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. Author manuscript; available in PMC: 2019 Feb 1.
Published in final edited form as: Int J Eat Disord. 2017 Dec 7;51(2):139–145. doi: 10.1002/eat.22811

Driven Exercise in the Absence of Binge Eating: Implications for Purging Disorder

Janet A Lydecker 1, Megan Shea 1,2, Carlos M Grilo 1
PMCID: PMC5796839  NIHMSID: NIHMS930899  PMID: 29215743

Abstract

Objective

Purging disorder (PD) is characterized by recurrent purging without objectively large binge-eating episodes. PD has received relatively little attention, and questions remain about the clinical significance of “purging” by exercise that is driven or compulsive (i.e., as extreme compensatory or weight-control behavior). The little available research suggests that individuals who use exercise as a compensatory behavior might have less eating-disorder psychopathology than those who purge by vomiting or laxatives, but those studies have had smaller sample sizes, defined PD using low-frequency thresholds, and defined exercise without weight-compensatory or driven elements.

Method

Participants (N=2017) completed a web-based survey with established measures of eating-disorder psychopathology, depression, and physical activity. Participants were categorized (regular compensatory driven exercise, PD-E, n=297; regular compensatory vomiting/laxatives, PD-VL, n=59; broadly-defined anorexia nervosa, AN, n=20; and no eating-disordered behaviors, NED, n=1658) and compared.

Results

PD-E, PD-VL and AN had higher eating-disorder psychopathology and physical activity than NED but did not significantly differ from each other on most domains. PD-VL and AN had higher depression than PD-E, which was higher than NED.

Discussion

Findings suggest that among participants with regularly compensatory behaviors without binge eating, those who use exercise alone have similar levels of associated eating-disorder psychopathology as those who use vomiting/laxatives, although they have lower depression levels and overall frequency of purging. Findings provide further support for the clinical significance of PD. Clinicians and researchers should recognize the severity of driven exercise as a compensatory behavior, and the need for further epidemiological and treatment research.

Keywords: purging disorder, driven exercise, compulsive exercise, other specified feeding or eating disorder

In addition to the formal eating disorders included in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) (1), there are five “other specified feeding and eating disorders.” Within this “other” diagnostic category is purging disorder (PD), defined by regular purging unaccompanied by objectively large binge-eating episodes (1). While recognized as an “other specified” disorder in the DSM-5 (1), PD does not have specific diagnostic criteria, nor is it included in the ICD-10 (2). Without codified diagnostic criteria, research to date on PD has used different definitions that have resulted insufficient understanding of the characteristics of PD, such as typical presentations of the disorder and grades of severity. Attempts have been made to standardize its definition as an initial step moving towards establishing criteria (3).

Despite the absence of a formal diagnosis, PD is an important area for study because emerging research suggests it has similar prevalence, clinical distress and functional impairment as other eating disorders (4). The Australian Twin Study (5), a community study that examined prevalence of eating disorders, found that PD occurred more frequently than formal eating disorders, including anorexia nervosa (AN), bulimia nervosa (BN), and binge-eating disorder (BED). However, PD has elsewhere been reported to have a lower prevalence than formal eating disorders (6). PD has a higher mortality than BN, and shares several associated medical complications such as electrolyte imbalances (7). PD has similar psychiatric comorbidities as other eating disorders, including depression, anxiety, psychiatric disorders, and suicidality (4–6, 8–10). There is some overlap between BN and PD in eating-disorder psychopathology, such as body dissatisfaction (11), although other work has shown differences in shape/weight concern between BN and PD (8, 11, 12). Equivocal findings such as these indicate the need for more research on the characteristics of PD to inform and facilitate continued work on its validity and distinctiveness as an eating disorder.

There is a particular absence of research on exercise as a “purging” behavior (i.e., exercise used as an extreme compensatory or weight-control behavior with a driven or compulsive element). Indeed, among the suggested list of purging/compensatory behaviors in the definition of PD in the DSM-5, exercise is neither included nor discussed, although it is not explicitly excluded (1). Indeed, it is difficult to classify exercise in the context of eating disorders (13). Although many individuals may engage in physical activity with the purpose of “healthy” weight control, when the exercise has a compulsive or driven motivation and extends beyond normative exercise, it can be viewed as an inappropriate compensatory behavior (14). Yet, driven exercise (DE) can also be viewed as “purgative” if individuals exercise specifically to expel or expend calories after an objectively or subjectively large binge-eating episode. In one study that examined possible broad and narrow definitions of PD, DE was included as a weight-compensatory behavior in the broad PD definition (15). In contrast to the DSM-5 definition of PD, exercise is mentioned in the diagnostic criteria for BN and AN. Collectively, this suggests a need to improve our understanding of the potential significance of DE as a purging/compensatory behavior in PD.

Previous studies that focused on purging in patients with BN have examined DE. In one study, individuals with bulimia nervosa who purged by vomiting or laxatives (n=17) had more psychiatric comorbidities such as depression, anxiety and substance abuse, compared with those with bulimia nervosa who purged by exercise, diuretics, diet pills or fasting (n=45) (16). In another study, a similar pattern emerged for psychopathology: individuals with AN binge-purge subtype (n=49) and individuals with BN who purged by vomiting or laxatives (n=144) were more likely to have had repeated suicide attempts than those with AN restricting subtype (n=38) and those with BN who purged by exercise or fasting (n=14) (17). It is important to note, however, that the sample sizes in these studies were small and combined fasting and exercise into the same category, which makes it difficult to understand the specific role of DE.

Two additional studies examined DE specifically, albeit not in the context of clinical eating disorders (18, 19). In one study, individuals with “exercise addiction” (based on their Exercise Addiction Inventory score) had higher eating-disorder psychopathology than those without exercise addiction, but lower than individuals with eating disorders (19). In another study, college students who used only exercise as a compensatory behavior (at any frequency) did not have significantly different eating-disorder psychopathology from those who denied purging/compensatory behaviors (18). It is important to note, however, that the way DE was operationalized in these studies may not extend to PD. For example, in the study of exercise addiction (18), participants in the DE group had one or more episodes of DE with the intent to control shape or weight in the past month. Definitions that require this low-frequency threshold do not parallel other eating disorder criteria (e.g., BN requires weekly binge-eating and purging episodes) or the proposed PD criteria (3). Furthermore, definitions of DE that focus on intensity or frequency fail to include the essential weight-control feature of this behavior that distinguishes it from healthy exercise. The intent (i.e., weight control) and attitudes (e.g., guilt about not exercising) related to exercise are the factors that are associated with eating-disorder psychopathology (20), rather than intensity or frequency alone (21, 22). Exercise is not intrinsically disordered and can be healthy and normative. Defining exercise without acknowledging intent or attitudes about it limit application to clinical eating disorders.

Aim of the current study

Because there is minimal literature on PD, and because DE has not been well-examined as a purging behavior, the aim of the current study was to compare eating-disorder psychopathology, frequency of purging behaviors, depression, and physical activity among individuals who reported regular methods of purging/compensatory behaviors. Specifically, we compared individuals who regularly used DE alone as a purging/compensatory method (PD-E group) with individuals who regularly used vomiting or laxative misuse as a purging/compensatory method (PD-VL group). To provide further context, we included two additional relevant study groups for comparison: individuals who met broadly-defined criteria for anorexia nervosa (AN group) and individuals who denied eating-disorder behaviors (NED group). Of note, group definitions required weekly purging/compensatory behaviors to be consistent with frequencies in other eating disorder diagnoses (e.g., BN) and with previous work on PD as an eating disorder (e.g., 10, 23, 24). Based on earlier work, we hypothesized that the PD-VL and AN groups would have significantly greater eating-disorder psychopathology compared with the PD-E group. We also hypothesized that the PD-E group would have significantly greater eating-disorder psychopathology than the NED group. In addition, we hypothesized that depression would be higher in the PD-VL and AN groups compared to the PD-E group, which in turn would have higher depression than the NED group because the previous literature generally found that purging by vomiting or laxative misuse was associated with greater psychopathology. As an exploratory aim, we examined whether the PD-E group was more physically active (i.e., in lifestyle physical activity) than the other groups.

Methods

Participants

Participants (N=2026) were recruited from the Mechanical Turk website to complete an online survey about weight and eating. Mechanical Turk is an online recruitment platform that yields high-quality and convenient data. Recent comparisons indicate psychometric properties of measures completed by Mechanical Turk participants do not differ in reliability or validity from participants recruited using traditional sources (25). Additionally, samples have greater diversity in geography and demographic characteristics than undergraduate samples (25–27). Mechanical Turk has been used in psychological and psychiatric research (28), including eating disorder research (29, 30). To be eligible to complete the survey, participants had to be at least 21 years old. This study was reviewed and approved by our university’s institutional review board; all participants provided informed consent.

Measures

Body Mass Index (BMI)

Participants self-reported their height and weight, which were used to calculate BMI.

Eating Disorder Examination Questionnaire (EDE-Q)

The EDE-Q retrospectively measures eating-disorder psychopathology over the past 28 days on seven-point scales (31). The current study used a brief version of the full scale, which has three subscales (Restraint, Overvaluation, Dissatisfaction) and a Global scale. The brief version has been shown to demonstrate superior psychometric properties in nonclinical (32) and clinical (33) studies compared with those from the original measure; subscales were internally consistent in earlier work, α= .89–.91 (32), and in the current study α= .80–.92. Behaviors include objective binge-eating episodes (i.e., eating an unusually large amount of food while feeling a sense of loss of control) within the past 28 days, and purging/compensatory behaviors (i.e., vomiting, laxative misuse, DE) within the past 28 days. Note that these behavioral (i.e., binge-eating episodes, vomiting, laxative misuse, DE) items are not included in the subscale or global scores.

Godin Leisure Time Exercise Questionnaire (GLTEQ)

The GLTEQ assesses the frequency of physical activity across levels of intensity during a typical week. Participants report the number of times per week they spend more than 15 minutes engaged in either mild, moderate or strenuous exercise (34).

Patient Health Questionnaire-2 (PHQ-2)

The PHQ-2 is a two-item questionnaire that assesses depressed mood over the past two weeks on a scale of 0 to 6 (35). The PHQ-2 has similar psychometric properties to the PHQ-9 (36).

Creation of Study Groups

Scoring algorithms created groups using EDE-Q behavior items. Individuals meeting criteria were identified among a larger sample of participants. Participants in the PD-E group (n=297) endorsed at least weekly DE (exercise that felt driven or compulsive and was for the purpose of weight loss; EDE-Q Brief item 15, score 4 or greater accepted) over the past 28 days and denied weekly binge-eating episodes (eating an unusually large amount of food and perceiving eating to be out of control; EDE-Q Brief item 11, score 0 through 3 accepted) and denied weekly purging by vomiting and/or laxative use (EDE-Q Brief items 13 and 14, score 0 through 3 accepted) over the past 28 days. Participants in the PD-VL group (n=59) endorsed at least weekly purging by vomiting (EDE-Q Brief item 13, score 4 or greater accepted) and/or at least weekly purging by laxative misuse (EDE-Q Brief item 14, score 4 or greater accepted) and denied weekly binge-eating episodes over the past 28 days (EDE-Q Brief item 11, score 0 through 3 accepted). Participants in the AN group (n=20) had a BMI below 18.5 kg/m2 and endorsed restraint over eating (EDE-Q Brief item 1, score 4 or greater accepted), food avoidance (EDE-Q Brief item 2, score 4 or greater accepted), or dietary rules (EDE-Q Brief item 3, score 4 or greater accepted). Participants in the no-eating disorder group (NED; n=1658) denied weekly binge eating (EDE-Q Brief item 11, score 0 through 3 accepted) and inappropriate compensatory behaviors (EDE-Q Brief items 13, 14, and 15, score 0 through 3 accepted), and had a body mass index above 18.5 kg/m2.

Statistical analyses

Multivariate analysis of variance (MANOVA) compared scores on the EDE-Q Brief subscales between the PD-VL, PD-E, AN and NED groups. Post hoc analyses examined pairwise differences in eating-disorder psychopathology. ANOVAs also compared demographic characteristics, depression, and the frequencies of purging, DE, and physical activity across groups. Chi-square tests evaluated differences in categorical variables across groups, including clinical overvaluation of shape/weight.

Results

Table 1 summarizes demographic characteristics and statistical comparisons for the PD-VL, PD-E, AN and NED groups. Age and BMI significantly differed across groups. The PD-E group had more men than the PD-VL, AN and NED groups. The PD-E group had fewer White participants and more Asian participants than the NED group. There were no significant differences in education among groups.

Table 1.

Demographic Characteristics by Eating Disorder Group

Variable PD-VL (n=59) PD-E (n=297) AN (n=20) NED (n=1658) X2 N p φ
n (%) n (%) n (%) n (%)
Sex 13.38 2026 .004 .081
 Male 17 (28.8%)a 130 (44.1%)b,c,d 3 (15.0%)a 588 (35.6%)a
 Female 42 (71.2%)a 165 (55.9%)b,c,d 17 (85.0%)a 1064 (64.4%)a
Education 3.61 2034 .729 .042
 High school or less 10 (16.9%) 40 (13.5%) 4 (20.0%) 216 (13.0%)
 Some college 22 (37.3%) 96 (32.3%) 8 (40.0%) 540 (32.6%)
 College degree or more 27 (45.8%) 161 (54.2%) 8 (40.0%) 902 (54.4%)
Race 14.98 2034 .092 .086
 White 47 (79.7%) 220 (74.1%)b 15 (75.0%) 1357 (81.8%)a
 Black 2 (3.4%) 10 (3.4%) 0 (0.0%) 31 (1.9%)
 Asian 5 (8.5%) 36 (12.1%)b 4 (20.0%) 133 (8.0%)a
 Other 5 (8.5%) 31 (10.4%) 1 (5.0%) 137 (8.3%)
Ethnicity 6.34 2034 .096 .056
 Hispanic 16 (27.1%)b 60 (20.2%) 2 (10.0%) 281 (16.9%)c
 Not Hispanic 43 (72.9%)b 237 (79.8%) 18 (90.0%) 1377 (83.1%)c
M (SD) M (SD) M (SD) F Total df p ηp2
Age, years 30.20 (9.29)b 33.28 (10.10)b 30.95 (11.34)b 36.28 (11.82)a,b,c 11.33 2032 < .001 .016
Body Mass Index 28.88 (6.31)b,d 27.41 (6.08)d 17.20 (1.30)a,b,c 27.13 (6.72)c,d 16.66 2016 < .001 .024
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Note. Percentages reflect the proportion of participants from one eating disorder group (column) in the demographic category (row).

a

Significantly different from PD-E at p < .05.

b

Significantly different from NED at p < .05.

c

Significantly different from PD-VL at p < .05.

d

Significantly different from AN at p < .05.

Table 2 summarizes means and group differences in eating-disorder psychopathology, purging frequency, physical activity frequency and depression scores. Eating-disorder psychopathology differed significantly by group (Wilks’ λ=0.879, F(9,4935.77)=29.83, p<.001, ηp2=.042). Specifically, restraint, overvaluation of shape/weight, and the global score were significantly higher in the PD-VL, PD-E, and AN groups compared with the NED group, and dissatisfaction was significantly higher in the PD-VL and PD-E groups compared with the NED group. The PD groups did not differ significantly from each other. Further inspection of the overvaluation items revealed that more individuals in the PD-VL and PD-E groups endorsed at least moderate clinical overvaluation of shape/weight compared with the NED group, but these groups again did not differ significantly from each other. The AN group did not significantly differ from any other group.

Table 2.

Analyses of Variance and Pairwise Comparisons

PD-VL (n=59) PD-E (n=297) AN (n=20) NED (n=1658) F Total df p ηp2
M (SD) M (SD) M (SD) M (SD)
EDE-Q Psychopathology
 Restraint 3.50 (1.90)b 3.75 (1.91)b 4.13 (1.41)b 2.11 (2.09)a,c,d 63.74 2034 < .001 .086
 Overvaluation 4.10 (1.74)b 3.78 (1.58)b 3.65 (1.99)b 2.46 (1.84)a,c,d 58.97 2034 < .001 .080
 Dissatisfaction 4.07 (1.58)b,d 3.44 (1.80)b 2.53 (1.56)c 2.68 (1.90)a,c 22.93 2034 < .001 .033
 Global 3.84 (1.53)b 3.67 (1.37)b 3.54 (1.29)b 2.37 (1.61)a,c,d 71.55 2034 < .001 .096
Godin Physical Activity Frequency
 Strenuous 3.45 (8.04)b 3.14 (2.46)b 2.05 (2.54) 1.43 (1.92)a,c 51.40 1967 < .001 .073
 Moderate 3.87 (6.75)b 3.34 (2.59)b 3.20 (3.14) 2.42 (2.67)a,c 12.69 1967 < .001 .019
 Mild 4.91 (8.03) 3.67 (2.78) 3.65 (3.00) 3.63 (4.26) 1.64 1967 .179 .002
PHQ Depression 3.20 (1.84)a,b 1.69 (1.69)b,c,d 2.60 (2.04)a,b 1.24 (1.57)a,c,d 35.68 2009 < .001 .051
Purging Frequency 19.00 (17.44)a,b,d 11.86 (7.23)b,c,d 7.85 (15.48)a,b,c 0.12 (0.52)a,c,d 924.84 2034 < .001 .577
Driven Exercise Frequency 7.29 (8.72)a,b,d 11.65 (7.18)b,c,d 4.85 (10.11)a,b,c 0.10 (0.45)a,c,d 1093.69 2034 < .001 .618
n (%) n (%) n (%) n (%) X2 N p φ
Clinical Overvaluation of Weight and/or Shape 45 (76.3%)b 222 (74.7%)b 12 (60.0%) 668 (40.3%)a,c 143.43 2034 < .001 .266
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Note. PD-E regular purging by exercise alone; PD-VL regular purging by vomiting and/or laxatives; NED no eating disorder. Godin Physical Activity Frequency assesses how many times the individual engages in physical activity in a typical week. The PHQ Depression scale assesses depressed mood over the past 2 weeks on a scale of 0–6. All other scales represent psychopathology or frequency of behaviors in the past 28 days. Percentages reflect the proportion of participants from one eating disorder group (column) in the category (row).

a

Significantly different from PD-E at p < .05.

b

Significantly different from NED at p < .05.

c

Significantly different from PD-VL at p < .05.

d

Significantly different from AN at p < .05.

Purging frequency also differed significantly by group. The PD-VL group reported more episodes of purging (vomiting, laxatives, and/or exercise) in the last 28 days than the PD-E group, which in turn reported significantly more episodes of purging than the AN group, which in turn reported significantly more episodes of purging than the NED group. Further, the PD-E group had the most DE episodes, followed by the PD-VL group, followed by the AN group, followed by the NED group.

Physical activity frequency differed significantly across groups (Wilks’ λ=0.921, F(9,4772.71)=18.23, p<.001, ηp2=.027). The PD-VL and PD-E groups reported significantly more frequent strenuous exercise than the NED group, but did not differ significantly from each other. Similarly, the PD-VL and PD-E groups reported significantly more frequent moderate exercise than the NED group, but did not differ significantly from each other. The AN group did not differ significantly from any other group across physical activity frequencies. None of the four groups differed significantly on the frequency of mild exercise.

Depression scores differed significantly across groups. The PD-VL and AN groups had significantly higher depression scores than the PD-E group, which in turn had significantly higher depression scores than the NED group.

Discussion

Our study provides new evidence about driven exercise as a purging behavior in the psychopathology of individuals who engage in regular purging/compensatory behaviors but do not binge eat. The emerging but still limited literature on PD is particularly lacking regarding exercise as a purging/compensatory method. This may be due in part to the lack of clarity as to whether exercise is a “purging” (i.e., expelling calories consumed during an objectively or subjectively large binge) and/or “compensatory” (i.e., compensating for calories consumed as an extreme weight-control behavior) and/or normative (i.e., to maintain healthy weight control) behavior. Overall, our findings suggest that individuals who engage in regular DE exclusively (i.e., exercise that is driven or compulsive and for the purpose of weight control) have similar psychopathology as those who purge regularly by vomiting or laxative misuse. Moreover, both PD groups were different from individuals who denied both binge eating and purging; this adds further support for the potential validity and clinical significance of PD. These findings, which are contrary to the hypothesis that the PD-VL group would have more severe psychopathology than the PD-E group, are perhaps surprising because exercise (unlike vomiting) can be construed as healthy and is socially acceptable. Notably, the findings that both PD groups significantly differed from the NED group, although not from each other, on the proportion of those with at least moderate overvaluation of shape/weight supports their conceptualization as eating disorders. Our findings suggest that clinicians and clinical researchers seeking to treat the psychopathology of regular purging should include DE among purging/compensatory methods assessed and considered in treatment. In addition, because the PD-VL group also used exercise to purge, the presence of DE is both potentially concerning on its own and an indicator that purging by vomiting and laxatives should be assessed.

The broadly-defined AN group had similar psychopathology to both PD groups, which were all significantly different from the NED group. This pattern further supports the clinical significance of the PD-E group. Moreover, the graded pattern of significance for purging frequency and driven exercise frequency, with the AN group reporting fewer episodes than both PD groups but more than the NED group, suggests a distinction between broadly-defined AN symptomatology and regular purging/compensatory behaviors.

Consistent with our hypotheses, we found that those who purged by vomiting/laxatives and those who had broadly-defined AN reported more depressive affect than those who purged by exercise alone. Although our study was cross-sectional and cannot speak to causality, we do cautiously speculate that these associations are consistent with maintenance models that depression and purging behaviors are inter-related. Relatedly, cognitive dissonance that arises from purging by less socially-acceptable means may contribute to greater depressive affect. Although lifestyle physical activity is generally inversely associated with depression (37), the PD-E groups engaged in the same frequency of lifestyle physical activity (across levels of intensity) as those in the PD-VL and AN groups, which suggests that differences in depression are not due to levels of lifestyle physical activity.

Findings that the PD-E group had a significantly greater proportion of men than the PD-VL and AN groups is also noteworthy especially in light of the gender disparity in many eating disorders (38). It is possible that men, who tend to have appearance goals related to muscularity rather than thinness (39), use exercise to control their shape because DE can build muscle whereas vomiting and laxatives cannot. Earlier research on PD has focused on women, and our findings related to sex differences support the need for more research on regular purging in men, particularly in the context of DE.

Our study’s findings should be considered in the context of its limitations. Participants were predominantly White, female and well-educated, and all were from the United States. These characteristics limit generalizability to other groups that may have different norms about eating and body image. Our sample was an online convenience sample rather than a clinical sample. The use of self-report measures rather than clinical or diagnostic interviews limit our characterization of our study groups based on regular purging behaviors and absence of regular binge eating within the past month, and cannot establish a PD or AN diagnosis. Self-reported attitudes and behaviors in an anonymous survey format, however, may lead to greater honesty because they are less hindered by a bias to provide socially-desirable answers or answers perceived to be desired by an interviewer (31). Furthermore, this study used Mechanical Turk as a recruitment platform, which allowed us to draw from the entire United States and include a wider age range, compared with local and university student samples. Moreover, samples recruited from Mechanical Turk have excellent reliability and validity and growing usage in psychological research.

Despite these limitations, this study also had significant strengths. Most importantly, DE included the intent of exercise embedded in its definition (i.e., to control weight/shape), which has been the key feature of exercise in earlier work on eating-disorder psychopathology (20–22). Additionally, DE required at least weekly behavior for inclusion in the PD-E group, which parallels criteria for other EDs such as BN, and the key diagnostic behavioral criteria for PD (3).

Our findings suggest several avenues for future research. Regular DE in both PD groups suggests that DE may be a more common form of purging/compensatory behavior, or people may be more willing to report it, which makes it an important behavioral feature of EDs to assess epidemiologically as well as in clinical settings with individual patients. Likewise, it also warrants investigation whether DE precedes other purging/compensatory behaviors in longitudinal studies; determining the order of onset for DE and other behaviors could inform targeted prevention and early treatment efforts. Additionally, our findings about the similarity between exercise and vomiting/laxatives on eating-disorder psychopathology suggest the need to perform more comprehensive and multimodal research with individuals who purge by different methods, such as has been done with non-exercise purging (40). For example, physical comorbidities may vary. Likewise, behavioral trajectories (e.g., whether exercise progresses to vomiting) and diagnostic crossover may vary.

The current study adds to the existing literature by examining DE versus vomiting/laxatives and showing their similar eating-disorder psychopathology. Regular driven exercise seems to warrant the same clinical attention in treatment and clinical research settings as regular vomiting/laxative use. Further research is needed to determine if differences in onset, associated clinical problems, or treatment outcomes are present among individuals across regular purging/compensatory methods; this research could help to develop treatment and prevention programs that address PD across various clinical presentations.

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