Night eating syndrome (NES) was first described by Stunkard in the 1950s , but has only been introduced as a diagnostic classification in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5; American Psychiatric Association)  under the other specified feeding or eating disorder (OSFED) umbrella category. It is characterised by recurrent episodes of night eating defined as eating more than 25% of one’s daily caloric intake after the evening meal, not better explained by external influences, social norms, another psychiatric disorder, medical disorder or effect of medication. Typically, individuals with NES believe they must eat in order to sleep and are aware of consuming food at night, unlike the parasomnia sleep-related eating disorder [3, 4]. Since NES was only included in the DSM-5, research on its aetiology is limited.
Although NES is defined as a separate diagnosis within the OSFED classification it is often comorbid with other eating disorder (ED) diagnoses, particularly bulimia nervosa (BN) and binge eating disorder (BED). Whilst in the general population, the prevalence of NES is 1.5% (Milano et al., 2011), up to 52% of people with binge eating disorder (BED) and 35% of those with bulimia nervosa (BN) meet criteria for NES, compared with around 10% of people with anorexia nervosa (AN) .
Individuals who have more symptoms of NES have been reported to have greater psychological morbidity, including higher stress , higher impulsivity [7, 8], lower self-esteem, greater functional impairment , and more comorbid psychiatric mood and anxiety disorders [10, 11]. Emotional eating, defined as eating in the absence of hunger or in response to negative emotional cues such as anxiety [12, 13], is also common in people with NES .
Previous research suggests that certain TCI personality traits, such as harm avoidance, could increase a person’s risk of developing an ED , and possibly predict prognosis and drop-out in ED interventions . Furthermore, cognitive behavioural therapy (CBT) for BN was found to decrease harm avoidance and increase self-directedness. Improvement in these personality traits may predict successful outcome in CBT, but CBT may affect positive change in elements that contribute to these traits, for example resourcefulness and self-acceptance, both elements of self-directedness . However, the correlation between certain personality traits and ED symptoms may be moderated by other ED symptoms, such as the presence of purging behaviour [18, 19]. Hence, beginning to understand which personality traits are associated with NES may pave the way to more targeted aetiological research, necessary to identify potential targets for intervention.
To date, only two studies have investigated personality traits in individuals with NES, finding that those with NES report higher harm avoidance [20, 8] and lower self-directedness . These studies, however, have a number of limitations. Both had very small NES sample sizes (N = 18; , and N = 24; ), which may have resulted in type I and II errors. One of these studies  included only individuals with a very high body mass index (BMI). The other study  included only individuals who engaged in nocturnal eating after falling asleep, which is not a specific requirement of NES, and may have also included those with a parasomnia, sleep-related eating disorder (SRED). Finally, previous studies have not appropriately accounted for confounding factors, adjusting for only BMI and age, which may have led to biased estimates. Previous research suggests factors such as ethnicity and employment are associated with eating behaviours [21, 22] and personality traits .
To address these limitations, the current study investigated the cross-sectional association between a range of personality traits and NES symptoms in a sample of treatment-seeking women with binge eating disorder or bulimia nervosa, adjusting for multiple confounders, whilst using a dimensional measure of night eating.