Comparing Momentary Predictors of Binge Eating between Groups
The current study aimed to identify and compare the momentary predictors of binge eating episodes and heavy drinking episodes among individuals with co-morbid binge eating and heavy drinking (BE+HD). The results indicate that the strength of the relationship between momentary risk factors, in particular the presence of food and the presence of within-day dietary restraint, and risk for subsequent binge eating episodes were either equivalent between groups or stronger for the BE-only group compared to the BE+HD group. These results differ from theoretical models suggesting that the underlying traits associated with BE+HD (e.g., impulsivity, reward sensitivity, affect dysregulation) result in a higher susceptibility for binge eating in response to momentary risk factors compared to BE-only. One possibility is that individuals with BE+HD exhibit varying levels of these underlying traits and that there is a subset of individuals with BE+HD that are at a higher risk for binge eating in response to momentary cues. Future research should investigate if individuals with BE+HD scoring higher on these underlying traits (e.g., more impulsive, more sensitive to rewards) are more likely to binge eat following momentary risk factors.
Although the hypothesized moderation model was not supported by the study results, an important finding to highlight is that the presence of food and the presence of dietary restraint were related to increased odds for binge eating for both BE+HD and BE-only. These results suggest that the processes through which the presence of food and dietary restraint maintain binge eating in individuals with BE-only also contributes to the maintenance of binge eating for individuals with BE+HD (Sobik et al., 2005; Stice, 2001). These results may indicate that treatments such as Cognitive Behavioral Therapy for binge eating (CBT-E), which targets dietary restraint and urges to binge eat when palatable foods are available, will likely also be effective at reducing binge eating for BE+HD . There is preliminary research to support that CBT-E improves eating disorder symptomology for individuals with BE+HD (Karačić et al., 2011). However, given the limited number of studies on treatment effectiveness for patients with BE+HD, further research is needed to assess if clinical interventions targeting dietary restraint and urges to binge eat when in the presence of palatable foods improve binge eating outcomes for individuals with BE+HD.
Predictors of Binge Eating and Heavy Drinking among BE+HD
While results are preliminary and require replication, our findings suggest some potential high-risk situations that could be targeted in clinical interventions. For example, results found that situations where alcohol was easily accessible increased the risk for binge eating and heavy drinking for BE+HD. One possibility is that the presence of alcohol increased risk for binge eating and heavy drinking by lowering inhibitions. Exposure to alcohol cues (e.g., pictures of alcohol, alcohol smells) has been shown to negatively impact inhibitory control in non-clinical samples [32,33], which could result in difficulty resisting urges to binge eat or drink and greater risk for subsequent binge eating and heavy drinking for individuals with BE+HD. Alternatively, surveys when participants reported the presence of alcohol could be an indicator of modest alcohol use (e.g., consuming one or two alcoholic drinks). Modest alcohol consumption has been shown to “prime” an individual to consume more alcohol  and may increase risk heavy drinking in BE+HD. Furthermore, research from nonclinical samples demonstrates an effect of modest alcohol consumption on elevated hunger [35,36], which could increase urges to binge eat among BE+HD. Since the current study did not measure modest alcohol consumption, surveys when participants endorsed the presence of alcohol may also capture modest drinking episodes that did not reach heavy drinking levels (i.e., three or more alcoholic drinks), and this modest alcohol consumption could have increased risk for binge eating and heavy drinking. Whether directly or indirectly, our findings suggest that situations where alcohol is present are particularly high-risk for individuals with BE+HD. Since the presence of alcohol was reported at more than 50% of surveys by individuals with BE+HD in our study, limiting access to alcohol in one’s daily environment may be a useful clinical intervention to reduce risk for binge eating and heavy drinking for BE+HD. Further research should clarify whether the presence of alcohol alone, without alcohol consumption, increases binge eating and heavy drinking risk, and investigate whether clinical interventions that target the availability of alcohol in one’s environment impact treatment outcomes for BE+HD.
Even though individuals with BE+HD reported the presence of food more frequently than BE-only, having palatable foods accessible did not increase risk for subsequent binge eating for BE+HD as we originally anticipated. Instead, instances when individuals with BE+HD reported the absence of palatable foods were associated with a higher likelihood of heavy drinking. These results suggest that individuals with BE+HD may be more likely to turn to heavy drinking when binge eating foods are not available. It is also possible that a combination of momentary factors may increase risk for heavy drinking. For example, individuals with BE+HD may be more likely to engage in heavy drinking in situations when palatable foods are not available and alcohol is available. Other factors such as affect or social context may also contribute risk for heavy drinking during times when palatable foods are not available. Future research should aim to identify specific high-risk situations for BE+HD by testing the interactive effects of momentary risk factors on subsequent binge eating or heavy drinking.
Consistent with studies conducted among BE-only and HD-only, the current study found that attempting to restrict dietary intake on a given day was related to a higher likelihood of same-day binge eating and same-day heavy drinking for individuals with BE+HD. While we previously noted the potential benefit of treatments that target dietary restraint (e.g., CBT-E) for reducing binge eating among BE+HD, these findings suggest that treatments that target dietary restraint may also be beneficial for improving heavy drinking outcomes. In the one study to date testing the effectiveness of CBT-E on alcohol outcomes, individuals with BE+HD reported significantly greater reductions in alcohol intake at the end of treatment than BE-only (Karačić et al., 2011). It is important to note that almost 50% of patients with BE+HD in this study were still engaging in high levels of heavy drinking at the end of treatment even though their alcohol intake had decreased (Karačić et al., 2011). Therefore, although treatments targeting dietary restraint such as CBT-E show promise for improving heavy drinking outcomes in BE+HD, these treatments may need to include other relevant treatment targets (e.g., urges when alcohol is present) to affect clinically meaningful change in BE+HD.
Contrary to our initial hypotheses, affect and social context were not predictive of subsequent binge eating or heavy drinking episodes for individuals with BE+HD. These results were surprising given previous cross-sectional findings that affect was associated with risk for binge eating and heavy drinking in women with BE+HD (Birch et al., 2007). We considered a few possible explanations for these results. First, there was limited variability in affect ratings among BE+HD in our sample, which may preclude our ability to detect significant results. Second, affect was measured using a small number of EMA items (i.e., four items for negative affect, two items for positive affect) and may not have captured other relevant affective experiences (e.g., irritability, shame). Third, although social context was identified as a potential momentary risk factor given prior research in binge eating and heavy drinking literature, assessing specific environmental stressors (e.g., parties, holiday events, bars, restaurants) may provide better insight into risk factors for binge eating or heavy drinking. Overall, research with a larger sample using more affective and environmental EMA items should be conducted to understand how affect and social context impact risk for binge eating and heavy drinking among BE+HD.
Simultaneous Binge Eating and Heavy Drinking Episodes
The current study included an exploratory aim to characterize the frequency and momentary precipitants of simultaneous binge eating and heavy drinking episodes. At the surveys prior to simultaneous binge eating and heavy drinking episodes, individuals with BE+HD reported greater increases in negative affect and greater increases in positive affect (relative to their average affect ratings) and were more likely to report being with other people compared to surveys prior to non-simultaneous binge eating or heavy drinking episodes. Additionally, individuals with BE+HD reported similar rates of presence of food and presence of alcohol prior to simultaneous binge eating and heavy drinking episodes and prior to heavy drinking-only episodes. While these preliminary results suggest that momentary predictors of simultaneous binge eating and heavy drinking episodes may differ from non-simultaneous episodes among BE+HD, it is important to note that 7 of the 9 simultaneous episodes that were included in analyses were from one participant so findings may be influenced by individual factors. Future research testing momentary precipitants of simultaneous binge eating and heavy drinking episodes should consider targeted recruitment of individuals with co-occurring binge eating and heavy drinking to increase statistical power for analyses.
Limitations and Future Directions
Strengths of the current study include the use of EMA for measuring risk factors and behavior. By using repeated assessments administered multiple times a day, our study was able to examine the micro-processes maintaining binge eating and heavy drinking behavior, which is necessary for informing clinical intervention targets. The use of EMA also improved the validity and generalizability of the data, as participants were less prone to the inaccuracies of memory recall that occur in retrospective self-reports. An additional strength of the study was the focus on heavy drinking episodes (i.e., three or more alcoholic drinks in one sitting). While heavy drinking is considered less pathological than a DSM-5 alcohol use disorder or drinking episodes involving a higher quantity of alcohol (e.g., binge drinking, high-intensity drinking), the high prevalence and negative consequences associated with comorbid binge eating and heavy drinking supported the clinical relevance of studying heavy drinking in the current study.
The results of the study should be interpreted in the context of the study’s limitations. The statistical power of the current study was limited by the sample size and by the high percentage of binge eating and heavy drinking episodes not included in statistical models due to either missing data at the previous survey and binge eating or heavy drinking occurring at the first survey of the day. Another limitation was that the BE+HD group was defined by presence of heavy drinking during the EMA period, rather than through clinical interview of past drinking behavior. By choosing to define BE+HD based on data gathered through the EMA, some participants in the BE-only group may have engaged in heavy drinking recently (e.g., in the past month) but not during the EMA period, which could have reduced our ability to detect differences between groups. Future research may consider assessing BE+HD through semi-structured clinical interviews administered at baseline (e.g., Alcohol Timeline Followback; Structured Clinical Interview for DSM-5). While the use of EMA has many benefits, one limitation of EMA is the reliance on participants to accurately self-report binge eating and heavy drinking episodes. Participants may have difficulty identifying instances of loss of control during eating or quantifying amount of alcohol consumed, and therefore may misreport binge eating and heavy drinking episodes. Experimental study designs involving clinician-rated loss of control and standardization of alcohol consumed may be beneficial for objectively measuring binge eating and heavy drinking and minimizing risk for missing data. Lastly, the generalizability of our results is limited by the homogeneity of the current sample (i.e., primarily White and female). Future research should aim to replicate the current study’s results using a larger, more diverse sample of individuals with BE+HD.
Strengths and Limits
The current study was strengthened by its use of ecological momentary assessment for identifying momentary predictors of behavior and by its focus on heavy drinking, a clinically relevant problematic alcohol use behavior that occurs frequently among individuals with binge eating. Limitations of the current study include reduced statistical power, the absence of a clinical interview of alcohol use, the subjective measurement of binge eating and heavy drinking through participant self-report, and the homogeneity of the sample.