in patients with BED 910 and minimally (mainly case studies) among patients with BN 91112131415161718. Debate continues in the literature regarding the relations between NES and EDs. NES has been conceptualized as a subtype of obesity, a sleep-related eating disorder (SRED), a variant of other EDs, a separate syndrome among EDs, and a sleeping disorder 8.

One of the common symptoms in EDs, specifically among patients with BED and BN, is BE behavior, which is also a primary symptom of NES. BE behavior is characterized by eating a large amount of food, considered excessive, in a defined period of time. This behavior is accompanied by a sense of lack of control over one’s eating throughout the episode. Such BE episodes are associated with: rapid eating, eating until uncomfortably full, eating large amounts when not hungry, solitary eating because of embarrassment, and feeling disgusted, depressed and guilty. These diagnostic symptoms and associated behaviors overlap across the range of EDs, especially among individuals with BED and BN; however, significant differences exist between the two 319. The main difference is that individuals with BN end their binges using compensatory behaviors such as self-induced vomiting, laxative abuse, diuretics, enemas, or excessive exercise – which are not apparent among individuals with BED. Nevertheless, high psychiatric comorbidity exists among individuals who exhibit BE behavior, including both those with BN and BED 2021, as well as among those with a diagnosis of NES 22. Studies indicate that NES and BE behavior commonly occur simultaneously in individuals who have been assessed for BED and NES 523.

Some researchers suggest that although these behaviors may well overlap, NES and BED have different underlying behavioral constructs. Moreover, they propose that BED-only, BED with NES, and NES-only subgroups lie on a continuum of psychopathology, where BED-NES is considered the more extreme psychopathological form and NES-only is considered the less extreme form 5232425.

In addition, these conditions may be differentiated by the nature of their binge episodes, concerns about weight, and loss of control over eating. During BE episodes, individuals with BED are more likely to consume a higher number of calories than individuals with NES and to report a greater sense of loss of control 112627282930. Individuals with NES report fewer concerns about their body weight or shape than those with BED 2431 and fewer instances of compensatory behaviors.

The few prior studies that documented the similarities and differences of individuals with BN versus NES mostly examined patients seeking treatment for sleep disorders at a sleep laboratory 6910. Two case studies from the late 1980s provided initial reports on the clinical and psychological characteristics of patients with BN who also suffer from NES 1718. Yet, the relations among SRED, NES, and daytime ED, in particular in patients with BN, remain unclear. The question of whether BN together with NES is a new subgroup of EDs and should be called BN with SRED or just BN with NES remains unanswered. NES among patients with BN without SRED has been described only in the last decade by groups of researchers in Israel and Missouri who are experts in eating and sleep disorders 6810.

Despite their similarities, NES and BE (which includes BE in BN and BED) also have distinct features. Specifically, as opposed to NES, BE does not include sleep disturbances such as waking up in the middle of the night and having a binge episode 8. Some NES patients indicate full consciousness of their Night Ingestion episodes, while some indicate total amnesia 913161718,32333435. Few studies have examined the relations between sleep disorders, BE, and NES 3536. Most research examined SRED classified according to the American Academy of Sleep Medicine's International Classification of Sleep Disorders 37.

According to sleep researchers, NES is a sleep-related disorder, in particular among those who wake up to eat during the night or who have Night Ingestion. According to the American Academy of Sleep Medicine, SRED represents a break in the night time, when a patient awakens from sleep to eat prior to the final morning awakening. The Academy suggested that a variety of underlying pathological processes lead to Night Ingestion. However, recent evidence suggests this pattern of eating in order to return to sleep bears a striking similarity to the motor restlessness of restless leg syndrome. Importantly, both Night Ingestion and motor restlessness frequently arise and exist simultaneously, suggesting that many cases of Night Ingestion represent a non-motor manifestation of restless leg syndrome 38. Some cases of Night Ingestion may also represent features similar to sleepwalking, where patients partially arouse from sleep and ambulate to the kitchen to eat 38.

Despite such research demonstrating that this population deserves a unique diagnosis, SRED was excluded from the new NES diagnostic criteria in the DSM-5 because it is considered part of existing sleep disorders and not a separate ED 1. Nevertheless, most studies reported to date were conducted before the new diagnostic criteria of NES 1. To the best of our knowledge, none of the studies conducted thus far have related to both populations of BN and BED patients, with and without NES, in clinical settings – to compare their sleep disturbances using the new diagnostic criteria.

Therefore, the two aims of the current study were to compare (a) the subjective (self-reported) and objective (actigraph) sleep patterns, and (b) the levels of ED-related psychopathology characterizing three groups of patients: NES with and without Binge Eating Behavior (NES-only; NES-BE (including those with BED and BN), and BE-only.

Measures included demographic and clinical information, intake procedures for diagnosing NES and BE-related EDs, objective (actigraph) and subjective (self-report) measures of sleep disturbance, two self-reports on disordered eating pathology (ED-related psychopathology and eating attitudes), self-reported night eating and depression questionnaires.

The study was approved by the Ministry of Health and Helsinki ethics committee, and all participants provided written informed consent. All patients who were approached to participate in the study gave consent after they were fully informed about the nature of the study and their right to exit at any stage.

Study procedures were conducted in three separate meetings. The first meeting comprised collection of demographic and clinical information and full psychiatric evaluation and diagnosis as part of general admission to the clinic. Those who met criteria for NES and/or a BE-related ED were recruited for the study. In the second meeting, those who agreed to participate received in-depth explanation about the study and procedures from the principal investigator, signed informed consent, and were given self-report questionnaires and a mini-actigraph to monitor sleep patterns. After one week, participants met again with the principal investigator and returned the completed actigraph and questionnaires. After the meeting researchers analyzed sleep patterns based on the mini-actigraph and provided an individual report to each participant with specific recommendations for further treatment as needed.

One-way ANOVA was used to compare the three groups (BE-only, NES-only, NES-BE) on actigraphic data and on sleep and eating related psychopathology self-report questionnaires. To assess the contributions of sleep pathology and eating psychopathology variables to the NES assessment measure, block multiple linear regressions were performed for the total NEQ score, with sleep measures included in the first block and eating measures included in the second block.

To the best of our knowledge, this study is the first systematic investigation comparing sleep-wake patterns and ED psychopathology among patients with BED and BN, with and without NES. In addition, most of the studies reported to date were conducted in community samples and used different diagnostic criteria for NES. In the current study, we assessed patients from a clinical setting who sought treatment for EDs and used the new NES diagnostic criteria 1. This is also the first study using the new diagnostic criteria that continuously monitored this population's sleep patterns via actigraph for a full week. Actigraph monitoring enables recording in a natural environment and reveals sleep-wake patterns that cannot be demonstrated under normal laboratory conditions. Therefore, the aims of this study wereto compare sleep patterns, both subjective and objective, and level of ED-related psychopathology among patients with NES with and without BE behavior (including BED and BN).

Our results indicated that objective sleep monitoring revealed no significant differences between the three study groups of NES-only, BE-only, and NES-BE, except a borderline significant difference in sleep duration. On average, the NES-only group slept about 30 minutes longer than participants in the other two groups, according to the actigraphic monitoring. One explanation why the NES-only group's actigraph reports showed longer sleep duration could be related to the phenomenon of multiple nighttime waking incidents among individuals who demonstrate Night Ingestion. In order to compensate for their disturbed sleep, they may sleep for a longer duration. Another explanation for excessive daytime sleepiness could be related to the possibility of breathing problems during sleep in the NES-only group and for BED, which may be linked to their higher BMI. The lack of significant group differences in sleep onset time may be related to the higher prevalence of BE episodes that occurs mainly during the late evening time among patients with BN, with BED, and with NES associated with Evening Hyperphagia 19. However, it is important to note that all three groups suffered from an objectively slightly lower level of sleep efficiency relative to the norms for the healthy population 6.

These results are in line with previous research examining sleep-wake cycles and associated characteristics of Night Ingestion in BN and BED patients 6. In prior research, these patients' actigraph results showed no significant differences in nocturnal ingestion between the BN and BED patients. However, these researchers' sample included patients whose primary concern was Night Ingestion symptoms and did not include patients with Evening Hyperphagia 6.

Beyond high lighting objective sleep data, the current findings yielded significant group differences in subjective sleep patterns based on the MSQ self-report. The NES-only and NES-BE groups subjectively described more sleep disturbance symptoms than the BE-only group. This result may be explained by the fact that patients with NES, in particular those with Night Ingestion, tend to wake up several times during the night in order to eat. As mentioned above, these multiple nighttime waking incidents may cause sleep deprivation that can lead to a sense of sleepiness during the day. These results are in line with previous research demonstrating high levels of sleep disturbances among BED and BN patients with NES 6.

These differences between groups in subjective sleep patterns may also be a function of weight-related physical discomfort manifested in breathing problems while sleeping. The NES-only and NES-BE groups demonstrated higher BMI in comparison to the BE-only group, which imply weight problems that may affect breathing, which in turn would be reflected in objective actigraphic sleep measurements. In this context, the differentiation between the BN and BED subgroups within the BE-only group may be relevant. As found in our study and supported by the literature, patients with BN are in the normal range weight whereas patients with BED and or NES are usually overweight 19. Thus, the significant differences may be related specifically to the BED and/or NES groups who present overweight and obesity that may result in breathing problems during sleep. Furthermore, these subjective sleep discrepancies may indicate that the NES-only and NES-BE groups have higher levels of psychiatric comorbidity than the BE-only group. Additionally, these results might indicate traumatic life events that precipitated BE episodes in the NES-only and NES-BE groups, as found in previous studies 65136626364656667.

No significant differences were found in level of psychopathology between the three groups in this study. This results contrast with previous research outcomes indicating higher levels of psychopathology among patients who demonstrate NES together with BE 25. Thus, it is still unclear whether prevalence of psychiatric comorbidity and traumatic life events is higher among patients with EDs together with NES versus patients with just EDs.

This study is the first using the new diagnostic criteria of NES and applying them to a group of ED patients. Our results show that NES in ED patients, in-particular in Evening Hyperphagia, may represent an ED subgroup [of BN and / or BED) as opposed to a separate entity. Further research must be conducted to clarify this hypothesis.

Several limitations of this study should be considered. First, the small sample size reduces statistical power for detecting group differences and for generalizing the findings overall. A larger sample size would also permit differentiation between BN and BED patients to identify possible differences in psychopathology levels, instead of combining these subgroups into one BE behavior group as needed for statistical analysis of the current sample. Second, future research is necessary to further clarify the definition of NES, which currently includes both Night Ingestion and Evening Hyperphagia subsyndromes. That is as Evening Hyperphagia is very similar to BED, it is important to separate these two subsyndromes in the ED population to determine if Evening Hyperphagia in fact constitutes its own ED subgroup rather than constituting a part of NES. Third, the present clinical sample included only patients with high levels of psychopathology who were seeking treatment for an ED. Such individuals usually tend to exhibit greater levels of psychopathology than those seeking treatment for weight loss or eating-related issues in nonclinical samples. Further research in a nonclinical community sample of individuals with NES may elucidate the differences between ED patients with NES and patients whose primary diagnosis is NES. It may also clarify where NES lies on the continuum of psychopathology. More extensive research is necessary to determine psychological characteristics and comorbidity associated with NES. Finally, we used actigraphic data to measure the sleep-wake cycle. However, these measurements cannot describe all disturbances; hence, further study in a sleep laboratory setting is necessary to understand similarities and differences in sleep-wake cycles between groups.