1. Introduction
Impulsivity is an umbrella term that encompasses various characteristics related to impulsive thoughts, behavior, and decisional processes [
1]. Delay discounting (DD) describes the tendency to choose smaller immediate rewards over larger delayed rewards and is considered to represent decisional impulsivity [
2]. A robust body of literature, including several meta-analyses [
3,
4] has demonstrated that elevated DD (i.e., a preference for smaller immediate rewards) is associated with greater substance use behavior. Most of the literature has examined the discounting of money, which has an explicit value across participants and can readily be compared across studies. Thus, most work has demonstrated that greater discounting of money is strongly associated with greater substance use behaviors.
More recently, advancements in the DD research domain have yielded more nuanced examinations of preferences for money relative to rewards that are most relevant to a disorder (e.g., alcohol for individuals with risky drinking behavior), termed cross-commodity DD. Importantly, cross-commodity DD paradigms can enhance the ecological validity of DD tasks by asking participants to choose between disorder-relevant rewards (e.g., alcohol) and a strong alternative reward (i.e., money), which may better parallel decisions made in the real world. Additionally, single-commodity DD tasks may facilitate simple explanations of decision-making behavior that in reality may be more nuanced [
5]. For example, high DD in single-commodity tasks is typically interpreted as individuals having an inability to wait for a delayed rewards (because they typically choose the immediate reward in the task). However, an alternative interpretation is that individuals may disprefer the reward available at a delay (e.g., large quantities of a substance may be considered aversive), and therefore, individuals may tend to select the immediate reward. Individuals may be willing to wait for a disorder-specific reward under certain conditions; however, this cannot be elucidated from single-commodity tasks. Cross-commodity DD can overcome this limitation and can more clearly elucidate patterns of preference and decision-making by switching the immediate and delayed reward types across tasks (e.g., tasks of alcohol now money later or money now alcohol later). In doing so, researchers can distinguish whether individuals may prefer a reward when immediately available and whether they are willing to wait for their preferred reward at a delay because the alternative reward (e.g., money) in the task would be different from the target reward (e.g., alcohol). Thus, cross-commodity DD tasks help to more thoroughly elucidate choice patterns for different health-relevant rewards. In support of this premise, cross-commodity DD studies have found that individuals who engaged in greater substance use exhibited a preference for immediate rewards and were willing to wait for their substance of choice (e.g., alcohol and cannabis) when available at a delay [
6,
7]. Thus, cross-commodity DD tasks can reveal choice patterns and willingness to wait for a commodity that is aligned with an individual’s use behavior or disorder.
Binge eating behaviors have notable parallels with substance use, both in patterns of use and decisional processes that may lead to use [
8,
9]. Regarding use patterns, binge eating and substance use both occur on a dimensional scale from infrequent, occasional use of a substance/rewarding food to compulsive and excess use in binge drinking occasions or binge eating episodes. Binge eating behavior may range from passive overconsumption, which may occur when inattentively consuming highly rewarding foods, to loss of control eating, which is more characteristic of objective binge eating behavior identified in the eating disorder literature [
10,
11,
12,
13]. On this continuum, as has been observed with substances, individuals may be motivated to consume palatable foods for their acute rewarding effects and/or to cope with negative emotions during binge eating occasions [
14,
15,
16,
17,
18]. Foods that are acutely rewarding to consume and are typically the target of binge eating occasions [
14,
16] are hyper-palatable foods (HPFs), which contain combinations of palatability-inducing nutrients (e.g., fat and sodium) at moderate to high levels that do not occur in nature [
19,
20,
21,
22]. HPFs are strong reinforcers similar to other psychoactive substances and are hypothesized to influence wanting and drive to consume them in a similar manner as psychoactive substances [
21,
23,
24]. The incentive sensitization theory of motivational behavior, which was originally developed to describe substance use behavior [
25] and was subsequently applied to food [
26], posits that individuals initially may seek out HPFs due to the initial liking and acute rewarding effects of the foods [
27,
28]. Over time, repeated exposure to HPFs through binge eating may disrupt reward and motivation pathways in the brain and serve to dysregulate food reinforcement processes. Individuals may experience greater wanting or desire to consume HPFs and become hyper-sensitive to food cues in the environment, termed sensitization, leading to further HPF seeking and intake behavior [
29,
30,
31]. Sensitization may lead to increased cravings and compulsive eating and drive further HPF intake during binge episodes.
Given that binge eating of HPFs shares similar reinforcement and sensitization patterns to substance use, it may be reasoned that decisional processes related to DD may also play a role in binge eating as they do in substance use behavior. For example, individuals with elevated DD may prefer the immediate rewarding effects of HPFs over delayed rewards such as long-term physical and mental health. This premise aligns with findings in the literature that demonstrated individuals who engaged in binge eating had higher instances of health conditions such as obesity [
32,
33] and type 2 diabetes [
33,
34], which may indicate individuals who binge eat may prefer immediate rewards from HPFs over larger delayed rewards such as healthy body weight. Therefore, binge eating may be associated with higher rates of DD, which would mirror the robust literature on DD for substance use [
35].
Among preliminary studies of individuals who engage in binge eating behavior, discounting of money has been examined [
36,
37]; however, discounting of HPFs has not, which represents a significant gap in the literature. In the closest area of the literature to date, one prior study that used cross-commodity DD tasks revealed that individuals with excess dietary intake of HPFs and elevated HPF cravings tended to discount HPFs more steeply compared with a strong alternative reward (money), suggesting that discounting was specific to HPFs and not to rewards generally [
38]. Thus, preliminary evidence suggests that the discounting of HPFs may be particularly relevant for individuals who engage in excess HPF intake behavior. In addition to preliminary evidence, there are known characteristics of binge eating that may be expected to increase DD for HPFs specifically (and not rewards generally). For example, binge eating often involves elements of waiting to consume HPFs [
39]. For example, individuals who binge eat are typically constrained by their environment (e.g., work and social events), may be unable to engage in binge eating at a specific moment, and may wait until later, effectively engaging in excess HPF intake at a time delay. Additionally, binge eating behaviors are commonly preceded by dietary restraint and caloric restriction [
40,
41,
42], which can lead to increased discounting of food due to physiological hunger [
43,
44] and urges [
45,
46,
47,
48]. Thus, research is needed to distinguish DD for HPFs specifically from a general inability to wait for rewards, which can be achieved via cross-commodity DD tasks, while accounting for factors like hunger to address potential dietary restriction.
While motives to consume HPFs (e.g., to experience their rewarding effects or to cope with negative emotions) and binge eating behavior may be most robust among clinical populations with binge-spectrum disorders, both occur on a continuum among the general population [
49] and are implicated in a variety of physical and mental health consequences such as insulin resistance (pre-diabetes), obesity, mood disturbances, and anxiety [
50,
51,
52,
53]. However, no prior work has examined the role of DD in motives to consume HPFs and binge eating behavior among the general population; all prior work has focused on clinical populations. Understanding the potential role of DD in eating motives and binge eating on a dimensional scale in the general population is critical from a prevention perspective; if DD plays a role in binge eating behavior, which may have downstream physical and mental health consequences, early intervention approaches could be designed to target DD as a risk factor, to prevent future health consequences.
The purpose of the current study was to examine the associations between the DD of HPFs, and palatable eating motives and binge eating behavior among a general population sample, characterizing binge eating behavior on a dimensional scale. DD was examined using single- and cross-commodity discounting tasks with HPF and money to distinguish the DD of HPF relative to other rewards (e.g., money). We hypothesized that greater willingness to wait for HPFs when available at a delay and a relative preference for HPFs when available immediately would be associated with the endorsement of higher binge eating behavior and palatable eating motives (i.e., coping and reward enhancement).
4. Discussion
This study examined the role of delay discounting (DD) in palatable eating motives and binge eating behavior, characterized on a continuum in a general population sample. Overall, the findings demonstrated that the tendency to choose HPFs now over a strong alternative reward (money) was positively associated with binge eating behavior and the motive to consume HPFs for their rewarding effects. Notably, the findings were specific to the discounting of HPFs and were not observed in other discounting conditions with money as the reward. Thus, the findings suggested that discounting specific to HPFs, and not the tendency to discount delayed rewards more generally, may play a role in reward-motivated eating and binge eating behavior. The effects were present in both small- and large-magnitude DD conditions, which indicated the stability of the findings. The observed effect sizes were small to moderate and were consistent with the prior literature on the DD of HPFs for HPF-intake related outcomes [
38] and the broader DD substance use literature [
3]. Considered collectively, our findings and the robust prior literature suggests that DD is a relevant and consistent factor in decision-making related to health behaviors [
3,
4]. There were no other significant associations between the single- and other cross-commodity conditions, and eating to cope or binge eating behavior. Thus, our findings overall suggest that individuals among the general population who exhibit decisional impulsivity specific to HPFs may endorse greater motivation to consume HPFs for their rewarding effects and may engage in greater binge eating behavior.
The current study was the first to examine the role of discounting in palatable eating motives and found that elevated DD was associated with the motive to consume HPFs for their rewarding effects (i.e., reward enhancement motive). The effects were small in magnitude but were replicated across low- and high-magnitude DD conditions, suggesting the effect may be reliable and worth further examination. Considered in the context of theoretical support, the reward enhancement motive may be viewed as reflecting wanting or drive to consume HPFs, which occurs via sensitization [
27]. DD for HPFs may facilitate acting on strong wanting and drives to consume HPFs, particularly in the presence of HPF cues (e.g., advertisements and signs) in the environment [
28,
31]. Furthermore, with repeated HPF consumption over time, HPFs may have impacts on areas of the brain involved in self-regulation [
29,
64,
65], which may exacerbate existing discounting tendencies and facilitate further HPF seeking and intake. Nevertheless, due to the preliminary nature of these findings, future research is needed to examine these processes longitudinally.
The null findings from the coping analyses suggest that decisional impulsivity may not play a major role in coping-motivated eating. The results were surprising given that eating to cope with negative emotions has been a robust and reliable correlate with excess HPF intake and disordered eating behavior in the literature [
66]. It may be that eating to cope is more of a planned experience and not driven by decisional impulsivity. However, if this was the case, we would have expected to observe a positive correlation between willingness to wait for HPFs later in the DD tasks and coping motive endorsement, although we did not. In the broader literature, specific types of impulsivity (e.g., reward sensitivity and attentional impulsivity) have been associated with HPF intake and related outcomes [
67,
68,
69,
70]. Therefore, more work is needed to understand whether and to what degree various types of impulsivity may be involved in coping-motivated eating.
Our findings extend the existing literature on DD for binge eating, which to date has focused on the DD of money using single-commodity tasks [
36]. Given that components of the binge eating process may be expected to elevate discounting of HPF specifically, our methodological advancement in the use of cross-commodity DD tasks that assessed preferences for HPF relative to money represents a particular strength of this study. Furthermore, our use of a binge eating measure that was appropriate for healthy (non-clinical) populations facilitated a dimensional characterization of binge eating behavior. The participants utilized most of the binge eating behavior scale, which provided high variability in their responses and likely increased our ability to detect associations with discounting. Our resulting findings were nuanced and aligned with the premise that binge eating behavior may be related to decisional impulsivity specific to HPFs (and not decisional impulsivity more broadly). Our findings are consistent with one prior study that used a cross-commodity DD task and found that the tendency to choose HPFs immediately over delayed money was associated with the excess dietary intake of HPFs, craving for HPFs, and body mass index among a general population sample [
38]. Overall, examining the cross-commodity DD of HPFs and money may have utility in characterizing the role of decisional impulsivity in excess HPF intake behaviors and, if our findings were to be replicated, may suggest that decisional impulsivity specific to HPFs may play a role in binge eating behavior.
In contrast to our hypotheses, we did not find that individuals who engaged in binge eating behavior were willing to wait for HPFs when available at a delay. While this was the first study to test this premise with binge eating, prior work in the substance use literature has reported that individuals with risky substance use were willing to wait for their substance of choice, assessed using cross-commodity discounting paradigms [
5,
6,
7]. It may be that individuals with high decisional impulsivity toward HPFs are not willing to wait for HPFs, which may represent a distinction from substance use behavior. Another consideration may be that HPFs saturate the US food environment (69% of available foods as of 2018) [
71] and are readily available in a manner distinct from other substances (e.g., alcohol and opioids). In this regard, the DD task may have had limited ecological validity for participants and may be reflected in the null findings.
Another consideration is that this study focused on one type of impulsivity (i.e., decisional impulsivity) and did not address other established eating constructs, such as emotional eating, which could have influenced the findings. For example, another aspect of impulsivity that may be relevant for our findings is urgency, defined as acting rashly in response to strong emotions. Urgency may be considered to reflect emotional eating, as addressed in the disordered eating literature, which involves eating in response to distress and negative emotions [
72]. In our study, urgency and emotional eating would be most closely reflected in the coping motive, which addressed eating to cope with stress and negative emotions [
49,
73,
74,
75]. If urgency/emotional eating had a substantial role in the findings, we would have expected to observe significant associations across both coping and reward enhancement motives with DD of HPFs. However, there were no significant correlations between coping motive endorsement and the DD of HPFs (or money); rather, significant associations were observed only between reward enhancement and the DD of HPFs. Thus, our findings do not support the premise that urgency or emotional eating may explain our observed results. However, given the robust associations observed in the prior literature regarding emotional eating, urgency, and disordered eating, future work is needed to replicate and extend these findings.
This study had several limitations. First, the sample was a convenience sample primarily comprising White, college-educated individuals, which may limit generalizability to the broader US population. Additionally, this sample was drawn from a crowdsourcing platform, and as such, there may be additional limitations to generalizability; the individuals may have had familiarity with experimental and behavioral tasks and had awareness of the attention check procedures commonly employed in crowdsourced surveys to ensure data quality [
76]. Furthermore, the participants were aware that they were completing a study on food choices, which may have introduced demand characteristics. It is possible that implicit measures (e.g., implicit association tests) may have additive utility in examining the relationship between decisional impulsivity, and binge eating and eating motives in such contexts. Third, this study used hypothetical rather than real rewards in the DD task [
77], which may impact the perception of risk and decision-making during the task [
78]. Specifically, using hypothetical rewards may have introduced response bias as participants’ choices may have been different if presented with real rewards (e.g., actual food and money). Nevertheless, research specifically comparing hypothetical and real DD data that use food rewards has indicated they may closely align [
44]. Another important limitation is this study did not include a validated dietary restraint measure. Given that dieting practices like dietary restraint and caloric restriction have been found to be a predictor of binge eating [
40,
41,
42], it is important to account for how such behaviors may influence their discounting. We attempted to address this limitation by including hunger as a covariate in all analyses to serve as a proxy for measuring dietary restriction, which is supported by prior work [
14]. However, future research should include more standardized measures of dietary restraint to further refine the analyses. Finally, our study was cross-sectional, and causal inferences cannot be drawn from our findings. For example, we were unable to test whether greater decisional impulsivity for HPFs may lead to increased risk for binge eating behavior over time. Future work should investigate these relationships, leveraging a longitudinal study design that can further establish causal relationships.