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. Author manuscript; available in PMC: 2024 Sep 3.
Published in final edited form as: Eat Disord. 2022 Nov 23;31(5):415–439. doi: 10.1080/10640266.2022.2145258

Weight status is associated with clinical characteristics among individuals with bulimia nervosa

Paakhi Srivastava a, Emily K Presseller a,b, Joanna Y Chen b, Kelsey E Clark a,b, Rowan A Hunt c, Olivia M Clancy a,b, Stephanie Manasse a, Adrienne S Juarascio a,b
PMCID: PMC11253114  NIHMSID: NIHMS2006789  PMID: 36419352

Abstract

Recent studies have found increasing rates of overweight and obesity in bulimia nervosa (BN). However, the relationships between body mass index (BMI) and BN symptoms and other clinically relevant constructs are unknown. Participants (N = 152 adults with BN) were assigned to three groups by BMI: group with no overweight or obesity (NOW-BN; BMI <25; N = 32), group with overweight (OW-BN; BMI ≥25 and <30; N = 66), and group with obesity (O-BN; BMI ≥30; N = 54). We compared the groups on demographics, diet and weight histories, body esteem, BN symptoms, and depression using chi square, analysis of variance, analysis of covariance, and Poisson regression models. The O-BN group was older (d = 0.57) and OW-BN and O-BN groups had greater proportions of race/ethnic minorities than NOW-BN group. The O-BN group was significantly younger at first diet (d = 0.41) and demonstrated significantly higher cognitive dietary restraint (d = 0.31). Compared to NOW-BN, O-BN participants had lower incidence of objective binge eating (incidence rate ratio [IRR] = 4.86) and driven exercise (IRR = 7.13), and greater incidence of vomiting (IRR = 9.30), laxative misuse (IRR = 4.01), and diuretic misuse (d = 2.08). O-BN participants also experienced higher shape (d = 0.41) and weight (d = 0.42) concerns than NOW-BN and OW-BN, although NOW-BN experienced higher shape (d = 0.44) and weight (d = 0.39) concerns than OW-BN. Groups did not differ on depression scores. These results were replicated when examining BMI as a continuous predictor across the full sample, with the exception of objective binge eating and driven exercise, which were not signifi-cantly associated with BMI. Individuals with BN and comorbid obesity have distinct clinical characteristics. Existing interventions may need to be adapted to meet clinical needs of these individuals.

Introduction

Bulimia nervosa (BN) is characterized by shape/weight overvaluation, recurrent binge eating, and inappropriate compensatory behaviors (American Psychiatric Association, 2013). Historically, individuals with BN typically presented with body mass index (BMI, a height-adjusted proxy for adiposity) in the no overweight or obesity weight range (Hudson et al., 2007). Several recent large population-based studies have detected that the average BMI for individuals with BN is now in the overweight (Jordan et al., 2014; Thomas et al., 2014; Udo & Grilo, 2018) or obese weight range (Bagaric et al., 2020; Darby et al., 2009; Hay et al., 2015; Da Luz et al., 2018). Notably, treatment and treatment-seeking samples have mirrored these findings. For instance, a study examining temporal changes in lifetime prevalence of obesity rates in a sample of adult women seeking treatment for eating disorders reported a threefold increase in obesity (i.e., from 13.6% in 2001 to 37.8% 2010) in the BN population over the last 10 years (Villarejo et al., 2012). Similar observations on comorbid overweight or obesity and BN have been made previously (Bulik et al., 2012; Jordan et al., 2014). These findings suggest that the average BMI for BN may be trending towards overweight or obesity. This trend coincides with the increase in global population average BMI and increased worldwide prevalence of higher-weight BMI categories in recent decades (Collaboration, 2016). While a large body of research in BN has been conducted in samples without overweight or obesity, these results may not always generalize to samples with overweight or obesity. Thus, research elucidating BN presentation among individuals with overweight and obesity is warranted.

The clinical presentation of BN in individuals with concurrent overweight or obesity may be different from those without overweight or obesity. Demographic characteristics, such as age at presentation for treatment, may differ across BMI status. In the general population, body weight increases until around age 60 and then begins to decrease (Seidell & Visscher, 2000). Because many individuals with BN do not seek treatment until many years into their disorder (Hart et al., 2011) and engagement in bingeing and purging can lead to weight gain over time (Herzog et al., 2010; Lowe et al., 2006), individuals with BN who are at an older age at treatment presentation may be more likely to have comorbid overweight/obesity. Other clinically relevant variables including diet and weight histories and weight suppression (defined as the discrepancy between an individual’s highest adult weight, and their current weight; Lowe, 1993) may also differ across BMI status. A history of weight loss (and the resultant weight suppression) is evidenced to impact a variety of biological variables that encourage weight regain over time (e.g., slower metabolism, increased appetite in people with and without eating disorders). These biological variables can therefore impact behavior (e.g., encourage dieting/dietary restraint) and other facets of BN symptomatology. Demographic characteristics, dieting and weight history, and weight suppression at presentation may influence treatment expectations. For instance, younger and weight-suppressed individuals without overweight or obesity may expect to improve BN symptoms and maintain weight. However, those who are older, non-weight suppressed and have obesity may desire weight loss in addition to reducing BN symptoms because both older age and obesity are related to higher risk for negative health consequences (Zamboni et al., 2005). Despite the potential impact of BMI on these clinically relevant variables (i.e., demographic characteristics, dieting and weight history, weight suppression) and its implications for treatment, no study to date has specifically compared individuals with BN across different BMI statuses on these variables.

Understanding the association of BMI with BN symptomatology and depression may have relevance for treatment planning and implementation, and is therefore worth elucidating. Among individuals with BN who overvalue body weight/shape, discrepancies between desired and current body weight can lead to body dissatisfaction (Lantz et al., 2018; Strauman et al., 1991; Wonderlich et al., 2008), a key maintenance factor of disordered eating behaviors. Concurrent overweight or obesity may likely cause greater discrepancy between desired and actual body weight (Chernyak & Lowe, 2010) and may contribute to severe body dissatisfaction, weight and shape concerns, which may in turn drive greater efforts to control body weight or shape. Studies of individuals without eating disorders indicate higher body dissatisfaction is observed in the obese BMI category compared to lower-weight BMI categories (Weinberger et al., 2016) and higher BMI is correlated with eatingrelated variables such as lower cravings for high-fat foods and greater frequency of emotional eating (Abdella et al., 2019), further emphasizing the potential significance of weight status. Thus, it is possible that individuals with BN who are in the overweight or obese weight range may demonstrate more frequent engagement in disordered eating behaviors (e.g., binge eating, self-induced vomiting, other inappropriate compensatory behaviors, dietary restraint/restriction) or engagement in larger, higher calorie binge eating episodes compared to those without overweight or obesity. Alternatively, it may also be possible that engagement in specific eating disorder behaviors such as compulsive exercise may be higher among individuals without overweight or obesity which may explain lower weight in this subgroup of BN population. Research examining group differences in bulimic symptomatology across BMI status (i.e., without overweight or obesity, with overweight, and with obesity) may clarify whether and how standard treatments for BN need to be adapted to meet the unique needs of individuals based on their BMI. Finally, there may be differences in rates of comorbid depression at presenta-tion based on BMI status. Individuals with obesity are already more likely to have higher rates of depression compared to those without overweight or obesity and those with overweight; furthermore, concurrent obesity in individuals with BN may contribute to severe body dissatisfaction—a significant source of distress (Paxton et al., 2006; Shepherd & Ricciardelli, 1998).

To our knowledge, only three studies have examined BMI group differences among individuals with BN. (Other extant studies that have observed prevalence of BMI categories have pooled participants across the eating disorder diagnostic spectrum [e.g., Villarejo et al. (2012) included patients diagnosed with anorexia nervosa and binge eating disorder].) The findings regarding BMI group differences in BN symptomatology from these three studies are varied (note: some studies did not include body dissatisfaction/body image concern measures, and no studies examined depression). One study (Rotella et al., 2013) detected greater body dissatisfaction and greater body image concerns in individuals with BN having overweight compared to those without overweight or obesity, but this study did not find differences in eating disorder behaviors (i.e., binge eating, inappropriate compensatory behaviors, dietary restraint/restriction) related to weight status. One study (Masheb & White, 2012) demonstrated lower dietary restraint in individuals with BN having overweight compared to those without overweight or obesity, but also did not find differences in other eating disorder behaviors (i.e., binge eating, inappropriate compensatory behaviors, dietary restraint/restriction) after controlling for BMI. Finally, only one (Mitchell et al., 1990) out of the three studies demonstrated that individuals with BN having overweight reported fewer binge eating episodes and less frequent self-induced vomiting, but more frequent laxative abuse relative to their counterparts without overweight or obesity. One reason for the mixed results observed in past studies may be due to methodological limitations in previous studies. First, all three studies divided their BN sample into a group without overweight or obesity (i.e., BMI <25 kg/m2) and a group including those with overweight and obesity (i.e., BMI ≥25 kg/m2). Because individuals with obesity were included in the overweight group, it is difficult to understand whether the observed differences in BN symptomatology between the groups were due to overweight or obesity. Second, all of the previous research has solely utilized self-report measures to assess BN symptomatology (e.g., Eating Disorder Examination-Questionnaire (Fairburn & Beglin, 1994); Eating Disorder Questionnaire (Mitchell et al., 1985)). Because the core features of BN (e.g., loss of control) are complex in form, self-assessment of BN symptoms (e.g., binge eating) could have introduced some biases (such as overreporting of binge epi-sodes). Thus, more research is needed to replicate previous findings and to examine the independent impact of distinct BMI statuses on presentation of BN symptomatology utilizing more reliable, interview-based assessment approaches.

The present study sought to extend the previous research by comparing three groups of adults with BN without overweight or obesity (NOW-BN, BMI <25 kg/m2), with overweight weight (OW-BN, BMI ≥25 kg/m2 and <30 kg/ m2), and with obesity (O-BN, BMI ≥30 kg/m2) on several clinically relevant constructs and BN symptomatology.

The first aim of the study was to compare the groups on demographics (i.e., age, race/ethnicity), diet and weight histories, and weight suppression. Given the absence of prior literature examining these questions, in line with the theory reviewed above (i.e., older age being associated with higher weight, individuals commonly seeking treatment after a long length of illness, higher weight suppression encouraging greater weight regain over time), we hypothe-sized that 1) O-BN group will be older in age than both OW-BN and NOW-BN, and OW-BN will be older in age compared to NOW-BN, and 2) O-BN group will have lowest weight suppression among the three groups followed by OW-BN and NOW-BN.

The second aim of the study was to compare the three groups on BN symptomatology and depression. Given that O-BN are likely to experience greater discrepancy between their ideal and current weight, it was hypothe-sized that compared to NOW-BN and OW-BN groups, O-BN group would 1) endorse greater shape/weight concerns (consistent with Rotella et al., 2013), 2) demonstrate lower body esteem (consistent with Rotella et al., 2013), 3) experience higher restraint over eating (i.e., cognitive and behavioral attempts to reduce caloric intake) but less actual caloric restriction (in contrast to Rotella et al. (2013), Masheb and White (2012), and Mitchell et al. (1990) because of the methodological concerns noted above —i.e., lack of separation between OW-BN and O-BN groups, use of solely self-report measures), 4) experience more frequent binge eating episodes and inappropriate compensatory behaviors (i.e., self-induced vomiting, laxative misuse, diuretics misuse, and driven exercise; consistent with Mitchell et al. (1990) regarding laxative misuse, but otherwise in contrast to Rotella et al. (2013), Masheb and White (2012), and Mitchell et al. (1990) because of the methodological concerns noted above—i.e., lack of separation between OW-BN and O-BN groups, use of solely self-report mea-sures), and 5) have greater comorbid depression (in line with theory reviewed above—i.e., higher weight associated with greater distress and depressive symptomatology).

Method

Participants

The current study represents a secondary analysis of adult (ages 18+) participants (N = 152) with BN-spectrum disorders from ongoing research studies, including four treatment trials for binge eating (n = 124; Juarascio, Srivastava et al., 2021; Juarascio, Parker et al., 2021; Juarascio et al., 2018; A. Juarascio et al., 2021), and two assessment-only studies (n = 28) (Presseller et al., 2020; Srivastava et al., 2021). For the current analyses, we included participants who met behavioral criteria for Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5; American Psychiatric Association, 2013) BN or met all DSM-5 beha-vioral criteria for BN but experienced subjectively large binge episodes (SBEs) rather than objectively large binge episodes (OBEs) in past three months. Exclusion criteria common to all studies included being under-weight; being unable to fluently speak, read, and write English; having an intellectual disability or experiencing severe comorbid psychopathology (e.g., psychosis, acute suicidality, or severe substance use disorder) that would inhibit engagement in study procedures; current or planned preg-nancy; and previous history of bariatric surgery. Participants were excluded from the four treatment studies if they were experiencing med-ical complications that prevent ability to safely engage in outpatient treatment, were receiving current eating disorder or structured weight loss treatment, or were unwilling to complete study procedures (e.g., complete surveys on their smartphone during treatment). The individual studies had some specific inclusion/exclusion criteria that differed across studies.

All participants were administered measures at the baseline assessment of the study, prior to randomization or initiation of treatment. However, due to differences in study protocols, the Body Esteem Scale was administered to only 93 of the participants. Study procedures for all parent studies were approved and overseen by the University Institutional Review Board.

Measures

Demographics

Participants provided information on their age, race/ethnicity, education, employment status, and marital/relationship status. Height and weight were measured with a digital scale and a stadiometer during in-person data collection (pre-COVID-19). During the COVID-19 pandemic, participants self-reported their height and self-reported weight using at-home digital scales.

Dieting and weight history and weight suppression

The Dieting and Weight History Questionnaire (DWHQ; Witt, Katterman, & Lowe, 2013), a 16-item self-report questionnaire, was used to assess partici-pants’ weight history, dieting history, current dieting, and weight suppression.

Shape and weight concerns, cognitive restraint, and bulimic symptomatology

Bulimic symptoms were assessed using the Eating Disorder Examination Interview 17.0 (EDE) (Fairburn & Beglin, 1994). The EDE is a widely used, semi-structured diagnostic interview for eating disorders. The EDE provides frequency ratings for OBEs, SBEs, and inappropriate compensatory behavior episodes over the past three months. Dietary restraint was assessed using the restraint subscale and shape and weight concerns were assessed using the shape concern and weight concern subscales of the EDE. Higher scores on the EDE subscales indicate more severe pathology. The EDE has demonstrated good interrater reliability and convergent and discriminant validity (Cooper et al., 1989; Rosen et al., 1990). We compared groups on all items of the restraint subscale (which measures attempts to restrict whether successful or not) and on frequency of meals and snacks reported over the past month in the EDE as a proxy for actual (i.e., successful) restriction (as has been substan-tiated by previous research; Cachelin et al., 2017). In the present study, Cronbach’s alpha for the restraint, shape concerns, weight concerns, eating concerns, and global scores were 0.93, 0.91, 0.88, 0.91, and 0.91, respectively. As we were interested in understanding cognitive component of control over food intake in order to influence body shape and weight, we used cognitive restraint scale of the Three Factor Eating Questionnaire (TFEQ) Revised 18-item version (TFEQ-R18; Karlsson, Persson, Sjostrom, & Sullivan, 2000). Cronbach’s alpha for the cognitive restraint scale of the TFEQ was .91 in the present study.

Body esteem

Body esteem was measured by the Body Esteem Scale (BES; Mendelson, Mendelson & White,2001) which has 23 items that measure general feelings about appearance, weight satisfaction, and evaluation attributed to others about one’s own body and appearance. Cronbach’s alpha was .89 in the present study.

Depression

Beck’s Depression Inventory-II (BDI-II) was used to assess the presence and severity of depression (Beck et al., 1996). Cronbach’s alpha was .91 in the present study.

Statistical analysis

An a priori power was not calculated as hypotheses in the current study. Previously published studies have reported adequate power for detecting medium-size effects using similar sample sizes (Chen et al., 2021).

Prior research has documented quadratic relationships between BMI and elevated psychopathology, such as suicidality (Zuromski, Cero, Witte, & Zeng, 2017); this relationship may be further moderated by binge eating (Brown, LaRose, Mezuk, 2018). Given this nonlinear relationship between BMI and psychopathology and eating pathology and the categorical approach used in previous research in this area (e.g., Chen et al., 2021; Masheb & White, 2012; Rotella et al., 2013), the sample was divided into three BMI groups using Centers for Disease Control (CDC, 2021) guidelines—without overweight or obesity (NOW-BN, BMI <25 kg/m2), with overweight weight (OW-BN, BMI ≥25 kg/m2 and <30 kg/m2), and with obesity (O-BN, BMI ≥30 kg/m2). For aim 1, chi square test of independence (χ2) was computed to compare groups on sociodemographic variables and categorical dieting and weight questions. Analysis of variance (ANOVA) was used to examine group differences in age, weight suppression, and continuous diet and weight questions. For aim 2, analysis of covariance (ANCOVA) was used to examine group differences on EDE shape and weight concerns subscales, TFEQ-Cognitive restraint, body esteem, and depression where age as a proxy for illness duration was included as a covariate. SPSS version 27.0 (Corp, 2020) was used to conduct these analyses.

For aim 2, preliminary Poisson regression models with OBEs as the outcome variable, BMI group as a three-level categorical predictor, and age as a covariate were fitted and assessed for overdispersion. Because OBEs and SBEs were overdispersed (variance of the distribution greater than the mean), a negative binomial regression model was selected as the most appropriate analytic method for this variable. Because behaviors including self-induced vomiting, laxative use, diuretic use, and driven exercise (i.e., outcome variables) are all count variables and include excess number of zero values, separate zero-inflated Poisson regression models with each of the outcome variable, BMI groups as a three-level categorical predictor with NOW-BN group as the reference group, and age as a covariate were fitted and assessed for overdispersion. As all of the outcome variables were overdispersed, zero-inflated negative binomial (ZINB) regression models were estimated (Atkins & Gallop, 2007). ZINB is an appropriate approach to handle several characteristics of count data, including positive skew, overdispersion, and nonnormality of residuals (Atkins & Gallop, 2007; Hilbe, 2011). For each analysis in ZINB regression, two models were estimated simultaneously: a logistic component and a count component. The logistic component estimates the probability of not engaging in the behavior and the count component estimates the association between the outcome and predictor variables among those people who engage in the behavior. Results from count model portions of these non-linear regressions, which were of primary interest, are presented in the results section. To simplify interpretation, incidence rate ratios (IRR) were estimated so that higher values indicated higher rates of engaging in BN symptoms relative to the reference group. As secondary analyses, we estimated negative binomial regression models for SBEs and ZINB for objective overeating episodes (OOEs). R version 2.8.1 (Therneau & Atkinson, 2009) was used for these analyses.

A parallel analysis was completed for both the study aims where linear regressions were run to test whether BMI predicts age, age at first diet, historical highest weight, weight suppression, cognitive restraint, depression, body esteem, and BN pathology (EDE scales). Several variables (including weight suppression, EDE-Restraint, EDE-global scores, age, TFEQ-Cognitive restraint, and depression) did not satisfy criteria for a normal distribution (skewness and kurtosis not exceeding an absolute value of 1), therefore square root, log, and inverse transformations were computed for each variable and compared to identify which brought the distribution closest to normality. With the exception of age, for which a log transformation was used, all of these variables were transformed using a square root transformation. After transformation, all variables satisfied criteria for a normal distribution, and the transformed versions of these variables were used in all analyses reported below. All regression assumptions of linearity, normality, homoscedasticity of residuals, and non-multicollinearity were met. Outliers were identified using studentized residuals, leverage and Cook’s distances, and between zero and four cases were removed from each analysis in the results reported below. The pattern of results was similar when all cases were included in the analyses. We considered having binge type as a covariate as binge size may contribute to differences in weight. However, only 19% of the sample reported only SBEs, and thus, we decided to not control for binge type in the statistical analysis. To control for multiple comparisons and Type I error, alpha levels of less than 0.01 were considered statistically significant.

Results

Demographics, diet and weight histories, and weight suppression

Descriptive statistics by BMI status and results of group comparisons on demographics, diet and weight histories, and weight suppression are shown in Table 1. Within our sample, 21.0% of participants did not have overweight or obesity, 43.4% had overweight, and 35.5% had obesity. Consistent with hypotheses, the groups significantly differed on age, with post hoc tests using Bonferroni corrections indicating that O-BN group was older than OW-BN and NOW-BN group and OW-BN group was older than NOW-BN group. A significantly greater percentage of participants in the O-BN (27.8%) and OW-BN groups (25.8%) belonged to racial/ ethnic minority groups compared to 17.6% in the NOW-BN group.

Table 1.

Comparison of groups on demographics, diet and weight histories, and weight suppression.

Variable No Overweight or Obesity (n = 32) Overweight (n = 66) Obesity (n = 54) F p d
Mean SD Mean SD Mean SD
Age (in years) 31.72 13.11 33.24 13.73 39.84 14.84 4.28 .003** 0.58
Current weight (in pounds) 145.96 34.95 182.62 51.01 196.88 52.52 9.71 <.001*** 0.55
BMI (kg/m2) 21.82 1.64 26.9 1.3 36.91 6.94 96.09 <.001*** 0.64
Percentage Number Percentage Number Percentage Number χ2 p
Sex (females) Ethnicity 85.0% 27 88.6 58 83.1 45 3.33 0.56
Caucasian 82.4% 26 74.2% 49 72.2% 39 8.82 .002**
Asian 9.5% 3 3.0% 2 5.0% 3
African American 4.5% 2 12.8% 8 13.0% 7
Hispanic 3.7% 1 10.0% 7 9.8% 5
Dieting and weight history Mean SD Mean SD Mean SD F p d
Historical highest weight (in pounds) 161.04 58.22 199.56 51.8 213.41 52.8 7.92 .003** 0.51
Age at first diet (in years) 18.55 6.97 14.55 5.6 11.47 7.1 6.29 <.001*** 0.41
Weight suppression (in pounds) 14.96 15.6 16.15 15.51 17.76 17.64 0.09 .90 0.002
Weight change in past 6 months 4.76 .57
No change 45.6% 15 40.0% 26 39.7% 21
Weight loss 4.5% 1 20.0% 13 0.0% 0
Weight gain 27.3% 9 20.0% 13 35.7% 19
Weight fluctuation 22.7% 7 20.0% 13 23.9% 13
Dieting status 1.52 .46
Dieters 33.3% 11 33.3% 22 54.5% 29
Non-dieters 66.7% 21 66.7% 44 45.5% 25
Reasons for dieting 10.80 .09
Dieting to lose weight 57.1% 18 36.8% 24 34.2% 18
Dieting to maintain weight 21.4% 7 21.1% 14 2.6% 1
Dieting history 12.29 .002**
Diet in the past 42.1% 13 51.4% 34 73.8% 40
Did not diet in past 13.0% 4 4.5% 3 2.6% 1
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Note: SD = standard deviation; d = Cohen′s d; BMI = body mass index; * p < .05; ** p < .01; *** p < .001

Between-group univariate ANOVA indicated significant differences between groups on age at first diet and historical highest weight. O-BN group had a significantly younger age at first diet than OW-BN and NOW-BN groups, which did not differ. Historical highest weight was significantly greater in the O-BN group compared to both OW-BN and NOW-BN groups, while OW-BN and NOW-BN groups did not significantly differ. A chi square test of independence showed significant differences for past dieting attempts between the groups. Significantly more individuals in the O-BN group endorsed dieting in past compared to OW-BN and NOW-BN groups. No significant differences between the three groups were found on current dieting status or reasons for dieting between the groups. Contrary to our hypothesis, the groups did not significantly differ on weight suppression.

As shown in Table 2, similar results were observed when BMI was included as a continuous variable, such that higher BMI significantly predicted older age, older age at first diet, and greater historical highest weight across the full sample (all ps < 0.01). Consistent with between-group comparisons, BMI examined continuously was not significantly associated with weight suppression (p > .05).

Table 2.

Association between BMI as a continuous variable with outcome variables.

Outcome variables BMI as predictor variable
b(SE) p ΔR2
Age 0.12 (0.22) 0.01** 0.19
Age at first diet 0.12 (0.19) <.001*** 0.17
Historical highest weight 0.14 (0.19) 0.01** 0.16
Weight suppression 0.09 (0.21) 0.09 0.06
BN pathology
EDE Shape concerns subscale 0.22 (0.08) 0.001** 0.19
EDE Weight concerns subscale 0.30 (0.11) <.001*** 0.22
EDE Eating concerns subscale 0.002 (0.12) 0.11 0.01
EDE Restraint subscale 0.18 (0.07) 0.001** 0.17
EDE global scores 0.01 (0.09) 0.10 0.01
Objective binge episodes 0.01 (0.22) 0.10 0.03
Subjective binge episodes 0.04 (0.18) 0.15 0.04
Objective overeating episodes 0.13 (0.09) 0.01** 0.15
Self-induced vomiting 0.17 (0.30) 0.01** 0.17
Laxative misuse 0.12 (0.13) 0.01** 0.11
Diuretics misuse 0.11 (0.19) 0.01** 0.14
Driven exercise 0.01 (0.11) 0.11 0.09
TFEQ Cognitive restraint subscale 0.11 (0.08) 0.01** 0.17
Body esteem −0.23 (0.19) <.001*** 0.21
Depression 0.003 (0.10) 0.18 0.01
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Note: ΔR2 = R-square change; EDE = Eating Disorders Examination version 17.0; TFEQ = Three Factor Eating Questionnaire 18-item Revised; ** p </ = .01; *** p < .001.

Bulimia nervosa symptomatology and depression

As shown in Table 3, between-group univariate ANCOVAs (age as proxy for illness duration included as covariate in analysis) indicated significant differences among groups on EDE shape and weight concern. Post hoc tests using Bonferroni corrections indicated that O-BN group scored significantly higher than the other groups on shape (p = .002, d = 0.41) and weight concerns (p = .002, d = 0.42), which is consistent with our hypothesis. NOW-BN group scored significantly higher than the OW-BN group on shape (p < .001, d = 0.44) and weight concerns (p = .009, d = 0.39). As hypothesized, O-BN group demonstrated significantly lower body esteem on BES (p = .008, d = 0.39) compared to other two groups. NOW-BN group demonstrated significantly lower body esteem (p = .009, d = 0.33) than the OW-BN group. When examining BMI as a continuous predictor across the full sample, BMI was significantly, positively associated with EDE shape and weight concerns and significantly, negatively associated with body esteem (all ps < .01; see Table 2). No differences were found between groups on EDE eating concern and global scores in either between-group analyses or when examining BMI as a continuous predictor.

Table 3.

Comparison of groups on shape and weight concerns, body esteem, and depression.

No Overweight or Obesity
(n = 32)		 Overweight
(n = 66)		 Obesity
(n = 54)		 F p d
Mean SD Mean SD Mean SD
EDE Shape Concern 3.32 1.81 2.32 1.05 4.82 1.06 4.75 <.001*** 0.42
EDE Weight Concern 1.98 0.99 2.28 1.44 4.01 0.98 4.01 .002** 0.41
BDI-II 23.88 10.36 24.00 12.46 23.36 8.23 0.22 .79 0.006
No Overweight or Obesity
(n = 31)		 Overweight
(n = 26)		 Obesity
(n = 36)		 F p d
BES 2.31 0.64 1.99 0.91 2.49 0.85 1.99 .008** 0.39
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Note: d = Cohen′s d; EDE = Eating Disorders Examination version 17.0; TFEQ = Three Factor Eating Questionnaire 18-item Revised; BES = Body Esteem Scale; BDI-II = Beck′s Depression Inventory-II; * p < .05; ** p < .01; *** p < .001

As shown in Table 4, between-group univariate ANCOVAs (age as proxy for illness duration included as covariate in analysis) indicated significant differences among groups on EDE restraint. As hypothesized, post hoc tests using Bonferroni corrections indicated that O-BN group scored significantly higher than the other groups on dietary restraint (p = .01, d = 0.31). OW-BN and NOW-BN did not significantly differ on restraint. Consistent with hypotheses, O-BN group also endorsed higher cognitive restraint subscale on TFEQ compared to the other groups. In regression model, where BMI was entered as a continuous variable, similar results were observed (see Table 2). BMI significantly predicted dietary restraint on EDE and cognitive restraint on TFEQ (both ps < 0.01), such that higher BMI was associated with greater dietary and cognitive restraint.

Table 4.

Comparison of groups on cognitive restraint and frequencies of meal and snacks consumption based on BMI status.

No Overweight or Obesity (n = 32) Overweight (n = 66) Obesity (n = 54)
Mean SD Mean SD Mean SD F p d
EDE Restraint Subscale 2.64 1.47 2.26 1.46 4.44 1.39 3.01 .01* 0.31
EDE Eating Concerns 2.26 1.34 3.08 1.21 2.26 1.17 0.32 .74 0.03
0.84 .84 0.09
TFEQ Cognitive Restraint Subscale 10.65 3.81 10.48 4.11 19.9 2.44 0.47 .003** 0.41
Frequencies of Meal and Snack Consumption by BMI Group
Frequency Breakfast Mid-morning Snack Lunch Mid-afternoon Snack Dinner Evening Snack Nocturnal Eating
Obesity (n = 54)
Absent 3 5.6% 7 13.0% 5 9.3% 10 18.5% 0 0.0% 1 1.9% 12 22.2%
1–5 days 2 3.7% 3 5.6% 4 7.4% 6 11.1% 0 0.0% 1 1.9% 28 51.9%
6–12 days 2 3.7% 4 7.4% 3 5.6% 6 11.1% 0 0.0% 2 3.7% 7 13.0%
13–15 days 2 3.7% 4 7.4% 3 5.6% 5 9.3% 0 0.0% 2 3.7% 2 3.7%
16–22 days 11 20.4% 9 16.7% 10 18.5% 7 13.0% 2 3.7% 4 7.4% 4 7.4%
23–27 days 16 29.6% 13 24.1% 13 24.1% 14 25.9% 1 1.9% 13 24.1% 1 1.9%
28 days 18 33.3% 14 25.9% 16 29.6% 6 11.1% 51 94.4% 31 57.4% 0 0.0%
Total N 54 100% 54 100% 54 100% 54 100% 54 100% 54 100% 54 100%
Overweight (n = 66)
Absent 21 31.8% 7 10.6% 12 18.1% 12 18.2% 0 0.0% 10 15.2% 53 80.3%
1–5 days 7 10.6% 14 21.2% 6 9.1% 14 21.2% 0 0.0% 7 10.6% 5 7.6%
6–12 days 8 12.1% 9 13.6% 5 7.6% 8 12.1% 0 0.0% 5 7.6% 8 12.1%
13–15 days 6 9.1% 9 13.6% 4 6.1% 7 10.6% 0 0.0% 2 3.0% 0 0.0%
16–22 days 6 9.1% 10 15.2% 9 13.6% 8 12.1% 5 7.6% 5 7.6% 0 0.0%
23–27 days 8 12.1% 9 13.6% 16 24.2% 8 12.1% 3 4.5% 12 18.2% 0 0.0%
28 days 10 15.2% 8 12.1% 14 21.2% 9 13.6% 58 87.9% 25 37.9% 0 0.0%
Total N 66 100% 66 100% 66 100% 66 100% 66 100% 66 100% 66 100%
No Overweight or Obesity (n = 32)
Absent 10 31.3% 20 62.5% 9 28.1% 5 15.6% 0 0.0% 9 28.1% 31 96.9%
1–5 days 4 12.5% 2 6.3% 5 15.6% 5 15.6% 0 0.0% 2 6.3% 0 0.0%
6–12 days 5 15.6% 3 9.4% 0 0.0% 6 18.8% 0 0.0% 2 6.3% 1 3.1%
13–15 days 3 9.4% 1 3.1% 0 0.0% 6 18.8% 0 0.0% 2 6.3% 0 0.0%
16–22 days 3 9.4% 0 0.0% 1 3.1% 1 3.1% 4 12.5% 8 25.0% 0 0.0%
23–27 days 3 9.4% 0 0.0% 5 15.6% 2 6.3% 5 15.6% 5 15.6% 0 0.0%
28 days 4 12.5% 6 18.8% 12 37.5% 7 21.9% 23 71.9% 4 12.5% 0 0.0%
Total N 32 100% 32 100% 32 100% 32 100% 32 100% 32 100% 32 100%
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Note: d = Cohen′s d; EDE = Eating Disorders Examination version 17.0; TFEQ = Three Factor Eating Questionnaire 18 item Revised; * p < .05; ** p < .01; *** p < .001

Comparisons of meal and snack frequencies were used to assess for the presence of actual caloric restriction. Chi-square analyses revealed significant differences in frequency of meal or snack consumption between the groups (all ps < .001). Table 4 shows the frequency of meals and snacks consumed in the past 28 days for all participants. As hypothesized, compared to the OW-BN and NOW-BN groups, on average, O-BN group ate more regularly throughout the day. For example, 25% of O-BN group consumed at least three meals and two snacks in the past 28 days compared to 12.1% and 13% in OW-BN and NOW-BN groups, respectively. Both NOW-BN and OW-BN evidenced dietary restriction. For example, 31.8% and 31.3% in the OW-BN and NOW-BN group, respectively, endorsed skipping breakfast and 18.1% and 28.1% reported skipping lunch on half of the past 28 days. Dinner was the most consumed meal for all the groups in the past 28 days.

The negative binomial regression revealed that BMI status significantly predicted OBE frequency. Unexpectedly, O-BN group endorsed 4.86 times lower rates of OBE relative to NOW-BN group (z = 0.94, p = .003). ZINB regression models showed that O-BN group endorsed 3.13 times greater rates of OOEs compared to NOW-BN group (z = 2.20, p = .002). Consistent with hypotheses, relative to NOW-BN group, O-BN group reported 4.30 times greater rates of self-induced vomiting (z = 2.20, p = .002), 4.01 times greater rates of laxative (z = 2.20, p = .002) and 2.08 times greater rates of diuretic misuse (z = 2.20, p = .002), and 7.13 times lower rates of driven exercise (z = 2.20, p = .002). No significant differences were found between OW-BN and NOW-BN groups on rates of these eating disorder behaviors (all ps > 0.01). No significant differences were found between O-BN and NOW-BN on rates of SBEs (p > .01) (see Tables 5 and 6). When examining BMI as a continuous predictor across the full sample, BMI was significantly, positively associated with past 28 days frequency of OOEs, self-induced vomiting, and laxatives and diuretics misuse. Continuous BMI did not significantly predict past 28 days frequency of OBEs, SBEs, and driven exercise episodes (see Table 3). Contrary to our hypothesis, groups did not differ on the degree and severity of depression (see Table 3). BMI was also not significantly associated with depression when examined continuously across the entire sample (p = .18; see Table 2).

Table 5.

Comparison of groups on disordered eating behaviors and pathology based on BMI status using means and standard deviations.

Eating Disorder Behavior in Past 28 days No Overweight or Obesity
(n = 32)		 Overweight
(n = 66)		 Obesity
(n = 54)
Mean SD Mean SD Mean SD
Objective binge episodes 17.93 22.66 11.57 10.24 7.59 12.70
Subjective binge episodes 8.59 11.80 7.70 11.73 5.69 8.71
Objective overeating episodes 1.83 5.27 1.76 4.22 4.02 8.49
Purging episodes 2.01 5.33 1.99 5.11 5.99 12.89
Self-induced vomiting episodes 2.00 9.43 2.62 8.41 15.28 20.59
Laxative misuse episodes 0.72 5.89 2.50 7.20 4.69 16.21
Diuretics misuse episodes 0.48 1.72 0.57 2.48 1.00 2.48
Driven exercise episodes 17.00 3.19 12.03 4.67 1.25 8.14
Eating Pathology
EDE global scores 2.98 1.35 2.91 1.88 2.03 1.09
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Table 6.

Comparison of groups on disordered eating behaviors based on BMI status using zero-inflated negative binomial regressions.

Eating Disorder Behavior Overweight (n = 66) Obesity (n = 54)
B SE IRR B SE IRR
Negative Binomial Regression
Objective binge episodes 0.39 0.06 1.02 −0.17 0.01 4.86
Subjective binge episodes 0.81 0.07 1.69 −0.11 0.01 1.45
Zero-Inflated Negative Binomial Regression Count Model
Objective overeating episodes 0.01 0.01 0.22 0.88 0.04 3.13
Self-induced vomiting 0.01 0.01 1.03 0.98 0.04 4.32
Laxative misuse 0.01 0.01 1.05 1.01 0.05 4.01
Diuretics misuse 0.01 0.01 1.01 0.85 0.04 2.08
Driven exercise 0.81 0.60 1.09 −0.06 0.01 7.13
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Note: NOW-BN group is the reference group

Discussion

The current study compared individuals with BN on several clinically relevant constructs by BMI status (i.e., NOW-BN, OW-BN, and O-BN). A significant majority of our sample with BN had concurrent overweight or obesity (OW-BN and O-BN), consistent with literature on increasing comorbid overweight and obesity among individuals with BN (Thomas et al., 2014; Bulik et al., 2012, Wilfley et al., 1993; Treasure et al., 1999). The average BMI of the O-BN group (BMIMean = 36.91) placed them at moderate risk for developing health-related conditions (Berrington de Gonzalez et al., 2010) in addition to those associated with BN symptoms, which may be of considerable personal significance to these individuals. The nature and magnitude of this significance may also impact treatment expectations (e.g., patients may expect treatment to facilitate both weight loss and a reduction in BN symptoms).

The first aim of the study was to compare the groups on demographics (e.g., age), diet and weight histories, and weight suppression. The groups significantly differed on age, with O-BN group being about 7 years older than NOW-BN and OW-BN groups. While we did not measure length of illness, results showed that O-BN group started dieting at a significantly younger age than OW-BN and NOW-BN groups, which could indicate an early disposition towards elevated body weight. These findings may suggest that individuals with O-BN have greater delays to receiving treatment for BN. Previous research has consistently shown that individuals having comorbid eating disorders and overweight are more likely to seek treatment for weight problems than for an eating disorder (Hart et al., 2011; Mond et al., 2009) which may explain these delays. This supports continued efforts to train healthcare providers to be attentive to potential eating pathology, even when patients do not fit the traditional stereotypical image of a patient with an eating disorder (i.e., young and thin), or when they seek treatment for other presenting problems (e.g., weight loss, bariatric surgery, anxiety, depression). Our results show that all groups had comparable weight suppression levels to those observed broadly in outpatient BN populations (Butryn, Lowe, Safer & Agras, 2006), suggesting that individuals with all weight statuses may not present to treatment at their highest weight. The lack of difference between BMI groups regarding dieting status, reasons for dieting, and weight suppression perhaps provides further support for extant theoretical models (e.g., the cognitive behavioral model of eating disorders) (Fairburn, 2008). It additionally speaks to the need for further examination of the construct of weight suppression, including determination of the most appropriate ways to calculate and categorize weight suppression values to support their clinical utility (Lowe et al., 2018).

Clinical implications of these findings include the utility of assessing weight history/trajectory (including weight suppression) during clinical intake. In individuals with BN and obesity, a combination of long history of weight control attempts, BMI associated with moderate health risks, and weight suppression (which predicts weight gain) could exacerbate BN symptoms and reduce motivation to comply with parts of treatment that could produce weight gain (e.g., regular eating, eating sufficient portions). This highlights the importance of clinical competence surrounding aligning with the patient to set treatment goals and form a working alliance, as patients may present to treatment desiring both BN symptom reduction and simultaneous weight loss. Clinicians may be encouraged to provide psychoeducation regarding the need to pause weight loss efforts to appropriately prioritize eating disorder treatment. Additionally, clinicians should perhaps be prepared to work with patients to navigate interpersonal challenges related to pausing weight loss (e.g., how to talk with healthcare providers if the patient is encouraged to lose weight, how to communicate food-related needs to family/friends and cope with pushback for not attempting to diet).

One-fourth of our sample with overweight or obesity belonged to a racial or ethnic minority group. This may reflect the limited validity of BMI across different racial groups and/or the increased prevalence of overweight and obesity in racial and ethnic minority individuals in general (Flegal et al., 2012). Studies have shown that despite elevated prevalence of overweight and obesity in some racial groups, there are marked differences in the association between overweight and obesity and negative health outcomes in these groups, indicating that BMI may be an invalid marker of health risk in non-White groups (Pan et al., 2004; Rush et al., 2007). Although studies have found similar rates of ED symptoms across racial and ethnic groups and the potentially limited validity of BMI as a marker of health risk in some racial and ethnic groups (Franko et al., 2007; Reagan & Hersch, 2005; Shaw et al., 2004), there may be instances in which it is relevant to consider differences in weight status in case conceptualization and treatment planning for racial and ethnic minorities with BN. For instance, emerging research has shown that some cultures (e.g., Latina/o/x) normalize overeating while simultaneously overvaluing shape and weight (Cachelin et al., 2014, 2017). Clinically, this suggests that treatments for BN for diverse racial and ethnic groups may need to incorporate different types of nutrition education (Cachelin et al., 2017) while also emphasizing self-acceptance and health at every size.

The second aim of our study was to examine the association between BMI and BN symptomatology and depression. Interestingly, both the NOW-BN and O-BN group demonstrated higher body dissatisfaction (i.e., shape and weight concerns, lower body esteem) than the OW-BN group. These findings may be explained by the self-discrepancy theory, which posits that discrepancies between ideal and actual body weight promote body dissatisfaction and maintain eating pathology (Lantz et al., 2018). The NOW-BN group may have abnormally high perception of their actual body or abnormally low body ideals which may contribute to higher shape and weight concerns and body dissatisfaction, whereas the O-BN group may experience higher shape and weight concerns and lower body esteem due to actual discrepancy between current and ideal weight. Treatment should focus on promoting acceptance of diverse body size and teaching skills (e.g., self-compassion exercises, radical acceptance strategies) for managing body dissatisfaction. Further clinical implications include the suggestion that clinicians consider addressing societal attitudes towards people with higher body weight (e.g., validating patients’ distress surrounding experiences with anti-fat bias/discrimination, assessing for internalized stigma against overweight/obesity). Our hypothesis that the OW-BN and O-BN groups would endorse greater depression than the NOW-BN group was also not supported, contradicting other studies that have found higher rates of depression among OW-BN and O-BN groups (Bulik et al., 2012; Masheb & White, 2012). These contradictory results may have been impacted by the COVID-19 pandemic, which began in the middle of data collection and thus affected some participants. The widespread mental health impact of the pandemic is well-documented (Dragioti et al., 2022), and depressive symptomatology is particularly prevalent. Broad increases in depressive symptoms may have flattened differences between groups. Further study, including utilization of more sensitive and nuanced assessment tools (e.g., semi-structured clinical interview), is recommended.

As hypothesized, O-BN group endorsed greater dietary restraint but lower actual restriction compared to NOW-BN and OW-BN groups. This finding is consistent with research in non-clinical samples that has shown that greater cognitive restraint is not associated with actual food restriction in naturalistic environment, such that individuals engaging in cognitive restraint maintain energy balance and weight (Stice et al., 2007, 2010). Additionally, no observed difference between NOW-BN and OW-BN groups on dietary restraint may suggest that both groups may similarly exert cognitive effort to restrain caloric intake to influence shape and weight. Future research should replicate our findings in laboratory settings and assess differences in cognitive restraint and actual eating behaviors among individuals with BN based on BMI status. Clinically, this underscores the importance of continually assessing attempted food restriction, and not just “successful” restriction efforts.

Unexpectedly, the O-BN group had fewer OBEs compared to NOW-BN and OW-BN groups. This finding may be attributed to the more regular eating pattern in the O-BN group which has been conceptualized to reduce binge eating (Fairburn, 2008), despite the elevated cognitive restraint reported by this group, further highlighting the need to distinguish cognitive restraint from actual restriction. However, the O-BN group reported greater frequency of binge eating and inappropriate compensatory behaviors and lower driven exercise compared to the NOW-BN and OW-BN groups. The presence of the elevated frequency of purging behaviors in O-BN, which have severe medical consequences (Forney et al., 2016), suggests that a higher weight status should not be viewed as an indicator of less severe BN symptomatology. Further, though speculative at this point, greater frequency of OOEs and inappropriate compensatory behaviors may partially explain the weight differences between groups. The absence of significant differences between OW-BN and NOW-BN groups on inappropriate compensatory behaviors (i.e., self-induced vomiting, laxative misuse, diuretic misuse, pathological exercise) is interesting, as it is aligned with prior literature (Masheb & White, 2012; Mitchell et al., 1990; Rotella et al., 2013) and perhaps lends support to our methodological change of distinguishing between OW-BN and O-BN groups to clarify those earlier findings.

Strengths and limitations

The current study was strengthened by the use of the EDE to assess BN symptoms. The current study had a number of limitations. The small sample size and cross-sectional design prevent causal conclusions. We did not collect data on whether disordered eating behaviors or obesity emerged first for the O-BN group. Although the DWHQ has demonstrated good psychometric properties and previous studies have substantiated the reliability of self-reported weight history (e.g., Tamakoshi et al., 2003), self-reported diet and weight histories may have been subjected to recall bias. Additionally, as is typically the case in eating disorders studies, most participants were female and white; thus, findings may not generalize to men and other racial and ethnic groups. Furthermore, given the association between weight status and proportion of racial minorities, it is possible that the observed differences in eating pathology severity are the result of differences in eating pathology across racial groups, rather than differences by weight status. Meal and snack frequencies were examined as a proxy for actual caloric restriction, although meal and snack frequencies may not directly correlate with caloric intake (for instance, individuals may eat infrequent but high calorie meals). Lastly, the study did not measure internalized weight bias, a construct that is shown to influence mood, body dissatisfaction, and eating disorder pathology. Internalized weight bias may have influenced the association between BMI and outcome variables. Future research will benefit from replicating our analysis controlling for this construct.

Overall, this study suggests that individuals with BN and obesity may have higher cognitive restraint, higher food avoidance, lower actual caloric restriction, frequent overeating episodes, and greater engagement in purging behaviors than individuals with BN without overweight or obesity and individuals with BN and overweight. Treatment for BN in individuals with concurrent obesity should focus on reducing cognitive restraint and teaching healthier weight control methods that do not reinforce body dissatisfaction (Neumark-Sztainer et al., 2004). (Additional clinical implications are included throughout the Discussion section.) Further research is warranted to better understand how existing treatment approaches should be modified for individuals with BN and comorbid obesity to better meet their clinical needs.

Increasingly, individuals with BN are presenting with comorbid over-weight or obesity. Findings from previous research comparing BN symp-toms by weight status have been mixed. Other clinically relevant characteristics such as demographic characteristics, diet and weight his-tories, and weight suppression may also differ by weight status, but these variables have never been compared across weight groups in BN. This study is the first to compare individuals with BN without overweight or obesity, individuals with BN and overweight, and individuals with BN and obesity on a number of clinical characteristics. Findings from the present study suggest that individuals with BN and comorbid obesity are older, more likely to belong to a race/ethnic minority group, began dieting at an earlier age, endorse greater attempted dietary restraint but lower actual restriction, and experience fewer objective binge episodes relative to individuals with bulimia without overweight or obesity and individuals with bulimia and overweight.

Clinical Significance.

  • Body mass index (BMI) may be related to bulimia nervosa (BN) symptoms.

  • Participants were assigned to three groups based on BMI: healthy weight, obese, and overweight.

  • Most notably, individuals with obesity and BN had distinct clinical characteristics.

  • Current treatments may need to be adapted to better address these differences.

Funding

National Institute of Mental Health, Grant/ Award Numbers: K23DK124514, R01MH122392, R34MH116021, Hilda and Preston Davis Foundation Junior Faculty Award and WELL Center Exceptional Student Award.

Footnotes

Disclosure statement

No potential conflict of interest was reported by the author(s).

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