An acute social stressor decreases reinforcing value of both high and low energy-dense food in college students in a randomized controlled trial

It is well known that a large portion of the population elevates their intake of high energy-dense foods during times of stress; however, it is understudied whether stress affects the reinforcing value of a food reward. Further knowledge of this relationship may help us better understand the positive correlation between reinforcing value of food and obesity. Therefore, it was tested if an acute stressor would increase the reinforcing value of low or high energy-dense food. Participants (N = 70) were randomized to a stress or no-stress condition after which they were allowed to work to gain access to a food reward and reading time. To determine if high energy-dense food was specifically affected, half the participants from each stress manipulation were randomly assigned to work for either grapes or chocolate candies. Participants in the stress condition worked less for food access than those in the no-stress condition, for both low and high energy-dense foods, but stress did not affect the reinforcing value of reading time. These results indicate that, contrary to our hypothesis, in a sample of college students, an acute stressor decreased reinforcing value of food, with no difference between a low and high energy-dense food item.

Modeling the effect of stress on vaping behavior among young adults: A randomized cross-over pilot study

BACKGROUND

Laboratory models have been useful in identifying the motivational processes underlying tobacco use. This pilot study aimed at (1)validating a human laboratory model initially developed for smokers to e-cigarette users; (2)applying this model to examine the effects of stress on the reinforcing value of nicotine among young adults.

METHODS

Using a randomized cross-over design, young e-cigarette users (n = 30) who were nicotine deprived were exposed to a stress or a non-stress task, and then engaged in a laboratory task assessing vaping's reward value on two separate days. During the first part of the task, participants had the option of initiating an e-cigarette self-administration session or delaying initiation for up to 50 min in exchange for money. During the second part of the task, participants chose between vaping or receiving money. The length of the delay and the number of e-cigarette uses consumed were the primary outcomes. Craving and puff topography were secondary outcomes.

RESULTS

There was no difference in the length of time that participants were able to refrain from vaping in the stress and control task (p = .90). Participants purchased and consumed more puffs after being exposed to the stress task compared to the control task (p<.001), puff topography and craving were unaffected.

CONCLUSIONS

Exposure to a stressor did not undermine the ability to resist vaping among deprived e-cigarette users (first part), but it influenced the number of uses purchased once users decided to vape (second part). This study evidences that these two parts of the task for assessing reward value are differentially sensitive to the stress manipulation.

Smartphones are more reinforcing than food for students

College students engage in high-frequency smartphone use, despite potential negative consequences. One way to conceptualize this behavior is to consider it a highly reinforcing activity. Comparing motivation for smartphones to a powerful primary reinforcer, such as food, can establish their relative reinforcing value. This study investigated whether smartphones were more reinforcing than food, as well as the relationships between smartphone reinforcement, texting use, and smartphone motives. Participants were 76 college students (50% female, M_age = 18.9, SD = 0.99) who had no access to food for three hours and to their smartphones for two hours. After this modest deprivation period, participants worked for time to use their smartphones and 100-cal portions of their favorite snack food concurrently, with the work to obtain portions of both commodities increasing. The amount of smartphone use earned during the task was manipulated across groups (20, 30, 60, 120 s) to establish what amount of smartphone use was needed to motivate responding. Additionally, reinforcing efficacy of smartphones and food using a hypothetical purchase task and motivations for smartphone use was collected. Smartphones were more reinforcing than food using either measurement methodology (p's < 0.001). Smartphone reinforcement predicted number of text messages, controlling for age, sex, and family income. Positive smartphone use motives were associated with reinforcing efficacy of smartphones. These data show that smartphones are potent reinforcers, and are more reinforcing than food given modest food deprivation. These methods provide one important reason why people may use smartphones.

Adding a reward increases the reinforcing value of fruit

Adolescents' snack choices could be altered by increasing the reinforcing value (RV) of healthy snacks compared with unhealthy snacks. This study assessed whether the RV of fruit increased by linking it to a reward and if this increased RV was comparable with the RV of unhealthy snacks alone. Moderation effects of sex, hunger, BMI z-scores and sensitivity to reward were also explored. The RV of snacks was assessed in a sample of 165 adolescents (15·1 (sd 1·5) years, 39·4 % boys and 17·4 % overweight) using a computerised food reinforcement task. Adolescents obtained points for snacks through mouse clicks (responses) following progressive ratio schedules of increasing response requirements. Participants were (computer) randomised to three experimental groups (1:1:1): fruit (n 53), fruit+reward (n 60) or unhealthy snacks (n 69). The RV was evaluated as total number of responses and breakpoint (schedule of terminating food reinforcement task). Multilevel regression analyses (total number of responses) and Cox's proportional hazard regression models (breakpoint) were used. The total number of responses made were not different between fruit+reward and fruit (b -473; 95 % CI -1152, 205, P=0·17) or unhealthy snacks (b410; 95 % CI -222, 1043, P=0·20). The breakpoint was slightly higher for fruit than fruit+reward (HR 1·34; 95 % CI 1·00, 1·79, P=0·050), whereas no difference between unhealthy snacks and fruit+reward (HR 0·86; 95 % CI 0·62, 1·18, P=0·34) was observed. No indication of moderation was found. Offering rewards slightly increases the RV of fruit and may be a promising strategy to increase healthy food choices. Future studies should however, explore if other rewards, could reach larger effect sizes.

A sipometer for measuring motivation to consume and reward value of foods and beverages in humans: Description and proof of principle

New methods, derived from animal work, for measuring food reward value (i.e. reinforcing value of food), and motivation (i.e. strength of desire) to consume, in humans are described and validated. A sipping device (sipometer) was developed that permits access to a liquid food or beverage on two reward schedules: continuous reinforcement (CR) and progressively increasing time spent exerting pressure on a straw (PR-schedule). In addition, a pictorial scale showing a cup, from which the 'amount wanted' could be marked was used to pre-test potential consumption. Intake, time spent sipping, breakpoint, and pressure exerted were the main dependent variables measured. Three pilot experiments were conducted. In Experiment 1, participants (n=8) consumed yogurt shakes after a 1-h or 21-h food deprivation period on both schedules. In Experiment 2, participants (n=8) sham-consumed (i.e. spit out) sweet and non-sweet beverages, utilizing both schedules. In Experiment 3, sham-consuming sweet and non-sweet beverages on both schedules and working for shake on the PR schedule were repeated, after three nights of either habitual sleep or short sleep duration (n=7) in a crossover design. In Experiment 1, participants sipped longer after 21-h vs. 1-h of food deprivation (13±3.0 vs. 8.0±2.1s; p=0.04), on the PR schedule. In Experiment 2, sham-intake (p=0.01) and sipping time (p=0.04) were greater for sweet than non-sweet beverages on the PR schedule and a similar, though not conventionally significant, effect was observed for exerted pressure (p=0.09). In both Experiment 2 and Experiment 3 after habitual sleep, on the PR schedule, cumulative pressure difference between sweet and non-sweet beverage increased with difference in amount wanted in the taste test. In contrast, after short sleep participants were less willing to work for sweet taste as their wanting increased, suggesting that sleep deprivation raises desire, but lowers behavioral output. Taken together these results demonstrate that the sipometer and associated ratings are reliable and useful measures of motivation to consume and reward value in humans. Participants were more motivated to obtain access to sweet beverages, especially when these were better liked than to obtain access to non-sweet beverages.

Taste and food reinforcement in non-overweight youth

Food reinforcement is related to increased energy intake, cross-sectionally related to obesity and prospectively related to weight gain in children, adolescents and adults. There is very limited research on how different characteristics of food are related to food reinforcement, and none on how foods from different taste categories (sweet, savory, salty) are related to food reinforcement. We tested differences in food reinforcement for favorite foods in these categories and used a reinforcing value questionnaire to assess how food reinforcement was related to energy intake in 198 non-overweight 8- to 12-year-old children. Results showed stronger food reinforcement for sweet foods in comparison to savory or salty foods. In multiple regression models, controlling for child sex, minority status and age, average reinforcing value was related to total energy and fat intake, and reinforcing value of savory foods was related to total energy and fat intake. Factor analysis showed one factor, the motivation to eat, rather than separate factors based on different taste categories. Liking ratings were unrelated to total energy intake. These results suggest that while there are differences in the reinforcing value of food by taste groups, there are no strong differences in the relationship between reinforcing value of food by taste groups and energy or macronutrient intake.