A Set of Meta-Analytic Studies on the Factors Associated with Disordered Eating
E Vince, I Walker
Keywords
anorexia nervosa, bulimia nervosa, eating disorders, meta analysis
Citation
E Vince, I Walker. A Set of Meta-Analytic Studies on the Factors Associated with Disordered Eating. The Internet Journal of Mental Health. 2007 Volume 5 Number 1.
Abstract
The work was conducted at the Department of Psychology, University of Bath, UK
Introduction
In the quest to understand the causes and development of eating disorders, many risk factors and associates have been proposed and investigated, and the research corpus has become incredibly large. A small proportion of this research has been longitudinal/prospective in design and so has firmly established certain factors (e.g., perfectionism, as contributory causes of eating disorders). These longitudinal studies have recently been subjected to a comprehensive meta-analysis ( 1 ) which provided perspective on current knowledge about eating disorder causal factors. A limitation to this meta-analysis, however, was the exclusion of studies with correlational and retrospective data. These data still have the potential to inform the field if treated appropriately. Specifically, although research on associates cannot reliably establish causes and effects, it can still inform us about factors associated with eating behaviours, and so remains of value to the researcher interested in eating disorders, especially given the large number of participants who have taken part in this research.
To dismiss these studies because their methodology does not allow conclusive statements about the aetiology of eating disorders, is premature and unnecessary. However, at the same time we feel a point has been reached where correlational research is in such abundance that there is a need to consolidate it to reveal the state of our knowledge about associates of eating disorders as a way of guiding future research efforts. This is particularly pressing given that the meta-analysis by Stice ( 1 ) did not cover a range of potential associate factors suggesting they have not yet been investigated via longitudinal methods (e.g., autonomy, exercise, and obsessive compulsive disorder (OCD)). Factors that seem most promising from this objective integration of the literature might then be studied using other and more powerful methods to investigate more accurately the issue of cause and effect.
Method
There are various ways to synthesize the data provided by reviewing a body of literature, and perhaps the most heralded is to use meta-analytic methods. To provide the broadest possible review of how eating behaviours and attitudes are related to the various associate factors under investigation, the primary research question was “which factors are associated with the presence of disturbed eating (defined as any disturbance, clinical or sub-clinical, measured with a clinical diagnosis or, in non-clinical populations, with a scale such as the Eating Disorder Inventory)?” Secondary research questions focused the review on more specific diagnoses: “which factors are associated with anorexia nervosa?” and “which factors are associated with bulimia nervosa?” where studies were only included if participants had received a clinical diagnosis. We maintained this classic diagnostic line of distinguishing between anorexia nervosa and bulimia nervosa as there is little data, especially from the older studies, on factors associated with the sub-types of these disorders, or the presence of specific behaviours such as purging.
Several
Search strategy
Articles that met the inclusion criteria outlined above were identified as follows: 1) a computer search of PsycINFO, BIDS, Ingenta, ScienceDirect (medicine, psychology, and social science categories), and Web of Science electronic publication databases was conducted for the relevant years, using the search terms “eating disorders” “anorexia nervosa”, “bulimia nervosa” “risk factors” and where appropriate excluding “prospective” and “longitudinal” with the resultant studies assessed for relevance by the researcher and categorised under 12 headings (e.g., “abuse”, “exercise”, and “race”); 2) each category of factor was then subjected to a further search utilising category-specific search terms (e.g., search terms relating to the abuse category included “abuse”, “sex abuse”, “physical abuse”, “emotional abuse”, and “childhood sexual abuse”); 3) the References sections of all the articles were examined; 4) all articles in the authors' possession were checked for relevance and their References sections also examined; 5) in attempting to locate articles, papers were requested from authors, which often led them to send other articles that they had written.
Of the several thousand articles retrieved through this strategy, 700 were deemed appropriate for further scrutiny, of which 232 were included in the review. This demonstrates just how large the field of eating disorder research has become, and in particular, how much correlational data has been generated. We feel this amply justifies this review, as synthesizing this large body of research is likely the most appropriate way to derive concrete conclusions from such a vast volume of data.
Procedure
Data were extracted by the principal author (EV), in line with the coding sheet developed for this review. In the event of uncertainty regarding the data, the second author independently extracted the data and results were compared. Any inconsistencies were discussed until an agreement was reached. As long as the data met the criteria outlined above, the study was included.
The meta-analyses were conducted using Schwarzer's ( 4 ) freely available software
When the data allowed, further analyses were conducted to look at the relationships between each associate factor and the two clinical forms of eating disorder, anorexia nervosa (AN) and bulimia nervosa (BN). In some cases it was also appropriate to sub-divide the overall factor – for example, in the substance use analysis, separate analyses for the different types of substance use were conducted, first with general eating disturbance, and then with anorexia and bulimia where possible, providing a more detailed picture of any associations.
Effect sizes
As the emphasis of this paper is the co-occurrence of associate factors and eating disorders,
Results
For each meta-analysis, number of studies (
Due to the retrospective nature of the factors in this series of meta-analyses, we have been carefully neutral about using the term “associate factors” rather than “risk factors”. Although it is the assumption of much work to date that many of the factors are probably causes of the eating disorders, many of these risk factors are also plausibly consequences of the eating disorder rather than antecedents. With this meta-analysis providing clear evidence of which factors have definite relationships with eating disorders, it is for future research to further explore which are causes and which are consequences of the eating problems.
The meta-statistics for each analysis can be found in Table 1 below, whereas the details of the studies included in the analysis can be found in Appendix 1.
Figure 1
Abuse
Based on our analysis, women who have suffered abuse are more likely to display eating disturbances. Abuse, in general, was related to eating disturbance with a small effect size (
Sexuality
While there was a small association (
Self-harm
Based on our analyses, women with disturbed eating behaviour exhibited a higher level of self-harm behaviours than do non-eating disturbed women. To highlight, disturbed eating showed a modest relationship (
Relationship with Primary Care Giver
Two main concepts were combined and investigated, both assessing the quality of the fundamental relationship with the primary caregiver: attachment style and perceived parental bonding. The overall analysis found a moderate association (
Family environment
Analyses of family environment were mixed in result, but overall indicate that women displaying disordered eating, especially AN and BN, report more family dysfunction than control groups. There was a small association (
Stress
Stress was not associated with disturbed eating (
Irrational cognitions
An overall analysis found an association (
Overall, the analyses demonstrated that women with disturbed eating, and AN and BN specifically, show higher levels of irrational cognitions than do women with no eating problems, although there is substantial variance in the strength of this finding. When cognitions are assessed by the DAS, the relationship appears more stable and robust than when measured with other relevant measures. However, we suggest more work is needed to further explore possible reasons for the range of effect sizes.
Exercise
Exercise level showed a small association with disturbed eating (
Substance use
Disturbed eating was associated with overall substance use level (
Socio-cultural pressures
As socio-cultural pressure is a multi-faceted concept, it was broken down into three areas: internalisation of the thin-ideal, the influence of media, and peer and family teasing/pressure. No association was found between internalisation and disturbed eating (
Race
There was no association between race and the presence of disturbed eating behaviours or attitudes in this very large analysis (
Individual differences
As such a large number of individual difference factors have been linked to eating disorders in the literature, we divided our analyses into 12 sub-studies.
Discussion
The purpose of this review was to consolidate, using meta-analyses, the vast body of retrospective eating disorder associate-factor literature published between 1987 and 2003 to identify which of the many factors linked with eating disorders show a true association with general problematic eating and the clinical forms of AN and BN.
In total, 74 meta-analyses (47 main analyses and 27 follow-ups) were conducted on 12 main areas, comprising 232 published studies involving 87,878 participants. Only 14 of all the analyses (19%) resulted in clear associations (see Table 2 for a descriptive summary of the results), highlighting the range of study and participant features that vary across the research. A further 38 analyses (51%) found agreement on the direction of effects, differing only on the magnitude of the association.
In keeping with a continuity perspective (e.g., 26 , 27 ), it was expected that the analyses investigating the specific clinical eating disorders would show larger associations with each factor than general disturbed eating. This was found to be true in many cases: in seven analyses at least one of the clinical diagnoses showed higher associations and in six analyses both diagnoses had stronger associations than did general disturbed eating. These findings support those of Stice ( 1 ), who reported that studies predicting general disordered eating had smaller effect sizes than studies focused on specific eating disorders. Using the results in combination, it can be speculated that these levels would be higher if analyses comparing clinical AN and BN with controls had been possible for each analysis.
As expected from the literature, the results also showed that although the diagnoses of AN and BN do share common relationships with factors, they also demonstrated disorder-specific relationships with associates. For example, both AN and BN had strong links with cognitions, anxiety and depression, but BN additionally showed a strong relationship with poor caregiver relationships, and AN with temperament and low self-esteem. Clinically this is important as it highlights both the overlapping and unique aspects of the disorders allowing a profile of each disorder to be constructed which in turn can lead to disorder specific strategies to be developed in terms of both treatment and prevention. Additionally, it can inform further research on the interplay of the specific factors to determine the weight each individual factor contributes to the specific diagnosis when in combination with all the other factors. Again this would be valuable to both treatment and prevention efforts.
Figure 2
The results from this series of meta-analytic studies justify the decision to extend the meta-analysis of Stice ( 1 ) demonstrating that the vast amount of research on eating disorder associates can make a very useful contribution to the body of knowledge on this topic. The available literature resulted in the two studies covering, to a degree, different factors; some of the factors investigated in this series of studies simply were not covered by the Stice analyses, presumably due to the lack of prospective research available. Therefore although this review consolidates some of the findings from the Stice review ( 1 ), reviewing the retrospective research also adds information to the general discussion and highlights areas where further longitudinal work would be very useful.
This series of meta-analytic studies resulted in a number of important findings. The first is that race has no association with disordered eating, that is being Caucasian carries no more risk of problematic eating than being of any other ethnic origin. As this analysis included data from over 31,000 women, our conclusion adds substantial weight to the long-standing debate in this area, and suggests that in detecting eating disorders, clinicians should not assume Caucasians are more at risk. It must be noted, however, that the analyses presented were intentionally concerned only with race: that is, colour of skin, with no account being made of culture or country of origin, which could be addressed in future work. A further two striking findings were the substantial relationships between all forms of eating disorder with anxiety and depression. One can give extra weight and confidence for these findings as they included exceptionally large sample sizes. However, the results still do not answer the question of whether the eating disorders are variants of these two co-morbid disorders, or are separate entities that share commonalties.
A surprising finding was the mixed results of the self-esteem analyses, which showed a wholly inconclusive relationship with general disordered eating, no relationship with BN, but a strong varied association with AN. An obvious link between low self-esteem and disturbed eating in general has been presumed based on the assumption that the individual must feel their body is inadequate in order to desire to change it so desperately ( 28 ), and feeling inadequate goes hand-in-hand with low self-esteem. However, based on our analyses, this relationship may only apply in the case of AN. It is likely the surprising result is due to methodological differences between the studies investigating this concept – for example, whether self-esteem was treated as a uni- or multi-dimensional concept. It is plausible that self-esteem
The socio-cultural pressure analyses also provided interesting results. Despite the stressed importance of media influence and internalisation of the thin-ideal in the literature and in popular media, they surprisingly showed little association with disordered eating. However, this could be due to desensitisation caused by overexposure to the thin-ideal and/or a clearer understanding that many magazine pictures are altered. Additionally, when assessment measure was taken into account, it appeared that assessing dissatisfaction with body-parts ( 19 ) rather than overall body dissatisfaction lowered the overall effect. The media tend to promote an overall desirable body shape, rather than focusing on separate parts of the body, and so it appears that studies focusing on the latter may be missing the important aspects of this concept.
Our analyses demonstrated a strong association between disordered eating and weight- and shape-related teasing. This is an interesting finding as it suggests that weight/shape teasing, which in varying levels may feature commonly in the everyday lives of some adolescent girls, may have lasting implications and lead to a general level of disturbed eating.
The inductive moderator searches conducted when effect sizes showed heterogeneity revealed some interesting insights. In the family environment analysis it was suggested that as one gets older, family dysfunction no longer places one at an increased risk of eating disturbance. This may be due to no longer living with the family unit, or that memory of poor family environment diminishes with age. Similarly, in the sexuality analysis it was shown that age and culture may explain the variance in effect sizes. The data suggested that Australian lesbian women may perceive less weight and shape pressures in comparison to American lesbian women, and additionally, lesbian women overall may become less concerned with weight and shape as they get older to a greater extent than do heterosexual women overall.
The medium-strength relationship between disturbed eating and self-harm behaviours was found to be affected by the assessment measures used. It appears that when a measure specific for self harm is used the resultant effect is smaller, suggesting that non-specific measures may be tapping into other phenomena associated with disturbed eating, and therefore to gain the true effect, a measure specifically designed for the purpose should be used. In the substance use analysis, associations were detected between disturbed eating and smoking and illegal drug use, but not between disturbed eating and alcohol use. This could be due to a perception that alcohol is a weight-gaining substance, whereas cigarettes and some illegal drugs are perceived to have a weight-reducing effect. Finally, in the exercise analysis it was found that studies reporting a negative effect size predominately assessed eating-disorder prevalence in athletes versus non-athletes, whereas the studies with positive effect sizes assessed exercise in eating disordered versus non-disordered women. Although not wholly clear-cut due to some reminaing heterogentity in the analysis, this suggests that women with disordered eating appear to exercise more than other women, but athletes are no more likely to have an eating disorder than non-athlete controls.
Meta-analysis has its limitations. We are sensitive that the findings reported in this paper are dependent on the methods and decisions we applied (i.e., our decisions to use Fishers
A second limitation of the analyses is connected with the multi-dimensional nature of many of the measures used in the aggregated studies: for example, the restraint scale ( 29 ) measures dieting behaviour, binge eating and weight fluctuation. The decision in this analysis to average scores across all sub-scales to produce one effect size for each study means that how the specific dimensions vary in their contribution to the effects found was not considered. Stice ( 1 ) suggests that for a clearer interpretation of study findings, measures that assess concepts in a unitary fashion are needed rather than multidimensional measures. Additionally, there are potential problems with assuming a consistent definition for measures such as body dissatisfaction. Studies use and assess this outcome in different ways, and where one study may assess BD as a behavioural measure, another may assess it as an attitude. While this is a limitation of this meta-analysis, it is also a limitation of the research collated, as the majority of the studies did not clearly define such constructs. Further consolidation of how concepts are defined and measured in the eating disorder field is needed to provide analytic clarity to study findings.
A third limitation of the study is that data was abstracted from all relevant studies with no methodological assessment of the studies in which the data came from. This approach was taken as it was felt important to get the broadest summary of the non-longitudinal data as possible. The main study characteristics were coded using the developed coding scheme in the hope that if methodological heterogeneity existed between the studies it would have been detected by the inductive moderator searchers performed for each analysis. However, in a number of the analyses heterogeneity could not be explained by the characteristics coded for. To strengthen our observations of associations, in retrospect it would have been preferable to assess the included studies for methodological quality, especially in terms of control of confounders; the likely cause of the varied effect sizes.
We must mention that the main reason studies were excluded from these analyses was due to a lack of appropriate statistics: 33% of the excluded studies (150 studies) were left out for this reason. There was a surprising lack of inferential statistics in many of the viewed studies, and even commonplace descriptive statistics, such as means and standard deviations, were often not reported; many studies gave only percentages, which were unable to be used for the particular effect size approach used in our meta-analysis. We found the standard of reporting in the literature lacking and hope our experience of examining the whole research corpus serves as a reminder to researchers in this field that quantitative data can be used beyond the particular study, and so should always be reported as fully as possible.
As a final point, the results of this meta-analysis are mainly based on retrospective methods of data collection, which are open to respondent bias, and also highlight associations or relationships between eating disturbance and various factors, and do not give the ability to derive interpretations regarding cause and effect. Many of the factors investigated could just as plausibly be consequences of the disorder, rather than antecedents, and so it cannot be concluded that these relationships are evidence that the factor precedes the onset of the disorder. The very nature of this review in taking retrospective, correlational studies for analysis automatically limits the review findings to the same correlational, retrospective level. To confirm, for example, that people with BN experience more stress than healthy women rather than just report/perceive more, or to allow causality to be implied, further prospective, longitudinal work must be conducted. We hope our analysis will be valuable for guiding such efforts.
Conclusions
Based on the findings from this series of meta-analytic studies it is possible to sketch a profile of women with disturbed eating, AN and BN. Women with disordered eating are: more likely than controls to have experienced abuse, especially sexual abuse; have a dysfunctional attachment, and a tendency to come from a more dysfunctional family background; to have higher levels of distorted/irrational cognitions; to have experienced weight- or shape-related teasing; to more likely utilise maladaptive coping strategies and immature defences, to smoke and take illegal drugs, but be no more likely to use alcohol; are perfectionists who show higher levels of anger and hostility, shame and guilt, neuroticism, and have anxious, depressive, borderline, and obsessive-compulsive traits. However, women with disordered eating are not more likely to: be of any given sexuality; self-harm; have higher levels of stress; exercise; or be more, or less, extroverted in their behaviour; be more likely to internalise norms, or differ in temperament. In addition to this overall profile, women with AN and BN are more likely than women with general disordered eating to have dysfunctional attachments, to be depressed and anxious, and to have higher levels of obsessive compulsive disorders; they also show higher levels of irrational cognitions, anger and hostility. Further, women with BN are more likely than women with disturbed eating and AN to come from families with dysfunctional backgrounds, be stressed and show reduced autonomy, whereas women with AN are more likely than women with disturbed eating and BN to have high levels of general personality disorders, and low self-esteem.
With regard to direction for future longitudinal and experimental research, our suggestions fall into three categories. First, the results of the race, and temperament analyses suggest that no more research, either longitudinal or correlational, is needed, as these are simply not associated with eating pathology. Second, certain factors should receive more cross-sectional research, or further investigation of the association moderators, before money and time are invested on large-scale prospective studies. Specifically, self-harm, irrational beliefs, anger and hostility, coping, and self-esteem could potentially benefit from further investigation of the moderators involved in the associations, or further work on the definition/measurement of the concepts, whilst defence style, personality traits, and borderline personality disorder would all benefit from further correlational work due to the small number of studies currently available. Third, there are factors that are deemed important and interesting enough to warrant the investment of time and money in prospective and experimental studies. There are promising associations between abuse and family environment and the different forms of eating pathology. Despite these areas being assumed to have a role in eating pathology development, Stice ( 1 ) found few longitudinal studies on these areas and as such it would be highly beneficial to investigate these two areas in an empirical manner. Moreover, autonomy, negative cognitions, shame and guilt, attachment with primary caregiver, exercise and obsession-compulsion were all strongly associated with eating disturbance in this review but were not assessed by Stice ( 1 ), so offer further scope for longitudinal investigation. Finally, there were some factors in this review, which although associated with eating pathology and previously assessed by Stice ( 1 ), would still merit further prospective investigation due to a lack of studies on specific associations with AN or BN. For example, the various concepts of socio-cultural pressure and substance use have been suggested to be related in different ways to each form of disorder, and determining whether these speculations are correct would enrich the profiles of the two disorders.
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Acknowledgements
This work was funded by a PhD fellowship from the ESRC. The authors would like to thank Dr. Christopher Eccleston and Dr. Sarah Milne for their advice on meta-analysis procedures.
Correspondence to
Dr. Emma Vince, Department of Primary Care and General Practice, University of Birmingham, Edgbaston Birmingham, B15 2TT, United Kingdom. E-mail: E.P.Vince@bham.ac.uk Fax: +44 (0)121 4146571
References followed by * are those included in the meta-analyses.