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The relative-reinforcing value of food under differing levels of food deprivation and restriction
Appetite 40 (2003) 15–24 www.elsevier.com/locate/appet
Research Report
The relative-reinforcing value of food under differing levels of food deprivation and restriction Hollie A. Raynor, Leonard H. Epstein* State University of New York, University at Buffalo, Buffalo, NY 14214-3000, USA Received 28 June 2002; revised 30 September 2002; accepted 2 November 2002
Abstract Food deprivation and restriction both increase food consumption. Food deprivation also increases the reinforcing value of food, but it is unknown if food restriction alone or combined with deprivation increases the reinforcing value of food. Forty, normal-weight, college-aged, unrestrained females were randomized to one of four conditions that crossed food deprivation (Dep) and restriction (Res): Dep/Res, Dep/No Res, No Dep/Res, No Dep/No Res. All participants arrived at least 13 h food-deprived, and non-deprived participants consumed at least 365 cal from a drink during the session. Restriction was manipulated by placing snack food in front of participants, without access for 15 min during the session, or having no snack food placed in front of participants. Following the experimental manipulations, participants completed a computer choice task to determine the reinforcing value of food. Repeated measures analysis of variance found a significant main effect of deprivation ( p , 0.05) and trials ( p , 0.001) for food points earned. Deprived participants found food to be more reinforcing, and the reinforcing value of food decreased over time. This suggests that while short-term food deprivation increases the relative-reinforcing value of food, short-term food restriction has no effect on the relative-reinforcing value of food in unrestrained eaters. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Food deprivation; Food reinforcement; Food restriction
Food deprivation, a reduction of overall caloric intake, and food restriction, conditions in which cognitive or environmental constraints have been implemented so that there is limited access to certain foods, are main features of anorexia and bulimia nervosa (American Psychiatric Association (APA), 1994). In anorexia nervosa, low-body weight is achieved through food deprivation, but often times the deprivation is preceded by a stage of restricting specific foods from the diet (APA, 1994). In bulimia nervosa, food deprivation and restriction are believed to be important cognitive and behavioral components of the maintenance, and perhaps initiation, of binge eating (Brewerton et al., 2000; Howard and Porzelius, 1999; Polivy and Herman, 1993; Westenhoefer and Pudel, 1993). Not surprisingly, high levels of food deprivation and/or restriction are associated with poorer treatment outcome in patients with bulimia nervosa (Bulik et al., 1998). * Corresponding author. Address: Division of Behavioral Medicine, Departments of Pediatrics, State University of New York at Buffalo, Farber Hall, Room G56, 3435 Main Street, Building #26, Buffalo, NY 142143000, USA. Tel.: þ1-716-829-3400; fax: þ 1-716-829-3993. E-mail address: [email protected] (L.H. Epstein).
Specific food restrictions (e.g. high-fat and/or sugar foods) and food deprivation are also central components of dietary treatments for obesity. Restriction and/or deprivation may actually contribute to overeating, thereby reducing the effectiveness of obesity treatment (Corwin, 2000). In laboratory investigations, acute food deprivation (e.g. not eating for 1 – 48 h) is associated with increased consummatory behavior in animals (Bolles, 1965; DiBattista, 1987; Falk, 1981; Grill and Berridge, 1985; Hursch and Beck, 1971; Oatley and Tonge, 1969; Savory, 1988; Tolman and Wilson, 1965) and in humans with (Hetheringon et al., 2000; Telch and Agras, 1996) and without eating pathology (Drobes et al., 2001; Hill, 1974; Spiegel et al., 1989). The effects of chronic food deprivation on current eating behavior has also been examined in animals (DiBattista, 1987; Hagan and Moss, 1991, 1997), demonstrating that a history of food deprivation may influence current eating behaviors, causing a similar response as acute food deprivation. A history of food deprivation does appear to affect current eating behavior in humans (Franklin et al., 1948; Polivy et al., 1994). For example, men who had
0195-6663/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0195-6663(02)00161-7
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reduced intake to around 1500 kcal/day for 24-weeks reported problems with uncontrollable eating and increased appetites for sweet foods even after weight regain occurred (Franklin et al., 1948). Additionally, Polivy and colleagues (1994) documented a significantly higher prevalence of self-reported binge eating in prisoners of World War II who had a history of severe food deprivation 50 years ago as compared to those World War II veterans who had not experienced severe food deprivation. Restriction, or limited access, also appears to increase consummatory behavior. Studies investigating the effects of restricted access to alcohol on alcohol intake found that as restriction of alcohol availability increases, consumption of alcohol increases during access periods (Files et al., 1994; Marcucella and Munro, 1987; Marcucella et al., 1984; Pinel and Huang, 1976; Pinel et al., 1976; Wise, 1973). Studies involving food restriction in animals also reported an increase in food consumption of the restricted food during access periods as food restriction increased (Corwin et al., 1998; Wayner et al., 1972). Restricting access to certain foods for brief periods (e.g. 5 min) has also been found to increase children’s preferences for (Birch et al., 1980; Lepper et al., 1982 and intake of these foods (Fisher and Birch, 1999a,b). However, with adults, Mann and Ward (2001) found that while short-term food restriction (5 min) did produce an increase in thoughts about and desire for the restricted food, there was no change in consumption of the restricted food when the restriction was removed. Deprivation and restriction may affect consummatory behavior by focusing attention on the removed or limited access object. Self-reported preoccupation with food and eating is a cognitive symptom commonly reported in individuals with anorexia or bulimia nervosa (Stewart and Samoluk, 1997). In the Stroop task, delayed latency with food-related words has been reported in individuals with eating disorders (Ben-Tovim et al., 1989; Channon et al., 1988; Cooper et al., 1992), restrained eaters (Francis et al., 1997; Green and Rogers, 1993; Lattimore et al., 2000; Perpina et al., 1993; Stewart and Samoluk, 1997), and in individuals who have experienced acute food deprivation (Channon and Hayward, 1990). Increased attention on food under conditions of food deprivation and/or restriction may then increase the desire to obtain the deprived or restricted object, causing it to become more reinforcing. Food deprivation has shown to decrease self-control and increase impulsivity around food reinforcers in humans (Kirk and Logue, 1997; Logue and King, 1991) and in animals (Eisenberger et al., 1982). The increased impulsivity associated with the deprivation is hypothesized to be a consequence of an increase in the incentive value associated with the reinforcer (Eisenberger et al., 1982). An increase in the reinforcing value of food may cause individuals to more likely choose to eat instead of participate in non-eating activities, or may predispose individuals to be more susceptible to eating when exposed
to eating cues (Epstein and Saelens, 2000). Consequently, as the reinforcing value of food increases, so should food consumption. Therefore, factors that increase the reinforcing value of food may interfere with the ability to reduce energy intake that is recommended for weight control programs, or engage in alternative activities that may help reduce increased intake associated with binge eating (Epstein and Saelens, 2000). Behavioral economic theory (Rachlin, 1989) and laboratory choice paradigms provide a model to assess the relative-reinforcing value of two choices (Saelens and Epstein, 1996). Studies using a behavioral economics paradigm found that food deprivation is related to the absolute amount of work animals will do for food (Herrnstein and Loveland, 1974) and affects the relativereinforcing value of food substances in humans (Bulik and Brinded, 1994; Bulik et al., 1995; Epstein et al., 1991; Lappalainen and Epstein, 1990), such that deprivation is associated with increased work and reinforcing value of food substances. However, the effect of food restriction alone, and the combined effects of food deprivation and restriction on the relative-reinforcing value of food are not known. This study was designed to examine the independent and interacting effects of food deprivation (Dep) and restriction (Res) on the relative-reinforcing value of food and food consumption. Four conditions were used in the investigation: Dep/Res, Dep/No Res, No Dep/Res, No Dep/No Res. All participants worked toward earning points for eating the food and a preferred sedentary activity. It was expected that short-term food deprivation and restriction would increase the relative-reinforcing value of the snack food due to the increased food consumption associated with food deprivation and restriction. Consequently, participants in food-deprived, foodrestricted, and food-deprived and-restricted conditions would earn more snack food points during the choice task, and consume more kcals from a highly-rated snack food, as compared to participants in the non-fooddeprived and -restricted conditions.
1. Method 1.1. Participants Participants consisted of 40 healthy, non-smoking, normal weight (body mass index [BMI] , 85th percentile) (Must et al., 1991a,b) female adults, recruited from the State University of New York (SUNY) at Buffalo. Additionally, participants reported no allergies or unfavorable preferences towards foods used in the investigation; regular consumption of breakfast and/or lunch (e.g. eating at least one of these meals 75% of the days in the past month); could be classified as an unrestrained eater (scoring # 12 on the Restraint Scale [RS]) (Gorman and Allison, 1995; Herman
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and Polivy, 1980); and showed no indications of eating disorder pathology, scoring # 27 on the binge eating scale (BES) (Gormally et al., 1982) and # 30 on the eating attitudes test (EAT) (Garner and Garfinkel, 1979). On average, participants were 18.4 (SD ¼ 0.8) years of age and had a BMI of 21.5 (SD ¼ 2.0). The ethnicity of the participants was the following: 58% Caucasian, 20% Asian, 15% African-American, and 7% of other descent. All participants received $20 compensation for their participation. This investigation was approved by the Social Sciences Human Subject Review Board of the SUNY at Buffalo. 1.2. Design and procedure The investigation used a 2 £ 2 £ 8 mixed design, with food deprivation (food-deprived versus non-food-deprived) and food restriction (food-restricted versus non-foodrestricted) as the between-subject factors, and computer game trials with differing reinforcing schedules (1 – 8), as the within-subject factor. The primary dependent variable in the investigation was the amount of food points earned in the computer game. Female undergraduate students (N ¼ 137) recruited from undergraduate psychology classes and from flyers posted around the campus completed a phone screen to assess height, weight, age, health status, medication usage, dietary restrictions, smoking status, food allergies, dieting status, food preferences, usual eating patterns, and the RS (Herman and Polivy, 1980). After the phone screen, a laboratory screening session was scheduled between 10 a.m. and 1 p.m. for 58 participants who met entrance criteria. All participants were instructed to not eat 2 h before the screening session. Upon arrival to the screening session, participants were taken to a small room equipped with a closed-circuit television monitor and an intercom providing two-way communication with the adjoining room. Participants completed a consent form and were asked if they had eaten in the last 2 h. Then, participants sampled the drinks, snack foods, and activities used in the investigation. The sampled drinks were one tablespoon each of three flavors, chocolate, vanilla, and strawberry, of a nutritionally-balanced liquid drink (Boost Plus, Mead Johnson; Evansville, Indiana) chilled to 68C, approximating 70 kcals. The sampled snack foods were 4 g each of Doritos nacho cheese tortilla chips (Frito-Lay; Plano, TX), Twix candy bars (MandM/Mars; Hackettstown, NJ) and Chips Ahoy chocolate chip cookies (Nabisco; Hanover, NJ), which was approximately 60 kcals. Participants were instructed to take a sip of water, consume the first sample, provide an hedonic rating of the drink/snack food using a 100 mm visual analogue scale (VAS,) and indicate if they would consume the drink/snack food. They repeated this procedure for the other samples. If a participant indicated
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that she would not consume at least one of the drinks/snack foods rated $ 50, the participant was not included in the study. The mean hedonic ratings of the drinks for participants completing the investigation were: chocolate ¼ 66.2 (SD ¼ 23.4); vanilla ¼ 63.0 (SD ¼ 25.7); and strawberry ¼ 39.9 (SD ¼ 28.8). The highest rated drink was used as the meal in the non-deprived condition. Mean hedonic ratings of the snack foods for participants completing the investigation were: Doritos ¼ 89.3 (SD ¼ 13.3); Twix ¼ 84.5 (SD ¼ 20.8); and cookies ¼ 74.1 (SD ¼ 22.8). The highest rated snack food was used in the choice task and as the restricted food. Participants then sampled three sedentary activities, playing a video game, watching videos, and reading current popular magazines, for 2 min. After sampling an activity, participants provided an hedonic rating of the activity using a 100 mm VAS, answered if they would do the activity, and repeated this procedure for the other activities. If a participant indicated that she would not do at least one of the activities rated $ 50, the participant was not included in the study. The mean hedonic ratings of the activities for participants completing the investigation were: video games ¼ 70.9 (SD ¼ 30.3); videos ¼ 85.7 (SD ¼ 15.0); and magazines ¼ 82.5 (SD ¼ 17.9). The highest rated sedentary activity was used in the choice task. Next, participants completed the BES (Gormally et al., 1982), the EAT (Garner and Garfinkel, 1979) and had height measured by a stadiometer (Seca, Columbia, MD), calibrated in 1/8 inch intervals, and weight measured by a balance beam scale (Healthometer, Model 402, Bridgeview, IL), calibrated in 1/4 pound intervals, using standard procedures (Lohman et al., 1988). BMI (kg/m2) was calculated from this information. Participants were scheduled for their second session, at 1 or 2 p.m., occurring within one-week of the screening session. Participants were instructed to not eat after midnight of the night prior to their session. Screening measures indicated that 14 participants did not meet the criteria for the investigation: eight participants did not rate any of the foods or drinks used in the study as being pleasant; three participants’ BMI exceeded the 85th BMI percentile; one participant scored too high on the EAT; one participant had a medical condition (hypoglycemia) that prevented her from being able to follow the food deprivation directions; and one participant indicated that she did not regularly eat breakfast or lunch. Additionally, after completing the screening session, two participants chose to withdraw from the study, and two participants had procedural errors during the experimental session. Consequently, the sample size of the investigation was 40. Participants were randomly assigned to one of four experimental groups: Dep/Res, Dep/No Res, No Dep/Res, No Dep/No Res. The experimental session began with assessment of compliance with deprivation instructions by a 24-h dietary recall. Three participants had eaten in
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the morning prior to their experimental session and these sessions were rescheduled. Ratings of level of hunger were taken using a 100 mm VAS. In the non-deprived condition, participants were served a liquid meal, consisting of two cups of a nutritionallybalanced liquid drink (approximately 730 kcals) (Boost Plus), served in a clear plastic cup and chilled to 68C. Participants were instructed to consume at least half (approximately 365 kcals) of the drink, and then consume as much as they wanted until they felt pleasantly satisfied. Participants had 15 min to consume the drink. In the deprived condition, participants sat quietly for the same 15 min session. After the 15 min meal session, all participants again rated their feelings of hunger using the VAS. For the restricted condition, a plate full (approximately 50 g) of the highest rated snack food was placed on the table in front of the participant during the 15 min meal session. Participants were informed that they could not eat any of the snack food, but that they would be answering questions about the appearance of the food later in the session so they should pay attention to the food. During this 15 min session, all participants were closely observed through the monitor to ensure that the restricted food was not eaten. After 15 min, the restricted food was removed, and after completing the second hunger VAS, participants completed two questions regarding the appearance of the restricted food. In the non-restricted condition, the plate of snack food was not brought into the session. Participants were then instructed on how to play a computer game in which points could be earned for their highest rated food and sedentary activity. During the games, participants responded (using a computer joystick) on one of two screens, each of which was associated with a reinforcement schedule and different reinforcer (food or sedentary activity). Responses on one of the joystick buttons allowed participants to switch screens. The presentation of which reinforcer appeared on the first screen was counterbalanced across participants. Within each screen, a press of the other joystick button caused colored shapes to spin, much like a slot machine game. When each of the three colored shapes matched, the participant received one point toward the reinforcer specified on the screen. A concurrent reinforcement schedule was implemented by varying the probability of earning points with each response. The reinforcement schedule remained at VR2 for all eight trials for the sedentary activity, while the schedule for the snack food was set at VR2, VR4, VR6, VR8, VR10, VR12, VR14, and VR16 across trials. The exchange rate was 10 food points ¼ 10 g of food (participants were shown this amount of food in a clear cup) and 10 activity points ¼ 1 min to spend doing the sedentary activity. Participants could earn 15 points per trial and were verbally notified of their total points at
the end of each trial. Additionally, the points were displayed on the computer screen. As the trials progressed, participants were verbally informed about the change in the schedules across the trials (e.g. “It will be more difficult now to earn points for the food”). Upon completing all trials, participants traded in points earned towards their reinforcers. Upon consuming the food and engaging in the sedentary activity time for which they had earned, participants were debriefed, received their compensation for participating in the study, thanked for their participation, and escorted from the laboratory. 1.3. Measures Visual analogue scales were used to determine the pleasantness of the drinks, snack foods, and sedentary activities; and hunger. Participants rated each of these dimensions on 100 mm scales, with pleasantness measures anchored by do not like at all/like very much and hunger anchored by extremely hungry/overly full. Food intake from the previous day was assessed by a 24-h food recall, in which participants were asked to provide detailed information regarding what they had eaten and how it was prepared, along with serving size information. Food items and amounts from the 24-h recalls were entered into Nutritionist V (First DataBank; San Bruno, CA), and the caloric intake; grams of protein, fat, and carbohydrate; and percent calories from protein, fat, and carbohydrate were obtained. To determine caloric intake in the non-deprived session prior to the computer game, cups containing the drink served to participants were weighed on a balance beam food scale (Ohaus; Florham Park, NJ) calibrated to the 0.1 g, and the amount consumed was determined by subtracting the post-meal weight from the pre-meal weight. Calories per gram of the drink were assessed using manufacturer information. Total calories were determined by multiplying total grams consumed by the amount of calories per gram of the food. The primary dependent variable in the investigation was number of points earned for each option during the trials of the choice task for each session. The number of points earned for each option was recorded at the end of every trial so comparisons across trials could be made as the schedule for one of the reinforcers changed. Additionally, caloric intake from the food reinforcers earned from the choice task was determined by multiplying the total grams consumed, as measured by the balance beam food scale, by the amount of calories per gram of food, as determined using manufacturer information. 1.4. Data analysis A series of two factor analyses of variance (ANOVA), with food deprivation (food-deprived versus non-fooddeprived) and food restriction (food-restricted versus
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non-food-restricted) as the between-subject factors, were conducted to examine differences between the groups on baseline characteristics; hedonic ratings of the highest rated drink, food, and sedentary activity; caloric and macronutrient intake from the day prior to the experimental session; and baseline hunger and hours of deprivation. To increase the sensitivity of the omnibus ANOVA, variables that are different and contribute a significant amount of variance to the primary dependent variable should be used as covariates (Tabachnick and Fidell, 1996). If there is no significant relationship between the dependent variable and potential covariates, the covariates should not be used in the analysis due to the loss of degrees of freedom in the analysis (Tabachnick and Fidell, 1996). While hours of deprivation were significantly different between groups, there was no significant relationship between this variable and the primary dependent variable, and it was not used as a covariate in other analyses. The effectiveness of the experimental manipulation of deprivation was assessed by the change in hunger level during the session, using a 2 £ 2 £ 2 mixed repeated measures ANOVA, with food deprivation and restriction as the between-subject factors, and the time of assessment of the hunger ratings (pre-meal and post-meal) as the within-subject factor. The relative-reinforcing value of the food was analyzed using a 2 £ 2 £ 8 mixed repeated measures ANOVA, with food deprivation and restriction as the between-subject factors, and trials (VR2, VR4, VR6, VR8, VR10, VR12, VR14, VR16), as the within-subject factors, and food points earned in each trial as the dependent variable. A 2 £ 2 ANOVA, with food deprivation and restriction as the between-subject factors examined
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differences in caloric intake from the reinforcers. Where appropriate, Greenhouse-Geisser probability levels were used to adjust for sphericity. For significant outcomes, post-hoc comparisons with Bonferroni corrections, were conducted. Finally, Pearson product – moment correlations were conducted to explore the relationship between total food points and levels of self-reported initial hunger, previous day caloric intake, hours of deprivation, dietary restraint, and the hedonic ratings of the food reinforcer. All data were analyzed with SYSTAT (Wilkinson, 1996).
2. Results Baseline characteristics of the participants are summarized in Table 1. Two unrestrained eaters were dropped from the analyses due to being outliers within their specific group on the primary dependent variable (Tabachnick and Fidell, 1996), food points earned in the choice task. No significant difference was found between the groups for age; BMI; scores on the RS, BES, and EAT; hedonic ratings of the highest rated drink, food, and sedentary activity; and caloric and macronutrient intake on the day prior to the experimental session. There was no significant difference of baseline levels of self-reported hunger between the groups, indicating self-reported baseline hunger was consistent across groups; however, there was a significant main effect of deprivation, F(1,34) ¼ 9.2, p ¼ 0.005, for hours of deprivation. Participants in the deprived condition reported significantly more hours of deprivation (M ¼ 17, SD ¼ 1.9) than participants in the non-deprived condition (M ¼ 15.5, SD ¼ 1.2). Since hours
Table 1 Summary characteristics of participants (M ^ SD)
Age (yrs) BMI (kg/m2) RS BES EAT Hedonic rating of preferred drink Hedonic rating of preferred food Hedonic rating of preferred activity Previous day calories consumed Previous day protein (g) Previous day carbohydrate (g) Previous day fat (g) Previous day protein (% kcals) Previous day carbohydrate (% kcals) Previous day fat (% kcals) Hours of deprivation
D-R n ¼ 10
D-NR n ¼ 8
ND-R n ¼ 10
ND-NR n ¼ 10
p
18.3 ^ 0.7 21.6 ^ 1.9 6.6 ^ 1.9 5.5 ^ 3.7 6.1 ^ 2.8 86.0 ^ 10.3 91.4 ^ 10.7 91.1 ^ 11.0 2384.6 ^ 439.8 74.1 ^ 24.5 337.9 ^ 86.7 85.8 ^ 22.9 12.2 ^ 4.2 55.7 ^ 7.7 31.9 ^ 6.3 16.5 ^ 1.8
18.3 ^ 0.7 21.6 ^ 1.6 7.1 ^ 2.5 5.8 ^ 4.9 8.5 ^ 7.4 78.2 ^ 15.0 95.4 ^ 5.0 92.3 ^ 8.2 1895.1 ^ 133.1 64.6 ^ 15.7 271.7 ^ 61.0 65.3 ^ 18.8 13.5 ^ 3.7 56.1 ^ 11.4 30.5 ^ 9.5 17.6 ^ 2.0
18.4 ^ 1.2 21.3 ^ 2.3 6.6 ^ 3.1 5.7 ^ 2.5 9.4 ^ 7.6 76.8 ^ 12.5 94.8 ^ 5.8 92.2 ^ 10.0 2007.0 ^ 530.7 66.5 ^ 24.1 275.9 ^ 106.8 73.6 ^ 31.6 14.3 ^ 7.7 53.3 ^ 14.2 32.3 ^ 12.1 15.4 ^ 1.4
18.4 ^ 0.7 21.7 ^ 2.6 7.9 ^ 3.8 6.7 ^ 5.3 8.5 ^ 6.4 76.4 ^ 12.6 92.4 ^ 8.7 92.6 ^ 9.6 2005.4 ^ 570.0 72.5 ^ 21.8 267.5 ^ 81.9 74.9 ^ 35.7 14.5 ^ 2.6 53.3 ^ 10.4 32.1 ^ 9.8 15.6 ^ 1.1
NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS 0.005a
Note: D-R ¼ deprived and restricted; D-NR ¼ deprived and non-restricted; ND-R ¼ non-deprived and restricted; ND-NR ¼ non-deprived and non-restricted; NS ¼ no significance; BMI ¼ body mass index; RS ¼ Restraint Scale; BES ¼ binge eating scale; EAT ¼ eating attitudes test. a Main effect of deprivation.
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of deprivation were not significantly related to the primary dependent variable, it was not included as a covariate in remaining analyses. The analysis for the manipulation of deprivation showed a significant interaction of deprivation x time of assessment, F(1,34) ¼ 10.8, p ¼ .002. Follow-up analyses indicated that participants in the non-deprived condition had significantly higher ratings, F(1,34) ¼ 9.5, p ¼ .004 (M ¼ 41.2, SD ¼ 25.6), at the measurement taken after the meal session than participants in the deprived condition (M ¼ 19.0, SD ¼ 16.1), with higher ratings indicating increased feelings of fullness. The mean amount of kcals consumed by the non-deprived group in the session was 480.6 (SD ¼ 128.5), while the deprived group consumed 0 kcals in the session. These results indicate by self-report and objective measure, the manipulation of deprivation vs non-deprivation occurred. Results of the primary hypothesis of the relativereinforcing value of food versus sedentary activity demonstrated a significant main effect of deprivation, F(1,34) ¼ 6.4, p ¼ 0.016, and trials, F(7,238) ¼ 13.9, p , 0.001), for food points earned in each trial. The effect size for the main effect of deprivation, ES ( f) ¼ 0.41; (d) ¼ 0.82, and the main effect of trials, ES ( f) ¼ 0.58; (d) ¼ 1.16, was large (Cohen, 1992). Participants in the deprived condition earned significantly more food points (M ¼ 49.2, SD ¼ 12.8) than participants in the non-deprived condition (M ¼ 38.2, SD ¼ 12.6). Mean total food points earned by group is shown in Table 2. Using a Bonferroni correction of 0.007 (0.05/7), post-hoc analyses revealed that the food points earned in trial five were significantly less than the food points earned in trial one, F(4,34) ¼ 4.3, p ¼ 0.007. The food points earned in the remaining trials continued to be significantly less ( p , 0.001) than food points earned in the first trial. Fig. 1 illustrates the food points earned in the eight trials in the deprived and non-deprived conditions. A significant main effect of deprivation was found for calories consumed from the reinforcers, F(1,34) ¼ 6.5, p ¼ 0.015, with the deprived group consuming significantly more calories than the non-deprived group (see Fig. 2). The effect size, ES ( f) ¼ 1.0; (d) ¼ 2.0, was again large (Cohen, 1992). Pearson product-moment correlations indicated no significant associations between total food points and levels of self-reported initial hunger, previous day
Fig. 1. Food points earned across eight trials in the deprived and non-deprived conditions (M ^ SEM).
caloric intake, hours of deprivation, dietary restraint, and hedonic ratings of the food reinforcer.
3. Discussion This investigation tested the hypothesis that short-term food deprivation and food restriction affects the relativereinforcing value of food. It was hypothesized that participants would find food more reinforcing in the food-deprived and -restricted conditions, causing them to work harder for food points during a choice task when food-deprived, food-restricted, and food deprived and restricted, as compared to not being food-deprived or foodrestricted. Results from this study indicate that short-term food deprivation, but not short-term food restriction, affects the relative-reinforcing value of food. Food deprivation may change the reinforcing value of food by affecting dopaminergic pathways (Carr et al., 2001). Research suggests that central dopaminergic pathways are
Table 2 Total food points earned (M ^ SD) Group
n
Sum of food points
Deprived/restricted Deprived/non-restricted Non-deprived/restricted Non-deprived/non-restricted
10 8 10 10
51.9 ^ 15.0 45.8 ^ 9.2 38.5 ^ 12.1 37.9 ^ 13.7
Note: There was a main effect ( p , 0.05) of deprivation.
Fig. 2. Caloric intake from reinforcers in the deprived and non-deprived conditions (M ^ SEM).
H.A. Raynor, L.H. Epstein / Appetite 40 (2003) 15–24
involved in the reinforcing properties of primary occurring incentives such as food and water (Chausmer and Ettenberg, 1997; Nowend et al., 2001). Experiments show a decrease in operant response rates for food during dopamine (DA) receptor antagonist drug challenges—even at doses that do not produce obvious sedative or motor-incapacitating effects (Chausmer and Ettenberg, 1997). The two main subtypes of dopamine receptors that are believed to be involved in the reinforcing properties of food are the D1 and D2 receptors (Berridge, 1996). It has been proposed that chronic food deprivation, which produces a reduced body weight, may increase the reward value of food and drugs by increasing DA releasability or decreasing DA reuptake (Carr et al., 2001). This change in DA releasability or decrease in DA reuptake and consequential increase in the reinforcing value of food appears to functionally and mechanistically increase sensitization to food, causing an initial increase in the behavioral response in eating (Carr et al., 2001). A potential reason for failing to confirm the hypothesis about short-term food restriction affecting the relativereinforcing value of food is that the food restriction manipulation used in the study was not strong enough. While a five-minute food-restriction interval was long enough to affect pre-school aged children’s food selection and consumption (Fisher and Birch, 1999b), a 15 min food-restriction interval might not be long enough to affect adult eating behavior. Children have demonstrated less self-control and more impulsivity than adults in laboratory experiments (Logue and King, 1991), and consequently, may require a shorter period of food restriction to affect eating behavior. Mann and Ward (2001) found that 5 min of restriction produced an increase in thoughts about and desire for the restricted food; however, there was not an increase in consumption of the restricted food when the restriction was removed. It was proposed that longer periods of restriction combined with chronic deprivation, similar to what occurs during dieting, may more strongly influence eating behavior. Although long periods of food restriction have been accomplished in controlled settings with animals (Corwin et al., 1998; Wayner et al., 1972), this is more difficult to accomplish with humans. A longer period, of up to a day, of food restriction can occur in a controlled setting for humans, but a longer length of restriction would be difficult to achieve under controlled conditions. While less controlled, there are two ways to achieve longer bouts of food restriction. The first would be to instruct participants to avoid eating a food that they commonly eat and encounter (e.g. potato chips), for a specified period of time before coming to the experimental session (e.g. one week). Another method would be to choose a food that the participant is already trying to restrict a food in the diet, but that is eaten periodically, assess the period of time the restriction has occurred, and use that food in the experiment. Unfortunately, since both of these methods would rely on self-report to verify
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the occurrence of the implementation of the restriction, it would be more difficult to establish if the manipulation of restriction had actually occurred. Additionally, since the food restriction most eaters experience is self-imposed, perhaps a stronger manipulation of restriction in the current investigation would be for the participant to choose the food to be restricted, rather than the experimenter choosing the food to be restricted. This would change the attribution of the restriction, potentially making the restriction manipulation more potent. Finally, it is important to recognize that the food restriction seen in eating disorders is usually chronic, with the perception of removal of the restriction being far into the future (as compared to 15 min into the future) or not occurring at all. For this reason, these results should not be generalized to subjects with eating disorders. Future investigations should address the effects of different durations of food restriction on eating behavior that may be relevant to those who experience more chronic degree of food restriction. The outcome of this investigation provides additional supporting evidence that short-term food deprivation increases the relative-reinforcing value of food. This increase in the reinforcing value of food under periods of short-term food deprivation indicates that when individuals are placed into food deprivation conditions, they are more likely to choose to engage in eating behaviors than in other pleasurable alternative activities. This increased engagement in eating could potentially lead to overeating, which would be problematic for individuals with binge eating disorders or individuals trying to reduce caloric intake to achieve healthy weights. Cognitive-behavioral treatment for binge eating disorders (e.g. bulimia nervosa and binge eating disorder) recommends the development of a ‘normalized eating pattern’, an eating pattern that replaces deprivation with a fairly consistent eating pattern, in which food is consumed every 3 –4 h (Fairburn et al., 1993). The results of this study reinforce the importance of this recommendation. If food deprivation makes food more reinforcing, it may be more difficult to engage in other behaviors (e.g. pleasurable alternative behaviors) designed to disrupt binge eating if food has become that much more reinforcing due to a previous period of food deprivation. Also, if binge eating is a behavioral response to a negative mood, and binge eating is designed to help reduce a negative mood, this response might be amplified under periods of food deprivation; food would be more reinforcing than other activities under deprivation conditions and would consequently be more likely chosen than any other activity to improve a negative mood (Agras and Telch, 1998). This research also suggests that guidelines about the frequency of eating should be provided during obesity treatment to help reduce the occurrence of short-term food deprivation. If individuals go for long periods of
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time (e.g. skip eating during the morning and early afternoon) without eating, this could increase the reinforcing value of food in a population that already appears to find food more reinforcing than normal-weight individuals (Saelens and Epstein, 1996). This increase in the reinforcing value of food would make it more difficult to adhere to caloric prescriptions for weight loss. Consequently, feelings of food deprivation should be minimized in obesity treatment. In summary, the results of this investigation indicate that for normal-weight, healthy, unrestrained eating collegeaged females, short-term food deprivation increases the relative-reinforcing value of food. However, factors such as obesity status, gender, age, and indications of eating pathology influence eating behavior (Greeno and Wing, 1994), therefore it is expected that the outcome of this experiment would be different with differing populations. For example, a high level of dietary restraint is common in individuals with eating disorders (Howard and Porzelius, 1999). Restrained eaters are individuals who have engaged in intermittent and/or sporadic food deprivation and restriction to control weight (Polivy, 1996). This history of chronic and intermittent food deprivation and restriction may play a crucial role in how acute food deprivation and restriction affect eating behaviors. Consequently, the acute food deprivation and restriction used in this investigation may differentially affect the eating behavior in individuals with this history of chronic and intermittent deprivation and restriction as compared to those without this history (e.g. normal eaters). Additional investigations need to focus on using stronger manipulations of food restriction to determine if food restriction has an effect on the reinforcing value of food. Additionally, since more chronic forms of food deprivation and restriction are common in eating disorders and obesity treatment, it would be helpful if future studies address the effect of chronic, and or intermittent, food restriction and deprivation on the relative-reinforcing value of food under both acute and chronic periods of deprivation and restriction. If chronic and/or intermittent food deprivation and restriction affect the relative-reinforcing value of food, this would provide valuable information regarding etiological and maintenance factors important in eating pathology. Additionally, if chronic and intermittent food deprivation and restriction have an effect on the relative-reinforcing value of food, is this effect permanent, or when the deprivation and restriction are removed, does food become less reinforcing, and if so, what is the time course of that change? Moreover, does the effect of food deprivation on the relative-reinforcing value of food generalize to all foods or is it specific to highly palatable (e.g. snack foods)? The results of investigations addressing these questions could provide valuable information for the treatment of eating pathology.
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Hursh, S. R., & Beck, R. C. (1971). Bitter and sweet saccharin preference as a function of food deprivation. Psychological Reports, 29, 419–422. Kirk, J. M., & Logue, A. W. (1997). Effects of deprivation level on humans self-control for food reinforcers. Appetite, 28, 215 –226. Lappalainen, R., & Epstein, L. H. (1990). A behavioral economics analysis of food choice in humans. Appetite, 14, 81 –93. Lattimore, P. J., Thompson, G. M., & Halford, J. C. G. (2000). Developmental onset of eating-related color-naming interference: the role of restraint and eating psychology. The International Journal of Eating Disorders, 28, 27 –32. Lepper, M. R., Sagotsky, G., Dafoe, J. L., & Greene, D. (1982). Consequences of superfluous social constraints: effects on young children’s social inferences and subsequent intrinsic interest. Journal of Personality and Social Psychology, 42, 51– 65. Logue, A. W., & King, G. R. (1991). Self-control and impulsiveness in adult humans when food is the reinforcer. Appetite, 17, 105–120. Lohman, T. G., Roche, A. F., & Martorell, R. (1988). Anthropometric Standardization Reference Manual. Champaign: Human Kinetics Publishers. Mann, T., & Ward, A. (2001). Forbidden fruit: does thinking about a prohibited food led to its consumption? International Journal of Eating Disorders, 29, 319– 327. Marcucella, H., & Munro, I. (1987). Ethanol consumption of free feeding animals during restricted ethanol access. Alcohol and Drug Research, 7, 405– 414. Marcucella, H., Munro, I., & MacDonall, J. S. (1984). Patterns of ethanol consumption as a function of the schedule of ethanol access. The Journal of Pharmacology and Experimental Therapeutics, 230, 658– 664. Must, A., Dallal, G. E., & Dietz, W. H. (1991a). Reference data for obesity: 85th and 95th percentiles of body mass index and triceps skinfold thickness. American Journal of Clinical Nutrition, 53, 839 –846. Must, A., Dallal, G. E., & Dietz, W. H. (1991b). Reference data for obesity: 85th and 95th percentiles of body mass index—a correction. American Journal of Clinical Nutrition, 54, 773. Nowend, K. L., Arizzi, M., Carlson, B. B., & Salamone, J. D. (2001). D1 or D2 antagonism in nucleus accumbens core or dorsomedial shell suppresses lever pressing for food but leads to compensatory increases in chow consumption. Pharmacology, Biochemistry, and Behavior, 69, 373– 382. Oatley, K., & Tonge, D. A. (1969). The effect of hunger on water intake in rats. Quarterly Journal of Experimental Psychology, 21, 162– 171. Perpina, C., Hemsley, D., Treasure, J., & de Silva, P. (1993). Is the selective information processing of food and body words specific to patients with eating disorders? International Journal of Eating Disorders, 14, 359– 366. Pinel, J. P. J., & Huang, E. (1976). Effects of periodic withdrawal on ethanol and saccharin selection in rats. Physiology and Behavior, 16, 693– 698. Pinel, J. P. J., Mucha, R. F., & Rovner, L. I. (1976). Temporary effects of periodic alcohol availability. Behavioral Biology, 16, 227–232. Polivy, J. (1996). Psychological consequences of food restriction. Journal of the American Dietetic Association, 96, 589–592. Polivy, J., & Herman, C. P. (1993). Etiology of binge eating: psychological mechanisms. In C. G. Fairburn, & G. T. Wilson (Eds.), Binge Eating: Nature, Assessment, and Treatment (pp. 173 – 205). New York: Guilford Press. Polivy, J., Zeitlin, S. B., Herman, C. P., & Beal, A. L. (1994). Food restriction and binge eating: a study of former prisoners of war. Journal of Abnormal Psychology, 103, 409–411. Rachlin, H. (1989). Judgement, Decision, and Choice: A Cognitive/ Behavioral Synthesis. New York: W.H. Freeman. Saelens, B. E., & Epstein, L. H. (1996). Reinforcing value of food in obese and non-obese women. Appetite, 27, 41–50. Savory, C. J. (1988). Rates of eating by domestic fowls in relation to changing food deficits. Appetite, 10, 57–65.
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Research Report
The relative-reinforcing value of food under differing levels of food deprivation and restriction Hollie A. Raynor, Leonard H. Epstein* State University of New York, University at Buffalo, Buffalo, NY 14214-3000, USA Received 28 June 2002; revised 30 September 2002; accepted 2 November 2002
Abstract Food deprivation and restriction both increase food consumption. Food deprivation also increases the reinforcing value of food, but it is unknown if food restriction alone or combined with deprivation increases the reinforcing value of food. Forty, normal-weight, college-aged, unrestrained females were randomized to one of four conditions that crossed food deprivation (Dep) and restriction (Res): Dep/Res, Dep/No Res, No Dep/Res, No Dep/No Res. All participants arrived at least 13 h food-deprived, and non-deprived participants consumed at least 365 cal from a drink during the session. Restriction was manipulated by placing snack food in front of participants, without access for 15 min during the session, or having no snack food placed in front of participants. Following the experimental manipulations, participants completed a computer choice task to determine the reinforcing value of food. Repeated measures analysis of variance found a significant main effect of deprivation ( p , 0.05) and trials ( p , 0.001) for food points earned. Deprived participants found food to be more reinforcing, and the reinforcing value of food decreased over time. This suggests that while short-term food deprivation increases the relative-reinforcing value of food, short-term food restriction has no effect on the relative-reinforcing value of food in unrestrained eaters. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Food deprivation; Food reinforcement; Food restriction
Food deprivation, a reduction of overall caloric intake, and food restriction, conditions in which cognitive or environmental constraints have been implemented so that there is limited access to certain foods, are main features of anorexia and bulimia nervosa (American Psychiatric Association (APA), 1994). In anorexia nervosa, low-body weight is achieved through food deprivation, but often times the deprivation is preceded by a stage of restricting specific foods from the diet (APA, 1994). In bulimia nervosa, food deprivation and restriction are believed to be important cognitive and behavioral components of the maintenance, and perhaps initiation, of binge eating (Brewerton et al., 2000; Howard and Porzelius, 1999; Polivy and Herman, 1993; Westenhoefer and Pudel, 1993). Not surprisingly, high levels of food deprivation and/or restriction are associated with poorer treatment outcome in patients with bulimia nervosa (Bulik et al., 1998). * Corresponding author. Address: Division of Behavioral Medicine, Departments of Pediatrics, State University of New York at Buffalo, Farber Hall, Room G56, 3435 Main Street, Building #26, Buffalo, NY 142143000, USA. Tel.: þ1-716-829-3400; fax: þ 1-716-829-3993. E-mail address: [email protected] (L.H. Epstein).
Specific food restrictions (e.g. high-fat and/or sugar foods) and food deprivation are also central components of dietary treatments for obesity. Restriction and/or deprivation may actually contribute to overeating, thereby reducing the effectiveness of obesity treatment (Corwin, 2000). In laboratory investigations, acute food deprivation (e.g. not eating for 1 – 48 h) is associated with increased consummatory behavior in animals (Bolles, 1965; DiBattista, 1987; Falk, 1981; Grill and Berridge, 1985; Hursch and Beck, 1971; Oatley and Tonge, 1969; Savory, 1988; Tolman and Wilson, 1965) and in humans with (Hetheringon et al., 2000; Telch and Agras, 1996) and without eating pathology (Drobes et al., 2001; Hill, 1974; Spiegel et al., 1989). The effects of chronic food deprivation on current eating behavior has also been examined in animals (DiBattista, 1987; Hagan and Moss, 1991, 1997), demonstrating that a history of food deprivation may influence current eating behaviors, causing a similar response as acute food deprivation. A history of food deprivation does appear to affect current eating behavior in humans (Franklin et al., 1948; Polivy et al., 1994). For example, men who had
0195-6663/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0195-6663(02)00161-7
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reduced intake to around 1500 kcal/day for 24-weeks reported problems with uncontrollable eating and increased appetites for sweet foods even after weight regain occurred (Franklin et al., 1948). Additionally, Polivy and colleagues (1994) documented a significantly higher prevalence of self-reported binge eating in prisoners of World War II who had a history of severe food deprivation 50 years ago as compared to those World War II veterans who had not experienced severe food deprivation. Restriction, or limited access, also appears to increase consummatory behavior. Studies investigating the effects of restricted access to alcohol on alcohol intake found that as restriction of alcohol availability increases, consumption of alcohol increases during access periods (Files et al., 1994; Marcucella and Munro, 1987; Marcucella et al., 1984; Pinel and Huang, 1976; Pinel et al., 1976; Wise, 1973). Studies involving food restriction in animals also reported an increase in food consumption of the restricted food during access periods as food restriction increased (Corwin et al., 1998; Wayner et al., 1972). Restricting access to certain foods for brief periods (e.g. 5 min) has also been found to increase children’s preferences for (Birch et al., 1980; Lepper et al., 1982 and intake of these foods (Fisher and Birch, 1999a,b). However, with adults, Mann and Ward (2001) found that while short-term food restriction (5 min) did produce an increase in thoughts about and desire for the restricted food, there was no change in consumption of the restricted food when the restriction was removed. Deprivation and restriction may affect consummatory behavior by focusing attention on the removed or limited access object. Self-reported preoccupation with food and eating is a cognitive symptom commonly reported in individuals with anorexia or bulimia nervosa (Stewart and Samoluk, 1997). In the Stroop task, delayed latency with food-related words has been reported in individuals with eating disorders (Ben-Tovim et al., 1989; Channon et al., 1988; Cooper et al., 1992), restrained eaters (Francis et al., 1997; Green and Rogers, 1993; Lattimore et al., 2000; Perpina et al., 1993; Stewart and Samoluk, 1997), and in individuals who have experienced acute food deprivation (Channon and Hayward, 1990). Increased attention on food under conditions of food deprivation and/or restriction may then increase the desire to obtain the deprived or restricted object, causing it to become more reinforcing. Food deprivation has shown to decrease self-control and increase impulsivity around food reinforcers in humans (Kirk and Logue, 1997; Logue and King, 1991) and in animals (Eisenberger et al., 1982). The increased impulsivity associated with the deprivation is hypothesized to be a consequence of an increase in the incentive value associated with the reinforcer (Eisenberger et al., 1982). An increase in the reinforcing value of food may cause individuals to more likely choose to eat instead of participate in non-eating activities, or may predispose individuals to be more susceptible to eating when exposed
to eating cues (Epstein and Saelens, 2000). Consequently, as the reinforcing value of food increases, so should food consumption. Therefore, factors that increase the reinforcing value of food may interfere with the ability to reduce energy intake that is recommended for weight control programs, or engage in alternative activities that may help reduce increased intake associated with binge eating (Epstein and Saelens, 2000). Behavioral economic theory (Rachlin, 1989) and laboratory choice paradigms provide a model to assess the relative-reinforcing value of two choices (Saelens and Epstein, 1996). Studies using a behavioral economics paradigm found that food deprivation is related to the absolute amount of work animals will do for food (Herrnstein and Loveland, 1974) and affects the relativereinforcing value of food substances in humans (Bulik and Brinded, 1994; Bulik et al., 1995; Epstein et al., 1991; Lappalainen and Epstein, 1990), such that deprivation is associated with increased work and reinforcing value of food substances. However, the effect of food restriction alone, and the combined effects of food deprivation and restriction on the relative-reinforcing value of food are not known. This study was designed to examine the independent and interacting effects of food deprivation (Dep) and restriction (Res) on the relative-reinforcing value of food and food consumption. Four conditions were used in the investigation: Dep/Res, Dep/No Res, No Dep/Res, No Dep/No Res. All participants worked toward earning points for eating the food and a preferred sedentary activity. It was expected that short-term food deprivation and restriction would increase the relative-reinforcing value of the snack food due to the increased food consumption associated with food deprivation and restriction. Consequently, participants in food-deprived, foodrestricted, and food-deprived and-restricted conditions would earn more snack food points during the choice task, and consume more kcals from a highly-rated snack food, as compared to participants in the non-fooddeprived and -restricted conditions.
1. Method 1.1. Participants Participants consisted of 40 healthy, non-smoking, normal weight (body mass index [BMI] , 85th percentile) (Must et al., 1991a,b) female adults, recruited from the State University of New York (SUNY) at Buffalo. Additionally, participants reported no allergies or unfavorable preferences towards foods used in the investigation; regular consumption of breakfast and/or lunch (e.g. eating at least one of these meals 75% of the days in the past month); could be classified as an unrestrained eater (scoring # 12 on the Restraint Scale [RS]) (Gorman and Allison, 1995; Herman
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and Polivy, 1980); and showed no indications of eating disorder pathology, scoring # 27 on the binge eating scale (BES) (Gormally et al., 1982) and # 30 on the eating attitudes test (EAT) (Garner and Garfinkel, 1979). On average, participants were 18.4 (SD ¼ 0.8) years of age and had a BMI of 21.5 (SD ¼ 2.0). The ethnicity of the participants was the following: 58% Caucasian, 20% Asian, 15% African-American, and 7% of other descent. All participants received $20 compensation for their participation. This investigation was approved by the Social Sciences Human Subject Review Board of the SUNY at Buffalo. 1.2. Design and procedure The investigation used a 2 £ 2 £ 8 mixed design, with food deprivation (food-deprived versus non-food-deprived) and food restriction (food-restricted versus non-foodrestricted) as the between-subject factors, and computer game trials with differing reinforcing schedules (1 – 8), as the within-subject factor. The primary dependent variable in the investigation was the amount of food points earned in the computer game. Female undergraduate students (N ¼ 137) recruited from undergraduate psychology classes and from flyers posted around the campus completed a phone screen to assess height, weight, age, health status, medication usage, dietary restrictions, smoking status, food allergies, dieting status, food preferences, usual eating patterns, and the RS (Herman and Polivy, 1980). After the phone screen, a laboratory screening session was scheduled between 10 a.m. and 1 p.m. for 58 participants who met entrance criteria. All participants were instructed to not eat 2 h before the screening session. Upon arrival to the screening session, participants were taken to a small room equipped with a closed-circuit television monitor and an intercom providing two-way communication with the adjoining room. Participants completed a consent form and were asked if they had eaten in the last 2 h. Then, participants sampled the drinks, snack foods, and activities used in the investigation. The sampled drinks were one tablespoon each of three flavors, chocolate, vanilla, and strawberry, of a nutritionally-balanced liquid drink (Boost Plus, Mead Johnson; Evansville, Indiana) chilled to 68C, approximating 70 kcals. The sampled snack foods were 4 g each of Doritos nacho cheese tortilla chips (Frito-Lay; Plano, TX), Twix candy bars (MandM/Mars; Hackettstown, NJ) and Chips Ahoy chocolate chip cookies (Nabisco; Hanover, NJ), which was approximately 60 kcals. Participants were instructed to take a sip of water, consume the first sample, provide an hedonic rating of the drink/snack food using a 100 mm visual analogue scale (VAS,) and indicate if they would consume the drink/snack food. They repeated this procedure for the other samples. If a participant indicated
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that she would not consume at least one of the drinks/snack foods rated $ 50, the participant was not included in the study. The mean hedonic ratings of the drinks for participants completing the investigation were: chocolate ¼ 66.2 (SD ¼ 23.4); vanilla ¼ 63.0 (SD ¼ 25.7); and strawberry ¼ 39.9 (SD ¼ 28.8). The highest rated drink was used as the meal in the non-deprived condition. Mean hedonic ratings of the snack foods for participants completing the investigation were: Doritos ¼ 89.3 (SD ¼ 13.3); Twix ¼ 84.5 (SD ¼ 20.8); and cookies ¼ 74.1 (SD ¼ 22.8). The highest rated snack food was used in the choice task and as the restricted food. Participants then sampled three sedentary activities, playing a video game, watching videos, and reading current popular magazines, for 2 min. After sampling an activity, participants provided an hedonic rating of the activity using a 100 mm VAS, answered if they would do the activity, and repeated this procedure for the other activities. If a participant indicated that she would not do at least one of the activities rated $ 50, the participant was not included in the study. The mean hedonic ratings of the activities for participants completing the investigation were: video games ¼ 70.9 (SD ¼ 30.3); videos ¼ 85.7 (SD ¼ 15.0); and magazines ¼ 82.5 (SD ¼ 17.9). The highest rated sedentary activity was used in the choice task. Next, participants completed the BES (Gormally et al., 1982), the EAT (Garner and Garfinkel, 1979) and had height measured by a stadiometer (Seca, Columbia, MD), calibrated in 1/8 inch intervals, and weight measured by a balance beam scale (Healthometer, Model 402, Bridgeview, IL), calibrated in 1/4 pound intervals, using standard procedures (Lohman et al., 1988). BMI (kg/m2) was calculated from this information. Participants were scheduled for their second session, at 1 or 2 p.m., occurring within one-week of the screening session. Participants were instructed to not eat after midnight of the night prior to their session. Screening measures indicated that 14 participants did not meet the criteria for the investigation: eight participants did not rate any of the foods or drinks used in the study as being pleasant; three participants’ BMI exceeded the 85th BMI percentile; one participant scored too high on the EAT; one participant had a medical condition (hypoglycemia) that prevented her from being able to follow the food deprivation directions; and one participant indicated that she did not regularly eat breakfast or lunch. Additionally, after completing the screening session, two participants chose to withdraw from the study, and two participants had procedural errors during the experimental session. Consequently, the sample size of the investigation was 40. Participants were randomly assigned to one of four experimental groups: Dep/Res, Dep/No Res, No Dep/Res, No Dep/No Res. The experimental session began with assessment of compliance with deprivation instructions by a 24-h dietary recall. Three participants had eaten in
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the morning prior to their experimental session and these sessions were rescheduled. Ratings of level of hunger were taken using a 100 mm VAS. In the non-deprived condition, participants were served a liquid meal, consisting of two cups of a nutritionallybalanced liquid drink (approximately 730 kcals) (Boost Plus), served in a clear plastic cup and chilled to 68C. Participants were instructed to consume at least half (approximately 365 kcals) of the drink, and then consume as much as they wanted until they felt pleasantly satisfied. Participants had 15 min to consume the drink. In the deprived condition, participants sat quietly for the same 15 min session. After the 15 min meal session, all participants again rated their feelings of hunger using the VAS. For the restricted condition, a plate full (approximately 50 g) of the highest rated snack food was placed on the table in front of the participant during the 15 min meal session. Participants were informed that they could not eat any of the snack food, but that they would be answering questions about the appearance of the food later in the session so they should pay attention to the food. During this 15 min session, all participants were closely observed through the monitor to ensure that the restricted food was not eaten. After 15 min, the restricted food was removed, and after completing the second hunger VAS, participants completed two questions regarding the appearance of the restricted food. In the non-restricted condition, the plate of snack food was not brought into the session. Participants were then instructed on how to play a computer game in which points could be earned for their highest rated food and sedentary activity. During the games, participants responded (using a computer joystick) on one of two screens, each of which was associated with a reinforcement schedule and different reinforcer (food or sedentary activity). Responses on one of the joystick buttons allowed participants to switch screens. The presentation of which reinforcer appeared on the first screen was counterbalanced across participants. Within each screen, a press of the other joystick button caused colored shapes to spin, much like a slot machine game. When each of the three colored shapes matched, the participant received one point toward the reinforcer specified on the screen. A concurrent reinforcement schedule was implemented by varying the probability of earning points with each response. The reinforcement schedule remained at VR2 for all eight trials for the sedentary activity, while the schedule for the snack food was set at VR2, VR4, VR6, VR8, VR10, VR12, VR14, and VR16 across trials. The exchange rate was 10 food points ¼ 10 g of food (participants were shown this amount of food in a clear cup) and 10 activity points ¼ 1 min to spend doing the sedentary activity. Participants could earn 15 points per trial and were verbally notified of their total points at
the end of each trial. Additionally, the points were displayed on the computer screen. As the trials progressed, participants were verbally informed about the change in the schedules across the trials (e.g. “It will be more difficult now to earn points for the food”). Upon completing all trials, participants traded in points earned towards their reinforcers. Upon consuming the food and engaging in the sedentary activity time for which they had earned, participants were debriefed, received their compensation for participating in the study, thanked for their participation, and escorted from the laboratory. 1.3. Measures Visual analogue scales were used to determine the pleasantness of the drinks, snack foods, and sedentary activities; and hunger. Participants rated each of these dimensions on 100 mm scales, with pleasantness measures anchored by do not like at all/like very much and hunger anchored by extremely hungry/overly full. Food intake from the previous day was assessed by a 24-h food recall, in which participants were asked to provide detailed information regarding what they had eaten and how it was prepared, along with serving size information. Food items and amounts from the 24-h recalls were entered into Nutritionist V (First DataBank; San Bruno, CA), and the caloric intake; grams of protein, fat, and carbohydrate; and percent calories from protein, fat, and carbohydrate were obtained. To determine caloric intake in the non-deprived session prior to the computer game, cups containing the drink served to participants were weighed on a balance beam food scale (Ohaus; Florham Park, NJ) calibrated to the 0.1 g, and the amount consumed was determined by subtracting the post-meal weight from the pre-meal weight. Calories per gram of the drink were assessed using manufacturer information. Total calories were determined by multiplying total grams consumed by the amount of calories per gram of the food. The primary dependent variable in the investigation was number of points earned for each option during the trials of the choice task for each session. The number of points earned for each option was recorded at the end of every trial so comparisons across trials could be made as the schedule for one of the reinforcers changed. Additionally, caloric intake from the food reinforcers earned from the choice task was determined by multiplying the total grams consumed, as measured by the balance beam food scale, by the amount of calories per gram of food, as determined using manufacturer information. 1.4. Data analysis A series of two factor analyses of variance (ANOVA), with food deprivation (food-deprived versus non-fooddeprived) and food restriction (food-restricted versus
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non-food-restricted) as the between-subject factors, were conducted to examine differences between the groups on baseline characteristics; hedonic ratings of the highest rated drink, food, and sedentary activity; caloric and macronutrient intake from the day prior to the experimental session; and baseline hunger and hours of deprivation. To increase the sensitivity of the omnibus ANOVA, variables that are different and contribute a significant amount of variance to the primary dependent variable should be used as covariates (Tabachnick and Fidell, 1996). If there is no significant relationship between the dependent variable and potential covariates, the covariates should not be used in the analysis due to the loss of degrees of freedom in the analysis (Tabachnick and Fidell, 1996). While hours of deprivation were significantly different between groups, there was no significant relationship between this variable and the primary dependent variable, and it was not used as a covariate in other analyses. The effectiveness of the experimental manipulation of deprivation was assessed by the change in hunger level during the session, using a 2 £ 2 £ 2 mixed repeated measures ANOVA, with food deprivation and restriction as the between-subject factors, and the time of assessment of the hunger ratings (pre-meal and post-meal) as the within-subject factor. The relative-reinforcing value of the food was analyzed using a 2 £ 2 £ 8 mixed repeated measures ANOVA, with food deprivation and restriction as the between-subject factors, and trials (VR2, VR4, VR6, VR8, VR10, VR12, VR14, VR16), as the within-subject factors, and food points earned in each trial as the dependent variable. A 2 £ 2 ANOVA, with food deprivation and restriction as the between-subject factors examined
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differences in caloric intake from the reinforcers. Where appropriate, Greenhouse-Geisser probability levels were used to adjust for sphericity. For significant outcomes, post-hoc comparisons with Bonferroni corrections, were conducted. Finally, Pearson product – moment correlations were conducted to explore the relationship between total food points and levels of self-reported initial hunger, previous day caloric intake, hours of deprivation, dietary restraint, and the hedonic ratings of the food reinforcer. All data were analyzed with SYSTAT (Wilkinson, 1996).
2. Results Baseline characteristics of the participants are summarized in Table 1. Two unrestrained eaters were dropped from the analyses due to being outliers within their specific group on the primary dependent variable (Tabachnick and Fidell, 1996), food points earned in the choice task. No significant difference was found between the groups for age; BMI; scores on the RS, BES, and EAT; hedonic ratings of the highest rated drink, food, and sedentary activity; and caloric and macronutrient intake on the day prior to the experimental session. There was no significant difference of baseline levels of self-reported hunger between the groups, indicating self-reported baseline hunger was consistent across groups; however, there was a significant main effect of deprivation, F(1,34) ¼ 9.2, p ¼ 0.005, for hours of deprivation. Participants in the deprived condition reported significantly more hours of deprivation (M ¼ 17, SD ¼ 1.9) than participants in the non-deprived condition (M ¼ 15.5, SD ¼ 1.2). Since hours
Table 1 Summary characteristics of participants (M ^ SD)
Age (yrs) BMI (kg/m2) RS BES EAT Hedonic rating of preferred drink Hedonic rating of preferred food Hedonic rating of preferred activity Previous day calories consumed Previous day protein (g) Previous day carbohydrate (g) Previous day fat (g) Previous day protein (% kcals) Previous day carbohydrate (% kcals) Previous day fat (% kcals) Hours of deprivation
D-R n ¼ 10
D-NR n ¼ 8
ND-R n ¼ 10
ND-NR n ¼ 10
p
18.3 ^ 0.7 21.6 ^ 1.9 6.6 ^ 1.9 5.5 ^ 3.7 6.1 ^ 2.8 86.0 ^ 10.3 91.4 ^ 10.7 91.1 ^ 11.0 2384.6 ^ 439.8 74.1 ^ 24.5 337.9 ^ 86.7 85.8 ^ 22.9 12.2 ^ 4.2 55.7 ^ 7.7 31.9 ^ 6.3 16.5 ^ 1.8
18.3 ^ 0.7 21.6 ^ 1.6 7.1 ^ 2.5 5.8 ^ 4.9 8.5 ^ 7.4 78.2 ^ 15.0 95.4 ^ 5.0 92.3 ^ 8.2 1895.1 ^ 133.1 64.6 ^ 15.7 271.7 ^ 61.0 65.3 ^ 18.8 13.5 ^ 3.7 56.1 ^ 11.4 30.5 ^ 9.5 17.6 ^ 2.0
18.4 ^ 1.2 21.3 ^ 2.3 6.6 ^ 3.1 5.7 ^ 2.5 9.4 ^ 7.6 76.8 ^ 12.5 94.8 ^ 5.8 92.2 ^ 10.0 2007.0 ^ 530.7 66.5 ^ 24.1 275.9 ^ 106.8 73.6 ^ 31.6 14.3 ^ 7.7 53.3 ^ 14.2 32.3 ^ 12.1 15.4 ^ 1.4
18.4 ^ 0.7 21.7 ^ 2.6 7.9 ^ 3.8 6.7 ^ 5.3 8.5 ^ 6.4 76.4 ^ 12.6 92.4 ^ 8.7 92.6 ^ 9.6 2005.4 ^ 570.0 72.5 ^ 21.8 267.5 ^ 81.9 74.9 ^ 35.7 14.5 ^ 2.6 53.3 ^ 10.4 32.1 ^ 9.8 15.6 ^ 1.1
NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS 0.005a
Note: D-R ¼ deprived and restricted; D-NR ¼ deprived and non-restricted; ND-R ¼ non-deprived and restricted; ND-NR ¼ non-deprived and non-restricted; NS ¼ no significance; BMI ¼ body mass index; RS ¼ Restraint Scale; BES ¼ binge eating scale; EAT ¼ eating attitudes test. a Main effect of deprivation.
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of deprivation were not significantly related to the primary dependent variable, it was not included as a covariate in remaining analyses. The analysis for the manipulation of deprivation showed a significant interaction of deprivation x time of assessment, F(1,34) ¼ 10.8, p ¼ .002. Follow-up analyses indicated that participants in the non-deprived condition had significantly higher ratings, F(1,34) ¼ 9.5, p ¼ .004 (M ¼ 41.2, SD ¼ 25.6), at the measurement taken after the meal session than participants in the deprived condition (M ¼ 19.0, SD ¼ 16.1), with higher ratings indicating increased feelings of fullness. The mean amount of kcals consumed by the non-deprived group in the session was 480.6 (SD ¼ 128.5), while the deprived group consumed 0 kcals in the session. These results indicate by self-report and objective measure, the manipulation of deprivation vs non-deprivation occurred. Results of the primary hypothesis of the relativereinforcing value of food versus sedentary activity demonstrated a significant main effect of deprivation, F(1,34) ¼ 6.4, p ¼ 0.016, and trials, F(7,238) ¼ 13.9, p , 0.001), for food points earned in each trial. The effect size for the main effect of deprivation, ES ( f) ¼ 0.41; (d) ¼ 0.82, and the main effect of trials, ES ( f) ¼ 0.58; (d) ¼ 1.16, was large (Cohen, 1992). Participants in the deprived condition earned significantly more food points (M ¼ 49.2, SD ¼ 12.8) than participants in the non-deprived condition (M ¼ 38.2, SD ¼ 12.6). Mean total food points earned by group is shown in Table 2. Using a Bonferroni correction of 0.007 (0.05/7), post-hoc analyses revealed that the food points earned in trial five were significantly less than the food points earned in trial one, F(4,34) ¼ 4.3, p ¼ 0.007. The food points earned in the remaining trials continued to be significantly less ( p , 0.001) than food points earned in the first trial. Fig. 1 illustrates the food points earned in the eight trials in the deprived and non-deprived conditions. A significant main effect of deprivation was found for calories consumed from the reinforcers, F(1,34) ¼ 6.5, p ¼ 0.015, with the deprived group consuming significantly more calories than the non-deprived group (see Fig. 2). The effect size, ES ( f) ¼ 1.0; (d) ¼ 2.0, was again large (Cohen, 1992). Pearson product-moment correlations indicated no significant associations between total food points and levels of self-reported initial hunger, previous day
Fig. 1. Food points earned across eight trials in the deprived and non-deprived conditions (M ^ SEM).
caloric intake, hours of deprivation, dietary restraint, and hedonic ratings of the food reinforcer.
3. Discussion This investigation tested the hypothesis that short-term food deprivation and food restriction affects the relativereinforcing value of food. It was hypothesized that participants would find food more reinforcing in the food-deprived and -restricted conditions, causing them to work harder for food points during a choice task when food-deprived, food-restricted, and food deprived and restricted, as compared to not being food-deprived or foodrestricted. Results from this study indicate that short-term food deprivation, but not short-term food restriction, affects the relative-reinforcing value of food. Food deprivation may change the reinforcing value of food by affecting dopaminergic pathways (Carr et al., 2001). Research suggests that central dopaminergic pathways are
Table 2 Total food points earned (M ^ SD) Group
n
Sum of food points
Deprived/restricted Deprived/non-restricted Non-deprived/restricted Non-deprived/non-restricted
10 8 10 10
51.9 ^ 15.0 45.8 ^ 9.2 38.5 ^ 12.1 37.9 ^ 13.7
Note: There was a main effect ( p , 0.05) of deprivation.
Fig. 2. Caloric intake from reinforcers in the deprived and non-deprived conditions (M ^ SEM).
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involved in the reinforcing properties of primary occurring incentives such as food and water (Chausmer and Ettenberg, 1997; Nowend et al., 2001). Experiments show a decrease in operant response rates for food during dopamine (DA) receptor antagonist drug challenges—even at doses that do not produce obvious sedative or motor-incapacitating effects (Chausmer and Ettenberg, 1997). The two main subtypes of dopamine receptors that are believed to be involved in the reinforcing properties of food are the D1 and D2 receptors (Berridge, 1996). It has been proposed that chronic food deprivation, which produces a reduced body weight, may increase the reward value of food and drugs by increasing DA releasability or decreasing DA reuptake (Carr et al., 2001). This change in DA releasability or decrease in DA reuptake and consequential increase in the reinforcing value of food appears to functionally and mechanistically increase sensitization to food, causing an initial increase in the behavioral response in eating (Carr et al., 2001). A potential reason for failing to confirm the hypothesis about short-term food restriction affecting the relativereinforcing value of food is that the food restriction manipulation used in the study was not strong enough. While a five-minute food-restriction interval was long enough to affect pre-school aged children’s food selection and consumption (Fisher and Birch, 1999b), a 15 min food-restriction interval might not be long enough to affect adult eating behavior. Children have demonstrated less self-control and more impulsivity than adults in laboratory experiments (Logue and King, 1991), and consequently, may require a shorter period of food restriction to affect eating behavior. Mann and Ward (2001) found that 5 min of restriction produced an increase in thoughts about and desire for the restricted food; however, there was not an increase in consumption of the restricted food when the restriction was removed. It was proposed that longer periods of restriction combined with chronic deprivation, similar to what occurs during dieting, may more strongly influence eating behavior. Although long periods of food restriction have been accomplished in controlled settings with animals (Corwin et al., 1998; Wayner et al., 1972), this is more difficult to accomplish with humans. A longer period, of up to a day, of food restriction can occur in a controlled setting for humans, but a longer length of restriction would be difficult to achieve under controlled conditions. While less controlled, there are two ways to achieve longer bouts of food restriction. The first would be to instruct participants to avoid eating a food that they commonly eat and encounter (e.g. potato chips), for a specified period of time before coming to the experimental session (e.g. one week). Another method would be to choose a food that the participant is already trying to restrict a food in the diet, but that is eaten periodically, assess the period of time the restriction has occurred, and use that food in the experiment. Unfortunately, since both of these methods would rely on self-report to verify
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the occurrence of the implementation of the restriction, it would be more difficult to establish if the manipulation of restriction had actually occurred. Additionally, since the food restriction most eaters experience is self-imposed, perhaps a stronger manipulation of restriction in the current investigation would be for the participant to choose the food to be restricted, rather than the experimenter choosing the food to be restricted. This would change the attribution of the restriction, potentially making the restriction manipulation more potent. Finally, it is important to recognize that the food restriction seen in eating disorders is usually chronic, with the perception of removal of the restriction being far into the future (as compared to 15 min into the future) or not occurring at all. For this reason, these results should not be generalized to subjects with eating disorders. Future investigations should address the effects of different durations of food restriction on eating behavior that may be relevant to those who experience more chronic degree of food restriction. The outcome of this investigation provides additional supporting evidence that short-term food deprivation increases the relative-reinforcing value of food. This increase in the reinforcing value of food under periods of short-term food deprivation indicates that when individuals are placed into food deprivation conditions, they are more likely to choose to engage in eating behaviors than in other pleasurable alternative activities. This increased engagement in eating could potentially lead to overeating, which would be problematic for individuals with binge eating disorders or individuals trying to reduce caloric intake to achieve healthy weights. Cognitive-behavioral treatment for binge eating disorders (e.g. bulimia nervosa and binge eating disorder) recommends the development of a ‘normalized eating pattern’, an eating pattern that replaces deprivation with a fairly consistent eating pattern, in which food is consumed every 3 –4 h (Fairburn et al., 1993). The results of this study reinforce the importance of this recommendation. If food deprivation makes food more reinforcing, it may be more difficult to engage in other behaviors (e.g. pleasurable alternative behaviors) designed to disrupt binge eating if food has become that much more reinforcing due to a previous period of food deprivation. Also, if binge eating is a behavioral response to a negative mood, and binge eating is designed to help reduce a negative mood, this response might be amplified under periods of food deprivation; food would be more reinforcing than other activities under deprivation conditions and would consequently be more likely chosen than any other activity to improve a negative mood (Agras and Telch, 1998). This research also suggests that guidelines about the frequency of eating should be provided during obesity treatment to help reduce the occurrence of short-term food deprivation. If individuals go for long periods of
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time (e.g. skip eating during the morning and early afternoon) without eating, this could increase the reinforcing value of food in a population that already appears to find food more reinforcing than normal-weight individuals (Saelens and Epstein, 1996). This increase in the reinforcing value of food would make it more difficult to adhere to caloric prescriptions for weight loss. Consequently, feelings of food deprivation should be minimized in obesity treatment. In summary, the results of this investigation indicate that for normal-weight, healthy, unrestrained eating collegeaged females, short-term food deprivation increases the relative-reinforcing value of food. However, factors such as obesity status, gender, age, and indications of eating pathology influence eating behavior (Greeno and Wing, 1994), therefore it is expected that the outcome of this experiment would be different with differing populations. For example, a high level of dietary restraint is common in individuals with eating disorders (Howard and Porzelius, 1999). Restrained eaters are individuals who have engaged in intermittent and/or sporadic food deprivation and restriction to control weight (Polivy, 1996). This history of chronic and intermittent food deprivation and restriction may play a crucial role in how acute food deprivation and restriction affect eating behaviors. Consequently, the acute food deprivation and restriction used in this investigation may differentially affect the eating behavior in individuals with this history of chronic and intermittent deprivation and restriction as compared to those without this history (e.g. normal eaters). Additional investigations need to focus on using stronger manipulations of food restriction to determine if food restriction has an effect on the reinforcing value of food. Additionally, since more chronic forms of food deprivation and restriction are common in eating disorders and obesity treatment, it would be helpful if future studies address the effect of chronic, and or intermittent, food restriction and deprivation on the relative-reinforcing value of food under both acute and chronic periods of deprivation and restriction. If chronic and/or intermittent food deprivation and restriction affect the relative-reinforcing value of food, this would provide valuable information regarding etiological and maintenance factors important in eating pathology. Additionally, if chronic and intermittent food deprivation and restriction have an effect on the relative-reinforcing value of food, is this effect permanent, or when the deprivation and restriction are removed, does food become less reinforcing, and if so, what is the time course of that change? Moreover, does the effect of food deprivation on the relative-reinforcing value of food generalize to all foods or is it specific to highly palatable (e.g. snack foods)? The results of investigations addressing these questions could provide valuable information for the treatment of eating pathology.
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