Sensitization of the reinforcing value of food: a novel risk factor for overweight in adolescents

Translational science approaches for food insecurity research

Food insecurity is a pervasive problem that impacts health and well-being across the lifespan. The human research linking food insecurity to poor metabolic and behavioral health outcomes is inherently correlational and suffers from a high degree of variability both between households and even within the same household over time. Further, food insecurity is impacted by societal and political factors that are largely out of the control of individuals, which narrows the range of intervention strategies. Animal models of food insecurity are being developed to address some of the barriers to mechanistic research. However, animal models are limited in their ability to consider some of the more complex societal elements of the human condition. We believe that understanding the role that food insecurity plays in ingestive behavior and chronic disease requires a truly translational approach, and that understanding the health impacts of this complex social phenomenon requires understanding both its psychological and physiological dimensions. This brief review will outline some key features of food insecurity, highlighting those that are amenable to investigation with controlled animal models and identifying areas where integrating animal and human studies can improve our understanding of the psychological burden and health impacts of food insecurity. In the interest of brevity, this review will largely focus on food insecurity in the United States, as the factors that contribute to food insecurity vary considerably across the globe.

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.

The relationship among disordered eating behavior, power of food scale and sensitization of the reinforcing value of food

INTRODUCTION

Disordered eating behaviors are a current public health concern since their progression can lead to the development of a full criteria eating disorder. Sensitization to repeated intake of high energy density (HED) foods is associated with excess weight gain over time, but less is known about relationships with assessments of disordered eating. Thus, this study aims to understand how disordered eating behaviors refunlate to the influence of the food environment and sensitization.

METHOD

163 adolescents - 50 % female and 13.2 mean age - were followed for 24 months. Sensitization was assessed by comparing the relative reinforcing value (RRV) of HED food at baseline and after two weeks of daily intake; sensitization was defined as RRV of food after repeated intake. Study participants also completed the EDE-Q, and Power of Food Scale (PFS). We conducted multivariate general linear models to examine these associations.

RESULTS

Sensitization status and PFS scores at baseline were positively associated with EDE-Q subscale scores cross-sectionally, but not longitudinally, at baseline and 24 months. We found that sensitization to HED food and higher susceptibility to food cues relates to increased disordered eating behaviors and both at baseline and at 24-months.

DISCUSSION

These findings suggest that sensitization to repeated HED food intake and the food environment might be a risk factor for later engagement in disordered eating behaviors. Future studies should address the temporal relationships among these factors and the role that social norms around body weight and weight stigma may play in the development of these behaviors.

Restriction and Pressure to Eat Are Associated Cross-Sectionally, But Not Longitudinally, With BMI z-Score in a Longitudinal Cohort Study of Adolescents

Background: Parents can influence child weight through their use of food parenting practices, although data are limited in adolescents. The purpose of this study was to examine the cross-sectional and longitudinal relationships between BMI z-Score (zBMI) and restriction and pressure to eat in adolescents. Methods: Adolescents (12-14 years of age at baseline; N = 236) had their height/weight measured at baseline and 24 months and their parent completed the Child Feeding Questionnaire. Linear regressions examined relationships between food parenting practices and zBMI. Results: Cross-sectionally, restriction was positively associated with zBMI at both baseline (β = 0.28, p < 0.001) and 24 months (β = 0.141, p = 0.039). In contrast, pressure to eat was negatively associated with zBMI at both baseline (β = -0.30, p < 0.001) and 24 months (β = -0.31, p < 0.001). Neither restriction (β = -0.028, p = 0.446) nor pressure to eat (β = -0.027, p = 0.493) at baseline predicted 2-year changes in zBMI. zBMI at baseline did not predict 2-year changes in either restriction (β = -0.003, p = 0.965) or pressure to eat (β = -0.056, p = 0.611). Conclusion: Findings highlight that adolescents perceive moderate levels of restriction and pressure to eat, with levels differing by weight status. These findings suggest that the bidirectional relationships between child weight status and food parenting practices are likely established before adolescence, but persist throughout adolescence. Further longitudinal studies should examine the impact of restriction and pressure to eat early in childhood on weight trajectories into adolescence and adulthood. Clinicaltrials.gov: NCT04027608.

The Influence of Relative Reinforcing Value of Food, Sensitization, Energy Intake and Diet Quality on zBMI Change over Two Years in Adolescents: A Longitudinal Cohort Study

The relative reinforcing value (RRV) of food and sensitization are associated with zBMI and zBMI change over time, but the mechanisms underlying these relationships is unknown. The purpose of this study was to test the hypothesis that greater RRV and sensitization to HED food is associated with lower diet quality and greater energy intake at baseline and again at 24 months and that these relationships result in greater zBMI gain. The RRV of HED and LED food and dietary intake were measured at baseline and again after 24 months in a cohort of 202 boys and girls of 12-14 years old. The baseline RRV of HED food was associated with lower diet quality and lower energy intake at 24 months. zBMI gain was positively associated with the baseline energy intake but not baseline RRV of HED food or diet quality. However, diet quality moderated the relationship between baseline energy intake and zBMI change, with no difference in zBMI change as a function of energy intake when diet quality was high but significant and opposite relationships with energy intake when diet quality was low. This study suggests that high diet quality can reduce the negative impact of greater energy intake on zBMI change in adolescents.

Highly processed foods can be considered addictive substances based on established scientific criteria

BACKGROUND

There is growing evidence that an addictive-eating phenotype may exist. There is significant debate regarding whether highly processed foods (HPFs; foods with refined carbohydrates and/or added fats) are addictive. The lack of scientifically grounded criteria to evaluate the addictive nature of HPFs has hindered the resolution of this debate.

ANALYSIS

The most recent scientific debate regarding a substance's addictive potential centered around tobacco. In 1988, the Surgeon General issued a report identifying tobacco products as addictive based on three primary scientific criteria: their ability to (1) cause highly controlled or compulsive use, (2) cause psychoactive (i.e. mood-altering) effects via their effect on the brain and (3) reinforce behavior. Scientific advances have now identified the ability of tobacco products to (4) trigger strong urges or craving as another important indicator of addictive potential. Here, we propose that these four criteria provide scientifically valid benchmarks that can be used to evaluate the addictiveness of HPFs. Then, we review the evidence regarding whether HPFs meet each criterion. Finally, we consider the implications of labeling HPFs as addictive.

CONCLUSION

Highly processed foods (HPFs) can meet the criteria to be labeled as addictive substances using the standards set for tobacco products. The addictive potential of HPFs may be a key factor contributing to the high public health costs associated with a food environment dominated by cheap, accessible and heavily marketed HPFs.

Sensitization of the reinforcing value of high energy density foods is associated with increased zBMI gain in adolescents

Background/Objectives

Characterizing behavioral phenotypes that predict increased zBMI gain during adolescence could identify novel intervention targets and prevent the development of obesity. The purpose of this study was to determine if sensitization of the relative reinforcing value (RRV) of high (HED) or low energy density (LED) foods predicts adolescent weight gain trajectories. A secondary aim was to test the hypothesis that relationships between sensitization of the RRV of food and weight change are moderated by delay discounting (DD).

Subjects/Methods

We conducted a prospective, longitudinal cohort study in 201 boys and girls with an average zBMI of 0.4, who began the study between the ages of 12 and 14 years and completed the study 2 years later. Participants completed five laboratory visits where the RRV of HED and LED, and DD were assessed at a baseline (visits 1, 2, and 4) and then RRV was measured again after participants consumed a portion of the same HED and LED food for 2 weeks (visits 3 and 5; order counterbalanced). Increases (>1) in the RRV from baseline to post-daily intake were categorized as “sensitization” and decreases (≤1) were categorized as “satiation.” Participants returned to the laboratory for follow-up visits at 6, 15, and 24 months to have height and weight taken and to complete additional assessments.

Results

Sensitization to HED food was associated with a greater zBMI change over time (β = 0.0070; p = 0.035). There was no impact of sensitization to LED food or interaction between sensitization to HED and LED food on zBMI change and no moderation of DD on the relationship between HED sensitization and zBMI change (all p > 0.05).

Conclusion

Our prior work showed that sensitization to HED food is cross-sectionally associated with greater zBMI. This study extends this work by demonstrating that sensitization to HED food prospectively predicts increased zBMI gain over time in adolescents without obesity. Future studies should determine if sensitization can be modified or reduced through behavioral intervention.

Trial registration

Clinicaltrials.gov: NCT04027608.

Temporal discounting as a candidate behavioral marker of obesity

Although obesity is a result of processes operating at multiple levels, most forms result from decision-making behavior. The aim of this review was to examine the candidacy of temporal discounting (TD) (i.e. the reduction in the value of a reinforcer as a function of the delay to its receipt) as a behavioral marker of obesity. For this purpose, we assessed whether TD has the ability to: identify risk for obesity development, diagnose obesity, track obesity progression, predict treatment prognosis/outcomes, and measure treatment effectiveness. Three databases (Pubmed, PsycINFO, and Web of Science) were searched using a combination of terms related to TD and obesity. A total of 153 papers were reviewed. Several areas show strong evidence of TD's predictive utility as a behavioral marker of obesity (e.g., distinguishing obese from non obese). However, other areas have limited and/or mixed evidence (e.g., predicting weight change). Given the positive relationship for TD in the majority of domains examined, further consideration for TD as a behavioral marker of obesity is warranted.

Having less and wanting more: an investigation of socioeconomic status and reinforcement pathology

BACKGROUND

In the United states obesity and socioeconomic status (SES), or one's standing in society based on income, education, and/or occupation, are strongly associated. The mechanisms for this relationship may include having high levels of motivation to get food (reinforcing value of food; RRV) and low levels of inhibitory control (delay discounting; DD) which, when combined, is referred to as reinforcement pathology (RP). We sought to examine the relationships among multiple measures of household SES, RP, and age-adjusted body mass index (zBMI) among adolescents.

METHODS

These data were collected as part of ongoing longitudinal study of risk factors for obesity in 244 adolescents. The adolescents and one parent/guardian had height and weight measured and completed surveys. The adolescents completed an adjusting amount DD task and a computer-based RRV task. Analyses consisted of correlations among measures of SES and RRV, DD, and BMI z-scores. In the case of significant associations, multiple regression models were created with theoretically informed covariates.

RESULTS

Household income, parent/guardian education, parent/guardian occupation, and food insecurity status were all related to one another. Among the adolescents, a significant portion of the variance in RRV was accounted for by household income after controlling for covariates. For DD, it was parent/guardian education that was most associated after controlling for covariates.

CONCLUSION

When low income and low parent/guardian education occur together, there may be an increased risk of RP. Separately, food insecurity was predictive of higher parent/guardian BMI. Future research should continue to explore the effects of low income and parent/guardian education on RP among youth by examining them over time.

Appetite self-regulation declines across childhood while general self-regulation improves: A narrative review of the origins and development of appetite self-regulation

This narrative review discusses the origins and development of appetite self-regulation (ASR) in childhood (from infancy to age 6 or 7 years). The origins, or foundations, are the biological infrastructure associated with appetite regulation and appetite self-regulation. Homeostatic regulation in infancy is examined and then evidence about developmental change in components of ASR. The main ASR-related components covered are: delay-of-gratification, caloric compensation, eating in the absence of hunger, food responsiveness/hedonics and fussy eating. The research included behavioral measures, parent-reports of appetitive traits and fMRI studies. There were two main trends in the evidence: a decline across childhood in the components of ASR associated with food approach (and therefore an increase in disinhibited eating), and wide individual differences. The decline in ASR contrasts with general self-regulation (GSR) where the evidence is of an improvement across childhood. For many children, bottom-up automatic reactive processes via food reward/hedonics or food avoidance as in fussy eating, appear not to be matched by improvements in top-down regulatory capacities. The prominence of bottom-up processes in ASR could be the main factor in possible differences in developmental paths for GSR and ASR. GSR research is situated in developmental science with its focus on developmental processes, theory and methodology. In contrast, the development of ASR at present does not have a strong developmental tradition to access and there is no unifying model of ASR and its development. We concluded (1) outside of mean-level or normative changes in the components of ASR, individual differences are prominent, and (2) there is a need to formulate models of developmental change in ASR together with appropriate measurement, research designs and data analysis strategies.