Trait Impulsivity and Choice Impulsivity in Young Adults With Binge Eating Disorder

Background: Binge Eating Disorder (BED) as a public health problem has been included in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). Akin to addictive disorders, impulsivity-related neuropsychological constructs might be potentially involved in the onset and development of BED. However, it remains unclear which facets of impulsivity are connected to overeating and binge eating behaviors among general populations. The present study aimed to detect the relationship between impulsivity and BED both on the personality-trait and behavioral-choice levels in undiagnosed young adults. Methods: Fifty-eight BED individuals and 60 healthy controls, matched on age, gender, and educational level, were assessed by using a series of self-report measurements, including the Barratt Impulsiveness Scale (BIS-11), UPPSP Impulsive Behaviors Scale (UPPSP), Delay Discounting Test (DDT), and Probability Discounting Test (PDT). Results (cid:0) Multivariate analysis of variance models revealed that compared with healthy controls, the BED group showed elevated scores on the BIS-11 Attentional and Motor impulsiveness, and on the UPPSP Negative Urgency, Positive Urgency, and Lack of Perseverance. However, BED subjects had similar discounting rates on the DDT and PDT with healthy controls. Regression models found that Negative Urgency was the only risk factor positively predicting BED. Conclusions (cid:0) These ndings suggested that typical facets of trait impulsivity, which have been recognized in addictive disorders, were associated with BED in young adults, whereas choice impulsivity was not aberrantly seen in BED. This study might promote a better understanding of the pathogenesis of BED. of this study was to explore the links of trait impulsivity and choice impulsivity with binge eating in non-treatment-seeking populations of BED. Our ndings highlighted that Negative Urgency might serve as a risk factor for BED on the personality-trait level of impulsivity, while choice impulsivity on the behavioral level was not observed to play a predictive role for BED in our study. found group higher scores on Attentional Impulsiveness d Motor showed signicant between-group differences on Urgency of Perseverance 2p and Positive Urgency 20.553, p 2p but on Lack of Premeditation (F (1,115) = 0.548, p 0.461) and Sensation Seeking (1,115) = 0.890, p Post-hoc comparisons that the BED group should be interpreted more carefully because of the possible subjective bias, and other facets of impulsivity should be further investigated using more objective tasks. In despite of these limitations, the present study rstly looked into the associations between various aspects of impulsivity and binge-eating behavior in non-clinical samples of BED, using a case-control design. Our results indicated that Attentional Impulsiveness, Motor Impulsiveness, Negative Urgency, Lack of Perseverance, and Positive Urgency were elevated in BED and especially, Negative Urgency was the only risk factor positively predicting BED. These ndings suggested that typical facets of trait impulsivity, which have been recognized in addictive disorders, were associated with BED in young adults, whereas choice impulsivity was not aberrantly seen in BED.


Introduction
Binge eating disorder (BED) is characterized by overwhelming eating desire with recurrent episodes of binge eating (at least once a week during the last three months), and lack of control over binge-eating behavior [1]. BED has been included as a separate category within the Feeding and Eating Disorders in the latest version of the Diagnostic and Statistical Manual of Mental Disorders (i.e., DSM-5) [2]. The lifetime prevalence for BED in adults is about 2% worldwide, with females having a higher risk than males [3]. In recent studies, the prevalence of BED among obese adolescents aged 12-17 years has been over 33% [4]. Adolescents and young adults have a high risk for BED due to their immature cognitive control abilities [5,6]. Interestingly, although most studies focused on clinical samples of BED, some data showed that in non-clinical populations with a normal Body Mass Index (BMI), over-eating behavior could also be seen and it might increase the risk of developing into BED in young adults [7,8]. Nevertheless, it remains unclear which neuropsychological constructs might be potentially involved in the onset and development of BED among general adolescents and young adults.
Impulsivity is a hallmark feature in various mental disorders including addictive behaviors, as well as in so-called "food addiction", which has been largely controversial [8]. Many studies suggested that impulsivity might be a vulnerability trait for both behavioral and substance-related addictions [9,10,11]. Importantly, individuals with BED and drug addicts shared similar intense cravings, disinhibition over the intake of drugs or foods, and altered reward sensitivity [12,13]. Therefore, impulsivity might also play a part in the onset of BED. However, the relationship between impulsivity and BED remains to be further understood.
Generally, impulsivity refers to a tendency to act without careful thinking or to react prematurely [14,15,16,17]. Although impulsivity is a multifaceted construct, at least two different connotations of impulsivity may be separately detected with different measurements [18], that is, personality-level trait impulsivity, measured by some self-report scales such as the Barratt Impulsiveness Scale (BIS-11) [19], and behavioral-level choice impulsivity, assessed by some reward discounting tasks such as the Delay-discounting Test (DDT) [20].
Trait impulsivity refers to a stable and inherited feature of self-reported attributions of self-regulatory ability [21]. Many previous studies have linked trait impulsivity to binge eating [22,23,24], yet the samples were mostly limited to clinical patients with BED. These patients always had high comorbidity with impulsivity-related psychopathology, including attention-de cit/hyperactivity disorder(ADHD) [25], anxiety disorders [26], and substance use disorders [27]. This thus might lead to confounding results when detecting the effects of impulsivity implicated in BED.
Moreover, limited data on the associations of trait impulsivity and BED have been incongruous among general populations. Some data suggested that heightened impulsivity was found in young adults with BED or BN compared to healthy controls [28,29,30,31], while others showed no group differences [32,33]. Findings were also inconsistent when speci c facets of impulsive traits were taken into account [8, 34,35]. One prior study found that Attentional, Motor, and Non-planning Impulsiveness were signi cantly related to binge eating in normal-weighted females [24], but another study showed that only Attentional and Motor Impulsiveness were elevated in obese patients with overeating [33].
Choice impulsivity is considered an irrational decision-making process in uenced by motivations and affects [36,37,38]. Recent meta-analyses have demonstrated impaired choice impulsivity in BED [39,40]. Clinical patients with BED (normal-weighted and over-weighted) displayed steeper delay discounting than controls [35,41,42]. Delay discounting has been regarded as a robust shared robust marker of psychiatric disorders [43]. Thus, the aberrant delay discounting of BED patients might also result from other comorbid psychiatric disorders, which were probably seen in these clinical BED patients. Despite little evidence, several studies including non-clinical samples have revealed that adults with BED exhibited steeper delay discounting compared to normal controls [44,45]. However, negative results also showed that binge eaters and healthy controls had no differences on delay discounting tasks [46,47]. Regarding probability discounting, limited studies suggested that obese women with BED tended to discount probabilistic rewards less steeply than healthy controls [44,48,49], but young college students with BED showed similar performance on the probability discounting tasks with those without BED [50]. More studies are needed to elucidate the relationship between binge eating and choice impulsivity among general populations.
The current study thus aimed to further detect the associations between impulsivity and binge eating among non-treatment-seeking samples. The Barratt Impulsiveness Scale-11 (BIS-11) and UPPSP Impulsive Behaviors Scale (UPPSP) were employed to measure trait impulsivity, and the Delay Discounting test (DDT) and Probability Discounting test (PDT) were used to assess choice impulsivity, comparing BED subjects with healthy controls (HCs). It was generally hypothesized that heightened trait impulsivity and choice impulsivity would be linked to BED, as possible risk factors or vulnerability markers for binge eating behaviors.

Participants and procedure
A total of 118 young adults participated in this study, recruited from a local university in Guiyang, China. They were invited to provide demographic information and complete a series of self-report questionnaires in the laboratory. The inclusion criteria included: 1) ≥ 18 years of age; and 2) willingness to participate in this study. The exclusion criteria included: 1) a history of major psychiatric disorders (e.g., schizophrenia, major depressive disorder, bipolar disorder); 2) use of the psychoactive substance (e.g., cocaine, heroin, amphetamine); and 3) a history of brain trauma or neurological diseases. All subjects gave informed consent and were compensated with a gift equal to RMB ¥50. The current study was reviewed and approved by the Human Research Ethics Committee at the Guizhou Medical University. The proposed study design, recruitment process, and our plans to compensate the participants were in accordance with the Declaration of Helsinki.

Binge Eating Classi cation
Binge eating status was de ned by using the Binge Eating Scale (BES) [51]. BES is a 16-item self-report questionnaire designed to assess behavioral, emotional, and cognitive symptoms of binge eating. Items were rated on a 5-point Likert scale from 0 (not at all) to 4(very much), with a total score ranging from 0 to 46. Higher total scores indicate more severe binge eating problems. Subjects with a score of 17 and less are considered individuals without binge eating, and those with a score ≥ 18 are considered individuals with binge eating. Thus, in this study, the Binge Eating Disorder group (BED) consisted of 58 subjects (average age = 19.34 ± 1.15 years; 10 males, 17.24%; mean BES score = 21.78 ± 4.02), and the Healthy Control group (HC) consisted of 60 subjects (average age = 19.10 ± 0.78 years; 10 males, 16.67%; mean BES score = 5.43 ± 2.23). The Cronbach's α of the BES was 0.874 in this study.

Measurements
Body Mass Index (BMI). Standard procedures were used to measure weight and height, and BMI was calculated as weight divided by the square of height (i.e., kg/ m 2 ). Trait Impulsivity. Participants completed the Barratt Impulsiveness Scale (BIS-11) [52], a 30-item self-report inventory that measures impulsive personality in terms of three factors: Motor Impulsiveness (MI), Attentional Impulsiveness (AI), and Non-planning Impulsiveness (NI). Items were rated on a 4-point Likert scale. A higher score of each dimension indicates a higher level of trait impulsivity. The Cronbach's s α was 0.796 in this study. Participants also completed the UPPSP Impulsive Behaviors Scale (UPPSP) [53], which is a 59-item self-report questionnaire used to Choice Impulsivity. The Delay Discounting Test (DDT) and Probability Discounting Test (PDT) were used to evaluate choice impulsivity. Both tasks were designed to estimate discounting degrees of hypothetical monetary rewards. The DDT [54] is a xed serial of 27-item choice questionnaire between a smaller immediate monetary reward and a larger delayed monetary reward. For the DDT, k parameter indicates the degree of delay discounting, calculated by the equation: V = A/(1 + kD). In this equation, V refers to the individual subjective value of the delayed reward, A is the nominal amount of the delayed reward, and D is the length of the delay. A higher k indicates a higher degree of delay discounting. The PDT [50] is a three-part monetary choice questionnaire, with 10 items in each part. Participants were told to choose between a smaller amount of monetary reward obtained for sure and a larger amount of monetary reward obtained probabilistically (e.g., "$20 for sure" VS "10% chance of obtaining $80"). The h parameter is calculated by the hyperbolic equation: V = A/(1 + hθ). In this equation, V refers to the present subjective value of the probabilistic reward A. A lower h value implies that the probabilistic rewards are less steeply discounted, suggesting a reduction in risk aversion.

Statistical Analyses
Data analysis was performed with the Statistical Package for the Social Sciences for Windows, Version 22.0. (SPSS Inc., Chicago, IL, USA). Chisquare tests were used to test group differences on categorical variables (i.e., ethnicity, gender, home locality, smoking, and drinking status). Ttests were used to analyze group differences on descriptive statistics including the Body Mass Index (BMI) and age. Multivariate analysis of variance (mANOVA) models were used to compare task scores between the two groups. Partial correlation was tested between the BIS, UPPSP, DDT, PDT, and BES scores, controlling for age, BMI, gender, ethnicity, home locality, smoking, and drinking status. In addition, a multivariate linear regression analysis was conducted to test the effects of the impulsivity scores on BES scores, and logistic regression analyses were used to test the predictive effects of different dimensions of impulsivity on binge eating behavior. According to the standardized variance in ation factor (VIF), multi-collinearity was not a problem for any variable in these regression models (VIF < 10). Signi cance was de ned as p < 0.05, two-tailed.

Partial Correlation and Linear Regression Outcomes
As seen in Table 2, signi cant positive correlations were detected between the BES scores and BIS Attentional Impulsiveness, Motor Impulsiveness, Non-planning Impulsiveness, UPPSP Negative Urgency, Lack of Perseverance, and Positive Urgency scores (r p =0.24-0.57, ps < 0.05). Nevertheless, no signi cant correlations were detected between the BES scores and UPPSP Lack of Premeditation, Sensation Seeking, DDT k value (log-transformed), and PDT h values (log-transformed) of three parts. The multivariate linear regression analyses were used to test the effect of BIS, UPPSP, DDT, and PDT scores on the BES scores, with a 2-step design. BMI was entered in step 1 as the control variable, and the impulsivity scores were entered in step 2 as the predictor variables. Table 3 displayed that only UPPSP Negative Urgency positively predicted the BES scores, after controlling for the effect of BMI (F (13, 104) = 4.53, p < 0.001; ∆R 2 = 0.33, p < 0.001).

Logistic Regression Outcomes
The binary logistic regression models were conducted to examine the effects of the impulsivity scores on binge-eating behavior. A 2-step design was used: BMI was entered in step 1 as the control variable, and the three dimensions of BIS (Attentional Impulsiveness, Motor Impulsiveness, and Non-planning Impulsiveness), ve dimensions of UPPSP (Negative Urgency, Lack of Premeditation, Lack of Perseverance, Sensation Seeking, and Positive Urgency), DDT k value (log-transformed), and PDT h values (log-transformed) were entered in step 2. Table 4 revealed that only Negative Urgency positively predicted binge eating (OR = 1.50, p < 0.001, Nagelkerke R 2 = 0.608 for the model). Note. BED = Binge Eating Disorder; BIS = Barratt Impulsiveness Scale-11, UPPSP = UPPSP Impulsive Behaviors Scale. DDT = Delaydiscounting Test; PDT = Probability Discounting Test, k represents the delay discounting rate, and h represents the probability discounting rate. CI = con dence interval, OR = odds ratio; Dependent variable: BES scores. N = 118, Nagelkerke R 2 = 0.608; ***p < 0.001

Discussion
To the best of our knowledge, the present study was the rst to examine the associations between trait impulsivity, choice impulsivity, and bingeeating behavior in general samples. The results supported our hypotheses that individuals with binge eating disorder (BED) might have elevated impulsive personality traits than the healthy controls. Speci cally, the BED subjects showed higher levels of trait impulsivity on the BIS-11 (i.e., Attentional Impulsiveness, Motor Impulsiveness) and UPPSP (i.e., Negative Urgency, Lack of Perseverance, Positive Urgency). However, the BED group had a normal level of choice impulsivity both on the DDT and the PDT (except on the PDT Part A), compared with the healthy controls.
Signi cant positive correlations were found between BES scores and most impulsivity scores, including BIS Attentional Impulsiveness, Motor Impulsiveness, Non-planning Impulsiveness, UPPSP Negative Urgency, Lack of Perseverance, and Positive Urgency. More importantly, regression models showed that only Negative Urgency positively predicted binge eating as an important risk factor. These ndings suggested that different impulsivity facets were separately associated with BED, and certain trait impulsivity (i.e., Negative Urgency) might be considered a hallmark for BED in young adults.
Increased impulsivity has been proposed as a phenotype for addictive disorders as well as within the clinical obesity spectrum [55], and it might also increase the risk for BED. However, few studies have focused on the relationship between impulsivity and binge eating in non-treatmentseeking individuals with normal weight. The current study investigated the associations of trait impulsivity, choice impulsivity, and binge-eating behavior in common populations (i.e., young adult college students). The data showed that individuals with BED had elevated scores on measurements of trait impulsivity (i.e., Attentional Impulsiveness, Motor Impulsiveness, Negative Urgency, Lack of Perseverance, and Positive Urgency), consistent with previous reports on BED [34,56,57,58,59] and addictive disorders[60, 61, 62].
Furthermore, positive correlations were found between the BES score and these impulsivity scores (  70]. Among clinical samples of BED and obesity without BED, reduced reward processing in the striatal and amygdala regions indicated motivational hypo-function to non-food rewards [71,72]. However, a longitudinal study showed that the ventromedial prefrontal cortex (vmPFC) activation did not display a signi cant predictive effect on binge-eating severity in adolescent girls [73]. Therefore, further studies should be conducted to investigate the processes of delay grati cation and risk aversion in both clinical and nonclinical samples of BED.
Several limitations should be noted in the current study. Firstly, this study was a cross-sectional design in nature, and thus could not draw a causal conclusion between impulsivity and BED. Moreover, the samples consisted of young college students and our results could not be generalized to clinical samples with serious binge-eating problems. Future research should investigate the relationship of trait impulsivity (e.g., Negative Urgency) with binge-eating behaviors in more severe clinical patients. Thirdly, given that our study mainly focused on some aspects of impulsivity (i.e., trait impulsivity and choice impulsivity) measured by self-report scales, these ndings should be interpreted more carefully because of the possible subjective bias, and other facets of impulsivity should be further investigated using more objective tasks.
In despite of these limitations, the present study rstly looked into the associations between various aspects of impulsivity and binge-eating behavior in non-clinical samples of BED, using a case-control design. Our results indicated that Attentional Impulsiveness, Motor Impulsiveness, Negative Urgency, Lack of Perseverance, and Positive Urgency were elevated in BED and especially, Negative Urgency was the only risk factor positively predicting BED. These ndings suggested that typical facets of trait impulsivity, which have been recognized in addictive disorders, were associated with BED in young adults, whereas choice impulsivity was not aberrantly seen in BED. The procedures reported in this study were reviewed and approved by the Human Research Ethics Committee at the Guizhou Medical University, and the proposed recruitment process, study design and plans to compensate participants were carried out in accordance with the Declaration of Helsinki.

Consent for publication
Not applicable.

Availability of data and materials
The data and materials are available and could be requested and addressed to the corresponding author (email: yanwansen@163.com).

Competing interests
There are no competing interests declared by all the authors.