The relation of weight suppression and BMIz to bulimic symptoms in youth with bulimia nervosa
This study examined the association between WS and bulimic symptoms in a sample of treatment-seeking youth with BN. Youth with BN reported substantial WS at presentation to treatment (i.e., mean current WS was three-quarters of a standard deviation, representing 9.4 kg) as well as a history of substantial weight variability over time (i.e., mean greatest WS was one-and-a-half standard deviations, representing 18.1 kg), based on the CDC population BMI distribution [13]. Interestingly, current WS and greatest WS were highly negatively associated with current BMIz and lowest BMIz, respectively, despite non-significant associations in adults with BN [3, 5, 17, 18]. This may reflect the fact that youth with BN who have low current BMIz or low historical BMIz engage in weight loss behaviors developmentally earlier or more effectively than those with higher BMIz, resulting in greater current or historical weight loss, whereas those with higher BMIz may not yet have effectively engaged in behaviors that lead to WS, regardless of possible efforts to do so. In contrast, the non-significant association found in adults indicates that similar levels of WS are achieved across the BMI distribution, possibly related to greater age and more enduring attempts to suppress weight.
In keeping with WS findings in adults with BN, multivariable analyses with older youth suggest that as current WS increases, those with a high current BMIz engage in more frequent binge eating, while those with a low current BMIz engage in less frequent binge eating. This may highlight the fact that youth with lower BMIz and high WS have been more “successful” at restriction or that abstaining from binge eating becomes easier at a lower BMIz, potentially due to a dampening of hunger cues at a highly suppressed low weight. Conversely, youth with higher BMIz and high WS might be less “successful” at restricting, and more susceptible to binge eating. This suggests that WS may have a greater effect on youth with relatively higher premorbid BMIz.
Current WS was also related to compensatory behaviors in older youth with BN, in that lower current BMIz was associated with more frequent compensatory behaviors than higher current BMIz. Though the impact of BMIz on compensatory behaviors was weakened in youth with higher current WS, this finding likely suggests that youth who engage in more compensatory behaviors achieve lower BMIz, rather than the alternative potential explanation that youth with low BMIz engage in more compensatory behaviors. However, the impact of BMIz on compensatory behaviors was diminished by WS, which may reflect the fact that compensatory behaviors are less effective for maintenance of low weight in youth with higher WS.
Current and greatest WS were also associated with higher levels of dietary restraint, such that a history of WS predicts later dietary restraint, in addition to the contemporaneous relation between WS and restraint. This suggests that youth who were previously successful at restricting their intake (i.e., achieved high historical WS) are likely to continue engaging in higher levels of dietary restraint. In other words, historical WS can be viewed as a potential risk factor for ongoing dietary restraint. The relation between current WS and dietary restraint also suggests that youth with BN are relatively successful in their efforts to restrict. Despite small to medium correlations between greatest WS and older age, longer duration of illness, and greater weight and shape concern, greatest WS was not associated with bulimic behaviors after adjusting for these variables, despite the association found in adults with BN [3]. Together, these findings suggest that current WS is important in the conceptualization of BN psychopathology in youth, whereas historical WS (i.e., greatest WS) is less relevant given its association with dietary restraint only.
To our knowledge, this is the first study of WS in a sample of youth with BN. In keeping with the adult literature, analyses examined the potential interaction between WS and BMIz and adjusted for dietary restraint, as well as additional factors associated with WS (e.g., age, duration of illness, and weight and shape concern). Several limitations include the use of cross-sectional data within a modestly-sized treatment-seeking sample with missing data on weight history and the inability to examine WS in relation to eating concern. Furthermore, WS calculations were limited to using youth’s current height, which may have underestimated greatest WS. Reliance on self-report may have further biased WS estimates. Indeed, the discrepant results for youth ages 16 and older suggest that this method of assessing WS might have been inadequate for youth with more frequent changes in height (using age as a proxy for height stability). WS assessment in developing youth still growing in height may require a more sophisticated, developmentally sensitive approach given the need to account for age, height, and weight to properly calculate WS at times of interest. Rather than assessing highest and lowest weight, patient’s historical BMI-for-age growth charts should be used to determine highest and lowest BMI percentiles, using multiple weights, heights, and ages from medical records to calculate BMIz. Comprehensive growth charts for each patient would have provided a better estimate of WS, which was unfortunately not possible in the current study.