Dopamine and diet-induced obesity

Neural correlates of obesity across the lifespan

Associations between brain and obesity are bidirectional: changes in brain structure and function underpin over-eating, while chronic adiposity leads to brain atrophy. Investigating brain-obesity interactions across the lifespan can help better understand these relationships. This study explores the interaction between obesity and cortical morphometry in children, young adults, adults, and older adults. We also investigate the genetic, neurochemical, and cognitive correlates of the brain-obesity associations. Our findings reveal a pattern of lower cortical thickness in fronto-temporal brain regions associated with obesity across all age cohorts and varying age-dependent patterns in the remaining brain regions. In adults and older adults, obesity correlates with neurochemical changes and expression of inflammatory and mitochondrial genes. In children and older adults, adiposity is associated with modifications in brain regions involved in emotional and attentional processes. Thus, obesity might originate from cognitive changes during early adolescence, leading to neurodegeneration in later life through mitochondrial and inflammatory mechanisms.

The hedonic overdrive model best explains high-fat diet-induced obesity in C57BL/6 mice

OBJECTIVE

High-fat diets cause obesity in male mice; however, the underlying mechanisms remain controversial. Here, three contrasting ideas were assessed: hedonic overdrive, reverse causality, and passive overconsumption models.

METHODS

A total of 12 groups of 20 individually housed 12-week-old C57BL/6 male mice were exposed to 12 high-fat diets with varying fat content from 40% to 80% (by calories), protein content from 5% to 30%, and carbohydrate content from 8.4% to 40%. Body weight and food intake were monitored for 30 days after 7 days at baseline on a standard low-fat diet.

RESULTS

After exposure to the diets, energy intake increased first, and body weight followed later. Intake then declined. The peak energy intake was dependent on both dietary protein and carbohydrate, but not the dietary fat and energy density, whereas the rate of decrease in intake was only related to dietary protein. On high-fat diets, the weight of food intake declined, but despite this average reduction of 14.4 g in food intake, they consumed, on average, 357 kJ more energy than at baseline.

CONCLUSIONS

The hedonic overdrive model fit the data best. The other two models were not supported.

Diagnostic value of FOXF1 gene promoter-methylated DNA in the plasma samples of patients with colorectal cancer

BACKGROUND

Epigenetic modifications such as DNA methylation in the CpG islands of genes occur at a high rate. In this study, we measured the methylation level of the promoter region of the FOXF1 gene as a new blood biomarker for the detection of colorectal cancer in the early stages.

METHODS

The methylation level of the promoter region of the FOXF1 gene was measured in the plasma samples of 50 colorectal cancer patients and 50 normal individuals. DNA was extracted after exposure to sodium bisulfite by the MethyLight polymerase chain reaction (PCR) method. The percentage of promoter region was measured in all samples, and statistical analysis was done using SPSS v24 software.

RESULTS

The average promoter region between the plasma samples of colorectal cancer patients and healthy individuals had a significant difference (P < 0.001). The average promoter region of the FOXF1 gene in tumor plasma samples was 7.1 and in the control samples was 0.48. The sensitivity and specificity of the sample plasma levels were 78% and 89.5%, respectively.

CONCLUSION

The promoter region value of the FOXF1 gene in plasma samples using the MethyLight PCR method had high sensitivity and specificity as a non-invasive method for colorectal cancer diagnosis. This research is the first report that has been presented regarding the investigation of FOXF1 gene methylation in plasma samples in colorectal cancer. Therefore, it is necessary to conduct more studies with larger size samples to evaluate the efficiency of the gene under investigation.

Do executive functions differentiate Iranian children with attention-deficit/hyperactivity disorder with and without comorbid obesity?

OBJECTIVE

To compare multiple dimensions of executive function between children with attention-deficit/hyperactivity disorder (ADHD) with and without comorbid obesity.

METHOD

Participants were 90 Iranian children (ages 8-13, 50% female) who were equally dispersed across three study groups: typically developing (TD), ADHD with obesity (ADHD+O), and ADHD without obesity (ADHD-O). Study participants were administered a comprehensive battery of Iranian-adapted "cool" executive function tasks including Digit Span from the Wechsler Intelligence Scale for Children-Fifth Edition (WISC-V), Victoria Stroop Test (VST), Wisconsin Card Sorting Test (WCST), Tower of London, and dot-probe task (i.e., a task of attentional bias). Parents completed the Children's Scale for Future Thinking Questionnaire, which assesses future-oriented cognition (e.g., saving, planning, episodic foresight, delay of gratification), aligning more with "hot" executive functions. Groups were compared using multivariate and post-hoc univariate general linear models.

RESULTS

Significant group effects were observed for all executive function variables, broadly with the gradient pattern of TD > ADHD-O > ADHD+O. ADHD+O had poorer performances than ADHD-O for WISC-V Digit Span (d = -0.84), WCST Categories Completed (d = -0.55) and Perseverative Responses (d = 1.15), VST Interference Errors (d = 0.83) and Interference Time (d = 1.38), and Dot-Probe Task (d = 0.84). Relative to the ADHD-O group, ADHD+O had also poorer parent-reported Prospective Memory (d = -0.62), Episodic Foresight (d = -0.63), and Delay of Gratification (d = -0.54).

CONCLUSIONS

Children with ADHD-O have poorer executive functioning than those without obesity. We observed stronger effects for "cool" rather than "hot" domains of executive function, though this could be due to the former being performance-based and the latter parent-reported.

Liraglutide restores impaired associative learning in individuals with obesity

Survival under selective pressure is driven by the ability of our brain to use sensory information to our advantage to control physiological needs. To that end, neural circuits receive and integrate external environmental cues and internal metabolic signals to form learned sensory associations, consequently motivating and adapting our behaviour. The dopaminergic midbrain plays a crucial role in learning adaptive behaviour and is particularly sensitive to peripheral metabolic signals, including intestinal peptides, such as glucagon-like peptide 1 (GLP-1). In a single-blinded, randomized, controlled, crossover basic human functional magnetic resonance imaging study relying on a computational model of the adaptive learning process underlying behavioural responses, we show that adaptive learning is reduced when metabolic sensing is impaired in obesity, as indexed by reduced insulin sensitivity (participants: N = 30 with normal insulin sensitivity; N = 24 with impaired insulin sensitivity). Treatment with the GLP-1 receptor agonist liraglutide normalizes impaired learning of sensory associations in men and women with obesity. Collectively, our findings reveal that GLP-1 receptor activation modulates associative learning in people with obesity via its central effects within the mesoaccumbens pathway. These findings provide evidence for how metabolic signals can act as neuromodulators to adapt our behaviour to our body's internal state and how GLP-1 receptor agonists work in clinics.

The Genetic Basis of Childhood Obesity: A Systematic Review

Overweight and obesity in childhood and adolescence represents one of the most challenging public health problems of our century owing to its epidemic proportions and the associated significant morbidity, mortality, and increase in public health costs. The pathogenesis of polygenic obesity is multifactorial and is due to the interaction among genetic, epigenetic, and environmental factors. More than 1100 independent genetic loci associated with obesity traits have been currently identified, and there is great interest in the decoding of their biological functions and the gene-environment interaction. The present study aimed to systematically review the scientific evidence and to explore the relation of single-nucleotide polymorphisms (SNPs) and copy number variants (CNVs) with changes in body mass index (BMI) and other measures of body composition in children and adolescents with obesity, as well as their response to lifestyle interventions. Twenty-seven studies were included in the qualitative synthesis, which consisted of 7928 overweight/obese children and adolescents at different stages of pubertal development who underwent multidisciplinary management. The effect of polymorphisms in 92 different genes was assessed and revealed SNPs in 24 genetic loci significantly associated with BMI and/or body composition change, which contribute to the complex metabolic imbalance of obesity, including the regulation of appetite and energy balance, the homeostasis of glucose, lipid, and adipose tissue, as well as their interactions. The decoding of the genetic and molecular/cellular pathophysiology of obesity and the gene-environment interactions, alongside with the individual genotype, will enable us to design targeted and personalized preventive and management interventions for obesity early in life.

Eating regulation: How diet impacts food cognition

How diet alters brain physiology and impacts cognitive functions is poorly understood in any species. A new study has shown that a high-sugar diet disrupts the formation of food-odor associations in the brain of the fly Drosophila melanogaster in a manner that leads to increased food intake.

Identification of a novel link between adiposity and visuospatial perception

OBJECTIVE

Recent work has reported a negative association between BMI and performance on the Penn Line Orientation Task. To determine the reliability of this effect, a comprehensive assessment of visual function in individuals with healthy weight (HW) and those with overweight/obesity (OW/OB) was performed.

METHODS

Visual acuity/contrast, Penn Line Orientation Task, and higher-order visuospatial function were measured in 80 (40 with HW, 40 with OW/OB) case-control study participants. Adiposity, fasting glucose, hemoglobin A1c, diet, physical activity, and heart rate variability were also assessed. A subgroup of 22 participants plus 5 additional participants (n = 27) underwent functional magnetic resonance imaging scanning.

RESULTS

Compared with those with HW, individuals with OW/OB performed worse on tasks requiring judgments of line orientation. This effect was mediated by body fat percentage and was unrelated to other measures. Functional magnetic resonance imaging revealed a negative association between BMI and response in the primary visual cortex (V1) during line orientation judgment. Performance was unrelated to V1 response but positively correlated with response in a network of regions, including the lateral occipital cortex, when BMI was accounted for in the model.

CONCLUSIONS

These results demonstrate a selective deficit in line orientation perception associated with adiposity and blunted activation in the V1 that cannot be attributed to visual acuity and does not generalize to other visuospatial tasks.

Food memory circuits regulate eating and energy balance

In mammals, learning circuits play an essential role in energy balance by creating associations between sensory cues and the rewarding qualities of food. This process is altered by diet-induced obesity, but the causes and mechanisms are poorly understood. Here, we exploited the relative simplicity and wealth of knowledge about the D. melanogaster reinforcement learning network, the mushroom body, in order to study the relationship between the dietary environment, dopamine-induced plasticity, and food associations. We show flies that are fed a high-sugar diet cannot make associations between sensory cues and the rewarding properties of sugar. This deficit was caused by diet exposure, not fat accumulation, and specifically by lower dopamine-induced plasticity onto mushroom body output neurons (MBONs) during learning. Importantly, food memories dynamically tune the output of MBONs during eating, which instead remains fixed in sugar-diet animals. Interestingly, manipulating the activity of MBONs influenced eating and fat mass, depending on the diet. Altogether, this work advances our fundamental understanding of the mechanisms, causes, and consequences of the dietary environment on reinforcement learning and ingestive behavior.

Brain regulation of hunger and motivation: The case for integrating homeostatic and hedonic concepts and its implications for obesity and addiction

Obesity and other eating disorders are marked by dysregulations to brain metabolic, hedonic, motivational, and sensory systems that control food intake. Classic approaches in hunger research have distinguished between hedonic and homeostatic processes, and have mostly treated these systems as independent. Hindbrain structures and a complex network of interconnected hypothalamic nuclei control metabolic processes, energy expenditure, and food intake while mesocorticolimbic structures are though to control hedonic and motivational processes associated with food reward. However, it is becoming increasingly clear that hedonic and homeostatic brain systems do not function in isolation, but rather interact as part of a larger network that regulates food intake. Incentive theories of motivation provide a useful route to explore these interactions. Adapting incentive theories of motivation can enable researchers to better how motivational systems dysfunction during disease. Obesity and addiction are associated with profound alterations to both hedonic and homeostatic brain systems that result in maladaptive patterns of consumption. A subset of individuals with obesity may experience pathological cravings for food due to incentive sensitization of brain systems that generate excessive 'wanting' to eat. Further progress in understanding how the brain regulates hunger and appetite may depend on merging traditional hedonic and homeostatic concepts of food reward and motivation.

Large-scale GWAS of food liking reveals genetic determinants and genetic correlations with distinct neurophysiological traits

We present the results of a GWAS of food liking conducted on 161,625 participants from the UK-Biobank. Liking was assessed over 139 specific foods using a 9-point scale. Genetic correlations coupled with structural equation modelling identified a multi-level hierarchical map of food-liking with three main dimensions: "Highly-palatable", "Acquired" and "Low-caloric". The Highly-palatable dimension is genetically uncorrelated from the other two, suggesting that independent processes underlie liking high reward foods. This is confirmed by genetic correlations with MRI brain traits which show with distinct associations. Comparison with the corresponding food consumption traits shows a high genetic correlation, while liking exhibits twice the heritability. GWAS analysis identified 1,401 significant food-liking associations which showed substantial agreement in the direction of effects with 11 independent cohorts. In conclusion, we created a comprehensive map of the genetic determinants and associated neurophysiological factors of food-liking.

A Neuroeconomics Approach to Obesity

Obesity is a heterogeneous condition that is affected by physiological, behavioral, and environmental factors. Value-based decision making is a useful framework for integrating these factors at the individual level. The disciplines of behavioral economics and reinforcement learning provide tools for identifying specific cognitive and motivational processes that may contribute to the development and maintenance of obesity. Neuroeconomics complements these disciplines by studying the neural mechanisms underlying these processes. We surveyed recent literature on individual decision characteristics that are most frequently implicated in obesity: discounting the value of future outcomes, attitudes toward uncertainty, and learning from rewards and punishments. Our survey highlighted both consistent and inconsistent behavioral findings. These findings underscore the need to examine multiple processes within individuals to identify unique behavioral profiles associated with obesity. Such individual characterization will inform future studies on the neurobiology of obesity as well as the design of effective interventions that are individually tailored.

The role of the nucleus accumbens and ventral pallidum in feeding and obesity

Obesity is a growing global epidemic that stems from the increasing availability of highly-palatable foods and the consequent enhanced calorie consumption. Extensive research has shown that brain regions that are central to reward seeking modulate feeding and evidence linking obesity to pathology in such regions have recently started to accumulate. In this review we focus on the contribution of two major interconnected structures central to reward processing, the nucleus accumbens and the ventral pallidum, to obesity. We first review the known literature linking these structures to feeding behavior, then discuss recent advances connecting pathology in the nucleus accumbens and ventral pallidum to obesity, and finally examine the similarities and differences between drug addiction and obesity in the context of these two structures. The understanding of how pathology in brain regions involved in reward seeking and consumption may drive obesity and how mechanistically similar obesity and addiction are, is only now starting to be revealed. We hope that future research will advance knowledge in the field and open new avenues to studying and treating obesity.

Crème de la Créature: Dietary Influences on Behavior in Animal Models

In humans, alterations in cognitive, motivated, and affective behaviors have been described with consumption of processed diets high in refined sugars and saturated fats and with high body mass index, but the causes, mechanisms, and consequences of these changes remain poorly understood. Animal models have provided an opportunity to answer these questions and illuminate the ways in which diet composition, especially high-levels of added sugar and saturated fats, contribute to brain physiology, plasticity, and behavior. Here we review findings from invertebrate (flies) and vertebrate models (rodents, zebrafish) that implicate these diets with changes in multiple behaviors, including eating, learning and memory, and motivation, and discuss limitations, open questions, and future opportunities.

Brain on food: The neuroepigenetics of nutrition

Humans have known for millennia that nutrition has a profound influence on health and disease, but it is only recently that we have begun mapping the mechanisms via which the dietary environment impacts brain physiology and behavior. Here we review recent evidence on the effects of energy-dense and methionine diets on neural epigenetic marks, gene expression, and behavior in invertebrate and vertebrate model organisms. We also discuss limitations, open questions, and future directions in the emerging field of the neuroepigenetics of nutrition.

A Systematic Review of Obesity and Binge Eating Associated Impairment of the Cognitive Inhibition System

Altered functioning of the inhibition system and the resulting higher impulsivity are known to play a major role in overeating. Considering the great impact of disinhibited eating behavior on obesity onset and maintenance, this systematic review of the literature aims at identifying to what extent the brain inhibitory networks are impaired in individuals with obesity. It also aims at examining whether the presence of binge eating disorder leads to similar although steeper neural deterioration. We identified 12 studies that specifically assessed impulsivity during neuroimaging. We found a significant alteration of neural circuits primarily involving the frontal and limbic regions. Functional activity results show BMI-dependent hypoactivity of frontal regions during cognitive inhibition and either increased or decreased patterns of activity in several other brain regions, according to their respective role in inhibition processes. The presence of binge eating disorder results in further aggravation of those neural alterations. Connectivity results mainly report strengthened connectivity patterns across frontal, parietal, and limbic networks. Neuroimaging studies suggest significant impairment of various neural circuits involved in inhibition processes in individuals with obesity. The elaboration of accurate therapeutic neurocognitive interventions, however, requires further investigations, for a deeper identification and understanding of obesity-related alterations of the inhibition brain system.

Input-specific modulation of murine nucleus accumbens differentially regulates hedonic feeding

Hedonic feeding is driven by the "pleasure" derived from consuming palatable food and occurs in the absence of metabolic need. It plays a critical role in the excessive feeding that underlies obesity. Compared to other pathological motivated behaviors, little is known about the neural circuit mechanisms mediating excessive hedonic feeding. Here, we show that modulation of prefrontal cortex (PFC) and anterior paraventricular thalamus (aPVT) excitatory inputs to the nucleus accumbens (NAc), a key node of reward circuitry, has opposing effects on high fat intake in mice. Prolonged high fat intake leads to input- and cell type-specific changes in synaptic strength. Modifying synaptic strength via plasticity protocols, either in an input-specific optogenetic or non-specific electrical manner, causes sustained changes in high fat intake. These results demonstrate that input-specific NAc circuit adaptations occur with repeated exposure to a potent natural reward and suggest that neuromodulatory interventions may be therapeutically useful for individuals with pathologic hedonic feeding.

Substance use, mental health and weight-related behaviours during the COVID-19 pandemic in people with obesity

Studies have shown the negative impact of COVID-19 lockdown orders on mental health and substance use in the general population. The aim of this study was to examine the impact of the COVID-19 pandemic onsubstance use, mental health and weight-related behaviors in a sample of adults with obesity after lockdown orders were lifted (June-September 2020). A retrospective medical chart review identified patients with obesity from one university-based obesity medicine clinic, and two metabolic and bariatric surgery (MBS) practices. Patients who completed an online survey from June 1, 2020 to September 30, 2020 were included. The primary outcome measure was substance use (various drugs, alcohol, tobacco). Substance use and mental health survey questions were based on standardized, validated instruments. A total of 589 patients (83.3% female, mean age 53.6 years [SD 12.8], mean BMI 35.4 [SD 9.1], 54.5% Non-Hispanic white, 22.3% post-MBS) were included. Seventeen patients (2.9%) tested positive for SARS-CoV-2 and 13.5% reported symptoms. Nearly half (48.4%) of the sample reported recreational substance use and 9.8% reported increased use since the start of the pandemic. There was substantial drug use reported (24.3% opioids, 9.5% sedative/tranquilizers, 3.6% marijuana, and 1% stimulants). Patients who reported stockpiling food more (adjusted Odds Ratio [aOR] 1.50, 95% CI 1.03-2.18), healthy eating more challenging (aOR 1.47, 95% CI 1.01-2.16), difficulty falling asleep (aOR 1.64, 95% CI 1.14-2.34), and anxiety (aOR 1.47, 95% CI 1.01-2.14) were more likely to report substance use versus non-users. Results here show that the COVID-19 pandemic is having a deleterious impact on substance use, mental health and weight-related health behaviors in people with obesity regardless of infection status.

Effects of Risperidone in Autistic Children and Young Adults: A Systematic Review and Meta-Analysis

There are several studies investigating the effects of risperidone on autism, but many of these studies are contradictory or inconclusive. This systematic review and meta-analysis investigated the effects of risperidone on five domains of the Aberrant Behaviour Checklist (ABC) scale on Autism Spectrum Disorder (ASD), as well as weight gain and waist circumference. The protocol for the present systematic review and meta-analysis was registered on the International Prospective Register of Systematic Reviews (PROSPERO). For this study, we analysed articles (2,459), selecting them according to the PICOS strategy (Population, Intervention, Comparison, Outcome, Study design). Although risperidone is effective for the treatment of lethargy and inadequate speech, concerns about the association between weight gain, waist circumference and risperidone require a need for evaluation of the risk-benefit ratio in its use. There was a significant association between weight gain, waist circumference and risperidone. In conclusion, it was possible to suggest the efficacy of risperidone for the treatment of lethargy and inadequate speech. Finally, we emphasize that the risk-benefit in its use should be evaluated (Protocol number CRD42019122316).

High-fat food biases hypothalamic and mesolimbic expression of consummatory drives

Maintaining healthy body weight is increasingly difficult in our obesogenic environment. Dieting efforts are often overpowered by the internal drive to consume energy-dense foods. Although the selection of calorically rich substrates over healthier options is identifiable across species, the mechanisms behind this choice remain poorly understood. Using a passive devaluation paradigm, we found that exposure to high-fat diet (HFD) suppresses the intake of nutritionally balanced standard chow diet (SD) irrespective of age, sex, body mass accrual and functional leptin or melanocortin-4 receptor signaling. Longitudinal recordings revealed that this SD devaluation and subsequent shift toward HFD consumption is encoded at the level of hypothalamic agouti-related peptide neurons and mesolimbic dopamine signaling. Prior HFD consumption vastly diminished the capacity of SD to alleviate the negative valence associated with hunger and the rewarding properties of food discovery even after periods of HFD abstinence. These data reveal a neural basis behind the hardships of dieting.

Ultra-processed foods and binge eating: A retrospective observational study

OBJECTIVES

There is increasing evidence of the impact of ultra-processed foods on multiple metabolic and neurobiological pathways, including those involved in eating behaviors, both in animals and in humans. In this study we aimed to explore ultra-processed foods and their link with disordered eating in a clinical sample.

METHODS

This was a single site, retrospective observational study in a specialist eating disorder service using self-report on the electronic health records. Patients with a Diagnostic and Statistical Manual of Mental Disorders (fifth edition) diagnosis of anorexia nervosa (AN), bulimia nervosa (BN), or binge eating disorder (BED) were randomly selected from the service database in Oxford from 2017 to 2019. The recently introduced NOVA classification was used to determine the degree of industrial food processing in each patient's diet. Frequencies of ultra-processed foods were analyzed for each diagnosis at each mealtime and during episodes of binging.

RESULTS

A total of 70 female and 3 male patients were included in the study; 22 had AN, 25 BN, and 26 BED. Patients with AN reported consuming 55% NOVA-4 foods, as opposed to approximately 70% in BN and BED patients. Foods that were consumed in a binge pattern were 100% ultra-processed.

CONCLUSION

Further research into the metabolic and neurobiological effects of ultra-processed food intake on disordered eating, particularly on binging, is needed.

The neuroscience of sugars in taste, gut-reward, feeding circuits, and obesity

Throughout the animal kingdom sucrose is one of the most palatable and preferred tastants. From an evolutionary perspective, this is not surprising as it is a primary source of energy. However, its overconsumption can result in obesity and an associated cornucopia of maladies, including type 2 diabetes and cardiovascular disease. Here we describe three physiological levels of processing sucrose that are involved in the decision to ingest it: the tongue, gut, and brain. The first section describes the peripheral cellular and molecular mechanisms of sweet taste identification that project to higher brain centers. We argue that stimulation of the tongue with sucrose triggers the formation of three distinct pathways that convey sensory attributes about its quality, palatability, and intensity that results in a perception of sweet taste. We also discuss the coding of sucrose throughout the gustatory pathway. The second section reviews how sucrose, and other palatable foods, interact with the gut-brain axis either through the hepatoportal system and/or vagal pathways in a manner that encodes both the rewarding and of nutritional value of foods. The third section reviews the homeostatic, hedonic, and aversive brain circuits involved in the control of food intake. Finally, we discuss evidence that overconsumption of sugars (or high fat diets) blunts taste perception, the post-ingestive nutritional reward value, and the circuits that control feeding in a manner that can lead to the development of obesity.

Dietary sugar inhibits satiation by decreasing the central processing of sweet taste

From humans to vinegar flies, exposure to diets rich in sugar and fat lowers taste sensation, changes food choices, and promotes feeding. However, how these peripheral alterations influence eating is unknown. Here we used the genetically tractable organism D. melanogaster to define the neural mechanisms through which this occurs. We characterized a population of protocerebral anterior medial dopaminergic neurons (PAM DANs) that innervates the β’2 compartment of the mushroom body and responds to sweet taste. In animals fed a high sugar diet, the response of PAM-β’2 to sweet stimuli was reduced and delayed, and sensitive to the strength of the signal transmission out of the sensory neurons. We found that PAM-β’2 DANs activity controls feeding rate and satiation: closed-loop optogenetic activation of β’2 DANs restored normal eating in animals fed high sucrose. These data argue that diet-dependent alterations in taste weaken satiation by impairing the central processing of sensory signals.

Obesity is a major health problem affecting over 650 million adults worldwide. It is typically caused by overeating high-energy foods, which often contain a lot of sugar. Consuming sugary foods triggers the production of a reward signal called dopamine in the brains of insects and mammals, which reinforces sugar-consuming behavior. The brain balances this with a process called ‘sensory-enhanced satiety’, which makes foods that provide a stronger sensation of sweetness better at reducing hunger and further eating.

High-energy food was scarce for most of human evolution, but over the past century sugar has become readily available in our diet leading to an increase in obesity. Last year, a study in fruit flies reported that a sugary diet reduces the sensitivity to sweet flavors, which leads to overeating and weight gain. It appears that this sensitivity is linked to the effectiveness of sensory-enhanced satiety. However, the mechanism linking diets high in sugar and overeating is still poorly understood. One hypothesis is that fruit flies estimate the energy content of food based on the degree of dopamine released in response to the sugar.

May et al. compared the responses of neurons in fruit flies fed a normal diet to those in flies fed a diet high in sugar. As expected, both groups activated the neurons involved in the dopamine reward response when they tasted sugar. However, when the flies were on a sugar-heavy diet, these neurons were less active. This was because the neurons responsible for tasting sweetness were activated less in flies fed a high-sugar diet, leading to a lowered response by the neurons that produce dopamine. The flies in these experiments were genetically engineered so that the dopamine-producing neurons could be artificially activated in response to light, a technique called optogenetics. When May et al. applied this technique to the flies on a sugar-heavy diet, they were able to stop these flies from overeating.

These findings provide further evidence to support the idea that a sugary diet reduces the brain’s sensitivity to overeating. Given the significant healthcare cost of obesity to society, this improved understanding could help public health initiatives focusing on manufacturing food that is lower in sugar.

Fetal Programming by Methyl Donors Modulates Central Inflammation and Prevents Food Addiction-Like Behavior in Rats

Fetal programming by hypercaloric intake leads to food addiction-like behavior and brain pro-inflammatory gene expression in offspring. The role of methylome modulation during programming on central immune activation and addiction-like behavior has not been characterized. We employed a nutritional programming model exposing female Wistar rats to chow diet, cafeteria (CAF), or CAF-methyl donor’s diet from pre-pregnancy to weaning. Addiction-like behavior in offspring was characterized by the operant training response using Skinner boxes. Food intake in offspring was determined after fasting–refeeding schedule and subcutaneous injection of ghrelin. Genome-wide DNA methylation in the nucleus accumbens (NAc) shell was performed by fluorescence polarization, and brain immune activation was evaluated using real-time PCR for pro-inflammatory cytokines (IL-1β, TNF-1α, and IL-6). Molecular effects of methyl modulators [S-adenosylmethionine (SAM) or 5-azatidine (5-AZA)] on pro-inflammatory cytokine expression and phagocytosis were identified in the cultures of immortalized SIM-A9 microglia cells following palmitic acid (100 μM) or LPS (100 nM) stimulation for 6 or 24 h. Our results show that fetal programming by CAF exposure increases the number of offspring subjects and reinforcers under the operant training response schedule, which correlates with an increase in the NAc shell global methylation. Notably, methyl donor’s diet selectively decreases lever-pressing responses for reinforcers and unexpectedly decreases the NAc shell global methylation. Also, programmed offspring by CAF diet shows a selective IL-6 gene expression in the NAc shell, which is reverted to control values by methyl diet exposure. In vitro analysis identified that LPS and palmitic acid activate IL-1β, TNF-1α, and IL-6 gene expression, which is repressed by the methyl donor SAM. Finally, methylation actively represses phagocytosis activity of SIM-A9 microglia cells induced by LPS and palmitic acid stimulation. Our in vivo and in vitro data suggest that fetal programming by methyl donors actively decreases addiction-like behavior to palatable food in the offspring, which correlates with a decrease in NAc shell methylome, expression of pro-inflammatory cytokine genes, and activity of phagocytic microglia. These results support the role of fetal programming in brain methylome on immune activation and food addiction-like behavior in the offspring.

Trends in the Nutrition Profile of Menu Items at Large Burger Chain Restaurants

INTRODUCTION

Fast food restaurants, including top burger chains, have reduced calorie content of some menu items in recent years. However, the extent to which the nutrition profile of restaurant menus is changing over time is unknown.

METHODS

Data from 2,472 food items on the menus of 14 top-earning burger fast food chain restaurants in the U.S., available from 2012 to 2016, were obtained from the MenuStat project and analyzed in 2019. Nutrition Profile Index scores were estimated and used to categorize foods as healthy (≥64 of 100). Generalized linear models examined mean scores and the proportion of healthy menu items among items offered in all years (2012-2016) and items offered in 2012 only compared with items newly introduced in subsequent years.

RESULTS

Overall, <20% of menu items were classified as healthy with no change from 2012 to 2016 (p=0.91). Mean Nutrition Profile Index score was relatively constant across the study period among all food items (≈50 points, p=0.58) and children's menu items (≈56 points, p=0.73). The only notable change in Nutrition Profile Index score or in proportion of healthy items was in the direction of menu items becoming less healthy.

CONCLUSIONS

At large chain burger restaurants, most items were unhealthy, and the overall nutrition profile of menus remained unchanged from 2012 to 2016. Future research should examine the nutrition profile of restaurant menus in a larger, more diverse sample of restaurants over a longer timeframe and examine whether results are robust when other measures of nutritional quality are used.

Development and preliminary validation of the Anticipated Effects of Food Scale

Expectancy theory has been widely applied in substance use research but has received less attention in eating behavior research. Measuring food expectancies, or the anticipated outcomes of eating specific foods, holds theoretical and practical promise for investigations into nonhomeostatic eating behavior. The current study developed and assessed the psychometric properties of a novel measure of positively and negatively valenced highly (e.g., sweets, salty snacks, fast foods, sugary drinks) and minimally (e.g., fruits, vegetables) processed food expectancies. The Anticipated Effects of Food Scale (AEFS) was adapted from a self-report of alcohol expectancies, piloted for item generation/retention and readability, and preliminarily validated in an adult sample (N = 247; Mage = 36.84; 53.3% male; 74.5% White). Consistent with the substance expectancies literature, AEFS positive highly processed food expectancies were associated with greater added sugars intake, r = .17, p = .009, and food addiction symptoms, r = .56, p < .001. Of note, AEFS negative minimally processed food expectancies were robustly associated with food addiction symptoms, r = .81, p < .001, and, together with AEFS positive highly processed food expectancies, explained 67% of the variance in food addiction symptoms. Furthermore, AEFS food expectancies demonstrated incremental validity with food addiction symptoms above and beyond general eating expectancies. The AEFS seems to be a psychometrically sound measure and can be used to investigate cognitive-affective mechanisms implicated in highly processed food intake and food addiction. Moreover, the present results provide new insight into potential food expectancy challenge intervention approaches for preventing nonhomeostatic eating behavior. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Food reward and gut-brain signalling

The increasing availability of ultra-processed, energy dense food is contributing to the spread of the obesity pandemic, which is a serious health threat in today’s world. One possible cause for this association arises from the fact that the brain is wired to derive pleasure from eating. Specifically, food intake activates reward pathways involving dopamine receptor signalling. The reinforcing value of specific food items results from the interplay between taste and nutritional properties. Increasing evidence suggests that nutritional value is sensed in the gut by chemoreceptors in the intestinal tract and the hepatic portal vein, and conveyed to the brain through neuronal and endocrine pathways to guide food selection behaviour. Ultra-processed food is designed to potentiate the reward response through a combination of high fat and high sugar, therebye seeming highly appetizing. There is increasing evidence that overconsumption of processed food distorts normal reward signalling, leading to compulsive eating behaviour and obesity. Hence, it is essential to understand food reward and gut-brain signalling to find an effective strategy to combat the obesity pandemic.