The role of reward circuitry and food addiction in the obesity epidemic: An update

Neural mechanisms underlying the role of fructose in overfeeding

Fructose consumption has been linked with metabolic syndrome and obesity. Fructose-based sweeteners like high fructose corn syrup taste sweeter, improve food palatability, and are increasingly prevalent in our diet. The increase in fructose consumption precedes the rise in obesity and is a contributing driver to the obesity epidemic worldwide. The role of dietary fructose in obesity can be multifactorial by promoting visceral adiposity, hypertension, and insulin resistance. Interestingly, one emergent finding from human and animal studies is that dietary fructose promotes overfeeding. As the brain is a critical regulator of food intake, we reviewed the evidence that fructose can act in the brain and elucidated the major brain systems underlying fructose-induced overfeeding. We found that fructose acts on multiple interdependent brain systems to increase orexigenic drive and the incentive salience of food while decreasing the latency between food bouts and reducing cognitive control to disinhibit feeding. We concluded that the collective actions of fructose may promote feeding behavior by producing a hunger-like state in the brain.

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.

Exercise for Weight Loss: Further Evaluating Energy Compensation with Exercise

Purpose

This study assessed how individuals compensate for energy expended during a 12-wk aerobic exercise intervention, elucidating potential mechanisms and the role exercise dose plays in the compensatory response.

Participants and Design

Three-arm, randomized controlled trial among sedentary adults age 18 to 40 yr, body mass index of 25 to 35. Groups included six exercise sessions per week, two sessions per week, and sedentary control.

Methods

Rate of exercise energy expenditure was calculated from a graded exercise test averaged across five heart rate zones. Energy compensation was calculated as the difference between expected weight loss (based on exercise energy expenditure) and changes in fat and fat-free mass (DXA). Resting energy expenditure was assessed via indirect calorimetry and concentrations of acylated ghrelin, leptin, insulin, and Glucagon-like peptide 1 (GLP-1) were assessed fasting and postprandial (six timepoints over 2 h).

Results

The 6-d·wk⁻¹ group expended more energy (2753.5 kcal) and exercised longer (320.5 min) per week than the 2-d·wk⁻¹ group (1490.7 kcal, 1888.8 min, P < 0.05), resulting in greater fat loss compared with the 2-d or control groups (P < 0.05). Exercise groups did not differ in the % or total kcal compensated. Greater decreases in area under the curve (AUC) for acylated ghrelin predicted greater fat loss, regardless of group, energy expended per week, exercise duration, or exercise intensity. Changes in leptin AUC was the only independent predictor for energy compensation, with a greater decrease in leptin AUC predicting less energy compensation. Exercise frequency, energy expended, duration, or intensity did not influence energy compensation.

Conclusions

Leptin is an important factor in successful weight loss through exercise, with greater postprandial decreases promoting less compensation. Greater amounts of exercise do not influence the compensatory response to an exercise-induced energy deficit.

Food Addiction and Lifestyle Habits among University Students

The prevalence of overweight and obesity is increasing in our society, with a complex, multifactorial origin, and associated with greater morbidity and mortality in the population. Food addiction (FA) is a common disorder in overweight/obese people, which appears to be increasingly common in young people. This study analyzed food addiction in a group of young university students and to examine its association with body composition, quality of sleep, adherence to the Mediterranean diet, physical activity/sedentary habits, tobacco or alcohol consumption, and health status. A total of 536 undergraduate nursing students participated in a questionnaire that included the Yale Food Addiction Scale (YFAS 2.0). Up to 6.4% of the students presented FA. Statistically significant associations were observed in the variables for sleep quality odds ratio (OR) 4.8 (95% confidence interval (CI): 1.66-13.87), anxiety/depression OR 8.71 (95% CI: 3.93-19.27), body mass index (BMI) OR 8.32 (95% CI: 3.81-18.15) and sedentary lifestyle OR 2.33 (95% CI: 1.09-5.01). A predictive model was developed after binary logistic regression (area under the ROC curve 0.84 (95% CI: 0.77-0.91). Students with FA presented higher BMI values, worse sleep quality, anxiety or depression problems, and more time spent in sedentary behaviors.

Children, Media and Food. A New Paradigm in Food Advertising, Social Marketing and Happiness Management

The growing number of children who are obese or overweight in certain countries or geographical areas is a fact, as evidenced by the continuous studies and reports on the subject, endorsed or carried out by the World Health Organisation and independent research. In this context, food and beverage advertising can contribute to this. The main objective of this research is to evaluate compliance with the Food and Drink Advertising Code for Children (PAOS Code) in Spain and its relationship with nutritional habits on television, specifically on channels aimed at children. The methodology is therefore mixed: on the one hand, a qualitative technique based on discourse analysis and, on the other, a quantitative technique based on the content analysis of the advertising broadcast for seven consecutive days on three specialised channels and two generalist channels on Spanish television. The results reveal a systematic noncompliance with this code, which translates into inadequate eating habits among children. The immediate conclusion is that 9 out of 10 parts of food and drink advertising do not comply with any of the rules of the PAOS Code and that self-regulation by the advertising companies is negligible and insufficient.

Structural validity, measurement invariance, reliability and diagnostic accuracy of the Italian version of the Yale Food Addiction Scale 2.0 in patients with severe obesity and the general population

PURPOSE

To examine the structural validity, measurement invariance, reliability, and some other psychometrical properties of the Italian version of the Yale Food Addiction Scale 2 (I-YFAS 2.0) in patients with severe obesity and the general population.

METHODS

704 participants-400 inpatients with severe obesity and 304 participants enrolled from the general population-completed the I-YFAS 2.0 and questionnaires measuring eating disorder symptoms. A first confirmatory factor analysis (CFA) tested a hierarchical structure in which each item of the I-YFAS 2.0 loaded onto one of the twelve latent symptoms/criteria which loaded onto a general dimension of Food Addiction (FA). The second CFA tested a first-order structure in which symptoms/criteria of FA simply loaded onto a latent dimension. Measurement invariance (MI) between the group of inpatients with severe obesity and the sample from the general population was also tested. Finally, convergent validity, test-retest reliability, internal consistency, and prevalence analyses were performed.

RESULTS

CFAs confirmed the structure for the I-YFAS 2.0 for both the hierarchical structure and the first-order structure. Configural MI and strong MI were reached for hierarchical and the first-order structure, respectively. Internal consistencies were shown to be acceptable. Prevalence of FA was 24% in the group of inpatients with severe obesity and 3.6% in the sample from the general population.

CONCLUSIONS

The I-YFAS 2.0 represents a valid and reliable questionnaire for the assessment of FA in both Italian adult inpatients with severe obesity and the general population, and is a psychometrically sound tool for clinical as well as research purposes.

LEVEL OF EVIDENCE

Level V, descriptive study.

CB1/5-HT/GABA interactions and food intake regulation

Despite historically the serotonergic, GABAergic, and cannabinoid systems have been shown to play a crucial role in the central regulation of eating behavior, interest in the study of the interactions of these neurotransmission systems has only now been investigated. Current evidence suggests that serotonin may influence normal and pathological eating behavior in significantly more complex ways than was initially thought. This knowledge has opened the possibility of exploring the potential clinical utility of new therapeutic strategies more effective and safer than the current approaches to treat pathological eating behavior. Furthermore, the nature and complexity of the interactions between these neurotransmitter systems have provided a better understanding of the pathophysiological mechanisms not only of eating behavior and eating disorders but also of some of the comorbidities associated with modulation of cortical circuits, which are involved in high order cognitive processes. Accordingly, in the present chapter, the clinical and experimental findings of the interactions between serotonin, GABA, and cannabinoids are synthesized, emphasizing the pharmacological, neurophysiological, and neuroanatomical aspects that could potentially improve the current therapeutic approaches against pathological eating behavior.

Nicotine exposure during lactation causes disruption of hedonic eating behavior and alters dopaminergic system in adult female rats

Tobacco smoke during gestation is associated with increased consumption of palatable foods by the offspring in humans and rats. Postpartum relapse is observed in lactating women who quit smoking during pregnancy, putting their children at risk of adverse health outcomes caused by secondhand smoke. Nicotine is transferred through milk and alters the dopaminergic reward system of adult male rats, reducing dopamine action in the nucleus accumbens (NAc) and hypothalamic arcuate nucleus. Here, we evaluated the long-term effects of nicotine-only exposure during lactation on eating behavior, anxiety, locomotion, dopaminergic system, hypothalamic leptin signaling and nicotinic receptor in the adult female rat progeny. Two days after birth (PN2), Wistar rat dams were separated into control and nicotine (Nic) groups for implantation of osmotic minipumps that released respectively saline or 6 mg/kg nicotine. Lactating dams were kept with 6 pups. After weaning (PN21; nicotine withdrawal), only the female offspring were studied. Euthanasia occurred at PN180. Nic females showed hyperphagia, preference for a high-sucrose diet, increased anxiety-like behavior, lower tyrosine hydroxylase (TH), lower dopamine transporter and higher dopamine receptor (Drd2) in NAc; lower Drd1 in prefrontal cortex and lower TH in dorsal striatum (DS). These animals showed changes that can explain their hyperphagia, such as: lower leptin signaling pathway (Lepr^b, pJAK2, pSTAT3) and Chrna7 expression in hypothalamus. Neonatal nicotine exposure affects the brain reward system of the female progeny differently from males, mainly decreasing dopamine production in NAc and DS. Therefore, Nic females are more susceptible to develop food addiction and obesity.

Neural Mechanisms of Food Decision-Making in Children

PURPOSE OF REVIEW

The goal of the current paper is to review the literature on the neural and behavioral factors involved in food decision-making in youth.

RECENT FINDINGS

Recent neuroimaging studies that employ passive viewing paradigms have found that exposure to food-related cues activate reward, motor planning, and attentional salience signals in children. Greater activations of reward signals and/or lower activations of control signals are associated with overeating and weight gain. Neuroimaging studies with decision-making paradigms have found the reward network in the brain activates during food choices, while control network activates less strongly. Findings suggest that exposure to food cues activates reward/valuation network, but activation of control network tends to be relatively weaker in children. Hedonic aspects of foods are predominantly considered in children's food choices, and their dietary self-control is not matured yet. The increased activation in reward network and the decreased activation in control network are associated with risk of developing obesity.

Hippocampal-Dependent Inhibitory Learning and Memory Processes in the Control of Eating and Drug Taking

As manifestations of excessive and uncontrolled intake, obesity and drug addiction have generated much research aimed at identifying common neuroadaptations that could underlie both disorders. Much work has focused on changes in brain reward and motivational circuitry that can overexcite eating and drug-taking behaviors. We suggest that the regulation of both behaviors depends on balancing excitation produced by stimuli associated with food and drug rewards with the behavioral inhibition produced by physiological "satiety" and other stimuli that signal when those rewards are unavailable. Our main hypothesis is that dysregulated eating and drug use are consequences of diet- and drug-induced degradations in this inhibitory power. We first outline a learning and memory mechanism that could underlie the inhibition of both food and drug-intake, and we describe data that identifies the hippocampus as a brain substrate for this mechanism. We then present evidence that obesitypromoting western diets (WD) impair the operation of this process and generate pathophysiologies that disrupt hippocampal functioning. Next, we present parallel evidence that drugs of abuse also impair this same learning and memory process and generate similar hippocampal pathophysiologies. We also describe recent findings that prior WD intake elevates drug self-administration, and the implications of using drugs (i.e., glucagon-like peptide- 1 agonists) that enhance hippocampal functioning to treat both obesity and addiction are also considered. We conclude with a description of how both WD and drugs of abuse could initiate a "vicious-cycle" of hippocampal pathophysiology and impaired hippocampal-dependent behavioral inhibition.

The cafeteria diet: A standardized protocol and its effects on behavior

Obesity is a major health risk, with junk food consumption playing a central role in weight gain, because of its high palatability and high-energy nutrients. The Cafeteria (CAF) diet model for animal experiments consists of the same tasty but unhealthy food products that people eat (e.g. hot dogs and muffins), and considers variety, novelty and secondary food features, such as smell and texture. This model, therefore, mimics human eating patterns better than other models. In this paper, we systematically review studies that have used a CAF diet in behavioral experiments and propose a standardized CAF diet protocol. The proposed diet is ad libitum and voluntary; combines different textures, nutrients and tastes, including salty and sweet products; and it is rotated and varied. Our summary of the behavioral effects of CAF diet show that it alters meal patterns, reduces the hedonic value of other rewards, and tends to reduce stress and spatial memory. So far, no clear effects of CAF diet were found on locomotor activity, impulsivity, coping and social behavior.

Association between food addiction and body dissatisfaction among college students: The mediating role of eating expectancies

A positive association between food addiction (i.e., an addiction to compulsively overeat highly palatable foods) and body dissatisfaction in college students exists. However, little is known about the underlying mechanisms. Eating expectancies, one's learning history regarding the association between eating and its consequences, may provide potential pathways linking food addiction and body dissatisfaction. In the current study, five eating expectancies (i.e., eating helps manage negative affect, eating is pleasurable and useful as a reward, eating leads to feeling out of control, eating enhances cognitive competence, and eating alleviates boredom) were evaluated as potential mediators between food addiction and body dissatisfaction in 738 college students (mean age = 19.21 ± 1.63, 61.4% female). Students completed the Eating Pathology Symptoms Inventory, Yale Food Addiction Scale, and Eating Expectancy Inventory. Adjusting for sex, age, race, and body mass index, structural equation modeling was used to examine the bi-directional mediation effects of the eating expectancies between food addiction and body dissatisfaction. Results showed a bi-directional positive association between food addiction and body dissatisfaction (β = 0.12-0.26, standard error [SE] = 0.07-0.03, all p < 0.01) that was partially mediated by the expectancy that eating leads to feeling out of control, regardless of whether body dissatisfaction was included as the independent or dependent variable (β = 0.15-0.36, SE = 0.05-0.02, all p < 0.01). Findings suggest the need to address the influence of expecting eating to lead to feeling out of control in interventions for co-occurring food addiction and body dissatisfaction among college students.

Western Diet: Implications for Brain Function and Behavior

The Western diet (WD) pattern characterized by high daily intake of saturated fats and refined carbohydrates often leads to obesity and overweight, and it has been linked to cognitive impairment and emotional disorders in both animal models and humans. This dietary pattern alters the composition of gut microbiota, influencing brain function by different mechanisms involving the gut-brain axis. In addition, long-term exposure to highly palatable foods typical of WD could induce addictive-like eating behaviors and hypothalamic-pituitary-adrenal (HPA) axis dysregulation associated with chronic stress, anxiety, and depression. In turn, chronic stress modulates eating behavior, and it could have detrimental effects on different brain regions such as the hippocampus, hypothalamus, amygdala, and several cortical regions. Moreover, obesity and overweight induce neuroinflammation, causing neuronal dysfunction. In this review, we summarize the current scientific evidence about the mechanisms and factors relating WD consumption with altered brain function and behavior. Possible therapeutic interventions and limitations are also discussed, aiming to tackle and prevent this current pandemic.

The accelerator, the brake, and the terrain: associations of reward-related eating, self-regulation, and the home food environment with diet quality during pregnancy and postpartum in the pregnancy eating attributes study (PEAS) cohort

Background

Neurobehavioral factors, including reward-related eating and self-regulation, in conjunction with the food environment, may influence dietary behaviors. However, these constructs have not been examined in pregnancy and postpartum, a time of changing appetite and eating behaviors, and when dietary intake has implications for maternal and child health. This study examined associations of reward-related eating, self-regulation, and the home food environment with pregnancy and postpartum diet quality.

Methods

Participants in the Pregnancy Eating Attributes Study observational cohort were enrolled at ≤12 weeks gestation and followed through one-year postpartum. Pregnancy and postpartum Healthy Eating Index-2015 (HEI-total), and adequacy and moderation scores, respectively, were calculated by pooling 24-h diet recalls administered each trimester and during 2, 6, and 12 months postpartum. Participants completed four measures of reward-related eating – Modified Yale Food Addiction Scale (mYFAS), Power of Food Scale (PFS), Multiple Choice Procedure (MCP), and Reinforcing Value of Food Questionnaire (RVFQ); two measures of self-regulation – Barratt Impulsiveness Scale (BIS) and Delay of Gratification Inventory (DGI); and a Home Food Inventory (HFI), yielding obesogenic (OBES) and fruit/vegetables (FV) scores. Linear regression analyses estimated associations of reward-related eating, self-regulation, and home food environment with diet quality during pregnancy and postpartum, adjusting for sociodemographic characteristics.

Results

Pregnancy HEI-total was inversely associated with PFS (β = − 0.14 ± 0.05, p = 0.009), mYFAS(β = − 0.14 ± 0.06, p = 0.02), 2 of the 5 RVFQ indices, MCP (β = − 0.14 ± 0.05, p = 0.01), and DGI food subscale (β = 0.23 ± 0.05, p < 0.001), but associations of postpartum HEI-total with reward-related eating measures and self-regulation were small and not statistically significant. Pregnancy and postpartum HEI-total were associated inversely with HFI-OBES (β = − 0.17 ± 0.06, p = 0.004 and β = − 0.19 ± 0.07, p = 0.006, respectively), and positively with HFI-FV (β = 0.21 ± 0.05, p < 0.001 and β = 0.17 ± 0.06, p = 0.009, respectively).

Conclusions

Associations of poorer diet quality with greater reward-related eating during pregnancy but not postpartum suggests the need to better understand differences in the determinants of eating behaviors and approaches to circumvent or moderate reward-related eating to facilitate more optimal diet quality across this critical period.

Trial registration

Clinicaltrials.gov. URL – Registration ID – NCT02217462. Date of registration – August 13, 2014.

Validity and reliability of the Iranian version of the Yale Food Addiction Scale for obese women

OBJECTIVE

The face and construct validity of the Iranian version of the Yale Food Addiction Scale (YFAS) was evaluated, and the convergent validity and test-retest reliability of both Iranian and original versions of YFAS for obese women were assessed.

DESIGN

The internal consistency of the YFAS was analysed. Exploratory factor analysis for dichotomous data was performed by varimax rotation, polychoric correlation coefficients and confirmatory factor analysis (CFA). Convergent validity was established by evaluating the correlation between the original and the Iranian versions of YFAS and the Binge Eating Scale (BES). The intraclass correlation coefficient (ICC) was measured between test-retest results.

SETTING

A weight management clinic in Tehran.

PARTICIPANTS

450 obese women.

RESULTS

The single-factor structure indicated that the factor loadings for all the items were > 0·5, except for three items (explained proportion variance = 51 %). Based on CFA, the single factor had a better fit to the data after excluding three items. The Kuder-Richardson-20 coefficient was 0·86 for the total twenty-two items. The symptom count and diagnostic version of both the Iranian (ICC = 0·92 and 0·87, respectively) and original YFAS (ICC = 0·92 and 0·86, respectively) were stable over 2 weeks. Both the symptom count and the diagnostic version of these two scales had significant correlations with the measures of BES (P < 0·001).

CONCLUSIONS

The initial reliability and validity of the Iranian version of the YFAS among obese women are supported. Further studies should be conducted on men and normal/overweight samples.

Separating the Signal from the Noise: How Psychiatric Diagnoses Can Help Discern Food Addiction from Dietary Restraint

Converging evidence from both animal and human studies have implicated hedonic eating as a driver of both binge eating and obesity. The construct of food addiction has been used to capture pathological eating across clinical and non-clinical populations. There is an ongoing debate regarding the value of a food addiction "diagnosis" among those with eating disorders such as anorexia nervosa binge/purge-type, bulimia nervosa, and binge eating disorder. Much of the food addiction research in eating disorder populations has failed to account for dietary restraint, which can increase addiction-like eating behaviors and may even lead to false positives. Some have argued that the concept of food addiction does more harm than good by encouraging restrictive approaches to eating. Others have shown that a better understanding of the food addiction model can reduce stigma associated with obesity. What is lacking in the literature is a description of a more comprehensive approach to the assessment of food addiction. This should include consideration of dietary restraint, and the presence of symptoms of other psychiatric disorders (substance use, posttraumatic stress, depressive, anxiety, attention deficit hyperactivity) to guide treatments including nutrition interventions. The purpose of this review is to help clinicians identify the symptoms of food addiction (true positives, or "the signal") from the more classic eating pathology (true negatives, or "restraint") that can potentially elevate food addiction scores (false positives, or "the noise"). Three clinical vignettes are presented, designed to aid with the assessment process, case conceptualization, and treatment strategies. The review summarizes logical steps that clinicians can take to contextualize elevated food addiction scores, even when the use of validated research instruments is not practical.

Food Addiction Correlates with Psychosocial Functioning More Than Metabolic Parameters in Patients with Obesity

Aim: To investigate the association of food addiction (FA) with the psychosocial functioning and metabolic parameters in obese patients seeking weight-loss treatment. Methods: Two hundred twenty-four obese patients (male/female: 28/196) with a mean age of 44.5 ± 13.4 years and body mass index (BMI) of 41.6 ± 7.2 were included in the study. After receiving sociodemographic data and medical history, detailed physical examination, including anthropometric measurements, was performed by an experienced physician. Blood samples were taken after 8-12 hr of fasting. The presence of FA was evaluated by using Yale Food Addiction Scale (YFAS). Psychological evaluation was performed by using a self-reported Patient Health Questionnaire-9 (PHQ-9) and health-related quality of life using the 36-item short-form health survey (SF-36). Results: Seventy-two of 224 (32.1%) patients met the criteria for FA, according to YFAS. The mean age of patients with FA was younger compared with patients without FA (P < 0.001). There was no statistically significant difference between the patients with and without FA in terms of BMI, fat percentage, and waist circumference (P = 0.440, P = 0.644, and P = 0.144, respectively). The depression frequency was significantly higher (61.1%, P < 0.001), while the SF-36 score of mental health was lower (P = 0.027) in patients with FA than in the patients without FA. Age- and sex-adjusted mean fasting plasma glucose level was lower in patients with FA (P = 0.021), but serum insulin levels, HOMA-IR (homeostasis model assessment of insulin resistance), HbA1c (hemoglobin A1c), lipid parameters, and vascular adiposity index were comparable. Conclusions: We found that FA frequency was very high in obese patients seeking treatment for weight loss, and it correlates with psychosocial functioning more than metabolic parameters.

Power of mind: Attentional focus rather than palatability dominates neural responding to visual food stimuli in females with overweight

Research investigating neural responses to visual food stimuli has produced inconsistent results. Crucially, high-caloric palatable foods have a double-sided nature - they are often craved but are also considered unhealthy - which may have contributed to the inconsistency in the literature. Taking this double-sided nature into account in the current study, neural responses to individually tailored palatable and unpalatable high caloric food stimuli were measured, while participants' (females with overweight: n = 23) attentional focus was manipulated to be either hedonic or neutral. Notably, results showed that the level of neural activity was not significantly different for palatable than for unpalatable food stimuli. Instead, independent of food palatability, several brain regions (including regions in the mesocorticolimbic system) responded more strongly when attentional focus was hedonic than when neutral (p < 0.05, cluster-based FWE corrected). Multivariate analyses showed that food palatability could be decoded from multi-voxel patterns of neural activity (p < 0.05, FDR corrected), mostly with a hedonic attentional focus. These findings illustrate that the level of neural activity might not be proportionate to the palatability of foods, but that food palatability can be decoded from multi-voxel patterns of neural activity. Moreover, they underline the importance of considering attentional focus when measuring food-related neural responses.

Overeating and food addiction in Major Depressive Disorder: Links to peripheral dopamine

The concept of food addiction refers to addiction-like behaviours that develop in association with the intake of highly palatable foods. Previous research indicates that a high proportion of individuals with Major Depressive Disorder (MDD) meet the criteria for food addiction, and are also at an increased risk of weight gain and chronic disease. In the central nervous system, dopamine is a neurotransmitter associated with reward salience and food intake, whereas peripheral dopamine is involved in sympathetic stress regulation, digestion and gastrointestinal motility. However, little research has examined relationships between peripheral dopamine, depressive symptoms and problematic eating behaviours in MDD. Biometrics, psychopathology and plasma dopamine levels were compared between participants with MDD (n = 80) and controls (n = 60). Participants were sub-categorised into those meeting or not meeting Yale Food Addiction Scale (YFAS) criteria. Psychometric measures of mood and appetite were used to assess MDD symptoms, problematic eating behaviours and food-addiction related symptoms. Twenty-three (23; 29%) MDD participants met the Yale criteria for food addiction. Depressed individuals meeting YFAS criteria had significantly greater psychopathology scores for both mood and eating compared to depressed individuals not meeting YFAS criteria and controls. A significant interaction between food addiction status and sex was also observed for plasma dopamine levels. Plasma dopamine levels correlated positively with disordered eating behaviours in females, and negatively in males. The results provide evidence that depressogenic excess eating and weight gain are associated with peripheral dopamine levels. Longitudinal research is warranted investigating endocrine dysregulation and excess eating in MDD, which may inform interventions and reduce chronic disease risk in affected individuals.

Oxytocin reduces the functional connectivity between brain regions involved in eating behavior in men with overweight and obesity

Background:

Oxytocin (OXT), shown to decrease food intake in animal models and men, is a promising novel treatment for obesity. We have shown that in men with overweight and obesity, intranasal (IN) OXT reduced the functional magnetic resonance imaging (fMRI) blood oxygenation level-dependent signal in the ventral tegmental area (VTA), the origin of the mesolimbic dopaminergic reward system, in response to high-calorie food vs. non-food images. Here, we employed functional connectivity fMRI analysis, which measures the synchrony in activation between neural systems in a context-dependent manner. We hypothesized that OXT would attenuate the functional connectivity of the VTA with key food motivation brain areas only when participants viewed high-calorie food stimuli.

Methods:

This randomized, double-blind, placebo-controlled crossover study of 24 IU IN OXT included 10 men with overweight or obesity (mean±SEM BMI: 28.9±0.8 kg/m²). Following drug administration, subjects completed an fMRI food motivation paradigm including images of high and low-calorie foods, non-food objects, and fixation stimuli. A psychophysiological interaction analysis was performed with the VTA as seed region.

Results:

Following OXT administration, compared with placebo, participants exhibited significantly attenuated functional connectivity between the VTA and the insula, oral somatosensory cortex, amygdala, hippocampus, operculum, and middle temporal gyrus in response to viewing high-calorie foods (Z≥3.1, cluster-corrected, p<0.05). There was no difference in functional connectivity between VTA and these brain areas when comparing OXT and placebo for low-calorie food, non-food, and fixation images.

Conclusion:

In men with overweight and obesity, OXT attenuates the functional connectivity between the VTA and food motivation brain regions in response to high-calorie visual food images. These findings could partially explain the observed anorexigenic effect of OXT, providing insight into the mechanism through which OXT ameliorates food cue-induced reward anticipation in patients with obesity. Additional studies are ongoing to further delineate the anorexigenic effect of OXT in obesity.

Updating gender differences in the control of homeostatic and hedonic food intake: Implications for binge eating disorder

In an obesity pandemic context, eating disorders (ED) have arisen as serious illnesses associated with severe disturbances and has a clear gender dependent bias. In this manuscript, we provide an overview of the oestrogen role in the homeostatic and hedonic control of food intake. We draw attention to the role of oestrogens in the various reward processes and their possible implication in the development of ED, a condition much more common in women. In here, we have summarized the most relevant studies conducted in animal models over the last few years. In particular, we want to emphasize on the importance of continuing thorough investigations in female animal models. We believe that understanding the molecular mechanisms that regulate gender differences in food intake may provide new potential targets for ED treatment.

Fish as models for understanding the vertebrate endocrine regulation of feeding and weight

The frequencies of eating disorders and obesity have increased worldwide in recent years. Their pathophysiologies are still unclear, but recent evidence suggests that they might be related to changes in endocrine and neural factors that regulate feeding and energy homeostasis. In order to develop efficient therapeutic drugs, a more thorough knowledge of the neuronal circuits and mechanisms involved is needed. Although to date, rodents have mostly been used models in the area of neuroscience and neuroendocrinology, an increasing number of studies use non-mammalian vertebrates, in particular fish, as model systems. Fish present several advantages over mammalian models and they share genetic and physiological homology to mammals with close similarities in the mechanisms involved in the neural and endocrine regulation of appetite. This review briefly describes the regulation of feeding in two model species, goldfish and zebrafish, how this regulation compares to that in mammals, and how these fish could be used for studies on endocrine regulation of eating and weight and its dysregulations.

Hyper-Palatable Foods: Development of a Quantitative Definition and Application to the US Food System Database

OBJECTIVE

Extensive research has focused on hyper-palatable foods (HPF); however, HPF are defined using descriptive terms (e.g., fast foods, sweets), which are not standardized and lack specificity. The study purpose was to develop a quantitative definition of HPF and apply the definition to the Food and Nutrient Database for Dietary Studies (FNDDS) to determine HPF prevalence in the US food system.

METHODS

A numeric definition of HPF was developed by extracting common HPF descriptive definitions from the literature and using nutrition software to quantify ingredients of fat, simple sugars, carbohydrates, and sodium. The definition was applied to the FNDDS.

RESULTS

HPF from the literature aligned with three clusters: (1) fat and sodium (> 25% kcal from fat, ≥ 0.30% sodium by weight), (2) fat and simple sugars (> 20% kcal from fat, > 20% kcal from sugar), and (3) carbohydrates and sodium (> 40% kcal from carbohydrates, ≥ 0.20% sodium by weight). In the FNDDS, 62% (4,795/7,757) of foods met HPF criteria. The HPF criteria identified a variety of foods, including some labeled reduced or low fat and vegetables cooked in creams, sauces, or fats.

CONCLUSIONS

A data-derived HPF definition revealed that a substantial percentage of foods in the US food system may be hyper-palatable, including foods not previously conceptualized as hyper-palatable.

Weight gain in Major Depressive Disorder: Linking appetite and disordered eating to leptin and ghrelin

Major Depressive Disorder (MDD) involves changes in appetite and weight, with a subset of individuals at an increased risk of weight gain. Pathways to weight gain may include appetite disturbances, excess eating, and dysregulation of appetite hormones. However, little research has simultaneously examined relationships between hormones, eating behaviours and MDD symptoms. Plasma ghrelin and leptin, biometrics, eating behaviours and psychopathology were compared between depressed (n = 60) and control (n = 60) participants. Depressed participants were subcategorised into those with increased or decreased appetite/weight for comparison by subtype. The Dutch Eating Behaviours Questionnaire and Yale Food Addiction Scale measured eating behaviours. Disordered eating was higher in MDD than controls, in females than males, and in depressed individuals with increased, compared to decreased, appetite/weight. Leptin levels were higher in females only. Leptin levels correlated positively, and ghrelin negatively, with disordered eating. The results provide further evidence for high levels of disordered eating in MDD, particularly in females. The correlations suggest that excessive eating in MDD is significantly linked to appetite hormones, indicating that it involves physiological, rather than purely psychological, factors. Further, longitudinal, research is needed to better understand whether hormonal factors play a causal role in excessive eating in MDD.

Multiple Dimensions of Sweet Taste Perception Altered after Sleep Curtailment

Short sleep duration increases preferences for high-carbohydrate and high-fat foods. It is unclear if insufficient sleep-induced changes in food preference are mediated by changes in taste perception and if these changes are related to sweetener type (sucrose or sucralose) or sweet liking phenotype. The primary objective of this study was to determine if sleep curtailment results in changes in sweet taste perception after sleep curtailment. Forty participants used a single-channel electroencephalograph to record both a habitual and curtailed night (33% reduction) of sleep at home. The following morning, multiple dimensions of sweet taste perception were measured, including preferred sweetener concentrations, patterns of sweet liking, and intensity perception over a range of concentrations. After curtailment, a significant increase in preferred concentration for both sucrose and sucralose (p < 0.001 for both) was observed. The slope of sucrose sweet liking increased after curtailment (p = 0.001). The slope of sucralose liking also increased, but this was not significant (p = 0.129). Intensity perception of the sweeteners was not altered by curtailment. Hierarchical cluster analysis was used to classify participants by sweet liking phenotype. Phenotypes were found to predict preferred sweetener concentration. These findings illustrate a possible need to control for sleep in food sensory studies and suggest a potential mechanism by which insufficient sleep can lead to excess energy intake.

Disordered Eating Among Individuals with Excess Weight: a Review of Recent Research

PURPOSE OF REVIEW

The purpose of this review was to examine different forms of disordered eating among individuals with excess weight, including their rates, correlates, and psychosocial treatments.

RECENT FINDINGS

Binge eating/binge eating disorder, loss of control eating, emotional eating, and food addiction are all fairly prevalent among individuals with excess weight. They appear to share many of the same correlates, including broader eating disorder psychopathology, body/shape/weight concerns, depression, anxiety, and low self-esteem. Behavioral, cognitive-behavioral, and third-wave (e.g., acceptance, mindfulness) therapies appear effective in improving binge eating, loss of control eating, emotional eating, associated features (e.g., weight and shape concerns), and psychological distress (e.g., depression). Certain forms of disordered eating are elevated among individuals with excess weight, and psychosocial interventions have been found effective in improving symptomatology. Empirical research examining the efficacy of treatments for food addiction is lacking, and greatly needed given both its rate and controversy.

Human genes influence the interaction between Streptococcus mutans and host caries susceptibility: a genome-wide association study in children with primary dentition

Streptococcus mutans is a well-known cause of dental caries, due to its acidogenicity, aciduricity, and ability to synthesize exopolysaccharides in dental plaques. Intriguingly, not all children who carry S. mutans manifest caries, even with similar characteristics in oral hygiene, diet, and other environmental factors. This phenomenon suggests that host susceptibility potentially plays a role in the development of dental caries; however, the association between host genetics, S. mutans, and dental caries remains unclear. Therefore, this study examined the influence of host gene-by-S. mutans interaction on dental caries. Genome-wide association analyses were conducted in 709 US children (<13 years old), using the dbGap database acquired from the center for oral health research in appalachia (COHRA) and the Iowa Head Start programmes (GEIRS). A generalized estimating equation was used to examine the gene-by-S. mutans interaction effects on the outcomes (decayed and missing/filled primary teeth due to caries). Sequentially, the COHRA and GEIRS data were used to identify potential interactions and replicate the findings. Three loci at the genes interleukin 32 (IL32), galactokinase 2 (GALK2), and CUGBP, Elav-like family member 4 (CELF4) were linked to S. mutans carriage, and there was a severity of caries at a suggestive significance level among COHRA children (P < 9 × 10-5), and at a nominal significance level among GEIRS children (P = 0.047-0.001). The genetic risk score that combined the three loci also significantly interacted with S. mutans (P < 0.000 1). Functional analyses indicated that the identified genes are involved in the host immune response, galactose carbohydrate metabolism, and food-rewarding system, which could potentially be used to identify children at high risk for caries and to develop personalized caries prevention strategies.

Shared Behavioral and Neurocircuitry Disruptions in Drug Addiction, Obesity, and Binge Eating Disorder: Focus on Group I mGluRs in the Mesolimbic Dopamine Pathway

Accumulated data from clinical and preclinical studies suggest that, in drug addiction and states of overeating, such as obesity and binge eating disorder (BED), there is an imbalance in circuits that are critical for motivation, reward saliency, executive function, and self-control. Central to these pathologies and the extensive topic of this Review are the aberrations in dopamine (DA) and glutamate (Glu) within the mesolimbic pathway. Group I metabotropic glutamate receptors (mGlus) are highly expressed in the mesolimbic pathway and are poised in key positions to modulate disruptions in synaptic plasticity and neurotransmitter release observed in drug addiction, obesity, and BED. The use of allosteric modulators of group I mGlus has been studied in drug addiction, as they offer several advantages over traditional orthosteric agents. However, they have yet to be studied in obesity or BED. With the substantial overlap between the neurocircuitry involved in drug addiction and eating disorders, group I mGlus may also provide novel targets for obesity and BED.

Maternal coconut oil intake on lactation programs for endocannabinoid system dysfunction in adult offspring

Maternal exposure to coconut oil metabolically programs adult offspring for overweight, hyperphagia and hyperleptinemia. We studied the neuroendocrine mechanisms by which coconut oil supplementation during breastfeeding as well as continued exposure of this oil throughout life affect the feeding behavior of the progeny. At birth, pups were divided into two groups: Soybean oil (SO) and Coconut oil (CO). Dams received these oils by gavage (0.5 g/kg body mass/day) during lactation. Half of the CO group continued to receive CO in chow throughout life (CO + C). Adult CO and CO + C groups had overweight; the CO group had hyperphagia, higher visceral adiposity, and hyperleptinemia, while the CO + C group had hypophagia only. The CO group showed higher DAGLα (endocannabinoid synthesis) but no alteration of FAAH (endocannabinoid degradation) or CB1R. Leptin signaling and GLP1R were unchanged in the CO group, which did not explain its phenotype. Hyperphagia in these animals can be due to higher DAGLα, increasing the production of 2-AG, an orexigenic mediator. The CO + C group had higher preference for fat and lower hypothalamic GLP1R content. Continuous exposure to coconut oil prevented an increase in DAGLα. The CO + C group, although hypophagic, showed greater voracity when exposed to a hyperlipidemic diet, maybe due to lower GLP1R, since GLP1 inhibits short-term food intake.

Finding the balance between model complexity and performance: Using ventral striatal oscillations to classify feeding behavior in rats

The ventral striatum (VS) is a central node within a distributed network that controls appetitive behavior, and neuromodulation of the VS has demonstrated therapeutic potential for appetitive disorders. Local field potential (LFP) oscillations recorded from deep brain stimulation (DBS) electrodes within the VS are a pragmatic source of neural systems-level information about appetitive behavior that could be used in responsive neuromodulation systems. Here, we recorded LFPs from the bilateral nucleus accumbens core and shell (subregions of the VS) during limited access to palatable food across varying conditions of hunger and food palatability in male rats. We used standard statistical methods (logistic regression) as well as the machine learning algorithm lasso to predict aspects of feeding behavior using VS LFPs. We were able to predict the amount of food eaten, the increase in consumption following food deprivation, and the type of food eaten. Further, we were able to predict whether the initiation of feeding was imminent up to 42.5 seconds before feeding began and classify current behavior as either feeding or not-feeding. In classifying feeding behavior, we found an optimal balance between model complexity and performance with models using 3 LFP features primarily from the alpha and high gamma frequencies. As shown here, unbiased methods can identify systems-level neural activity linked to domains of mental illness with potential application to the development and personalization of novel treatments.

As neuropsychiatry begins to leverage the power of computational methods to understand disease states and to develop better therapies, it is vital that we acknowledge the trade-offs between model complexity and performance. We show that computational methods can elucidate a neural signature of feeding behavior and we show how these methods could be used to discover neural patterns related to other behaviors and reveal new potential therapeutic targets. Further, our results help to contextualize both the limitations and potential of applying computational methods to neuropsychiatry by showing how changing the data being used to train predictive models (e.g., population vs. individual data) can have a large impact on how model performance generalizes across time, internal states, and individuals.

Ethical, Stigma, and Policy Implications of Food Addiction: A Scoping Review

The concept of food addiction has generated much controversy. In comparison to research examining the construct of food addiction and its validity, relatively little research has examined the broader implications of food addiction. The purpose of the current scoping review was to examine the potential ethical, stigma, and health policy implications of food addiction. Major themes were identified in the literature, and extensive overlap was identified between several of the themes. Ethics sub-themes related primarily to individual responsibility and included: (i) personal control, will power, and choice; and (ii) blame and weight bias. Stigma sub-themes included: (i) the impact on self-stigma and stigma from others, (ii) the differential impact of substance use disorder versus behavioral addiction on stigma, and (iii) the additive stigma of addiction plus obesity and/or eating disorder. Policy implications were broadly derived from comparisons to the tobacco industry and focused on addictive foods as opposed to food addiction. This scoping review underscored the need for increased awareness of food addiction and the role of the food industry, empirical research to identify specific hyperpalatable food substances, and policy interventions that are not simply extrapolated from tobacco.

Increasing Chocolate's Sugar Content Enhances Its Psychoactive Effects and Intake

Chocolate elicits unique brain activity compared to other foods, activating similar brain regions and neurobiological substrates with potentially similar psychoactive effects as substances of abuse. We sought to determine the relationship between chocolate with varying combinations of its main constituents (sugar, cocoa, and fat) and its psychoactive effects. Participants consumed 5 g of a commercially available chocolate with increasing amounts of sugar (90% cocoa, 85% cocoa, 70% cocoa, and milk chocolates). After each chocolate sample, participants completed the Psychoactive Effects Questionnaire (PEQ). The PEQ consists of questions taken from the Morphine-Benzedrine Group (MBG), Morphine (M,) and Excitement (E) subscales of the Addiction Research Center Inventory. After all testing procedures, participants completed the Binge Eating Scale (BES) while left alone and allowed to eat as much as they wanted of each of the different chocolates. We found a measurable psychoactive dose⁻effect relationship with each incremental increase in the chocolate's sugar content. The total number of positive responses and the number of positive responses on the E subscale began increasing after tasting the 90% cocoa chocolate, whereas the number of positive responses on the MBG and M subscales began increasing after tasting the 85% cocoa chocolate sample. We did not find a correlation between BES scores and the total amount of chocolate consumed or self-reported scores on the PEQ. These results suggest that each incremental increase in chocolate's sugar content enhances its psychoactive effects. These results extend our understanding of chocolate's appeal and unique ability to prompt an addictive-like eating response.

Eating as a motivated behavior: modulatory effect of high fat diets on energy homeostasis, reward processing and neuroinflammation

Eating is a basic motivated behavior that provides fuel for the body and supports brain function. To ensure survival, the brain's feeding circuits are tuned to monitor peripheral energy balance and promote food-seeking behavior when energy stores are low. The brain's bias toward a positive energy state, which is necessary to ensure adequate nutrition during times of food scarcity, is evolutionarily conserved across mammalian species and is likely to drive overeating in the presence of a palatable, energy-dense diet. Animal models of diet-induced overeating have played a vital role in investigating how the drive to consume palatable food may override the homeostatic processes that serve to maintain energy balance. These animal models have provided valuable insights into the neurobiological mechanisms underlying homeostatic and non-homeostatic eating, motivation and food reward, and the development of obesity and related comorbidities. Here, we provide a brief review of this literature and discuss how diet-induced inflammation in the central nervous system impacts the neural control of food intake and regulation of body weight. The connection between diet and the immune system provides an exciting new direction for the study of ingestive behavior and the pathophysiology of obesity.

Sex Dimorphic Responses of the Hypothalamus-Pituitary-Thyroid Axis to Maternal Separation and Palatable Diet

Neonatal stress contributes to the development of obesity and has long-lasting effects on elements of the hypothalamus-pituitary-thyroid (HPT) axis. Given the importance of thyroid hormones in metabolic regulation, we studied the effects of maternal separation and a high-fat/high-carbohydrate diet (HFC), offered from puberty or adulthood, on HPT axis activity of adult male and female Wistar rats. Pups were non-handled (NH) or maternally separated (MS) 3 h/day at postnatal days (Pd) 2-21. In a first experiment, at Pd60, rats had access to chow or an HFC diet (cookies, peanuts, chow) for 1 month. Male and female NH and MS rats that consumed the HFC diet increased their caloric intake, body weight, and serum insulin levels; fat weight increased in all groups except in MS males, and serum leptin concentration increased only in females. Mediobasal hypothalamus (MBH) Pomc expression increased in NH-HFC females and Npy decreased in NH-HFC males. MS males showed insulinemia and hypercortisolemia that was attenuated by the HFC diet. The HPT axis activity response to an HFC diet was sex-specific; expression of MBH thyrotropin-releasing hormone-degrading ectoenzyme (Trhde) increased in NH and MS males; serum TSH concentration decreased in NH males, and T4 increased in NH females. In a second experiment, rats were fed chow or an HFC diet from Pd30 or 60 until Pd160 and exposed to 1 h restraint before sacrifice. Regardless of neonatal stress, age of diet exposition, or sex, the HFC diet increased body and fat weight and serum leptin concentration; it induced insulinemia in males, but in females only in Pd30 rats. The HFC diet's capacity to curtail the hypothalamus-pituitary-adrenal axis response to restraint was impaired in MS males. In restrained rats, expression of Trh in the paraventricular nucleus of the hypothalamus, Dio2 and Trhde in MBH, and serum thyroid hormone concentration were altered differently depending on sex, age of diet exposition, and neonatal stress. In conclusion, metabolic alterations associated to an HFC-diet-induced obesity are affected by sex or time of exposition, while various parameters of the HPT axis activity are additionally altered by MS, pointing to the complex interplay that these developmental influences exert on HPT axis activity in adult rats.

Neuroendocrinology of Adipose Tissue and Gut-Brain Axis

Food intake and energy expenditure are closely regulated by several mechanisms which involve peripheral organs and nervous system, in order to maintain energy homeostasis.Short-term and long-term signals express the size and composition of ingested nutrients and the amount of body fat, respectively. Ingested nutrients trigger mechanical forces and gastrointestinal peptide secretion which provide signals to the brain through neuronal and endocrine pathways. Pancreatic hormones also play a role in energy balance exerting a short-acting control regulating the start, end, and composition of a meal. In addition, insulin and leptin derived from adipose tissue are involved in long-acting adiposity signals and regulate body weigh as well as the amount of energy stored as fat over time.This chapter focuses on the gastrointestinal-, pancreatic-, and adipose tissue-derived signals which are integrated in selective orexigenic and anorexigenic brain areas that, in turn, regulate food intake, energy expenditure, and peripheral metabolism.

The dynamic nature of food reward processing in the brain

PURPOSE OF REVIEW

The dominant view in the literature is that increased neural reactivity to high-caloric palatable foods in the mesocorticolimbic system is a stable-specific characteristic of obese people. In this review, we argue that this viewpoint may not be justified, and we propose that the neural response to food stimuli is dynamic, and in synchrony with the current motivational and cognitive state of an individual. We will further motivate why a clear mental task in the scanner is a necessity for drawing conclusions from neural activity, and why multivariate approaches to functional MRI (fMRI) data-analysis may carry the field forward.

RECENT FINDINGS

From the reviewed literature we draw the conclusions that: neural food-cue reactivity depends strongly on cognitive factors such as the use of cognitive regulation strategies, task demands, and focus of attention; neural activity in the mesocorticolimbic system is not proportionate to the hedonic value of presented food stimuli; and multivariate approaches to fMRI data-analysis have shown that hedonic value can be decoded from multivoxel patterns of neural activity.

SUMMARY

Future research should take the dynamic nature of food-reward processing into account and take advantage from state-of-the-art multivariate approaches to fMRI data-analysis.

Food addiction and impaired executive functions in women with obesity

BACKGROUND

Individuals with obesity (OB) often report suffering from addiction-like symptoms. As in addictions, deficits in executive function domains, such as decision-making and sustained attention, are found in OB. No study to date has examined the associations between food addiction, OB, and neuropsychological performance.

METHOD

Thirty-three adult women with OB and 36 healthy weight controls completed the Yale Food Addiction Scale Version 2.0, a validated instrument used to assess food-related addictive behaviours. Additionally, participants completed computerized versions of the Iowa Gambling Task (IGT) and Conners' Continuous Performance Test, second edition (CPT-II) to examine decision-making and attentional control, respectively.

RESULTS

Food addiction criteria were met in 24.2% of the participants with OB and in 2.8% of the control group. In the OB group, food addiction severity levels were negatively correlated with overall scores on the IGT. Participants with OB meeting criteria for food addiction committed more omissions and perseveration errors on the CPT-II compared with those without food addiction.

CONCLUSIONS

Our results point to an association between food addiction severity levels and impairments in decision-making and attentional capacity in individuals with OB. Given the heterogeneity found in OB, it stands to reason that this subset of patients with food addiction could potentially benefit from interventions targeting neuropsychological deficits.

CRISPR/Cas9, the Powerful New Genome-Editing Tool for Putative Therapeutics in Obesity

The molecular technology known as clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) is revolutionizing the field of medical research and deepening our understanding of numerous biological processes. The attraction of CRISPR/Cas9 lies in its ability to efficiently edit DNA or modulate gene expression in living eukaryotic cells and organisms, a technology that was once considered either too expensive or scientifically risky. CRISPR/Cas9 has been successfully applied in agriculture to develop the next generation of disease-resistant plants. Now, the capability of gene editing has been translated to the biomedical area, focusing on the future of medicine faced with drug-resistant microbes by selectively targeting genes involved in antibiotic resistance, for example, or finding the ultimate strategy for cancer or HIV. In this regard, it was recently demonstrated that an injection of cancer-fighting CRISPR-modified white blood cells in a patient suffering from metastatic lung cancer could lead to promising results. Researchers and bioethicists are debating questions about the regulation of CRISPR/Cas9 that must be addressed. While legal challenges surround the use of this technique for genetically modifying cell lines in humans, we review the basic understanding of CRISPR/Cas9 and discuss how this technology could represent a candidate for treatment of non-communicable diseases in nutrition, such as obesity.

BRANCHED CHAIN AMINO ACIDS AT THE EDGE BETWEEN MENDELIAN AND COMPLEX DISORDERS

Branched chained amino acids (BCAA) are essential components of the human diet and important nutrient signals, which regain particular interest in recent years with the avenue of metabolomics studies suggesting their potential role as biomarkers. There is now compelling evidence for predictive role of BCAA in progression of diabetes, but causality relationship is still debated concerning insulin resistance and genetic versus non-genetic pathogenesis. Mendelian randomization studies in large cohorts of diabetes indicated pathogenic role of PPM1K (protein phosphatase Mg2+/Mn2+ dependent 1K) on Chr 4q22.1 gene, encoding for a phosphatase that activates BCKDH (branched chain keto acid dehydrogenase) complex. Recent studies indicated that insulin rapidly and dose-dependently regulates gene expression of the same complex, but the relationship with systemic insulin resistance and glucose levels is complex. Rare genetic syndromes due to Mendelian mutations in key genes in BCAA catabolism may be good models to understand potential role of gene of BCAA catabolism. However, in studying complex disorders geneticists are faced to complete new aspects of metabolic regulation complicating understanding genetics of obesity, diabetes or metabolic syndrome. A review of genetic syndromes of BCAA metabolism suggests that insulin resistance is not present, except rare cases of methylmalonic aciduria due to MUT (methylmalonyl-coA mutase) gene on Chr 6p12.3. Another aspect that complicates understanding is the new role of central nervous system (CNS) in insulin resistance. For a long time the hypothalamic hunger/satiety neuronal system was considered a key site of nutrient regulation. Genes may also affect the brain rewarding system (BRS) that would regulate food intake by modulating the motivation to obtain food and considering hedonic properties. Nutrigenomic and nutrigenetic investigations taking into account concurrently BCAA intake, metabolic regulation and gene variation have large perspectives to merge genetic and nutritional understanding in complex disorders.

Hyperpalatability and the Generation of Obesity: Roles of Environment, Stress Exposure and Individual Difference

PURPOSE OF REVIEW

This review investigates how exposure to palatable food and its associated cues alters appetite regulation and feeding behaviour to drive overeating and weight gain.

RECENT FINDINGS

Both supraphysiological and physiological feeding systems are affected by exposure to palatable foods and its associated cues. Preclinical research, largely using rodents, has demonstrated that palatable food modulates feeding-related neural systems and food-seeking behaviour by recruiting the mesolimbic reward pathway. This is supported by studies in adolescents which have shown that mesolimbic activity in response to palatable food cues and consumption predicts future weight gain. Additionally, stress exposure, environmental factors and individual susceptibility have been shown to modulate the effects of highly palatable foods on behaviour. Further preclinical research using free-choice diets modelling the modern obesogenic environment is needed to identify how palatable foods drive overeating. Moreover, future clinical research would benefit from more appropriate quantification of palatability, making use of rating systems and surveys.

Validation of the Spanish Version of the Yale Food Addiction Scale 2.0 (YFAS 2.0) and Clinical Correlates in a Sample of Eating Disorder, Gambling Disorder, and Healthy Control Participants

Aims: Due to the increasing evidence of shared vulnerabilities between addictive behaviors and excessive food intake, the concept of food addiction in specific clinical populations has become a topic of scientific interest. The aim of this study was to validate the Yale Food Addiction Scale (YFAS) 2.0 in a Spanish sample. We also sought to explore food addiction and its clinical correlates in eating disorder (ED) and gambling disorder (GD) patients. Methods: The sample included 301 clinical cases (135 ED and 166 GD), diagnosed according to DSM-5 criteria, and 152 healthy controls (HC) recruited from the general population. Results: Food addiction was more prevalent in patients with ED, than in patients with GD and HC (77.8, 7.8, and 3.3%, respectively). Food addiction severity was associated with higher BMI, psychopathology and specific personality traits, such as higher harm avoidance, and lower self-directedness. The psychometrical properties of the Spanish version of the YFAS 2.0 were excellent with good convergent validity. Moreover, it obtained good accuracy in discriminating between diagnostic subtypes. Conclusions: Our results provide empirical support for the use of the Spanish YFAS 2.0 as a reliable and valid tool to assess food addiction among several clinical populations (namely ED and GD). The prevalence of food addiction is heterogeneous between disorders. Common risk factors such as high levels of psychopathology and low self-directedness appear to be present in individuals with food addiction.

Intra-accumbens Raclopride Administration Prevents Behavioral Changes Induced by Intermittent Access to Sucrose Solution

Overeating is one of the most relevant clinical features in Binge Eating Disorder and in some obesity patients. According to several studies, alterations in the mesolimbic dopaminergic transmission produced by non-homeostatic feeding behavior may be associated with changes in the reward system similar to those produced by drugs of abuse. Although it is known that binge-eating is related with changes in dopaminergic transmission mediated by D2 receptors in the nucleus accumbens shell (NAcS), it has not been determined whether these receptors may be a potential target for the treatment of eating pathology with binge-eating. Accordingly, the aim of the present study was to evaluate whether sugar binging induced by intermittent access to a sucrose solution produced changes in the structure of feeding behavior and whether blocking D2 receptors prevented these changes. We used the intermittent access model to a 10% sucrose solution (2 h/day for 4 weeks) to induce sugar binging in Sprague Dawley female rats. Experimental subjects consumed in a 2-h period more than 50% of the caloric intake consumed by the subjects with ad-lib access to the sweetened solution without any increase in body weight or fat accumulation. Furthermore, we evaluated whether sugar binging was associated to the estrous cycle and we did not find differences in caloric intake (estrous vs. diestrus). Subsequently, we characterized the structure of feeding behavior (microstructural analysis) and the motivation for palatable food (breakpoints) of the subjects with sugar binging and found that feeding episodes had short latencies, high frequencies, as well as short durations and inter-episode intervals. The intermittent access model did not increase breakpoints, as occurred in subjects with ad-lib access to the sucrose. Finally, we evaluated the effects of D2 receptor blockade in the NAcS, and found that raclopride (18 nM) prevented the observed changes in the frequency and duration of episodes induced by intermittent access to the sucrose solution. Our results suggest that alterations in behavioral patterns associated with binge-eating behavior depend in part on the dopaminergic transmission in the NAcS and that the antagonism of D2 receptors may be a therapeutic tool for feeding pathology with binge-eating.

Decision Making Deficits in Relation to Food Cues Influence Obesity: A Triadic Neural Model of Problematic Eating

In this review article we propose a model of the brain systems, the deficiency of which may underlie problematic eating. This integrative model is based on studies that have focused on discrete brain components involved in problematic eating, combined with insights from studies on the neurocognitive basis of other addictive and problematic behaviors. The model includes: (a) a hyper-functioning reward anticipation and processing system (amygdala-striatum dependent) in response to food-related cues; (b) a hypo-functioning reflective and inhibitory control system (prefrontal cortex dependent), that fails to anticipate and properly weigh future outcomes; and (c) an altered interoceptive awareness system (insular cortex dependent) that translates homeostatic violation signals into a strong consumption desire that hijacks the inhibitory system and excites the reward system. We posit that when the abovementioned systems are imbalanced in such a way that the dopamine axis is hyperactive in relation to food cues and the inhibitory system is weak, and this is further aggravated by an altered interoceptive awareness system, people may experience loss of control or inability to resist tempting/rewarding foods. This loss of control over food consumption can explain, at least in part, the development of excess weight and contribute to the obesity epidemic.

Allostatic Load Is Linked to Cortical Thickness Changes Depending on Body-Weight Status

Objective: Overweight (body mass index or BMI ≥ 25 kg/m²) and stress interact with each other in complex ways. Overweight promotes chronic low-inflammation states, while stress is known to mediate caloric intake. Both conditions are linked to several avoidable health problems and to cognitive decline, brain atrophy, and dementia. Since it was proposed as a framework for the onset of mental illness, the allostatic load model has received increasing attention. Although changes in health and cognition related to overweight and stress are well-documented separately, the association between allostatic load and brain integrity has not been addressed in depth, especially among overweight subjects.

Method: Thirty-four healthy overweight-to-obese and 29 lean adults underwent blood testing, neuropsychological examination, and magnetic resonance imaging to assess the relationship between cortical thickness and allostatic load, represented as an index of 15 biomarkers (this is, systolic and diastolic arterial tension, glycated hemoglobin, glucose, creatinine, total cholesterol, HDL and LDL cholesterol, triglycerides, c-reactive protein, interleukin-6, insulin, cortisol, fibrinogen, and leptin).

Results: Allostatic load indexes showed widespread positive and negative significant correlations (p < 0.01) with cortical thickness values depending on body-weight status.

Conclusion: The increase of allostatic load is linked to changes in the gray matter composition of regions monitoring behavior, sensory-reward processing, and general cognitive function.