Food reinforcement during infancy

The motivation to eat, as operationalized by measuring how hard someone will work for food, is cross-sectionally and prospectively related to obesity. Persons high in food reinforcement consume more calories, and energy intake mediates the relationship between food reinforcement and obesity. Research has shown avid sucking for milk in early infancy predicts later adiposity, and the relationship between food reinforcement and excess body weight has been observed in infants as young as 9 months of age. New methodological developments in studying food reinforcement in infants and young children provide the first opportunity to study the origin of food reinforcement. This review seeks to provide background on the measurement of food reinforcement, and to present, for the first time, prenatal and postnatal predictors of infant food reinforcement. Lastly, potential mechanisms for an increasing trajectory of food reinforcement throughout development are proposed.     

Food reinforcement and obesity. Psychological moderators

The relative reinforcing value of food (RRV_food) provides an index of the motivation to eat. Research has shown that RRV_food is higher in obese individuals than their non-obese peers, is associated with greater energy intake, predicts weight gain and interacts with impulsivity to predict energy intake. This study was designed to determine whether dietary restraint, dietary disinhibition or hunger moderate the effect of RRV_food on the weight status and energy intake in 273 adults of various body mass index (BMI) levels. Hierarchical regression was used to assess the independent effects of RRV_food on BMI and energy intake, controlling for age, sex, income, education, minority status, and RRV_reading. Results showed that greater RRV_food, but not RRV_reading, was associated with greater BMI and energy intake. Dietary disinhibition and dietary restraint moderated the relationship between RRV_food and BMI, with dietary disinhibition being a stronger moderator of this relationship (r² = 0.20) than dietary restraint (r² = 0.095). In addition, dietary disinhibition moderated the effect of RRV_food on energy intake. These results replicate the importance of RRV_food as a predictor of obesity, and show that psychological factors moderate the effect of food reinforcement on body weight and energy intake. This trial was registered at clinicaltrials.gov as NCT00962117.     

Food reinforcement and impulsivity in overweight children and their parents

Pediatric obesity involves choices among healthy and less healthy alternatives, as well as choices whose consequences vary over time, such as engaging in unhealthy behaviors now at the expense of future health. The purpose of this study was to examine the relative reinforcing value of food and behavioral impulsivity under different experimental conditions in a sample of 50 families screened for participation in a pediatric obesity treatment program. Relative reinforcing value for food versus money was studied under conditions in which increased response requirements were placed on either access to food or money, and the amount of money, the alternative reinforcer, was varied. Impulsivity for small immediate versus larger delayed monetary rewards was studied under conditions in which the value of the immediate reward and the duration of the delay were varied. Results showed that response requirements affected the choice of food for both parents and children (p<0.001), and there was a significant correlation between the number of food reinforcers chosen by parents and children (r=0.57, p<0.001). The value of the immediate reward differentially influenced choice of the immediate reward for parents and children (p<0.05), with children (p<0.001) but not parents (p=0.36) more impulsive as value of the immediate reward increased. The length of the delay influenced both parent (p=0.004) and child (p<0.01) choice of the immediate reward. Parent and child impulsivity were not correlated (r=0.15, p=0.29). This study suggests that food reinforcement may be more similar between parents and children than behavioral impulsivity, though additional research using other measures of relative reinforcing value and impulsivity is warranted.     

Food cravings in food addiction: the distinct role of positive reinforcement

Craving for a particular substance is an essential characteristic of addictive behavior. Increasing evidence suggests that food cravings and excessive food consumption could similarly be due to addictive processes. Recently, the Yale Food Addiction Scale (YFAS) was introduced for identifying individuals with addictive eating patterns. We conducted an online study (n=616, 75.8% female) in which participants filled out the YFAS and the Food Cravings Questionnaire-Trait (FCQ-T). Participants diagnosed as being addicted to food using the YFAS had higher scores on all food craving subscales except for anticipation of positive reinforcement that may result from eating. In a subsequent regression analysis, all food craving subscales positively predicted food addiction symptoms while positive reinforcement negatively predicted food addiction symptoms. Similar to other addictive behaviors, results indicate that individuals with addictive eating patterns experience more food cravings, but concurrently do not expect a positive reinforcement through eating.     

GABAergic mechanisms of opiate reinforcement

The neurobiological mechanisms of opiate-induced reinforcement are still not completely understood. Over the past two decades, the vast majority of studies have focused on the role of the mesolimbic dopamine (DA) system. However, current studies strongly suggest that opiate actions on gamma-aminobutyric acid (GABA)-ergic cells in both the ventral tegmental area (VTA) and the nucleus accumbens (NAcc) appear to play critical roles. In this review, we focus on the neurochemical substrates of opiate reinforcement and review the role of DA and non-DA substrates, including opioid, GABA, glutamate and serotonin on opiate-reinforced behaviour and the activity of dopaminergic and GABAergic neurons in the VTA and the NAcc.     

Devaluation of ethanol reinforcement.

Postingestive CNS pharmacologic effects of ethanol are often assumed to provide the major stimuli for development and maintenance of ethanol self-administration in rats. However, there is little direct evidence to support this assumption. In all procedures that have been used to initiate ethanol intake in rats, some type of taste adaptation or taste conditioning could account for the increased and maintained ethanol intake. Thus, it remains critical to demonstrate that increased ethanol intake is related to postingestive CNS actions of ethanol, and not to a positive shift in the hedonic taste value of the solution. Two experiments were performed to examine this question. In both studies, rats were trained to self-administer 20% ethanol by using a sucrose-substitution initiation procedure. The rats were required to press a lever 25 or 30 times to gain access to 20% ethanol for 20 min from a sipper tube. Once initiated, extinction sessions were used to determine the strength of ethanol seeking by measuring the number of lever presses that occurred in 20 min with no presentation of the ethanol solution. After initial training, the rats were split into two groups: one that received pairings of a gavage of ethanol (1 g/kg), followed after 10 min by a lithium chloride (LiCl) injection (paired group), and one that also received ethanol gavage and LiCl injections, but separated by 24 h (unpaired group). This pairing of postingestive effects with the illness induced by LiCl injection has been shown to devalue other food and fluid reinforcers. In Experiment 1, the rats received four pairings, one after the other with no behavioral testing between. In Experiment 2, the rats received three pairings and were tested for devaluation after each pairing. Results from both experiments showed significant decreases in seeking behavior in both groups, but seeking behavior was decreased significantly greater in the paired group, even though neither group had access to ethanol during the extinction testing periods. In Experiment 1, when ethanol became available after the devaluation procedure, the pattern of intake in the paired group was unchanged early in the sipper tube availability period, supporting the suggestion that the devaluation effect was not mediated by taste stimuli. These findings support the assumption that postingestive effects contribute to the reinforcement produced by self-administered ethanol in rats.     

Food Insecurity,Neighborhood Food Access,and Food Assistance in Philadelphia

An estimated 17.6 million American households were food insecure in 2012, meaning they were unable to obtain enough food for an active and healthy life. Programs to augment local access to healthy foods are increasingly widespread, with unclear effects on food security. At the same time, the US government has recently enacted major cuts to federal food assistance programs. In this study, we examined the association between food insecurity (skipping or reducing meal size because of budget), neighborhood food access (self-reported access to fruits and vegetables and quality of grocery stores), and receipt of food assistance using the 2008, 2010, and 2012 waves of the Southeastern Pennsylvania Household Health Survey. Of 11,599 respondents, 16.7 % reported food insecurity; 79.4 % of the food insecure found it easy or very easy to find fruits and vegetables, and 60.6 % reported excellent or good quality neighborhood grocery stores. In our regression models adjusting for individual- and neighborhood-level covariates, compared to those who reported very difficult access to fruits and vegetables, those who reported difficult, easy or very easy access were less likely to report food insecurity (OR 0.62: 95 % CI 0.43–0.90, 0.33: 95 % CI 0.23–0.47, and 0.28: 95 % CI 0.20–0.40). Compared to those who reported poor stores, those who reported fair, good, and excellent quality stores were also less likely to report food insecurity (OR 0.81: 95 % CI 0.60–1.08, 0.58: 95 % CI 0.43–0.78, and 0.43: 95 % CI 0.31–0.59). Compared to individuals not receiving food assistance, those receiving Supplemental Nutrition Assistance Program (SNAP) benefits were significantly more likely to be food insecure (OR 1.36: 95 % CI 1.11–1.67), while those receiving benefits from the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) (OR 1.17: 95 % CI 0.77–1.78) and those receiving both SNAP and WIC (OR 0.84: 95 % CI 0.61–1.17) did not have significantly different odds of food insecurity. In conclusion, better neighborhood food access is associated with lower risk of food insecurity. However, most food insecure individuals reported good access. Improving diet in communities with high rates of food insecurity likely requires not only improved access but also greater affordability.     

Knee degeneration in concrete reinforcement workers

The loads on the knees in concrete reinforcement work and maintenance painting were analysed on eight construction work sites. A total of 352 reinforcement workers and 231 painters. Finnish men aged 20-64, were clinically and radiologically examined to determine the condition of the knee joints in active workers. The loads on the knees and the occurrence of minor injuries and accidents were higher in reinforcement work than in painting, but the occurrence of symptoms, clinical signs, and radiological findings was equally common in both groups. Reinforcement work seemed to provoke more symptoms from degenerated knees than painting.