Neuroscience and Biobehavioral Reviews 49 (2015) 125–134

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Review

Emotion regulation model in binge eating disorder and obesity - a systematic review Elisabeth J. Leehr a,∗ , Kerstin Krohmer b , Kathrin Schag a , Thomas Dresler c,d , Stephan Zipfel a , Katrin E. Giel a,e a Department of Psychosomatic Medicine and Psychotherapy, University Hospital Tuebingen, Internal Medicine VI, Osianderstraße 5, 72076 Tuebingen, Germany b Department of Clinical Psychology and Psychotherapy, University Tuebingen, Schleichstraße 4, 72076 Tuebingen, Germany c Department of Psychiatry and Psychotherapy, University of Tuebingen, Calwerstraße 14, 72076 Tuebingen, Germany d LEAD Graduate School, University of Tuebingen, Gartenstraße 29a, 72074 Tuebingen, Germany e Department of Medicine and Psychosomatics, Centre for Psychosocial Medicine, University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany

a r t i c l e

i n f o

Article history: Received 15 May 2014 Received in revised form 25 October 2014 Accepted 5 December 2014 Available online 19 December 2014 Keywords: Emotion regulation Affect Mood Binge eating Overeating Obesity Overweight

a b s t r a c t Deficits in emotion regulation processes are a common and widely used explanation for the development and maintenance of binge eating disorder (BED). It is assumed that BED patients – as they have difficulty regulating their negative emotions – use binge eating to cope with these emotions and to find relief. However, the number of experimental studies investigating this assumption is scarce and the differentiation of obese individuals with and without BED regarding the emotion regulation model is not verified. We reviewed literature for experimental studies investigating the emotion regulation model in obese patients (OB) with and without BED. Our search resulted in 18 experimental studies examining the triggering effect of negative emotions for binge eating or its effects on subsequent relief. We found evidence indicating that negative emotion serves as a trigger for binge eating in the BED group unlike the obese group without BED. Considering the small number of studies, we found evidence for a (short-term) improvement of mood through food intake, irrespective of group. © 2014 Elsevier Ltd. All rights reserved.

Contents 1. 2.

3.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Literature search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Eligibility criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Study selection and data collection procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Study selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Experimental studies with manipulation of emotion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1. Evidence for the trigger component of the emotion regulation model in BED, OB (BED?) and OB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2. Evidence for the relief component of the emotion regulation model in BED, OB (BED?) and OB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Experimental studies assessing emotions without manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1. Evidence for the trigger component of the emotion regulation model in BED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

126 127 127 127 129 129 129 129 129 130 130 130 130

Abbreviations: BED, binge eating disorder; BMI, body mass index; BN, bulimia nervosa; BPD, Borderline Personality Disorder; ED, eating disorder; EMA, ecological momentary assessment; LOC, loss of control; non-BED, sample without BED; NWC, normal weight controls; OB, obese sample without BED; OB (BED?), sample with missing information about a diagnosis of BED; N/A, not applicable, data not assessed. ∗ Corresponding author. Tel.: +49 7071 2983610. E-mail addresses: [email protected] (E.J. Leehr), [email protected] (K. Krohmer), [email protected] (K. Schag), [email protected] (T. Dresler), [email protected] (S. Zipfel), [email protected] (K.E. Giel). http://dx.doi.org/10.1016/j.neubiorev.2014.12.008 0149-7634/© 2014 Elsevier Ltd. All rights reserved.

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4.

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3.3.2. Evidence for the relief component of the emotion regulation model in BED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.3. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Summary of the results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Interpretation of the results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Methodological limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4. Conclusion and further directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction With the release of DSM-5 (American Psychiatric Association, 2013), binge eating disorder (BED) was introduced as a distinct eating disorder (ED) diagnosis. Therefore, it is important to gain a better knowledge of the development and maintenance of binge eating. Accordingly it is necessary to acquire a more precise understanding of the disorder, which will enable an improvement of therapeutic interventions. BED is characterised by recurrent binge eating episodes which are defined as eating an unusually large amount of food someone else would not eat in the same period of time and in a similar setting while experiencing loss of control (LOC) (American Psychiatric Association, 2013). Further attributes of binge eating episodes are: eating faster than normal, eating until feeling uncomfortably full, eating without feeling hungry, eating privately due to a feeling of shame and a feeling of guilt or disgust afterwards. Additionally, binge eating episodes are associated with distress and have to occur at least once a week over a period of three months. As self-induced compensatory behaviour (e.g. in bulimia nervosa (BN)) is not utilised, BED often co-occurs with overweight or obesity (de Zwaan, 2001). It has been suggested that obese individuals with BED represent a distinct neurobiological phenotype within the obesity spectrum (Carnell et al., 2012; Schag et al., 2013; Wang et al., 2011), which is characterised by an emotion regulation deficit (Brockmeyer et al., 2014; Danner et al., 2014). Neurobiological processes concerning self-regulation, including control over one’s own eating behaviour, are known to be strongly influenced by emotions (Heatherton and Wagner, 2011). Emotion regulation is defined as the “attempt to influence which emotions we have, when we have them, and how these emotions are experienced or expressed” (Gross, 1998, p. 224). If emotion regulation fails, self-regulation in other areas, like control over eating behaviour, can fail as well. Hence, it seems plausible that explanation models of binge eating behaviour in BED and overeating in obesity trace back to self-regulation failure caused by intense emotions. The term emotion can comprise very different meanings ranging from depicting a specific (negative) emotion (e.g. anger or sadness) to simply describing an unspecific emotional state like emotional stress. From a more behavioural perspective, several emotion regulation theories have been proposed. The theory of emotional eating understands eating as a coping strategy in response to emotional distress (Bennett et al., 2013; Bruch, 1973), hence describing a sub-clinical form of disordered eating behaviour in response to emotions. Especially in terms of obese and normal weight persons, emotional eating has been investigated (for an overview see Ganley, 1989; Konttinen et al., 2010; Rommel et al., 2012). There are several theories regarding a more disordered pattern of emotional eating, like overeating (eating a large amount of food) and binge eating (eating a large amount of food and experiencing loss of control). The escape theory (Heatherton and Baumeister, 1991) presumes an alleviation of aversive affect while bingeing, whereas other theories, like the affect regulation theory (Polivy and Herman, 1993), assume an improvement of affect after binge eating. According to the

130 130 130 130 131 131 132 132 132

emotional arousal theory, overeating is evoked by emotional arousals in order to reduce the level of arousal (Pine, 1985). Each of the emotion regulation theories mentioned above includes at least one of the following components: (1) specific or unspecific negative emotions as a trigger for binge eating (i.e. trigger component) and (2) down-regulation of specific or unspecific negative emotions (i.e. relief component) through binge eating in the short-term (while bingeing) or long-term (after a binge episode). To subsume both components, we propose the “emotion regulation model”, which includes the whole emotion regulation process (see Fig. 1). The components of the emotion regulation model as an account of binge eating have been also addressed in previous reviews. Ganley (1989) gave an overview of studies investigating the relation between emotion and eating in obesity; however, he did not differentiate between populations with or without BED. Another more current narrative review investigated capacities in emotion and impulse regulation, considering possible differences between obese people and people with binge eating (BED and BN) (Fischer and Munsch, 2012). Unfortunately, these two reviews have not been conducted systematically. In contrast, Aldao et al. (2010) conducted a large meta-analytic review concerning emotion regulation strategies in individuals with ED. This specific study did not differentiate between specific subtypes of ED. Affect regulation theory in BED and BN was also evaluated in another meta-analysis (Haedt-Matt and Keel, 2011). However, the focus of this review was restricted to naturalistic studies as they exclusively considered studies using ecological momentary assessment (EMA), thus making a generalisation of the results difficult. Furthermore, the authors focused on binge eating in BN and BED, but possible distinctive patterns of emotion regulation in obese people with and without BED were not addressed. Taking into account the ambiguous outcomes of studies and overcoming the limitations of the available reviews (e.g. no differentiation between overweight/obesity with and without ED, missing discrimination between different types of ED or investigating only naturalistic studies) we investigated the evidence for the emotion regulation model in a systematic review of experimental studies. We define experimental studies as all studies where at least one independent variable was manipulated or all variables have been assessed in a laboratory setting. We additionally aimed at investigating potential differences between overweight/obese individuals with and without BED with the purpose of a clearer distinction of the BED group. Therefore, the following research questions will be addressed: (1) Is there sufficient evidence for the two components (trigger component and relief component) of the emotion regulation model? (2) Are there substantial differences between obese individuals with and without BED regarding the emotion regulation model? trigger component

emotion regulation

relief component

(un-)specific negative emotions

overeating/ binge eating

down-regulation of (un-) specific negative emotions

Fig. 1. Components of the emotion regulation model.

E.J. Leehr et al. / Neuroscience and Biobehavioral Reviews 49 (2015) 125–134

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2. Methods

2.2. Eligibility criteria

The review process was conducted according to the PRISMAStatement (Liberati et al., 2009; Moher et al., 2009). The study selection process can be seen in Fig. 2.

We assessed the eligibility of search results according to modified PICOS-criteria (Liberati et al., 2009, Box 2). Only human studies were included with no restrictions regarding sex, age and ethnicity. The participants either had to show symptoms of BED, or had to be overweight/obese. Exclusion criteria were BN, anorexia nervosa (AN) or severe mental as well as somatic disorders influencing the eating behaviour (e.g. Prader–Willi Syndrome, dementia, schizophrenia). According to these eligibility criteria, we obtained three groups: (1) BED participants with full or subthreshold BED (sub-BED) symptoms, examined through expert interviews (e.g. Structural Clinical Interview for DSM-IV (First et al., 1996) or Eating Disorder Examination (Cooper and Fairburn, 1987)) or self-report measures of BED (e.g. Eating Disorder Examination Questionnaire (Fairburn and Beglin, 1994)). (2) OB (BED?) participants who are overweight or obese having a body mass index (BMI) > 25 kg/m2 and with missing information about a diagnosis of BED. (3) OB participants being overweight or obese, with a BMI > 25 kg/m2 and in which comorbid BED had been excluded through an expert interview. For BED participants, possible control groups are overweight/ obese or normal weight controls (NWC; BMI 18–25 kg/m2 ) without BED symptoms (non-BED). The control group for OB and OB (BED?) are NWC. Studies lacking control groups or a comparison between groups were excluded (cf. Kretsch et al., 1999; Ranzenhofer et al., 2013). Only experimental studies, as defined above, manipulating or measuring all variables in a laboratory setting and published in peer reviewed journals, are included. State and trait mood were

2.1. Literature search

Eligibility

Screening

Identification

We searched the databases PsychInfo, PubMed and Medline for articles published until September 2014. The first, third and sixth author performed additional hand searches with reference lists and consulted experts in the field. We chose search terms related to overweight and eating disorder, food and eating, as well as emotion regulation and mood. Our search contained the following terms in title and abstract: obes*, overweight, binge-eating disorder, binge eating, BED, loss of control, hyperphagia, overeating, emotional eat*. We also included the terms food and eating, emotion, emot*, emotion regulation, regulation strategies, mood and affect. In PubMed we used the possibility to apply Meshterms and attained the following complete search path: [(obesity[MeSH Terms] OR overweight[MeSH Terms] OR obes*[Title/Abstract] OR binge-eating disorder[MeSH Terms] OR “binge eating”[Title/Abstract] OR BED[Title/Abstract] OR “loss of control”[Title/Abstract] OR hyperphagia[MeSH Terms] OR overeating[Title/Abstract] OR emotional eat*[Title/Abstract]) AND (food[MeSH Terms] OR food[Title/Abstract] OR eating[MeSH Terms]) AND (emotion[MeSH Terms] OR emot*[Title/Abstract] OR “emotion regulation”[Title/Abstract] OR “regulation strategies”[Title/Abstract] OR mood[Title/Abstract] OR affect[MeSH Terms])] Filters: Humans.

Records identified through database searching: n = 2151

Additional records identified through other sources: n = 22

Records after duplicates removed: n = 2087

Records screened: n = 2087

Full-text articles assessed for eligibility: n = 200

Included

Studies included in qualitative synthesis: n = 18 (with n = 5 in children) Sample

n

BED

12

OB (BED?)

4

OB

2

Records excluded: n = 1887

Full-text articles excluded, with reasons (n = 182): - no experimental study: n = 99 - wrong sample: n = 32 - wrong/unclear group classification: n = 9 - no control group: n = 26 - no measure of mood: n = 3 - no measure of eating behaviour: n = 1 - no group comparison: n = 2 - wrong independent or dependent variable: n = 9 - language: n = 1

Fig. 2. PRISMA flow chart for study inclusion. BED, sample with binge eating disorder; OB (BED?), obese sample with missing information about a diagnosis of BED; OB, obese sample without binge eating disorder.

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Table 1 Experimental studies with mood induction. Study

Adult samples BED Telch and Agras (1996) Schulz and Laessle (2010) Zeeck et al. (2011)

Rosenberg et al. (2013)

Svaldi et al. (2014) Adult samples OB (BED?) Schneider et al. (2010) Appelhans et al. (2011) Lemmens et al. (2011) Adult samples OB Jansen et al. (2008)

Udo et al. (2013) Child samples Hilbert et al. (2010)

Goldschmidt et al. (2011)

Hilbert and Czaja (2011)

Laessle and Schulz (2013)

n

Sex (amount of female)

Independent variable

Outcome (a) food intake (b) loss of control

Evidence for the trigger component of the emotion regulation model

Evidence for the relief component of the emotion regulation model

BED OB BED OB BED non-BED (NWC, OB) BED OB

60

Female

Negative vs. neutral vivid imagery;

↓

↑ in both groups

84

Female

Neutral vs. stress;

↑

↑ in both groups

63

Female

Imagery; Mood prior to last binge (retrospective);

(a) Food intake (b) N/A (a) Food intake (b) N/A (a) Desire to eat (b) N/A

↑

N/A

71

Female

Neutral vs. stress;

↑

N/A

BED OB NWC BED OB

24

Both (16)

Neutral vs. stress;

↑

N/A

81

Female

Mood induction; Emotion regulation strategy;

(a) Food intake; initial eating rate; size of spoon-fulls (b) Change of eating rate (a) Sweet craving (b) Self-reported urge for uncontrolled eating (a) Food intake (b) N/A

↑

N/A

OB (BED?) NWC OB (BED?) NWC OB (BED?) NWC

61

Both (45)

Neutral vs. anxiety vs. anger;

↑ (conditioned)

N/A

61

Both (45)

↑ (conditioned)

N/A

42

Both (26)

Neutral vs. anger; Distraction as tempering anger; Rest vs. stress;

(a) Food intake (b) N/A (a) Food intake (b) N/A (a) Food intake (b) N/A

↑

N/A

OB NWC

91

Female

(a) Food intake; food craving (b) N/A

↑ (conditioned)

N/A

OB NWC

30

Female

Self-reported low vs. high negative affect (trait); Self-reported mood (state); Neutral vs. negative mood induction or exposure to food; Negative vs. positive imagery;

(a) Food intake; food craving (b) Disability to resist eating

↓

N/A

Both (68)

Neutral vs. negative interaction task; Parent-child test-meal vs. child-only snack eating;

(a) Food intake (b) Self-reported loss of control

↓

N/A

Female

Neutral vs. sad mood;

(a) Food intake (b) Self-reported loss of control

↓

N/A

Both (68)

Neutral vs. negative interaction task; Parent-child test-meal vs. child-only snack eating;

(a) Food intake (b) Bite size; velocity

↓

N/A

Female

Pleasant vs. neutral vs. unpleasant;

(a) Food intake; initial eating rate; size of spoon-fulls (b) Change of eating rate

↓

N/A

BED non-BED (NWC, OB) [8–13 y.] BED OB [6–12 y.] BED non-BED (NWC, OB) [8–13 y.] OB (BED?) NWC

120

26

120

86

BED, sample with binge eating disorder; OB (BED?), obese sample with missing information about a diagnosis of BED; OB, obese sample without binge eating disorder; NWC, normal weight controls; y, years; ↑ evidence supporting emotion regulation model; ↓, evidence not supporting emotion regulation model; N/A, not applicable, data not assessed.

E.J. Leehr et al. / Neuroscience and Biobehavioral Reviews 49 (2015) 125–134

Schulz and Laessle (2012)

Sample [age]

E.J. Leehr et al. / Neuroscience and Biobehavioral Reviews 49 (2015) 125–134

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Table 2 Experimental studies without mood induction. Study

Adult sample BED Geliebter et al. (2001) Nasser et al. (2004)

Child sample Hartmann et al. (2012)

Sample [age]

n

Sex (amount of female)

Independent variable

Outcome (a) food intake (b) loss of control

Evidence for the trigger component of the emotion regulation model

Evidence for the relief component of the emotion regulation model

BED OB BED sub-BED OB

85

Both (61)

Depression rating;

↓

N/A

33

Female

Mood;

(a) Food intake (b) N/A (a) Food intake (b) N/A

↓

N/A

LOC ADHD NWC [10–14 y.]

80

Both (44)

Mood; Impulsivity;

(a) Food intake (b) N/A

↓

↑ in all groups

BED, sample with binge eating disorder; OB (BED?), obese sample with missing information about a diagnosis of BED; OB, obese sample without binge eating disorder; NWC, normal weight controls; LOC, loss of control; ADHD, attention deficit hyperactivity disorder; y, years; ↑, evidence supporting emotion regulation model; ↓, evidence not supporting emotion regulation model; N/A, not applicable, data not assessed.

determined as independent variables (cf. Fig. 1 trigger component), e.g. experimentally induced by emotion induction techniques. The outcome measures, regarding binge eating as emotion regulation strategy, comprised food intake, craving, loss of control, the urge or desire to eat and behavioural variables representing binge eating such as increased bite size. To differentiate between overeating and binge eating, we report in Tables 1 and 2 if (a) the amount of food intake was assessed (i.e. overeating, desire to eat) and, if (b) an additional measurement of loss of control was used in order to define the episode of food intake as binge eating according to DSM5 criteria (American Psychiatric Association, 2013). Loss of control could be operationalised for example through self-report, inability to resist eating, increased bite size and velocity or change of eating rate. The relief component (cf. Fig. 1) could have been any measurement of mood after binge eating. Observational studies and pure questionnaire studies were excluded, as well as comments, reviews, book chapters, dissertations and conference papers. Only studies written in English, German or French were considered, with no restriction regarding the publication date up to September 2014. 2.3. Study selection and data collection procedure The first author ascertained the search terms and conducted the search in the three databases. After excluding duplicates, titles and abstracts of all search results were screened to identify relevant studies. Following the eligibility criteria, the first and second author rated every study for eligibility. With к = .92, interrater reliability was excellent. In case of differing judgement, the senior author was consulted as independent rater. The first author extracted relevant data from included studies following a priori developed data extraction forms based on modified PICOS-criteria (Liberati et al., 2009, Box 2). The relevant data comprised: (1) participants and control groups demographic and clinical characteristics (e.g. diagnosis and weight status), (2) type of independent variables (differentiating in state vs. trait mood), (3) outcome variable (e.g. food intake or self-reported desire to eat and loss of control) and (4) assessment of emotion after behaviour aggregated as outcome variable.

criteria and were discarded after reviewing the title and abstract. The remaining 200 studies were rated and 182 had to be eliminated as they did not fulfil eligibility criteria. Finally, we included 18 experimental-setting studies of which 5 investigated childhood and adolescent samples. Results are reported separately for studies actively manipulating emotion and studies that only assess current emotions. For an overview on the different study designs see Fig. 3. 3.2. Experimental studies with manipulation of emotion Emotion was actively manipulated in 15 studies (see Table 1). Several emotion induction methods were used: imagery or dietary recall to induce negative emotions (Appelhans et al., 2011; Schneider et al., 2010; Telch and Agras, 1996; Udo et al., 2013; Zeeck et al., 2011), emotion provocation via listening to music (Jansen et al., 2008) or watching a movie (Goldschmidt et al., 2011; Laessle and Schulz, 2013; Svaldi et al., 2014), implementing a stress test (Lemmens et al., 2011; Rosenberg et al., 2013; Schulz and Laessle, 2010, 2012) or a negative interaction task (Hilbert and Czaja, 2011; Hilbert et al., 2010). Emotions were investigated both as an antecedent or consequence of binge eating. Outcome variables were (a) measures of the amount of food intake and the desire to eat and (b) in some studies additional measures of loss of control (Goldschmidt et al., 2011; Hilbert and Czaja, 2011; Hilbert et al., 2010; Laessle and Schulz, 2013; Rosenberg et al., 2013; Schulz and Laessle, 2012; Udo et al., 2013). 3.2.1. Evidence for the trigger component of the emotion regulation model in BED, OB (BED?) and OB Nine studies out of 15 showed evidence for negative emotion or stress as being a trigger for binge eating or overeating (Appelhans et al., 2011; Jansen et al., 2008; Lemmens et al., 2011; Rosenberg et al., 2013; Schneider et al., 2010; Schulz and Laessle, 2010, 2012; Svaldi et al., 2014; Zeeck et al., 2011). Five studies investigating diagnostics

trigger component

induction of specific/ unspecific negative emotion

emotion regulation

overeating/ binge eating

overeating/ binge eating

relief component

assessment of emotions

assessment of emotions

assessment of specific/ unspecific negative emotion

3. Results 3.1. Study selection The search of electronic databases resulted in 2151 hits. Additionally, 22 studies were found by our hand search. We removed 86 duplicates and screened 2087 remaining studies. One thousand eight hundred and eighty-seven studies did not meet the eligibility

Fig. 3. Study designs of selected experimental studies with and without mood induction.

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adult BED samples (Rosenberg et al., 2013; Schulz and Laessle, 2010, 2012; Svaldi et al., 2014; Zeeck et al., 2011) revealed that people with BED show a higher amount of food intake and in two studies also higher loss of control after an induction of negative emotions (Rosenberg et al., 2013; Schulz and Laessle, 2012). One study did not find evidence for the trigger component in a BED sample (Telch and Agras, 1996). Interestingly, in OB (BED?) samples only one study found a higher food intake after stress as compared to a rest condition (Lemmens et al., 2011). In the remaining two studies with OB (BED?) the proof of specific negative emotions as trigger component seemed to be conditioned through trait anxiety (Schneider et al., 2010) or distraction as emotion regulation strategy (Appelhans et al., 2011). An OB sample showed higher craving and food intake after negative emotion induction only in the high negative affect subgroup (Jansen et al., 2008). No significant effect for negative emotion as antecedent for binge eating was found in an OB sample (Udo et al., 2013). In the four studies testing the emotion regulation model in children with BED and OB (BED?), none of the results supported the trigger component. The studies did not find an interaction of group and emotional state regarding the eating behaviour or indicated rather inconsistent results (Goldschmidt et al., 2011; Hilbert and Czaja, 2011; Hilbert et al., 2010; Laessle and Schulz, 2013). 3.2.2. Evidence for the relief component of the emotion regulation model in BED, OB (BED?) and OB With regard to an improvement of emotions through binge eating, only two studies reported results concerning post-meal emotions (Schulz and Laessle, 2010; Telch and Agras, 1996). Without differences between BED and OB, both samples reported fewer negative emotions after food intake compared to before food intake with no measurement of loss of control. 3.2.3. Conclusion Concluding the results of the studies using induction of emotion, the evidence for the emotion regulation model seems to be inconsistent. Depending on the sample, there are some studies showing that negative emotions precede and trigger binge eating, while others are not able to find this association. For the BED and the OB (BED?) adult samples, there appears to be evidence that negative emotions are antecedents for binge eating. The data for OB samples is very small (n = 2), thus strong conclusions cannot be drawn. Therefore, taking into account the available evidence regarding the research question concerning differences between obese individuals with and without BED, BED seems to represent a subgroup of obese people. Having deficits in emotion regulation in BED binge eating seems to be applied as a strategy to handle negative emotions. The assumption that binge eating or overeating is restoring mood is supported in both studies, which reported mood after overeating, without differences between OB and BED. 3.3. Experimental studies assessing emotions without manipulation We identified three studies investigating emotions as antecedents for binge eating in individuals with BED: two in adult samples (Geliebter et al., 2001; Nasser et al., 2004) and one in a child sample (Hartmann et al., 2012) (see Table 2). None of the studies applied induction of emotions; they only measured current emotions and depression. 3.3.1. Evidence for the trigger component of the emotion regulation model in BED Although adult BED samples had a significantly higher depression score, none of the studies comparing BED samples with

non-BED samples supported the trigger component of the emotion regulation model. A correlation between the tendency to act/react without thinking and the mood rating before food intake was found, which was interpreted as hint to binge eating in response to negative mood (Nasser et al., 2004). Yet, this interpretation was not reflected in the actual food intake. The study with a child sample did not prove that negative emotion influences food intake (Hartmann et al., 2012). 3.3.2. Evidence for the relief component of the emotion regulation model in BED In both adult studies, post meal mood was assessed, but data is not reported. A mood improvement after food intake across all groups was only found and reported in the child sample (Hartmann et al., 2012). 3.3.3. Conclusion Results of the studies measuring emotional trait or state do not support the trigger component of the emotion regulation model. None of the studies without active emotion manipulation could show emotional states to be relevant for subsequent eating in BED. Obviously the methodological lack of a manipulation of emotion seems to influence results and should be discussed as studies with emotion manipulation did show effects. The study with children revealed a mood improvement after food intake for all groups, affirming the results of studies with manipulation of emotions. 4. Discussion 4.1. Summary of the results In the present review, we tested the proposed emotion regulation model of binge eating in obese people with and without BED. We included experimental studies which investigated at least one of the two components of the proposed emotional regulation model in a laboratory setting. All in all, there is evidence for the trigger component that negative emotions trigger binge eating and overeating in adult BED and OB (BED?) samples. For OB adults, the data base is heterogeneous and too small to draw valid conclusions. For children with BED the emotion regulation model is lacking empirical evidence. The relief of negative emotions through binge eating (relief component) has hardly been investigated in experimental studies (n = 3), but results are supportive in all groups. The assumption of an emotion regulation model, consisting of a trigger component and a relief component thus seems to be plausible for BED and with less evidence for OB (BED?). To be more precise, negative emotions as a trigger for overeating seem to play a role for OB (BED?), but other variables condition the assumption of the trigger component. When involving other characteristics of the OB (BED?) sample in the data analysis such as trait anxiety (Schneider et al., 2010) or use of distraction as response strategy (Appelhans et al., 2011) negative emotions had an antecedent function for overeating. One could assume that the OB (BED?) subgroup with high negative trait anxiety or affect contains probably more individuals with BED. BED and OB (BED?) groups display higher food intake while experiencing negative emotions compared to relaxed states. This is relative to OB or NWC samples in which negative emotions do not indicate an effect on eating behaviour. Additionally, the data gathered suggests that BED individuals show less control over eating in negative emotional condition and report more negative mood on binge days than non-binge days (Schulz and Laessle, 2010). Interestingly, the manipulation of emotion seems to be significant for these results. The studies without emotion manipulation did not find any proof for the trigger component. A current non-manipulated emotional state does not seem to trigger

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binge eating/ overeating

BED OB (BED?)

& negative emotions

OB

binge eating/ overeating overeating

mood improvement ? mood improvement mood improvement

Fig. 4. Effects of negative emotions on binge eating and overeating in the different groups. BED, sample with binge eating disorder; OB (BED?), obese sample with missing information about a diagnosis of BED; OB, obese sample without binge eating disorder; — = evidence supporting emotion regulation model; --- = hints for evidence supporting emotion regulation model; ? = no statement possible.

binge eating and overeating per se in an experimental setting. A manipulation of (negative) emotion has to occur. Through means of manipulation, the negativity of emotion is ensured, although this intervention might induce individually deviant negative emotions and different intensities. In conclusion it can be stated that adult individuals with BED represent a distinct neurobiological phenotype compared to obese people without BED. The assumption that individuals with BED are characterised by difficulties in regulating negative emotions and thus react with binge eating has so far been supported with behavioural data ascertained by experimental studies. Data for the OB (BED?) sample points in the same direction regarding overeating. Assuming that at least some of the people in the OB (BED?) sample had a comorbid BED, other variables had to be taken into account (usage of certain emotion regulation strategy or the trait anxiety or trait negative affect in addition to the current present emotions) to show significant effects in this heterogeneous sample as well. In contrast, referring to two studies with an obese sample, negative emotional states do not seem to encourage obese people without BED to overeat or binge eat. Binge eating seems to demonstrate a specific symptom of BED that is triggered by negative emotions, whereas obese people without BED might exhibit other and maybe less dysfunctional emotion regulation strategies despite overeating. However, eating may have a relieving effect on mood in both groups: obese people with and without BED. For a visualisation of these findings, see Fig. 4. 4.2. Interpretation of the results In accordance with Heatherton and Wagner’s (2011) assumption mentioned above, results of this review suggest that in individuals with BED, negative emotions may impair processes of self-regulation. As a consequence, they engage in binge eating and overeating as other, more efficient strategies cannot be used, as it may be the case for obese individuals without BED. One plausible reason to explain states of negative emotion cause a self-regulation failure in people with BED, but not in OB or NWC, may be a lower emotion regulation capacity or the use of dysfunctional emotion regulation strategies. Several authors provide evidence that people with BED symptoms are less able to handle emotions or use more dysfunctional emotion regulation strategies like suppression (Bekker and Spoor, 2008; Czaja et al., 2009; Gilboa-Schechtman et al., 2006; Waller et al., 2003; Whiteside et al., 2007). Two studies in the present review indicate that higher negative state affect and distraction as response strategy are associated with higher food intake in negative emotional states as well. Interestingly, only studies experimentally inducing negative emotions (and manipulating state affect) could support the emotion regulation model; this suggests that trait affect is less relevant as a contributor to binge eating. Yet, trait affect might be a moderating factor. Considering the different emotion regulation theories introduced above, the results of our review affirm the escape theory, regarding the trigger component in BED samples and

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assumptions regarding the relief component in all groups. The assumption of an improvement of emotions in the affect regulation theory could be maintained for all groups (BED and OB) by results of experimental studies concerning the relief component, irrespective of an existing BED. Our results reviewing experimental studies are in line with results of Haedt-Matt and Keel (2011) from naturalistic studies regarding the trigger component. Furthermore, it proves that the trigger component only holds true for obese individuals with BED and not for obese people in general. Therefore, this review proved the legitimacy of treating individuals with BED as distinct group compared to obese people without BED. Moreover, we found evidence for the relief component in BED and OB samples in contrast to Haedt-Matt and Keel (2011). The number of studies is still rather small and the need for further investigation of the relief component (e.g. short term vs. long-term emotional relief) is evident. From a neurobiological point of view, hormonal influences and neurotransmitter circuits play a significant role in the explanation for why or how aversive emotional states can trigger binge eating and overeating. Cortisol secretion increases during stress and cortisol also regulates appetite and ingestion (Epel et al., 2001; Gluck, 2006). Two studies, one of them also included in the review, investigated cortisol, hunger, and the desire to binge in BED relative to non-BED women after exposure to stress. Results were contradictory, showing in one study (Gluck et al., 2004) a tendency for a higher cortisol level after a painful stressor in BED women as compared to non-BED women, whereas in the other study a blunted cortisol response was obtained (Rosenberg et al., 2013). In both studies the BED group showed a higher desire to binge after stress. Unfortunately, Gluck and colleagues (2004) did not survey mood, and stress was only investigated on a physiological but not a behavioural level. Also, serotonin plays a significant role in mediation of mood as well as in regulation of food intake (Sharma et al., 2013; Wallin and Rissanen, 1994). Several studies using functional magnetic resonance imaging provide evidence that the reward system of people with BED is more activated through food images than the reward system of overweight and normal-weight healthy control subjects (Schag et al., 2013). These results suggest that food seems to be very promising to compensate negative emotions in BED. Only one study integrated in the present review collected physiological data (Rosenberg et al., 2013). 4.3. Methodological limitations Methodological considerations are twofold: (1) regarding the way the review was conducted and (2) discussing the methodology of the studies included. First of all, as we only searched published studies, our results are at risk of publication bias, referring to a shift to significant but not insignificant results. We were, however, able to find studies with contradictory results, suggesting rather reliable data. Further on, we only integrated experimental studies, although there is a broad field of studies using ecological momentary assessment methods or similar observational measures. These studies have the advantage of a more realistic design, but results are strongly dependent on the compliance and – at least in most cases – the self-report of the participants. We decided to include only experimental studies due to reasons of homogeneity in the study design and the higher possibility to control potential confounding factors. Nevertheless, even in the experimental studies we found a large variety of methods. Therefore, we were very strict with our eligibility criteria and integrated only studies with the independent and dependent variables as primary focus. We excluded studies using pain as stressor (Gluck et al., 2004) or studies having other manipulations like food, mirror or body image exposure (cf. Jansen et al., 2003; Naumann et al., 2013;

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Svaldi et al., 2012). We decided that – even if this manipulation elicited negative mood – these stressors substantially differ, as they comprise physiological pain or shame when being confronted with their own body. Regarding the reviewed studies, the most important limitation is the heterogeneity of the studies. First, there are studies investigating state and trait mood, which substantially differ from studies actively manipulating emotions. Second, emotions are induced in very different ways, and mood induction procedures differ in their efficacy, advantages, and disadvantages (Gilet, 2008; Martin, 1990). Additionally, the variety of the investigated emotional states is tremendous. Specific negative emotions like anxiety, anger, and sadness, or unspecific negative emotional states like negative mood in general, as well as stress and remembering of the mood prior to the last binge, seem to be quite different conditions. Therefore, the range of negative emotional states in the different studies is broad and results are therefore rather unspecific. The measures used to collect state mood differed as well. Nevertheless, taking into account the different states, at least for BED, the majority of the results supported the triggering effect of negative emotions. Third, the operationalisation of the dependent variable (binge eating behaviour or overeating) varied across studies. More than the half of studies assessed the amount of food intake which in our opinion is merely an indicator for overeating. Loss of control as a second characteristic of binge eating was not consistently assessed. We tried to overcome this limitation by reporting precisely in Tables 1 and 2 whether both characteristics have been gathered or not. Even regarding the measurement of food intake several settings were used, ranging from multi item buffets (Goldschmidt et al., 2011; Telch and Agras, 1996), portions of individually rated food items up to chocolate pudding (Schulz and Laessle, 2012) and liquid test meals (Geliebter et al., 2001; Nasser et al., 2004). As individuals with BED have preferred binge food, the kind of food to measure binge eating and the setting appear to be relevant. Forth, unfortunately none of the studies, except for one study controlling for attention deficit hyperactivity disorder (Hartmann et al., 2012), assessed the occurrence of other psychiatric disorders or comorbidities with impulsive behaviour. Several study results suggest a high comorbidity between patients with BED and BPD (Friborg et al., 2014; Sansone and Sansone, 2013; Sansone et al., 2000; van Hanswijck de Jonge et al., 2003) and binge eating occurs also as a symptom in BPD (Lieb et al., 2004). Therefore, information about a comorbid BPD would strengthen the interpretation of the results. At least concerning the studies with children, different diagnostic criteria were used and the concept of loss of control eating, independent of the food amount eaten (Tanofsky-Kraff et al., 2008) was applied. Even if both have been proven as adequate for use with children (Hilbert and Czaja, 2009; Tanofsky-Kraff et al., 2009) one should keep in mind the differences concerning diagnostic criteria in adults.

Haedt-Matt and Keel (2011), who investigated the emotion regulation model in studies using EMA. In the three studies reporting mood after food intake – irrespective of the group – an improvement of mood was noted. However, up to now the relief component of the model, i.e. an improvement of mood through binge eating, is not sufficiently investigated and further exploration is obviously necessary. Especially a differentiation between short- and long-term mood improvements is proposed. The results of this study demand further research in this field, especially concerning seven major areas. (1) Several theories are discussed over why people with BED react with binge eating in the light of negative emotions and these theories have to be tested. (2) Integrating a neurobiological view seems unavoidable in order to find further evidence to come to a more specific emotion regulation model based on neurobiology. (3) The integration of ecological momentary assessment and controlled experimental settings would provide an optimal synthesis using the advantages of both study designs. (4) Emotions represent a broad concept; hence, the interpretation of effects has to take into account that investigating one emotional state restricts the generalisation on others. There are also first studies showing that positive emotions can also elicit overeating and binge eating (Bongers et al., 2013; Udo et al., 2013). (5) Comorbidites of BED and BPD should be considered. (6) It should be aimed at a proper differentiation between overeating and binge eating behaviour in studies with BED to increase validity. And (7): Further studies should be conducted, focusing on the behavioural level of emotion regulation as well as the implicit mechanisms. The identification of neurobiological and behavioural characteristics of BED could lead to a more detailed understanding of the entity and its subgroups, e.g. by differentiating between strategies or capacity of emotion regulation. Additionally, emotion regulation capacity in BED should be investigated in relation with other concepts (which already has happened in escape theory regarding self-awareness). A very promising concept to be included seems to be impulsivity, which is proven to be a relevant distinctive factor between obese people with and without BED (Schag et al., 2013). We vaguely hypothesise that impulsivity could possibly offer one explanation for the cause of binge eating triggered by negative emotions in spite of its lack of long-term-relief (referring to the diagnostic criterion of distress). On the basis of an emotion regulation deficit, individuals with BED do not have the capacity to handle emotions and might react with the dysfunctional and ineffective emotion regulation strategy binge eating because of their high level of impulsivity. Therefore, the integration of several concepts, precisely emotion regulation and impulsivity as well as various methods (neurobiological, naturalistic and experimental methods) will help to further contribute to the development of innovative therapeutic approaches, including psychotherapy as well as supportive pharmacology.

4.4. Conclusion and further directions

Acknowledgements

Although the two components of the emotion regulation model are often used in the discussion of aetiology and maintenance of binge eating and overeating, evidence from experimental studies supporting this association is relatively small and heterogeneous. Nevertheless, regarding adult BED samples, evidence for the model is rather consistent in the majority of studies in which moodinduction was used supporting the trigger component of the emotion regulation model. Even for OB (BED?) samples, there is some support for the emotion regulation model. Therefore, negative emotions evidently are important in eliciting binge eating. Interestingly, these results are in line with the meta-analysis by

EJL is supported by the “Studienstiftung des deutschen Volkes” (German National Academic Foundation). KEG receives a grant by the Ministry of Science Baden-Württemberg and the European Social Fund. TD was partly supported by the LEAD graduate school [GSC1028], a project of the Excellence Initiative of the German federal and state governments.

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