The Delay Discounting, Impulsivity And Its Relation To Eating Behavior In Overweight/Obese Adolescents

Objective:The Delay Discounting Task (DDT), as an effective behavior measure, reflects the impulsivity characteristic which closely related to human’s irrational decision making. In order to get the statistical analysis method and the measure indexes of DDT optimized and normalized, four prominent models of delay discounting (two one-parameter models:the exponential decay model and the hyperbola model; two two-parameter models:the hyperboloid-like model and the power exponential function model) were compared and the significance and applicability of DDT’s measure indexes were analyzed in our study. Afterwards, DDT was applied in adolescent on the bases of methodology about statistical analysis for a better understanding of the impulsive characteristics (except DDT, also included other impulsivity dimensions be reflected by another behavior measure and a questionnaire) related to adolescents’ overweight/obesity problems and its influence on eating behaviors.Methods:In study1, a sample of61general adolescents completed the food-money related DDT. All four discounting models were fit to the group and individual discounting data using nonlinear regression techniques. The R2values and the fitting curves were direct compared among four models at group level. In the individual level, the effectiveness, suitability and rationality of the four models were also analyzed through results which come form the percentage of effectively fitting cases, the R2values were subjected to Wilcoxon signed-rank tests, the parameter S subjected to t-ratio statistic and the S values between food and money related DDT were subjected to Wilcoxon signed-rank tests for each two-parameter model, so its meaning of different models was verified which could provide an important implication for the food-money related DDT’s description.In study2, a sample of38normal weight adolescents (other possible impulsive disorders has been eliminated) accomplished the food-money related DDT, the eating attitude scale (EAT) and general demographic information assessments. Several measurement indexes about areas and parameters were combined for their measuring significance and applicability analysis. Paired t-tests were used to compare the calculus area (CA) of delay discounting function versus the area under the curve (AUC) for calculation difference between two methods. Paired t-tests were also used to compare areas which come from CA or AUC method for food and money related rewords respectively, and the statistical results’difference between two ways were compared. The difference and the correlation between areas and parameters were analyzesed through the comparison of the fitting curves and the parameters of two groups of discount data with similar CA. Lastely, use these three measurements index compared discount difference of food and money by paired t test.In study3,52healthy-weight (31male,21male) and51overweight/obese (30male,21female) adolescents, sampled from the normal population, were tested on the food-money related Delay Discounting Task (Food-Money DDT), the Door Open Task (DOT), the Barratt Impulsiveness Scale-11(BIS-11),the Eating Attitude Test (EAT),the Eating Disorder Inventory (EDI) and some questionnaires on general demographic information. During the phase of experimental task test, participants also had their height and weight measured for the actual BMI values (BMI=Weight (kg)/height2(m2)). The group delay discounting data of each experimental groups were fitted by the hyperboloid-like model using non-linear regression and the fitted curves were compared. The impulsive variables were compared between groups using multivariable analysis of variance (ANOVA) with weight groups and sociodemographic variables as between-groups factors, and Interaction effect between weight group and sociodemographic variables also was observed. Partial correlation was used to explore the relations among different impulsive variables. Furthermore, the relationships between the BMI and impulsivity dimensions were also established by way of a series of regression analyses.In study4, the measuring tasks and procedure for this study was completely same as study3.84male and59female overweight/obesity adolescents were screened for this study, and some of these were directly come from the study3. One-way ANOVA was used for the difference of AUC and the scores of the eating attitude and the eating disorder scales between male and female groups. Considering the difference of gender differences, the correlation of delay discounting, eating attitude, eating disorder and its subscales was Pearson correlation for analysis. The sample was divided in to High and low groups acording the AUC and the score of the eating attitude, One-way ANOVA was used for eating attitude and disorder difference between high and low discounting degree groups, and was also used for difference analysis of the degree of discounting, eating disorder and each factor of eating disorder among normal, anorexia or bulimia tend group and most likely group.Results:In study1, the comparative results of R2at group and individual level have shown that two-parameter models would fit the discount data more suitability than one-parameter models. The fitting difference between two different two-parameter models was not significant. A portion of cases can’t be fitted effectively by the one-parameter models with exponential decay model nearly about30%and hyperbolic model nearly23%, whereas all cases’discount data could be fitted efficiently by two-parameter models. Nearly about63%of hyperbolic-like model and nearly about58%of the exponential function model whose parameter S were significantly less than1. Used reward as a within-group factor, parameter S was not significant for exponential function model between food and money (Z=-1.756, p=0.079<0.05, but difference significant for hyperbolic-like model (Z=-2.817, p=0.005<0.05, and it can reflect subjects’sensitivity to stimulants for food-money related DDT.In study2, AUC and CA were significant difference on individual specific area about delay discounting(food:t(37)=3.073,p<0.005;￥100: t(37)=4.057, p<0.005), but they are the same when they used for within-group comparison of area between food and money related DDT (CA:t(37)=2.411,p<0.005; AUC:t(37)=2.480, p<0.005),and the two histograms which present the average CA and AUC of all subjects are almost have the same height. So, the area and the parameters which present the delay discounting ability could be associated through the calculus of discount function. When two cases have similar CA, the parameter K can response curve steep degree, and the parameter S can response the curve’s stretching on horizontality with the delay time gone. There is no correlation between CA and LogK (for f or food-DDT: r=0.089, for money-DDT:r=0.055; p>0.05), but moderate negative correlated between CA and LogS (for food-related DDT:r=-0.413, for money-related DDT:r=0.509; p<0.05), and significant negative correlated between LogK and LogS(for food-DDT:r=-0.801, for money-DDT:r=-0.796; p<0.05). The within-group comparison between food and money-related DDT only found significant difference on CA (t=2.411, p<0.05).In study3, the impulse variables were not significant difference between groups which divided by demographic factors, such as age, gender, and family economic income (p>0.80). Simple-effects analyses found that overweight/Obese showed great significant difference with controls on AUC and the N’s of doors opened, they discounted more on food(F=15.37, p<0.01) and money (F=19.28, p<0.01), and opened more doors (F=10.74, p<0.01). No such differences were seen on other behavior impulsivity variables, total BIS and each subscale of it (p>0.05).Interaction analysis between experiment groups and demographic factors found a significant Genderxweight status interaction on AUC’s (for food-related DDT:F(1,101)=10.42, p=0.00; for money-DDT:F(1,101)=9.48, p=0.00) and the N’s of doors opened (F(1,101)=0.433,P=0.05).The significant difference of AUCs between overweight/obese and normal weight individuals was found only for female (for food-related DDT:F=26.38, P<0.01; for money-related DDT:F=44.86, P<0.01) but not for male (p>0.167). Furthermore, the significant difference of the N’s of doors opened was found both in female(F=4.80, P<0.05) and male(F=5.90; P<0.01), and the different degree was bigger in female. There is no correlation among three impulsive tasks (p>0.05). BMI showed a significant negatively correlation with AUCs(r=-0.229and-0.240for food-DDT and money-DDT, respectively), and BMI was uniquely associated with AUC for delay discounting for food (accounting for26.4%of the variance) and for money (accounting for33.4%of the variance).In study4, the correlation between AUC and eating attitudes, eating disorders, and the related all subscales was significant (p>.05) in femal but not in male overweight/obese. In female, AUC and the eating disorder tendency of slimming, gluttony, perfectionism and introspection (person r were-.268,-0.323,-0.297,-0.263respectively). The significant difference of AUC for money-DDT, total EDI and most of its subscales was found among the normal eating group, the bulimia or binge eating tendency group and possible group (p<0.05). Therefore, the overweight/obese female accompanied with bulimia or binge eating was discounted more and displayed more eating problems. High and low discounted groups only show significant difference on bulimia (F=3.752, p<.05) and introspection (F=4.098, p<.05).Conclusion:1. Comparing the one-parameter models, more discounting data would be fitted effectively and the R2was higher by the two-parameter models. That had shown the two-parameter models displayed low requirements and good description for discounting data. It was reasonable to add the parameter S for two two-parameter models. The cases of parameter S which significant less than1were more by hyperbolic-like model fitting, and they could reflect the sensitivity of the subjects on delayed reinforcers. All in all, the hyperbolic-like model could provide best description of food-money retaliated DDT.2. AUC and CA are on the same theoretical basis, they all reflect total discount level in a period of delay time. The parameters and the area were associated by the calculus of discounting function, and represented different aspects of discounting ability. In this way, it can solve describe difficult about same discounted areas but have different curve shapes.3. The results supported the hypothesis that overweight/obese individuals were more impulsive than the normal weight controls on behavior tasks but not on self-report scale. The impulsive difference between experiment groups performance different in different gender. To be specific, first, the overweight/obese subjects showed greater delay discounting than the normal-weight did, but this conclusion can’t be replicated in males; second, the verweight/obese subjects opened more doors than normal-weight did for the N’s of doors opened in both gender, but the difference were more significant in female. Three tasks reflect different impulsiviness dimensions. The relationship between BMI and delay discounting was closer, BMI has good predictive validity on discount level, the greater BMI (that is obesity), and the more tends to choose instant reward.4. There was some gender difference on the relation of delay discounting and eating variables. The relationship between them was more closely in female overweight/obese adolescents but no significant in male overweight/obese adolescents. The impulsive behavior which was reflected by DDT has a close relation to eating behavior and eating psychological characteristics, mainly reflected in the behavior of gluttony and three psychological characteristics aspects of tend to thin body, perfectionism and introspection. High impulsivity overweight/obese female students show serious gluttony symptoms and lower levels of emotional introspection. Moreover, the overweight/obese female students with anorexia or bulimia are more impulsive and even more serious in eating problems than the normal eating ones.