Theorists have suggested that both dieting and negative affect play a role in the development and maintenance of bulimia nervosa. Polivy and Herman (1985)
argue that diet-induced hunger increases the likelihood of binge eating and that a reliance on cognitive controls over eating leaves dieters vulnerable to overeating when these cognitive processes are disrupted. Dieting may also maintain bulimic pathology, as people who binge eat may redouble their dietary efforts to limit weight gain, which increases the risk of further binge eating (Fairburn et al., 2003
). It has also been theorized that people binge eat in an effort to reduce negative affect (McCarthy, 1990
). Negative affect might also maintain the binge-purge cycle because bulimic behaviors result in shame, guilt, and anxiety, which may prompt people to attempt to escape these emotions through further binge eating and purging (Waller, 2002
). The dual pathway model of bulimia nervosa (Stice, 2001
) proposes that both dieting and negative affect play a role in promoting bulimic pathology, in that individuals may initiate binge eating because of either dieting or negative affect, or a combination of these factors.
Adolescent girls from epidemiologic studies who report dieting, relative to their non-dieting peers, are at increased risk for future onset of bulimic symptoms (Field et al., 1999; Neumark-Sztainer et al., 2006; Stice & Agras, 1998
; Stice, Killen, Hayward, & Taylor, 1998
), onset of threshold and subthreshold bulimia nervosa (Killen et al., 1996
) and increases in bulimic symptoms (Johnson & Wardle, 2005; Stice, 2001
; Wertheim et al., 2001). Self-reported dieting predicted bulimic symptom persistence in one study (Stice & Agras, 1998
), but not another (Fairburn et al., 2003
). Negative affect has likewise predicted onset of bulimic symptoms (Field et al., 1999; Stice & Agras, 1998
) and bulimic pathology (Killen et al., 1996
) and future increases in bulimic symptoms (Cooley & Toray, 2001; Stice, 2001
). Negative affect predicted bulimic symptom persistence in one study (Fairburn et al., 2003
), but not another (Stice & Agras, 1998
One hypothesis that follows from these two accounts of bulimia nervosa is that there may be subtypes of this disorder that conform to the dietary restraint and negative affect models (Stice & Agras, 1999
). It is important to search for reliable subtypes of psychiatric disorders because of the implications for nosology. In addition, if the subtypes show differential treatment response and clinical course, it may suggest that there are different risk and maintenance factors for the two variants of the disorder, which could have implications for treatment planning. Identification of reliable subtypes could facilitate the development of tailored treatments that are more effective. Researchers have identified reliable subtypes of alcoholism that have been found to have distinct etiologic risk factors (e.g., unique genetic influences), psychiatric comorbidity, treatment utilization, clinical course, and response to treatments (e.g., Penick et al., 1999
; Pettinati, 2001
Studies have found that individuals with bulimia nervosa can be subtyped along dietary and negative affect dimensions. Using cluster analysis with 265 treatment-seeking women with bulimia nervosa, Stice and Agras (1999)
identified a dietary-negative affect subtype (38%) and a pure dietary subtype (62%) in spilt halves of the sample; relative to the dietary subtype, the dietary-negative affect subtype reported greater weight, shape, and eating concerns, functional impairment, comorbid mood, anxiety, eating, impulse control, and personality disorders, and poorer response to cognitive-behavioral treatment. Grilo, Masheb, and Berman (2001)
replicated the evidence of a dietary-negative affect subtype (56%) and a pure dietary subtype (44%) among 48 treatment-seeking women with bulimia nervosa, and found that the former reported greater weight, shape, and eating concerns, and body dissatisfaction and that various subtyping approaches produced converging results. Stice and Fairburn (2003)
found evidence of dietary-negative affect (56%) and dietary (44%) subtypes among 82 young women from a community-recruited natural history study of bulimia nervosa and found that the former reported more frequent binge eating, compensatory behaviors, greater weight, shape, and eating concerns, functional impairment, treatment seeking, mood and anxiety disorders, and greater persistence of binge eating over a 5-year follow-up. Chen and Le Grange (2007)
replicated the evidence of dietary-negative affect (62%) and dietary (38%) subtypes with 80 treatment-seeking adolescent girls and boys with bulimia nervosa and found that the former showed greater eating and weight concerns, psychiatric comorbidity, and lower rates of abstinence from compensatory behavior after treatment.
This subtyping distinction has also emerged with individuals with binge eating disorder. Stice, Agras, Telch, Halmi, Mitchel, and Wilson (2001)
identified dietary-negative affect (63%) and dietary (37%) subtypes among 159 treatment-seeking women with binge eating disorder; the former reported significantly greater binge eating, weight, shape, and eating concerns, lifetime psychiatric disorders, functional impairment, and lower abstinence rates following treatment than the latter. Grilo, Masheb, and Wilson (2001)
identified dietary-negative affect (33%) and dietary (67%) subtypes among 101 treatment-seeking women and men with binge eating disorder, found that the former reported greater weight, shape, and eating concerns, body dissatisfaction and impulsivity, and mood disorders than the dietary subtype, and found that this subtyping distinction showed 4-week test-retest reliability; 82% were similarly classified on the two occasions (κ = .55).
This subtying distinction has also emerged with individuals with subthreshold eating pathology. Grilo (2004)
identified dietary-negative affect (43%) and dietary (57%) subtypes among 137 female psychiatric inpatients with eating disorder features and found that the former reported greater binge eating frequency, eating pathology, body dissatisfaction, depression, suicidal tendencies, and personality disturbances. Chen and Le Grange (2007)
identified dietary-negative affect (65%) and dietary (35%) subtypes among 149 outpatient adolescent girls and boys from an eating and weight disorder treatment program and found that the former reported significantly greater binge eating, and eating, weight, and shape concerns.
In four studies the dieting-negative affect subtyping distinction showed stronger concurrent and predictive validity than the purging-nonpurging subtyping distinction from DSM-IV (American Psychiatric Association, 1994). This latter approach posits that individuals with bulimia nervosa who use vomiting or laxatives/diuretics as their primary compensatory behavior are qualitatively different than those who primarily use fasting and excessive exercise for compensatory purposes. Stice and Fairburn (2003)
found evidence of concurrent and predictive validity for 14 of the 16 validation variables for the dietary-negative affect distinction, but for only 2 of the 16 variables when participants who reported purging were compared to those who did not. Grilo (2004)
found evidence of concurrent and predictive validity for 14 of the 16 validation variables for the dietary-negative affect distinction, but for only 2 of the 16 variables when those reporting purging behavior were compared to those who did not. Chen and La Grange (2007)
found evidence of concurrent and predictive validity for 5 of 9 validation variables for the dietary-negative affect distinction, relative to 2 of the 9 variables when those reporting frequent purging were compared to those who did not. Parenthetically, Grilo, Masheb, and Wilson (2001)
found that the dietary-negative affect subtype differed significantly from the dietary subtype on 7 of the 16 validation variables, but that subtypes created based on the presence or absence of major depression differed only on 2 of the 16 variables.
The evidence that the dietary-negative affect subtype shows elevations on numerous eating pathology measures might be interpreted as suggesting that these subtypes capture a severity continuum, rather than represent true latent subtypes. However, three factors seem to argue against this interpretation. First, it is not always the case that the dietary-negative affect subtype shows elevations in core bulimic symptoms relative to the dietary subtype. For example, in the largest study to date, the two subtypes differed on frequency of laxative abuse and weight, shape, and eating concerns, but not on frequency of binge eating, vomiting, or diuretic abuse (Stice & Agras, 1999
). Second, the variance explained by bulimic symptom variables is typically small relative to that explained by negative affect variables. For instance, in Stice and Agras (1999)
eating disorder symptoms explained an average of 7% of the variance between subtypes, whereas the negative affect measures explained an average of 55% of the variance. Third, Grilo, Masheb, and Wilson (2001)
found that subtypes of binge eating disorder patients based on severity of binge eating differed on only 1 of the 16 validation variables, whereas those based on the dietary-negative affect distinction differed on 7 of these 16 variables.
Collectively, these studies provide considerable evidence that the dietary-negative affect subtyping distinction is reliable, in that similar results emerged from eight independent studies that examined treatment-seeking and community samples of individuals with bulimia nervosa, a mix of various eating disorders, binge eating disorder, and only eating disorder features. Moreover, similar results emerged when split half-replication was employed, when different cluster analytic algorithms were used, and when participants were subtyped repeatedly over time. These studies also provide considerable evidence for the validity of this distinction, in that the dietary-negative affect subtype typically evidenced greater eating pathology, functional impairment, psychiatric comorbidity, a poorer response to treatment, and a more protracted clinical course, relative to the dietary subtype. Further, this subtyping distinction had greater concurrent and predictive validity than the purging-nonpurging subtyping distinction. These findings suggest that dietary restraint is a central feature of bulimia nervosa, but that negative affect occurs in only a subset of cases and that the combination of dietary restraint and depressive affect signals a more severe variant of this disorder that is more difficult to treat and shows greater chronicity. Theoretically, elevations in negative affect that persist over time cause people to engage in maladaptive behaviors, such as binge eating and compensatory behaviors, to reduce negative affect, increase positive affect, or distract themselves from emotional distress (Stice & Agras, 1999
). The confluence of dietary restraint and affective disturbances may be particularly problematic because both increase the odds of persistent binge eating, which may result in elevated symptoms, functional impairment, treatment utilization, a longer clinical course, and a worse treatment response.
The mounting evidence for the reliability and validity of this subtyping distinction suggests that additional studies should investigate this subtyping distinction. This is particularly vital because of the call for empirical data to inform the revision of DSM (Walsh, 2007
). Thus, the first aim was to replicate this subtyping scheme in two independent samples to provide further evidence of the reliability of this distinction. Extending prior studies that have typically examined individuals with full threshold diagnoses, we examined participants with threshold and subthreshold bulimia nervosa. This is important because half of those seeking treatment for eating pathology do not meet full diagnostic criteria for anorexia and bulimia nervosa (Fairburn & Harrison, 2003
; Fisher, Schneider, Burns, Symons, & Mandel, 2001) and because subthreshold bulimic pathology is associated with current and future functional impairment, emotional distress, medical problems, and treatment seeking (Lewinsohn et al., 2000; Stice, Marti, Spoor, Presnell, & Shaw, 2008
; Striegel-Moore et al., 2003). Indeed, scholars have called for further research on subthreshold levels of eating pathology because this constitutes a large portion of Eating Disorder Not Otherwise Specified diagnoses (Fairburn & Harrison, 2003
; Wilson, Becker, & Heffernan, 2003). The second aim was to investigate the test-retest reliability of the dietary-negative affect distinction because only one prior study examined this question. The third aim was to further investigate the concurrent validity of this subtyping distinction by replicating the evidence that the dietary-negative affect subtype shows greater eating pathology and related disturbances, social impairment, and mental health treatment than the dietary subtype. The fourth aim was to generate additional evidence of predictive validity by testing whether the subtyping scheme predicted course of illness and change in body mass, as this would have implications for treatment planning. The fifth aim was to test whether the dietary-depressive subtyping distinction has greater concurrent and predictive validity than the purging-nonpurging subtyping distinction. A key question regarding a new subtyping distinction is whether it is an improvement over extant schemes (Wonderlich, Crosby, Mitchell, & Engel, 2007