Although seen less frequently in obese individuals than BED and NES, BN does occur in obese individuals [55] and thus should be assessed. In addition to regular binge eating episodes as defined in BED, a diagnosis of BN requires the use of problematic methods to prevent weight gain such as inducing vomiting, misuse of laxatives, prolonged fasting, and excessive exercise. The frequency of binge episodes and compensatory behaviors occur at least weekly and symptoms persist for at least 3 months .

Whereas the core feature of BED is episodes of overeating accompanied by a lack of control without the use of inappropriate compensatory behaviors, the core feature of NES is the delayed circadian shift of eating [8, 56]. First described by Stunkard et al. in 1955 [57], awareness of NES amongst clinicians and researchers has only recently emerged. It is now listed in the DSM-5 as an Other Specified Feeding or Eating Disorder but diagnostic criteria have not yet been fully quantified. Allison et al. [28] propose that for NES, as established by the International NES Working group, the core criterion is an abnormally increased food intake in the evening and/or at night, manifested by (1) consumption of at least 25 % of intake after the evening meal and before bedtime and/or (2) nocturnal awakenings with eating at least twice per week. In addition to distress or impairment in functioning, NES involves awareness of the eating episodes as this feature differentiates NES from sleep-related eating disorder (SRED) , a parasomnia in which individuals do not recall their night-time eating [28]. Allison et al. [28] propose additional criteria for NES that involves the endorsement of at least three of five additional symptoms: (1) lack of eating in the morning; (2) strong desire to eat between dinner and sleep or upon awakening from sleep; (3) insomnia; (4) belief that one must eat in order to get to sleep; and (5) low mood in the evening. These criteria must be met for a minimum duration of 3 months. These additional criteria are not required by the DSM-5 given that further research on night eating is needed; however, the criteria outlined by Allison et al. [28] are useful for differentiating NES from other disorders such as BED and SRED .

BED and NES are thought to be distinct disorders; however, they share the common feature of evening hyperphagia ([28], see Fig. 10.1). The rates of co-occurring BED and NES range from 7 to 25 % and approximately 9 % for BN and NES [28, 58].

NES can be distinguished from BED in that individuals with NES demonstrate a phase delay in the circadian pattern of eating leading them to consume more of their total energy intake later in the day and at night compared to individuals without NES [36, 46, 59]. Gluck et al. [46] found that after fasting for 8 h, night eaters reported less hunger before a daytime test meal. In terms of waking to eat, Birketvedt et al. [59] found that night eaters woke on average 3.6 times per night compared to only 0.3 times in controls and 52 % of awakenings in night eaters were accompanied by food intake. NES participants have been found to have lower disinhibition scores than individuals with BED, but higher than controls [60], and those with both BED and NES scored the highest. One difference that has been highlighted in the literature is that sleep disturbance is less common in individuals with BED compared to those with NES [4, 36].

Individuals with NES have also been found to exhibit less general psychological distress than individuals with BED [8]. Allison et al. [37] in their study comparing individuals with BED and NES found the BED group exhibited greater eating pathology and experienced many more objective binge eating episodes with loss of control. Some of the NES participants reported a loss of control during their night eating episodes, but this was rarely objectively large in terms of quantity of food. The eating patterns of the groups differed significantly as well, with the NES group eating far fewer meals during the first half of the day. The BED and NES groups ate a similar number of evening snacks after the main evening meal, indicating that both groups have some trouble regulating their eating in the evening hours before bedtime. The BED group had higher scores on the Eating Disorders Exam-Questionnaire ([61], please see Table 10.3 for a description of this measure) weight concern and shape concerns subscales than the NES group even after controlling for BMI differences. Allison et al. [37] note that since both the NES and BED groups were characterized by disordered eating, clinicians should attend to the assessment and regulation of meal patterns. For nocturnal ingestions, NES can also be distinguished from sleep-related eating disorder in that individuals with NES are awake when eating and can recall these episodes compared to individuals with SRED who are asleep when these eating episodes occur [5].

ARFID is characterized by an apparent lack of interest in eating or food, avoidance of food based on the food’s sensory characteristics, and avoidance of particular foods due to concerns about the negative consequences of eating, like abdominal discomfort. Unlike other eating disorders, the motivation to avoid eating is not to achieve or maintain a certain body weight or shape. ARFID can co-occur with a number of other mental disorders, in particular, with autism spectrum disorder and other neurodevelopmental disorders, as well as anxiety disorders [62]. Little research on ARFID in adults has been published and the prevalence of ARFID in obese individuals has not been documented. However, sufficient numbers of post-bariatric surgery patients across different countries and settings have been documented with problematic food aversions to have generated several publications and research studies (e.g., [63–67]. Although these studies do not diagnose these individuals with ARFID, the presentation may be similar to that of ARFID. Foods that are typically avoided after bariatric surgery tend to be tougher or denser in texture, particularly meats, rice, and pasta. These aversions usually develop after the foods in question lead to an episode of abdominal discomfort. However, these food avoidances tend to disappear over time and do not usually indicate a diagnosis of ARFID .

As with other psychiatric disorders, the eating disorders involve symptoms that are behavioral (e.g., bingeing, restriction), cognitive (e.g., prioritization of dietary restraint, negative body image), and affective (e.g., eating to regulate emotional distress) in nature and a complete, valid, and reliable assessment must consider all of these. Table 10.2 lists the symptoms and features that are typically found in eating disorders that should be assessed in all patients.

Regardless of whether the assessment is conducted for treatment or research purposes, a clinical interview should be the foundation of any valid eating disorders assessment. Based on the available research evidence and our clinical experience, clinician interviews are critical for understanding past and present eating behaviors and for obtaining accurate diagnoses in both bariatric surgery [68–71] and non-bariatric surgery populations [61]. The choice of particular interview and questionnaire instruments can then be based on factors such as time available to conduct the assessment and the type of information that is useful in a particular setting. Please see Table 10.3 for a description of the recommended eating disorder-specific interview and self-report assessment instruments.

The Eating Disorders Exam-Interview [72] is the most used and widely recognized interview used to diagnose eating disorders. The eating disorders modules of the Structured Clinical Interview [73] and the MINI Neuropsychiatric Interview are also available [74]. However, as of yet these measures do not include questions to assess NES or ARFID. The Night Eating Syndrome History and Inventory (NESHI) is a more recent addition to the field and can be used to guide the assessment of NES [75]. Currently there are no validated instruments for assessing ARFID. Therefore, a thorough understanding of when and how the food aversion developed, the persistence of the avoidance and associated distress and/or impairment are needed to inform diagnosis.

Self-report instruments are useful to screen for particular disorders like binge eating disorder or night eating syndrome and features like shape- and weight-related concerns. However, binge eating, which is necessary for diagnosing BED and BN, is difficult to assess accurately through self-report instruments. The bulk of the research conducted on the concordance between self-report and interview measures have compared the Eating Disorders Exam-Interview (EDE-I) to the Eating Disorders Exam-Questionnaire (EDE-Q) [76–79]. In summary, this research shows that self-report measures yield higher levels of binge eating compared to clinical interviews [61, 76–80]. As Fairburn and Beglin [61] note and our experience supports, this is because patients generally lack the knowledge required for accurately defining a binge. The term “binge eating” has entered the cultural lexicon, but individuals who do not have an understanding of the clinically defined features of a binge, such as the amount of food required for an objective binge, cannot accurately report on these symptoms. Clinical interviews thus allow for the probing that is needed to determine whether a patient who reports “binge eating” truly is binge eating according to the DSM-5.

In addition to binge eating, self-report measures as compared to clinical interviews tend to yield higher scores on weight- and shape-related concerns [81]. Fairburn and Beglin [61] posit that similarly to binge eating, laypersons lack the knowledge needed to assess clinically defined weight- and shape-related distress. The ability to differentiate normative dissatisfaction about shape and weight from the more extreme concerns typical in eating disorders requires clinical experience. However, they found little discrepancy between the EDE-Q and EDE-I in assessing the frequency of self-induced vomiting and laxative misuse, likely because these are behaviors that are simply either present or absent. The overall pattern of findings in this study suggested that self-report questionnaires can be used to assess clearly defined behavioral symptoms like self-induced vomiting, laxative misuse, and dietary restraint, but interviews should be used to assess binge eating and body dissatisfaction .

Once an obese patient has been diagnosed with an eating disorder, planning for treatment involves several considerations (see Table 10.4 for steps for triage following a diagnosis of an eating disorder).