A psychobioecological model to understand the income-food insecurity-obesity relationship.

Food insecurity, defined by unpredictable access to food that may not meet a person's nutritional needs, is associated with higher BMI (kg/m2) and obesity. People with food insecurity often have less access to food, miss meals and go hungry, which can lead to psychological and metabolic changes that favor energy conservation and weight gain. We describe a conceptual model that includes psychological (food reinforcement and delay discounting) and physiological (thermic effect of food and substrate oxidation) factors to understand how resource scarcity associated with food insecurity evolves into the food insecurity-obesity paradox. We present both animal and human translational research to describe how behavioral and metabolic adaptations to resource scarcity based on behavioral ecology theory may occur for people with food insecurity. We conclude with ideas for interventions to prevent or modify the behaviors and underlying physiology that characterize the income-food insecurity-obesity relationship.

Glucose response to sugar challenge moderates the effect of insulin resistance on reinforcing value of sugar-sweetened yogurt.

We have shown insulin resistance is associated with the choice of sugar-sweetened over monk fruit sweetened yogurt. This study extends this research by assessing the association between insulin resistance and reinforcing value for sugar versus monk fruit-sweetened yogurt, and testing the hypothesis that this effect is moderated by greater blood glucose response in people with insulin resistance. Eighteen people with overweight/obesity (BMI = 35.8 kg/m2, range 26.2-48.5) with varying degrees of insulin resistance (Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) = 2.6, range of 0.6-8.0) had blood glucose measured for 2 h after a sugar challenge. Over six days, they consumed, in a double-blind fashion, novel flavored-colored sugar or monk fruit-sweetened yogurts, and the reinforcing value of sugar or monk fruit-sweetened yogurts and delay discounting (DD) were measured. HOMA-IR (r = 0.62, p = .006) and insulin (r = 0.51, p = .03) were related to the reinforcing value of sugar-sweetened, but not monk fruit-sweetened yogurt (r = -0.07, -0.10, respectively). The blood glucose area under the curve moderated the relationship between HOMA-IR and the reinforcing value of sugar-sweetened yogurt (p = .02). People with greater HOMA-IR and greater blood glucose excursions responded the most for sugar-sweetened yogurt. These results extend previous research and confirm the hypothesis that individual differences in response to sugar may activate brain reward centers and condition people to prefer high-sugar foods. DD was related to sugar reinforcement (r = -0.46, p = .03), consistent with the idea that those with high sugar reinforcement desire immediate gratification, and DD moderated the relationship between HOMA-IR and the reinforcing value of sugar-sweetened yogurt (p < .001). Research should test whether reducing insulin resistance would permit people with insulin resistance to choose lower-sugar foods.

Transcranial Magnetic Stimulation for Reducing the Relative Reinforcing Value of Food in Adult Patients With Obesity Pursuing Metabolic and Bariatric Surgery: Protocol for a Pilot, Within-Participants, Sham-Controlled Trial.

BACKGROUND: Metabolic and bariatric surgery (MBS) is the most effective and durable obesity treatment. However, there is heterogeneity in weight outcomes, which is partially attributed to variability in appetite and eating regulation. Patients with a strong desire to eat in response to the reward of palatable foods are more likely to overeat and experience suboptimal outcomes. This subgroup, classified as at risk, may benefit from repetitive transcranial magnetic stimulation (rTMS), a noninvasive brain stimulation technique that shows promise for reducing cravings and consumption of addictive drugs and food; no study has evaluated how rTMS affects the reinforcing value of food and brain reward processing in the context of MBS. OBJECTIVE: The goal of the Transcranial Magnetic Stimulation to Reduce the Relative Reinforcing Value of Food (RESTRAIN) study is to perform an initial rTMS test on the relative reinforcing value (RRV) of food (the reinforcing value of palatable food compared with money) among adult patients who are pursuing MBS and report high food reinforcement. Using a within-participants sham-controlled crossover design, we will compare the active and sham rTMS conditions on pre- to posttest changes in the RRV of food (primary objective) and the neural modulation of reward, measured via electroencephalography (EEG; secondary objective). We hypothesize that participants will show larger decreases in food reinforcement and increases in brain reward processing after active versus sham rTMS. METHODS: Participants (n=10) will attend 2 study sessions separated by a washout period. They will be randomized to active rTMS on 1 day and sham rTMS on the other day using a counterbalanced schedule. For both sessions, participants will arrive fasted in the morning and consume a standardized breakfast before being assessed on the RRV of food and reward tasks via EEG before and after rTMS of the left dorsolateral prefrontal cortex. RESULTS: Recruitment and data collection began in December 2022. As of October 2023, overall, 52 patients have been screened; 36 (69%) screened eligible, and 17 (47%) were enrolled. Of these 17 patients, 3 (18%) were excluded before rTMS, 5 (29%) withdrew, 4 (24%) are in the process of completing the protocol, and 5 (29%) completed the protocol. CONCLUSIONS: The RESTRAIN study is the first to test whether rTMS can target neural reward circuits to reduce behavioral (RRV) and neural (EEG) measures of food reward in patients who are pursuing MBS. If successful, the results would provide a rationale for a fully powered trial to examine whether rTMS-related changes in food reinforcement translate into healthier eating patterns and improved MBS outcomes. If the results do not support our hypotheses, we will continue this line of research to evaluate whether additional rTMS sessions and pulses as well as different stimulation locations produce clinically meaningful changes in food reinforcement. TRIAL REGISTRATION: ClinicalTrials.gov NCT05522803; https://clinicaltrials.gov/study/NCT05522803. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/50714.

Late-stage Attentional Bias towards Food Cues Varies According to Weight Status.

The Current food environment has become increasingly obesogenic, with rates of obesity and related conditions continually rising. Advertisements for energy-dense foods are abundant and promote unhealthy eating behaviors by capitalizing on one's attentional bias towards food cues, a cognitive process resulting from the sensitization of highly reinforcing food. A heightened awareness towards food cues may promote overconsumption of energy-dense foods. The current study employed novel eye-tracking methodology to capture sustained, or late-stage, attentional bias towards food cues. Late-stage attentional bias is the aspect of attentional bias under conscious control and likely more prone to modification compared to initial/ early-stage attentional bias, which reflects automatic processes. The present study hypothesized late-stage attentional bias towards food cues is greater among individuals classified as overweight/obese than those classified as normal weight. Thirty (30) participants classified as overweight/obese (BMI ≥25) and 47 classified as normal weight (BMI <25) were assessed for late-stage attentional bias towards food cues, conceptualized as the percentage of time fixated on food cues when both food and neutral images were presented during a food-specific visual probe procedure task. Percentage of time fixated on food cues was 51.25 ± 1.27 (mean + SE) among individuals classified as overweight to obese while those classified as normal weight had a percent fixation of 47.26 ± 0.87 (P=0.03). In conclusion, individuals classified as overweight to obese have greater late-stage attentional bias towards food cues. This establishes an important factor influencing energy intake that may be modified in future clinical trials.

Reducing relative food reinforcement of infants using a music enrichment program: a randomized, controlled trial.

BACKGROUND: Food reinforcement or one's motivation to eat may be established early in life; it might not be the food reinforcement per se that drives weight gain, but rather the imbalance between food and nonfood reinforcement. OBJECTIVES: We implemented a 2-y randomized, controlled trial to assess the effects of a music enrichment program (music, n = 45) compared with an active play date control (control, n = 45) in 9- to 15-mo-old healthy infants who were strongly motivated to eat. METHODS: The 12-mo intensive intervention phase included 4 semesters of Music Together® or a play date program (Winter, Spring, Summer, and Fall), comprised of once per week group meetings, followed by a 12-mo maintenance phase with monthly meetings. Parents were encouraged to listen to the Music Together® program CD or play with the play date group's toy with their infants at home, respectively. We performed a modified intention-to-treat analysis using all randomly assigned, non-excluded subjects for the outcome measures [relative reinforcing value of food (RRVfood), food reinforcement, music reinforcement, and weight-for-length z-score (WLZ)]. RESULTS: There were significant differential group changes across time for RRVfood (group × month; P = 0.016; Cohen's f2 = 0.034). The music group had significantly greater RRVfood decreases than the control group from baseline to the end of the intensive intervention phase (music change = -0.211; control change = -0.015; P = 0.002; Cohen's D = 0.379). However, these differences were not maintained during months 12-24 (music change = -0.187; control change = -0.143; P = 0.448; D = 0.087). We observed an overall moderation effect by sex for food reinforcement and WLZ. Boys in the music group had a significant attenuation in food reinforcement and WLZ compared with boys in the control group. CONCLUSIONS: This study extends our knowledge in infant eating behavior by providing insight into the role of nonfood alternatives in altering one's motivation to eat. There may be sex differences in altering one's motivation to eat.This trial was registered at clinicaltrials.gov as NCT02936284.

The Effect of Financial Scarcity on Reinforcer Pathology: A Dyadic Developmental Examination.

This study investigated the effects of experimentally manipulated scarcity on the reinforcing value of food (RRVfood) and delay discounting (DD), which, together, create reinforcer pathology (RP) among parents and offspring. A stratified sample of 106 families (53 parent/child aged 7−10 dyads & 53 parent/adolescent aged 15−17 dyads) from high- and low-income households visited our laboratory for three appointments. Each appointment included an experimental manipulation of financial gains and losses and DD and RRV tasks. The results showed that, regardless of food insecurity or condition, children had greater RP (ß = 1.63, p < 0.001) than adolescents and parents. DD was largely unaffected by acute scarcity in any group, but families with food insecurity had greater DD (ß = −0.09, p = 0.002) than food-secure families. Food-insecure parents with children responded to financial losses with an increase in their RRVfood (ß = −0.03, p = 0.011), while food-secure parents and food-insecure parents of adolescents did not significantly change their responding based on conditions. This study replicates findings that financial losses increase the RRVfood among adults with food insecurity and extends this literature by suggesting that this is strongest for parents of children.

The effect of acute and chronic scarcity on acute stress: A dyadic developmental examination.

BACKGROUND: Food insecurity, obesity, and psychological stress are interrelated constructs which are thought to be connected through increased energy intake, but the underlying mechanisms for these relationships remain unclear. The current study used experimental methods to investigate how financial losses may influence acute stress in the context of food insecurity for both parents and offspring. This study also sought to examine the effect of acute stress related to financial losses on the reinforcing value of food (RRVfood) and delay discounting (DD). METHODS: One hundred and six families stratified by both offspring age (53 children aged 7-10, 53 adolescents aged 15-17) and household financial resources, visited our laboratory for three separate appointments. Each appointment included the experimental manipulation of financial gains and losses, saliva samples for cortisol assay, continuous heart rate monitoring, self-rated tension, and computer-based DD and RRVfood tasks. Participants also completed surveys to report perceived life stress level and food insecurity status. RESULTS: Among all participants, financial losses were related to decreased heart rates and increased self-rated tension. Among parents reporting food insecurity, acute financial losses resulted in an increase in cortisol levels. Changes in cortisol, heart rate, and tension were not related to RRVfood or DD. CONCLUSION: Food insecure parents are sensitive to financial losses and respond with an increase in cortisol. However, we found no evidence for a relationship between cortisol and RRVfood or DD. This sensitivity to financial losses did not extend to children or adolescents.

Food reinforcement and habituation to food are processes related to initiation and cessation of eating.

An individual bout of eating involves cues to start eating, as well as cues to terminate eating. One process that determines initiation of eating is food reinforcement. Foods with high reinforcing value are also likely to be consumed in greater quantities. Research suggests both cross-sectional and prospective relationships between food reinforcement and obesity, food reinforcement is positively related to energy intake, and energy intake mediates the relationship between food reinforcement and obesity. A process related to cessation of eating is habituation. Habituation is a general behavioral process that describes a reduction in physiological or affective response to a stimulus, or a reduction in the behavioral responding to obtain a stimulus. Repeated exposure to the same food during a meal can result in habituation to that food and a reduction in consumption. Habituation is also cross-sectionally and prospectively related to body weight, as people who habituate slower consume more in a meal and are more overweight. Research from our laboratory has shown that these two processes independently influence eating, as they can account for almost 60% of the variance in ad libitum intake. In addition, habituation phenotypes show reliable relationships with reinforcing value, such that people who habituate faster also find food less reinforcing. Developing a better understanding of cues to start and stop eating is fundamental to understanding how to modify eating behavior. An overview of research on food reinforcement, habituation and food intake for people with a range of weight status and without eating disorders is provided, and ideas about integrating these two processes that are related to initiation and termination of a bout of eating are discussed.

Consumption of a Variety of Vegetables to Meet Dietary Guidelines for Americans' Recommendations Does Not Induce Sensitization of Vegetable Reinforcement Among Adults with Overweight and Obesity: A Randomized Controlled Trial.

BACKGROUND: Food reinforcement, or the motivation to obtain food, can predict choice and consumption. Vegetable consumption is well below recommended amounts for adults, so understanding how to increase vegetable reinforcement could provide valuable insight into how to increase consumption. OBJECTIVES: We sought to determine whether daily consumption of the Dietary Guidelines for Americans (DGA) recommendations for vegetable intake induces sensitization of vegetable reinforcement in adults with overweight and obesity. METHODS: Healthy adults with a BMI ≥ 25 kg/m2 who consumed ≤1 cup-equivalent of vegetables/day were randomly assigned to a vegetable intervention (VI; n = 55) or an attention control (AC; n = 55) group. The VI consisted of the daily provision of vegetables in the amounts and types recommended by the DGA (∼270 g/day) for 8 weeks. Participants were followed for an additional 8 weeks to assess sustained consumption. Compliance was measured weekly by resonance Raman light-scattering spectroscopy (RRS). Vegetable reinforcement was tested at weeks 0, 8, 12, and 16 using a computer choice paradigm. RESULTS: In the VI group, RRS intensity increased from week 0 to 8 (from 22,990 to 37,220), returning to baseline by week 16 (27,300). No change was observed in the AC group. There was no main effect of treatment (P = 0.974) or time (P = 0.14) and no treatment x time interaction (P = 0.44) on vegetable reinforcement. There was no moderating effect of sex (P = 0.07), age (P = 0.60), BMI (P = 0.46), delay discounting (P = 0.24), 6-n-propylthiouracil taster status (P = 0.15), or dietary disinhibition (P = 0.82) on the change in vegetable reinforcement. CONCLUSIONS: These findings suggest no effects of the provision of a variety of vegetables to meet DGA recommendations for 8 weeks on vegetable reinforcement and highlight the difficulty in increasing vegetable consumption in adults. This trial was registered at clinicaltrials.gov as NCT02585102.

Effects of Sociality Level on Companion Dog Training through Food Reinforcement.

The purpose of this study was to investigate the effect of sociality level in dogs using food reinforcement. The companion dogs living mostly inside (IS) and those living mostly outside (OS) groups were further classified into high sociality (HS) and low sociality (LS) groups using a social test. The data were analyzed by observing videos of the dogs and recording nine categories of sociality. Passive; activity; and communication tasks were measured in terms of the time the dog first contacted the trainer; the time it took for the dog to approach within 1 m of the trainer, and the time the dog remained in contact. The IS and OS groups showed no significant differences in any category; except for close to trainer within 1 m of the active phase. However, in a comparison between the overall HS and LS groups; significant positive changes were observed in all items except for the first contact time to the trainer of the passive and active phase. This is an important result of the sociality level; as positive results can be predicted not only in a dog's ability to adapt to the environment but also in the communication and training exchanges between dogs and humans.

Effects of benztropine analogs on delay discounting in rats.

RATIONALE: Methylphenidate and d-amphetamine, medications used for treatment of attention deficit hyperactivity disorder (ADHD), are used recreationally and self-administered by laboratory animals. Benztropine (BZT) analogs, like those medications, increase synaptic dopamine levels but are less effective in maintaining self-administration, suggesting clinical utility with less abuse liability. OBJECTIVES: The current study was designed to evaluate potential therapeutic effects of BZT analogs related to ADHD. METHODS: Rats responded under a delay-discounting procedure in which responses on one lever produced immediate delivery of a single food pellet and alternative responses produced four food pellets either immediately or with various temporal delays, with those delays arranged in ascending or random orders in different groups of rats. Selection of the smaller more immediate reinforcer has been suggested as an aspect of "impulsivity," a trait with suggested involvement in ADHD. Other rats were studied under fixed-interval (FI) 300-s schedules to assess drug effects on behavior under temporal control. RESULTS: d-Amphetamine, methylphenidate, and the BZT analog AHN 1-055, but not AHN 2-005 or JHW 007, increased selection of the large, delayed reinforcer with either arrangement of delays. All drugs changed the temporal distribution of responses within the FI from one with responses concentrated at the end to a more uniform distribution. Changes in the temporal distribution of FI responding occurred with drugs that did not affect discounting suggesting that discounting does not arise directly from the same temporal control processes controlling FI responding. CONCLUSIONS: AHN 1-055 may be of clinical utility in the treatment of ADHD.

Infants with big appetites: The role of a nonfood environment on infant appetitive traits linked to obesity.

BACKGROUND: Individual differences in appetitive traits present in the first few weeks of life. Research has shown that infants with a greater food reinforcement ratio (FRR) have higher obesity risk. To date, limited work has examined the relation between FRR and appetitive traits of infants, and how FRR relates to appetitive traits and obesity development. OBJECTIVES: To examine the relation between appetitive traits and food and nonfood reinforcement of infants aged 9-18 mo, and to examine whether food and nonfood reinforcement mediate the relation between appetitive traits and weight-for-length z-score (zWFL). METHOD: This secondary data analysis was conducted by combining 4 different cohorts of infants (n = 143) who have complete data on the food/nonfood reinforcement task, Baby Eating Behavior Questionnaire, and anthropometrics and demographics assessments. Three different nonfood reinforcers were used: video (DVD; n = 27), playing with bubbles (Bubbles; n = 67), and music accompanied by instruments (Music; n = 49) for the nonfood portion of the task. For the food portion of the task, the infant's favorite food was used. RESULTS: General appetite positively correlated with FRR and zWFL, but negatively correlated with nonfood reinforcement; satiety responsiveness negatively correlated with food reinforcement, FRR, and zWFL. Mediational analysis showed that effects of general appetite on zWFL were mediated by FRR (indirect effect = 0.100, 95% CI: 0.041, 0.187) and nonfood reinforcement (indirect effect = 0.076, 95% CI: 0.025, 0.156). We also observed the mediating effect of FRR on the relation of satiety responsiveness and zWFL (indirect effect = -0.097, 95% CI: -0.204, -0.026). CONCLUSIONS: Our work contributes to the mechanistic understanding of the ontogeny of obesity development early in life among individuals who are born with appetitive drive for overconsumption. During early infancy, the nonfood environment may protect against this drive and prevent obesity development.

The association of food insecurity with the relative reinforcing value of food, BMI, and gestational weight gain among pregnant women.

OBJECTIVE: Food insecurity is associated with obesity among adults. During pregnancy, food insecurity increases obesity risk among mothers and infants. This study investigated the association of food security with pre-pregnancy body mass index (BMI), gestational weight gain (GWG) adequacy to date, and the relative reinforcing value (RRV) of food during pregnancy. METHODS: This secondary data analysis examined 258 pregnant women (mean gestational age = 21.21 ± 10.21 weeks) surveyed on pre-pregnancy weight, height, pregnancy due date and GWG to date, current diagnoses related to eating and pregnancy, and demographics. The survey also assessed current food security and RRV of meals, snacks, cognitive activities, and active activities. BMI was calculated from pre-pregnancy height and weight (kg/m2). Gestational weight gain adequacy to date was derived from the Institute of Medicine guidelines. Multivariable linear regression models were used to examine the relation of food security with pre-pregnancy BMI and RRVs of foods/activities. The relation between food security and GWG adequacy to date was examined using multinomial regression models. RESULTS: Lower food security was related to both greater pre-pregnancy BMI (ß = 0.60, p < .001) and greater RRV of snack foods (ß = 3.46, p < .05), after controlling for covariates. Lower food security was also related to GWG to date below recommended levels (OR = 1.25, p < .05). CONCLUSIONS: Food insecurity is related to higher relative food reinforcement during pregnancy, and greater pre-pregnancy weight status. Future research should replicate and extend these findings by assessing them longitudinally to better evaluate the directions of these relationships.

Effects of methamphetamine isomers on d-methamphetamine self-administration and food-maintained responding in male rats.

RATIONALE: Methamphetamine (METH) abuse is generally attributed to the d-isomer. Self-administration of l-METH has been examined only in rhesus monkeys with a history of cocaine self-administration or drug-naïve rats using high toxic doses. OBJECTIVES: In this study, the ability of l-METH and, for comparison, d-METH to engender self-administration in experimentally naïve rats, as well as to decrease d-METH self-administration and food-maintained responding, was examined. METHODS: Male Sprague-Dawley rats were used in 3 separate experiments. In experiment 1, the acquisition of l- or d-METH self-administration followed by dose-response determinations was studied. In experiment 2, rats were trained to self-administer d-METH (0.05 mg/kg/infusion) and, then, various doses of l- or d-METH were given acutely prior to the session; the effect of repeated l-METH (30 mg/kg) also was examined. In experiment 3, rats were trained to respond for food reinforcement and, then, various doses of l- or d-METH were given acutely prior to the session; the effect of repeated l-METH (3 mg/kg) also was examined. RESULTS: Reliable acquisition of l- and d-METH self-administration was obtained at unit doses of 0.5 and 0.05 mg/kg/infusion respectively. The dose-response function for l-METH self-administration was flattened and shifted rightward compared with d-METH self-administration, with peak responding for l- and d-METH occurring at unit doses of 0.17 and 0.025 respectively. l-METH also was approximately 10-fold less potent than d-METH in decreasing d-METH self-administration and 2-fold lower in decreasing food-maintained responding. Tolerance did not occur to repeated l-METH pretreatments on either measure. CONCLUSIONS: As a potential pharmacotherapeutic, l-METH has less abuse liability than d-METH and its efficacy in decreasing d-METH self-administration and food-maintained responding is sustained with repeated treatment.

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, Mage = 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.

Food and non-food reinforcement among pregnant women.

Excessive gestational weight gain (GWG) in pregnancy may be driven in part by greater motivation to eat, and studying the relative reinforcing value of food versus non-food commodities may provide insight into factors important for excessive GWG. This study was a cross-sectional examination of the relationship between women meeting the Institute of Medicine (IOM) guidelines for GWG and the relative reinforcing value of food vs. non-food commodities during pregnancy. Two-hundred and thirty-three pregnant women (1st trimester, n = 44; 2nd trimester, n = 105; 3rd trimester, n = 84), aged 18-40, were recruited via a crowdsourcing platform and completed an online survey. Relative food reinforcement (RRVfood), relative non-food activity reinforcement (RRVactive) and relative non-food cognitively enriching activity reinforcement (RRVcognitive) were measured by a questionnaire at the point of contact. Self-reports of gestational age and weight gain during pregnancy were collected. The relationship between food and non-food reinforcement was assessed based on IOM classifications for weight gain during pregnancy. After adjustment for women's education level and parity, higher RRVfood (p = 0.036) and lower RRVcognitive (p = 0.040) responses were associated with greater GWG. Food reinforcing ratio (FRR) analysis was then conducted to systematically examine the effect of non-food behaviors on GWG when food reinforcement was accounted for. Women who gained below the IOM weight gain guidelines had significantly higher FRRcognitive than those gaining above (p = 0.013), indicating cognitively enriching activities may better compete with food among pregnant women. Interventions that help to increase the reinforcing value of cognitively enriching activities may be a new avenue to regulate eating to minimize GWG.

Energy compensation in response to aerobic exercise training in overweight adults.

Weight loss from exercise is often less than expected. Putative compensatory mechanisms may limit exercise-induced reductions in body fat and might be proportional to exercise energy expenditure (ExEE). This study was conducted to determine compensation for (the difference between accumulated exercise energy expenditure and changes in body tissue energy stores) and compensatory responses to 1,500 or 3,000 kcal/wk of ExEE. Overweight-to-obese ( n = 36) sedentary men and women were randomized to groups expending 300 or 600 kcal/exercise session, 5 days/wk, for 12 wk. Fourteen participants in the 300-kcal group and 15 in the 600-kcal group completed the study. The primary outcome was energy compensation assessed through changes in body tissue energy stores. Secondary outcomes were putative compensatory responses of resting metabolic rate, food reinforcement, dietary intake, and serum acylated ghrelin and glucagon-like peptide-1. All measures were determined pre- and posttraining. The 3,000 kcal/wk group decreased ( P < 0.01) percentage and kilograms of body fat, while the 1,500 kcal/wk group did not. The 1,500 and 3,000 kcal/wk groups compensated for 943 (-164 to 2,050) and 1,007 (32 to 1,982) kcal/wk (mean, 95% CI, P ≥ 0.93), or 62.9% and 33.6% of ExEE, respectively. Resting metabolic rate and energy intake did not change. Food reinforcement and glucagon-like peptide-1 decreased ( P < 0.02), whereas acylated ghrelin increased ( P ≤ 0.02). Compensation is not proportional to ExEE. Similar energy compensation occurred in response to1,500 and 3,000 kcal/wk of ExEE. ExEE of 3,000 kcal/wk is sufficient to exceed compensatory responses and reduce fat mass.

Reinforcing value and hypothetical behavioral economic demand for food and their relation to BMI.

Food is a primary reinforcer, and food reinforcement is related to obesity. The reinforcing value of food can be measured by establishing how hard someone will work to get food on progressive-ratio schedules. An alternative way to measure food reinforcement is a hypothetical purchase task which creates behavioral economic demand curves. This paper studies whether reinforcing value and hypothetical behavioral demand approaches are assessing the same or unique aspects of food reinforcement for low (LED) and high (HED) energy density foods using a combination of analytic approaches in females of varying BMI. Results showed absolute reinforcing value for LED and HED foods and relative reinforcing value were related to demand intensity (r's = 0.20-0.30, p's < 0.01), and demand elasticity (r's = 0.17-0.22, p's < 0.05). Correlations between demographic, BMI and restraint, disinhibition and hunger variables with the two measures of food reinforcement were different. Finally, the two measures provided unique contributions to predicting BMI. Potential reasons for differences between the reinforcing value and hypothetical purchase tasks were actual responding versus hypothetical purchasing, choice of reinforcers versus purchasing of individual foods in the demand task, and the differential role of effort in the two tasks. Examples of how a better understanding of food reinforcement may be useful to prevent or treat obesity are discussed, including engaging in alternative non-food reinforcers as substitutes for food, such as crafts or socializing in a non-food environment, and reducing the value of immediate food reinforcers by episodic future thinking.

To free, or not to free: Social reinforcement effects in the social release paradigm with rats.

The present research measured social reinforcement in rats, using a social-release procedure in which lever presses permitted 10-s access to a familiar social partner. The work requirements for reinforcement increased systematically according to progressive-ratio (PR) schedules. Social and food reinforcement value were compared across blocks of sessions (Experiment 1) and concurrently within the same sessions (Experiment 2). To assess motivational effects, response and reinforcer rates for both reinforcer types were studied under food restriction, social restriction, and combined food and social restriction. Responding was maintained by both reinforcers, albeit at substantially higher levels for food than for social access. Responding for social access decreased to low levels under extinction conditions, demonstrating functional control by the social-reinforcement contingency. Sensitivity to social restriction was seen in some conditions in Experiment 2, in which social reinforcers were earned earlier in the session (at lower food prices) under social restriction than under the other deprivation conditions. Altogether, results are consistent with a social reinforcement conceptualization, and demonstrate an important role for social contact in social release behavior. The study demonstrates a promising set of methods for analyzing and quantifying social reinforcement.

Impact of Dietary Protein and Gender on Food Reinforcement.

Recent evidence suggests that increasing dietary protein may alter reward-driven eating behavior. However, the link between protein and food reinforcement is not known. We sought to determine the extent to which increasing dietary protein alters food reinforcement in healthy adults. In a randomized crossover study, 11 women (age = 25 ± 7 years; Body Mass Index (BMI) = 21 ± 2 kg/m²) and 10 men (age = 22 ± 2 years; BMI = 24 ± 2 kg/m²) consumed normal (15%) and high (30%) protein meals. Food reinforcement was assessed using a computer-based choice task (operant responding with concurrent log2(x) reinforcement schedules) 4 h after lunch. We found that food reinforcement was greater in men than women (p < 0.05) and greater for sweet than savory snack foods (p < 0.02). Gender interacted with dietary protein level (p = 0.03) and snack food type (p < 0.0001). Specifically, we found that increasing dietary protein decreased the reinforcing value of savory foods in women. The reinforcing value for sweet foods did not interact with dietary protein or gender. These results demonstrate the differential effects of dietary protein on the reinforcing value for energy-dense, highly palatable snack foods.