A Systematic Review of Moderators of the Association between Dietary Restraint and Binge Eating

: Obesity interventions typically involve some form of dietary restraint (i


Introduction
Obesity is associated with a constellation of mental and physical health problems [1][2][3] as well as an increased mortality risk [4].Therefore, efficacious interventions and preventions for reducing and managing weight and preventing excess weight gain are imperative.The primary components of interventions and preventions for obesity include dietary restraint-i.e., attempting to limit one's food intake, particularly consumption of highly palatable foods and fast food [5][6][7].
While some literature has demonstrated that dietary restraint is related to an increased risk of binge eating symptoms [8,9] and may not lead to lasting weight loss [10,11], other evidence suggests restraint is not universally associated with such outcomes across the literature [5,[12][13][14][15][16][17][18][19][20][21][22][23].That is, studies have shown that many individuals who engage in dietary restraint are successful in regulating their weight without experiencing binge eating symptoms [14][15][16][17].However, given that interventions increasing dietary restraint may lead to binge eating in some individuals, it is important to increase our understanding of factors that may strengthen or weaken the restraint-binge eating association, also known as moderators.
The relationship between dietary restraint and binge eating is complex, and factors such as biological and psychological vulnerabilities may play a role in the development of binge eating among individuals who engage in dietary restraint.There has been little theoretical work proposing moderators of the association between restraint and binge eating.Yet, of note, researchers have proposed a model in which negative affective states strengthen the association between restraint and binge eating [18].This model proposes that when individuals are restraining their dietary intake but experience negative emotions, they are more likely to engage in binge eating.Similarly, the resource depletion model suggests that engaging in restraint is cognitively taxing and diminishes self-control over time, thereby predisposing individuals to disinhibited eating in the face of momentary factors such as negative affect [19].However, beyond this, little theoretical work has described moderators of the relationships between dietary restraint and binge eating.
This review aimed to systematically evaluate the literature on moderators of dietary restraint and binge eating.Understanding moderators that influence the relationships between dietary restraint and binge eating can provide valuable insights into possible theoretical models of this association.Overall, this systematic review has implications for increasing the efficacy of obesity treatment while reducing development of binge eating and full-syndrome eating disorders.Further, the results of this review will increase our understanding of individual and contextual factors that may be associated with difficulty engaging in adaptive dietary restraint.

Method
Literature searches in the PsycInfo and PubMed databases were conducted across all dates through May 2023 using the following terms: "restraint" OR "restrict" AND binge* OR bulim* AND "moderator" OR "interaction".Inclusion criteria were (1) empirical study, (2) binge eating as a dependent measure, and (3) examination of at least one moderator of dietary restraint or restriction.Exclusion criteria were (1) treatment study and (2) non-human participants.Articles were each screened for inclusion by two authors.Abstracts were first screened for inclusion, and abstracts that clearly did not meet inclusion criteria were excluded.Studies that possibly met inclusion criteria were further screened for confirmation.References of articles meeting criteria were searched for additional papers that may meet criteria.See Figure 1 for the flow diagram of article selection using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [20].We identified 16 articles with 15 samples for inclusion in the review.Two authors extracted data; discrepancies were reviewed and discussed.Data were summarized and are presented in Table 1.Extracted data include sample size, sample characteristics, sample recruited, dietary restraint/restriction measure, moderator(s), binge eating measure, and moderation findings.There was a three-way interaction between restraint, attentional impulsivity, and negative affect, such that participants with elevated levels of all three factors reported the greatest levels of binge eating.There were no interactions with motor or nonplanning impulsivity.There was an interaction between baseline restraint and daily anger, such that those with low restraint had a stronger relationship between daily anger and binge eating.There were no two-way interactions between baseline restraint and daily anxiety, daily positive affect, or daily depressive affect.
No significant three-way interactions were found beween gender, affect, and restraint.Eating episodes in which participants reported a "3" on 5-point scale for overeating and loss of control items There was a three-way interaction between momentary restraint, negative affect, and eating expectancies, such that high levels of momentary restraint were related to binge eating only when both momentary negative affect and eating expectancies were high; low momentary restraint was generally associated with higher odds of binge eating, particularly when momentary negative affect and eating expectancies were higher.There was a three-way interaction between restraint, daily stress, and life event stress, such that for individuals with high life event stress, restraint strengthens the association between daily life stress and binge eating.
Note.BMI = body mass index.

Descriptive Findings
The There was a great deal of variability in the measure of restraint used, with most studies using the Eating Disorder Examination Questionnaire (k = 5), Restraint Scale (k = 3), a combined or study-developed scale (k = 3), Dutch Eating Behavior Questionnaire (k = 2), or Dietary Intent Scale (k = 2); the following scales were used in single studies: Three-Factor Eating Questionnaire Eating Inventory, Cognitive Restraint Scale, and Eating Pathology Symptoms Inventory.Similarly, there was variability for the binge eating measures, with most studies using the Eating Disorder Examination Questionnaire (k = 3), Revised Bulimia Test (k = 3), Minnesota Eating Behavior Scale (k 3), or a combined or study-developed scale (k = 3); the following scales were used in single studies: Binge Scale, Binge Eating Scale, Eating Disorder Inventory, and Eating Pathology Symptoms Inventory.Two studies were intensive longitudinal studies using daily or momentary measures of restraint and binge eating.No studies examined clinical samples of individuals diagnosed with eating disorders.Affect and cognitive variables were most commonly examined as moderators, with 44% of studies examining affective factors and 44% examining cognitive factors.

Primary Findings
Demographic factors.Two studies (one study of college students and one of adolescents) examined gender as a moderator of the relationship between dietary restraint and binge eating and found no moderation effects [28,33].
Genetic factors.In a sample of emerging adult female twins, dietary restraint did not moderate the shared environmental factors for binge eating, but genetic and non-shared environmental factors for binge eating increased at elevated levels of dietary restraint [31].
Body image.Two studies examined body image variables (i.e., body shame and body dissatisfaction) as moderators of the association between dietary restraint and binge eating, and both studies found no significant interactions [21,27].The samples in the two studies were different with one being female college students and the other being adults who used tobacco products.
Affect, stress, and coping.Three studies examined negative urgency (i.e., tendency to be impulsive when experiencing negative affect) as a moderator of the association between dietary restraint and binge eating, with only one finding a significant interaction.In a sample of female college students, Emery and colleagues [22] found that only among those who reported binge eating, controlling for baseline binge eating, higher dietary restraint was related to increased binge eating frequency three months later for those with low and mean negative urgency; those with high negative urgency had increased binge eating frequency regardless of restraint level.Yet, two other studies using cross-sectional data from college student females and female twins found no moderation effects of negative urgency [32,34].
Chervinko [21] found that there were no interactions between restraint and affect intensity, emotion-focused coping, and avoidance-focused coping in relation to binge eating in female college students.However, Stice and colleagues [18] reported that there were cross-sectional interactions between dietary restraint measures and negative affect in high school adolescents, such that higher negative affect strengthened the positive association between dietary restraint and binge eating in both females and males.However, there were no interactions longitudinally.
Another study of female college students found a significant interaction between restraint and biphasic symptoms (i.e., fluctuations from high to low mood/energy) in relation to binge eating, such that biphasic symptoms strengthened the association between restraint and higher binge eating [23].One study of female college students examined the three-way interaction between restraint, daily stress, and life event stress; for individuals with high life event stress, restraint strengthened the association between daily life stress and binge eating [35].
Two studies used daily diary methodology to study the associations between daily affect and binge eating in female college students.Nadel [28] reported an interaction between baseline restraint and daily anger, such that those with low restraint had a stronger relationship between daily anger and binge eating.However, both studies found that daily negative affect did not moderate the relationship between daily restraint and binge eating [25,28]; also, Nadel [28] reported no moderation effect for daily positive affect or anxiety and binge eating.

Cognitive Factors
In a mixed sample of female college students and female adults from the community, there was a significant interaction between flexible restraint (i.e., a less strict approach to restraint in which no foods are forbidden) and eating self-efficacy in relation to binge eating [24].The pattern of findings for the interaction suggested that having moderate or poor eating self-efficacy was associated with the highest levels of binge eating regardless of flexible restraint.However, elevated flexible restraint increased binge eating for individuals with high eating self-efficacy, but binge eating levels were still lower than those with moderate and low eating self-efficacy.There was no interaction between eating selfefficacy and rigid restraint (i.e., a highly strict form of restraint with many food rules) and binge eating.

Social Factors
In a daily diary study, Mason and colleagues [25] found that daily perceived social isolation did not moderate the relationship between daily restraint and binge eating in female college students.

Affect and Cognitive Factor Interactions
Among female college students, there was a three-way interaction between restraint, attentional impulsivity, and negative affect, such that the high levels of all three factors were associated with the greatest levels of binge eating [26].A separate study of young and middle-aged adults with obesity reported a three-way interaction between momentary, within-subject restraint, negative affect, and mood improvement eating expectancies, such that high levels of momentary restraint were related to binge eating only when both momentary negative affect and mood improvement eating expectancies were high; low momentary restraint was generally associated with higher odds of binge eating, particularly when momentary negative affect and eating expectancies were higher [29].

Genetic and Cognitive Factor Interactions
There were no two-or three-way interactions between dietary restraint, impulsivity, and serotonin genes in relation to binge eating among female college students [30].

Discussion
This systematic review examined the literature on moderators of the association between dietary restraint and binge eating.The existing literature was highly heterogeneous and inconsistent across the studies.The studies varied across sample composition, methodology (e.g., different measures of restraint and binge eating), constructs examined as moderators, and number of moderators.Overall, the findings were nuanced with little consistent evidence for any one candidate moderator as an important moderator of the association between dietary restraint and binge eating.
Most studies had large samples, suggesting adequate power to test for interactions, although a few studies may have been underpowered to detect interaction effects [36].Similarly to most research on eating behaviors, the samples were primarily heterosexual White female college students, which limits the diversity and generalizability of the findings to other groups.Only a minority of the studies reported BMI, with study means ranging from falling in the healthy category to the obesity category.The measurement of body composition is important to clarify how effects may differ as a function of weight status.
The measures of dietary restraint differed across the studies, which may be of concern given the differences in conceptualization and foci of varying measures of restraint (e.g., flexible vs. rigid restraint).For example, the Eating Disorder Examination Questionnaire Restraint subscale focuses on rigid forms of restraint such as strict food rules, limiting to influence shape/weight, and food exclusion [37], whereas the Three-Factor Eating Questionnaire Cognitive Restraint subscale and Dutch Eating Behavior Questionnaire focus primarily on portion control and eating less [38,39].Due to the varying conceptualizations of dietary restraint [40,41], different forms of restraint may dissimilarly interact with other variables to predict binge eating, necessitating improved and rigorous assessment of dietary restraint in future research.Recently, Polivy and colleagues [40] similarly concluded the need for carefully defining dietary restraint constructs and research questions to ensure the accurate measurement of dietary restraint and to be able to understand how different restraint constructs are associated with outcomes of interest.Similarly, the measures of binge eating varied across studies.Binge eating measures differ in examining the frequency of episodes vs. the severity of symptoms, as well as focusing on behavioral symptoms (e.g., overeating, loss of control) and/or associated psychological features (e.g., guilt, shame).The choice of measures may affect the findings and should be chosen in alignment with the research question and theoretical framework.
There was mixed evidence for affective factors alone as moderators of the association between dietary restraint and binge eating, and there were differences across affective constructs and study design.One early cross-sectional study showed that negative affect intensity strengthened the association of dietary restraint with binge eating in adolescents [18].This fits with models suggesting that dietary restraint and negative affect have a multiplicative effect in depleting self-regulatory resources, and, thus, increasing binge eating risk [19].Yet, this effect did not emerge in other studies that were reviewed, particularly ones using more rigorous intensive longitudinal methodology [25,28], and the findings varied somewhat depending on the affective constructs being studied (e.g., general negative affect, anger, stress).Future research would be strengthened by the examination of different affective constructs as moderators as well as by the development of theoretical models informing the choice of the affective constructs being studied as moderators.
However, a few studies found that the interplay between cognitive and affective factors with dietary restraint may be most strongly related to binge eating.For instance, Mason and colleagues [26] showed that female college students with elevated attentional impulsivity, negative affect, and dietary restraint engaged in the greatest binge eating.In addition, Pearson and colleagues [29] showed that the combination of elevated momentary restraint, negative affect, and mood improvement eating expectancies predicted the greatest probability of a subsequent binge eating episode in daily life.Taken together, negative affect may impact restraint-binge eating relationships only in combination with other cognitive factors.Therefore, there appears to be an important interactive role of cognitive and affective processes in interrupting the ability to engage in appropriate dietary restraint.This is consistent with recent calls for more research integrating cognitive and affective constructs into eating disorder models [42].
Interestingly, body image concerns did not moderate the association of dietary restraint and binge eating.Since individuals with body image concerns are at strong risk of binge eating [43,44], it might be expected that dietary restraint could be a precipitating factor for binge eating among those with this high vulnerability.For example, individuals with body image concerns have elevated attentional bias to body-and food-related cues [45], which could increase the probability of binge eating when engaging in restraint.Given the null findings for body image as a moderator, it will be important to examine other models of how body image may impact the restraint and binge eating association (e.g., including influence of attention biases).Furthermore, body image is a multifaceted construct and so other sub-constructs of body image should be explored as moderators in future studies (e.g., overvaluation of shape and weight).
There was a significant interaction between flexible restraint (i.e., a less strict approach to restraint in which no foods are forbidden) and eating self-efficacy in relation to binge eating such that those with strong self-efficacy who reported high flexible restraint increased in binge eating, although these individuals still engaged in less binge eating than those with moderate and poor eating self-efficacy [24].There was no interaction between eating self-efficacy and rigid restraint (i.e., a highly strict form of restraint with many food rules) in relation to binge eating.These results show complexities in the association between cognitive factors, restraint, and binge eating, in that individuals with positive eating-related traits may increase binge eating to a small extent in response to restraint.
Social and biological factors were rarely tested as moderators of the association between dietary restraint and binge eating.The current review found no evidence of social factors as moderators, although only one study looked at a social factor (i.e., daily perceived social isolation).A study of female twins found that dietary restraint moderated the genetic risk of binge eating, suggesting the need for future work on specific biological mechanisms that may increase binge eating in individuals engaging in restraint [31].However, another study reported null interactions between serotonin genes and restraint in relation to binge eating, and, thus, serotonin genes may not be an important candidate genetic moderator of restraint and binge eating [30].The small number of studies examining social and biological factors as moderators precludes any conclusions on their roles as moderators of dietary restraint and binge eating.Instead, the current findings of our review indicate much more research is needed in this area across an array of social and biological factors.
Gender did not moderate the relationships between dietary restraint and binge eating, suggesting that males and females may have similar associations between dietary restraint and binge eating.It is possible that sex-differentiated risk factors (e.g., sexism, sexual harassment, drive for muscularity) may explain how dietary restraint is associated with binge eating for males and females.Other demographic characteristics were not studied as moderators, yet it is possible that the association between restraint and binge eating may differ based on other characteristics, such as race, ethnicity, age, income, sexual and gender identity, and weight status.Furthermore, there may be unique moderators of the association between restraint and binge eating for demographic subgroups, which should be examined in future research.
This systematic review had several limitations to note, which are primarily shortcomings of the available literature.Most of the studies reviewed were cross-sectional, so directionality and causality cannot be concretely determined.Most of the studies did not examine differences based on demographic factors, which may be due to limited sample diversity.The measures used to assess dietary restraint, moderators, and binge eating were extremely varied across the studies, making it difficult to develop firm conclusions, particularly regarding any specific aspect of dietary restraint or moderators.Given the high variability in the constructs studied, a meta-analysis of studies could not be conducted.
In sum, much more research is needed to understand the complex interactions of trait and state moderators of the association between dietary restraint and binge eating.There are different conceptualizations of restraint (e.g., flexible vs. rigid).Further, eating disorderrelated restraint measures (e.g., Eating Disorder Examination Questionnaire) measure key restrictive eating behaviors (e.g., fasting, strict food rules), whereas other restraint measures (e.g., Three-Factor Eating Questionnaire) focus on approaches like limiting and portion control.This necessitates careful consideration of restraint measures and/or use of multiple measures.In addition, it will be important to study moderation by weight-related factors (i.e., weight status, weight suppression, weight-related treatment), which may impact the association between dietary restraint and binge eating.More diverse methodological approaches using longitudinal, experimental, and/or intensive longitudinal designs will help contribute to a more comprehensive understanding of moderators of the association between dietary restraint and binge eating.All the studies examined in our review used traditional survey measures, except for two that used daily diaries or ecological momentary assessment.In particular, ecological momentary assessment can help identify in which people dietary restraint predicts subsequent binge eating and in what internal and external contexts dietary restraint predicts binge eating.Ecological momentary assessment can also reduce the impact of self-report biases inherent in questionnaires requiring retrospective reporting over longer periods of time.Ultimately, expanding this body of research will help to understand whether, how, and for whom adaptive and maladaptive forms of restraint potentiate binge eating behavior.

Figure 1 .Figure 1 .
Figure 1.PRISMA diagram of study selection and review process.

Table 1 .
Description of studies included in the systematic review.