Metabolic vs. hedonic obesity: a conceptual distinction and its clinical implications

Practical strategies to manage obesity in type 2 diabetes

The rising phenomenon of obesity, a major risk factor for the development and progression of type 2 diabetes, is a complex and multifaceted issue that requires a comprehensive and coordinated approach to be prevented and managed. Although novel pharmacological measures to combat obesity have achieved unprecedented efficacy, a healthy lifestyle remains essential for the long-term success of any therapeutic intervention. However, this requires a high level of intrinsic motivation and continued behavioural changes in the face of multiple metabolic, psychological and environmental factors promoting weight gain, particularly in the context of type 2 diabetes. This review is intended to provide practical recommendations in the context of a holistic, person-centred approach to weight management, including evidence-based and expert recommendations addressing supportive communication, shared decision-making, as well as nutritional and pharmacological therapeutic approaches to achieve sustained weight loss.

Assessing the contribution of plastic-associated obesogenic compounds to cardiometabolic diseases

PURPOSE OF REVIEW

To present recent evidence that strengthens the concept that exogenous pollutants contribute to adipose dysfunction and increased rates of disease and to highlight the ineffective regulation of this risk as industry switches to related but similarly toxic variants.

RECENT FINDINGS

Substitutes for common phthalates and the highly regulated bisphenol A (BPA) show similar deleterious effects on adipocytes. The well tolerated limit for BPA exposure has been reduced in Europe to below the level detected in recent population studies. Additionally, the role for BPA-induced inflammation mediated by interleukin 17a has been described in animal and human studies.

SUMMARY

Despite experimental and associative evidence that supports plastics and plastic associated chemicals deleteriously influencing adipose homeostatasis and contributing to metabolic diseases, structurally related alternate chemicals are being substituted by manufacturers to circumvent trailing regulatory actions.

Changes in reward-induced neural activity upon Cafeteria Diet consumption

Excessive consumption of highly palatable foods rich in sugar and fat, often referred to as "junk" or "fast" foods, plays a central role in the development of obesity. The highly palatable characteristics of these foods activate hedonic and motivational mechanisms to promote food-seeking behavior and overeating, which is largely regulated by the brain reward system. Excessive junk food consumption can alter the functioning of this reward system, but exact mechanisms of these changes are still largely unknown. This study investigated whether long-term junk food consumption, in the form of Cafeteria (CAF) diet, can alter the reward system in adult, female Long-Evans rats, and whether different regimes of CAF diet influence the extent of these changes. To this end, rats were exposed to a 6-week diet with either standard chow, or ad libitum daily access to CAF diet, 30 % restricted but daily access to CAF diet, or one-day-a-week (intermittent) ad libitum access to CAF diet, after which c-Fos expression in the Nucleus Accumbens (NAc), Prefrontal Cortex (PFC), and Ventral Tegmental Area (VTA) following consumption of a CAF reward of choice was examined. We found that all CAF diet regimes decreased c-Fos expression in the NAc-shell when presented with a CAF reward, while no changes in c-Fos expression upon the different diet regimes were found in the PFC, and possibly the VTA. Our data suggests that long-term junk food exposure can affect the brain reward system, resulting in an attenuated activity of the NAc-shell.

Role of Endogenous Opioids in the Pathophysiology of Obesity and Eating Disorders

This second chapter in our trilogy reviews and critically appraises the scientific evidence for the role of endogenous opioid system (EOS) activity in the onset and progression of both obesity and eating disorders. Defining features of normative eating and maladaptive eating behaviors are discussed as a foundation. We review the scientific literature pertaining to the predisposing risk factors and pathophysiology for obesity and eating disorders. Research targeting the association between obesity, disordered eating, and psychiatric comorbidities is reviewed. We conclude by discussing the involvement of endogenous opioids in neurobiological and behavior traits, and the clinical evidence for the role of the EOS in obesity and eating disorders.

Obesity as a Neuroendocrine Disorder

Obesity is one of the most prevalent diseases in the world. Based on hundreds of clinical and basic investigations, its etiopathogenesis goes beyond the simple imbalance between energy intake and expenditure. The center of the regulation of appetite and satiety lies in the nuclei of the hypothalamus where peripheral signals derived from adipose tissue (e.g., leptin), the gastrointestinal tract, the pancreas, and other brain structures, arrive. These signals are part of the homeostatic control system (eating to survive). Additionally, a hedonic or reward system (eating for pleasure) is integrated into the regulation of appetite. This reward system consists of a dopaminergic circuit that affects eating-related behaviors influencing food preferences, food desires, gratification when eating, and impulse control to avoid compulsions. These systems are not separate. Indeed, many of the hormones that participate in the homeostatic system also participate in the regulation of the hedonic system. In addition, factors such as genetic and epigenetic changes, certain environmental and sociocultural elements, the microbiota, and neuronal proinflammatory effects of high-energy diets also contribute to the development of obesity. Therefore, obesity can be considered a complex neuroendocrine disease, and all of the aforementioned components should be considered for the management of obesity.

Attentional bias for high-calorie food cues by the level of hunger and satiety in individuals with binge eating behaviors

Introduction

The abnormal hyperreactivity to food cues in individuals with binge eating behaviors could be regulated by hedonic or reward-based system, overriding the homeostatic system. The aim of the present study was to investigate whether attentional bias for food cues is affected by the level of hunger, maintaining the normal homeostatic system in individuals with binge eating behaviors.

Methods

A total of 116 female participants were recruited and divided into four groups: hungry-binge eating group (BE) (n = 29), satiated BE (n = 29), hungry-control (n = 29), satiated control (n = 29). While participants completed a free-viewing task on high or low-calorie food cues, visual attentional processes were recorded using an eye tracker.

Results

The results revealed that BE group showed longer initial fixation duration toward high-calorie food cues in both hunger and satiety condition in the early stage, whereas the control group showed longer initial fixation duration toward high-calorie food cues only in hunger conditions. Moreover, in the late stage, the BE group stared more at the high-calorie food cue, compared to control group regardless of hunger and satiety.

Discussion

The findings suggest that automatic attentional bias for food cues in individuals with binge eating behaviors occurred without purpose or awareness is not affected by the homeostatic system, while strategic attention is focused on high-calorie food. Therefore, the attentional processing of food cues in binge eating group is regulated by hedonic system rather than homeostatic system, leading to vulnerability to binge eating.

Bean Leaves Ameliorate Lipotoxicity in Fatty Liver Disease

Bioactive compounds in plant-based food have protective effects against metabolic alterations, including non-alcoholic fatty liver disease (NAFLD). Bean leaves are widely cultivated in the world and are a source of dietary fiber and polyphenols. High fat/high fructose diet animal models promote deleterious effects in adipose and non-adipose tissues (lipotoxicity), leading to obesity and its comorbidities. Short-term supplementation of bean leaves exhibited anti-diabetic, anti-hyperlipidemic, and anti-obesity effects in high-fat/high-fructose diet animal models. This study aimed to evaluate the effect of bean leaves supplementation in the prevention of lipotoxicity in NAFLD and contribute to elucidating the possible mechanism involved for a longer period of time. During thirteen weeks, male Wistar rats (n = 9/group) were fed with: (1) S: Rodent Laboratory Chow 5001^® (RLC); (2) SBL: 90% RLC+ 10% dry bean leaves; (3) H: high-fat/high-fructose diet; (4) HBL: H+ 10% of dry bean leaves. Overall, a HBL diet enhanced impaired glucose tolerance and ameliorated obesity, risk factors in NAFLD development. Additionally, bean leaves exerted antioxidant (↑serum GSH) and anti-inflammatory (↓mRNA TNFα in the liver) effects, prevented hepatic fat accumulation by enhanced ↑mRNA PPARα (β oxidation), and enhanced lipid peroxidation (↓liver MDA). These findings suggest that bean leaves ameliorated hepatic lipotoxicity derived from the consumption of a deleterious diet.

Position statement on nutrition therapy for overweight and obesity: nutrition department of the Brazilian association for the study of obesity and metabolic syndrome (ABESO-2022)

Obesity is a chronic disease resulting from multifactorial causes mainly related to lifestyle (sedentary lifestyle, inadequate eating habits) and to other conditions such as genetic, hereditary, psychological, cultural, and ethnic factors. The weight loss process is slow and complex, and involves lifestyle changes with an emphasis on nutritional therapy, physical activity practice, psychological interventions, and pharmacological or surgical treatment. Because the management of obesity is a long-term process, it is essential that the nutritional treatment contributes to the maintenance of the individual's global health. The main diet-related causes associated with excess weight are the high consumption of ultraprocessed foods, which are high in fats, sugars, and have high energy density; increased portion sizes; and low intake of fruits, vegetables, and grains. In addition, some situations negatively interfere with the weight loss process, such as fad diets that involve the belief in superfoods, the use of teas and phytotherapics, or even the avoidance of certain food groups, as has currently been the case for foods that are sources of carbohydrates. Individuals with obesity are often exposed to fad diets and, on a recurring basis, adhere to proposals with promises of quick solutions, which are not supported by the scientific literature. The adoption of a dietary pattern combining foods such as grains, lean meats, low-fat dairy, fruits, and vegetables, associated with an energy deficit, is the nutritional treatment recommended by the main international guidelines. Moreover, an emphasis on behavioral aspects including motivational interviewing and the encouragement for the individual to develop skills will contribute to achieve and maintain a healthy weight. Therefore, this Position Statement was prepared based on the analysis of the main randomized controlled studies and meta-analyses that tested different nutrition interventions for weight loss. Topics in the frontier of knowledge such as gut microbiota, inflammation, and nutritional genomics, as well as the processes involved in weight regain, were included in this document. This Position Statement was prepared by the Nutrition Department of the Brazilian Association for the Study of Obesity and Metabolic Syndrome (ABESO), with the collaboration of dietitians from research and clinical fields with an emphasis on strategies for weight loss.

Reward Processing During Monetary Incentive Delay Task After Leptin Substitution in Lipodystrophy-an fMRI Case Series

Context

Behaviorally, the most pronounced effects of leptin substitution in leptin deficiency are the hunger-decreasing and postprandial satiety-prolonging effects of the adipokine. Previously, with functional magnetic resonance imaging (MRI), we and others showed that eating behavior-controlling effects are at least in part conveyed by the reward system. However, to date, it is unclear if leptin only modulates eating behavior specific brain reward action or if it also alters the reward function of the brain unrelated to eating behavior.

Objective

We investigated with functional MRI the effects of metreleptin on the reward system in a reward task unrelated to eating behavior, the monetary incentive delay task.

Design

Measurements in 4 patients with the very rare disease of lipodystrophy (LD), resulting in leptin deficiency, and 3 untreated healthy control persons were performed at 4 different time points: before start and over 12 weeks of metreleptin treatment. Inside the MRI scanner, participants performed the monetary incentive delay task and brain activity during the reward receipt phase of the trial was analyzed.

Results

We found a reward-related brain activity decrease in our 4 patients with LD over the 12 weeks of metreleptin treatment in the subgenual region, a brain area associated with the reward network, which was not observed in our 3 untreated healthy control persons.

Conclusions

These results suggest that leptin replacement in LD induces changes of brain activity during reward reception processing completely unrelated to eating behavior or food stimuli. This could suggest eating behavior-unrelated functions of leptin in the human reward system.

Trial registration

The trial is registered as trial No. 147/10-ek at the ethics committee of the University of Leipzig and at the State Directorate of Saxony (Landesdirektion Sachsen).

Severe Obesity in Women Can Lead to Worse Memory Function and Iron Dyshomeostasis Compared to Lower Grade Obesity

Objective

Obesity is one of the modifiable risk factors for dementia. Insulin resistance, the abundance of advanced glycated end-products, and inflammation are some of the mechanisms associated with the lower cognitive performance observed in obesity. This study aims to evaluate the cognitive function of subjects with distinct degrees of obesity, comparing class I and II obesity (OBI/II) to class III obesity (OBIII), and to investigate metabolic markers that can distinguish OBIII from OBI/II. Study Design. This is a cross-sectional study, in which 45 females with BMI varying from 32.8 to 51.9 kg/m² completed a set of 4 cognitive tests (verbal paired-associate test, stroop color, digit span, and Toulouse-Pieron cancellation test) and their plasma metabolites, enzymes, and hormones related to glycemia, dyslipidemia, and liver function, as well as the biomarkers of iron status, were concomitantly analyzed.

Results

OBIII showed lower scores in the verbal paired-associate test compared to OBI/II. In other cognitive tests, both groups showed similar performance. OBIII presented a lower iron status compared to OBI/II based on total iron binding capacity, degree of transferrin saturation, hemoglobin, mean corpuscular volume, and mean corpuscular hemoglobin. The levels of indicators for glycemia, liver function, and lipid metabolism were similar in both groups. Analysis of plasma metabolites showed that OBIII had lower levels of pyroglutamic acid, myoinositol, and aspartic acid and higher levels of D-ribose than OBI/II.

Conclusion

Iron is an essential micronutrient for several metabolic pathways. Thus, iron dyshomeostasis observed in severe obesity may aggravate the cognitive impairment by altering metabolic homeostasis and enhancing oxidative stress. These findings can contribute to searching for biomarkers that indicate cognitive performance in the population with obesity.

Added flavors: potential contributors to body weight gain and obesity?

BACKGROUND

Added flavors are a marker for ultra-processing of food and a strong link exists between the intake of ultra-processed food and the development of obesity. The objective of the present article is to assess animal and human data elucidating the impact of added flavors on the regulation of food intake and body weight gain, as well as to define areas for future research.

MAIN TEXT

Mechanistic studies suggest that added flavors induce overeating and body weight gain by two independent mechanisms: Added flavors promote hedonic eating and override homeostatic control of food intake, as well as disrupt flavor-nutrient learning and impair the ability to predict nutrients in food items. Supporting these potential mechanisms, added flavors increase feed intake and body weight as compared to non-flavored control diets in a broad range of animal studies. They are actively promoted by feed additive manufacturers as useful tools to improve palatability, feed intake, and performance parameters. In humans, added flavors are extensively tested concerning toxicity; however, no data exist concerning their impact on food intake and body weight.

CONCLUSIONS

Added flavors are potential contributors to the obesity epidemic and further studies focusing on their role in humans are urgently required. These studies include obesity interventions specifically targeting food items with added flavors and cohort studies on independent associations between added flavor intake and metabolic, as well as cardiovascular, morbidity, and mortality.

Impact of sleeve gastrectomy compared to Roux-en-y gastric bypass upon hedonic hunger and the relationship to post-operative weight loss

'Hedonic hunger' indicates the desire to consume food in the absence of an energy requirement. Hedonic hunger can be investigated using the validated Power of Food Scale (PFS). Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) are currently the most effective treatment options for severe obesity. Following RYGB, hedonic hunger diminishes, which may contribute to sustained weight loss. There are no data examining the effect of SG on hedonic hunger. We prospectively evaluated hedonic hunger using PFS in patients with severe obesity prior to and 6 months after SG (n = 95) or RYGB (n = 44) and investigated the procedure-specific relationship between percentage weight loss (%WL) and hedonic hunger. Anthropometric data were collected at baseline after 6 months, 12 months and 24 months post-operatively. PFS contains 15 items grouped into 3 domains considering when food is: available (FA), present (FP), tasted (FT) and a total score (TS). At 6 months, a significant reduction was seen in all categories post-SG (p < 0.0001) and in TS (p = 0.003), FA (p = 0.0006) and FP (p = 0.0007) post-RYGB. A significantly larger reduction in FP scores was seen post-SG (p = 0.01). Post-SG, a significant correlation with 6-month %WL was noted for changes in FP (p = 0.03) and TS (p = 0.03). Post-SG changes in FP and TS predicted 24-month %WL. Post-RYGB significant correlations were seen between 6-month %WL and dFA (p = 0.04) and dFP (p = 0.03). Changes in FA, FP and TS were predictive of 12-month %WL. HH is reduced following both SG and RYGB with a greater reduction following SG and is related to post-operative %WL. PFS may have a role as a predictive tool for post-operative outcomes following SG and RYGB.

Obesity I: Overview and molecular and biochemical mechanisms

Obesity is a chronic, relapsing condition characterized by excess body fat. Its prevalence has increased globally since the 1970s, and the number of obese and overweight people is now greater than those underweight. Obesity is a multifactorial condition, and as such, many components contribute to its development and pathogenesis. This is the first of three companion reviews that consider obesity. This review focuses on the genetics, viruses, insulin resistance, inflammation, gut microbiome, and circadian rhythms that promote obesity, along with hormones, growth factors, and organs and tissues that control its development. It shows that the regulation of energy balance (intake vs. expenditure) relies on the interplay of a variety of hormones from adipose tissue, gastrointestinal tract, pancreas, liver, and brain. It details how integrating central neurotransmitters and peripheral metabolic signals (e.g., leptin, insulin, ghrelin, peptide YY_3-36) is essential for controlling energy homeostasis and feeding behavior. It describes the distinct types of adipocytes and how fat cell development is controlled by hormones and growth factors acting via a variety of receptors, including peroxisome proliferator-activated receptor-gamma, retinoid X, insulin, estrogen, androgen, glucocorticoid, thyroid hormone, liver X, constitutive androstane, pregnane X, farnesoid, and aryl hydrocarbon receptors. Finally, it demonstrates that obesity likely has origins in utero. Understanding these biochemical drivers of adiposity and metabolic dysfunction throughout the life cycle lends plausibility and credence to the "obesogen hypothesis" (i.e., the importance of environmental chemicals that disrupt these receptors to promote adiposity or alter metabolism), elucidated more fully in the two companion reviews.

MicroRNAs signatures associated with vulnerability to food addiction in mice and humans

Food addiction is characterized by a loss of behavioral control over food intake and is associated with obesity and other eating disorders. The mechanisms underlying this behavioral disorder are largely unknown. We aimed to investigate the changes in miRNA expression promoted by food addiction in animals and humans and their involvement in the mechanisms underlying the behavioral hallmarks of this disorder. We found sharp similitudes between miRNA signatures in the medial prefrontal cortex (mPFC) of our animal cohort and circulating miRNA levels in our human cohort, which allowed us to identify several miRNAs of potential interest in the development of this disorder. Tough decoy (TuD) inhibition of miRNA-29c-3p in the mouse mPFC promoted persistence of the response and enhanced vulnerability to developing food addiction, whereas miRNA-665-3p inhibition promoted compulsion-like behavior and also enhanced food addiction vulnerability. In contrast, we found that miRNA-137-3p inhibition in the mPFC did not lead to the development of food addiction. Therefore, miRNA-29c-3p and miRNA-665-3p could be acting as protective factors with regard to food addiction. We believe the elucidation of these epigenetic mechanisms will lead to advances toward identifying innovative biomarkers and possible future interventions for food addiction and related disorders based on the strategies now available to modify miRNA activity and expression.

Obesity as a Condition Determined by Food Addiction: Should Brain Endocannabinoid System Alterations Be the Cause and Its Modulation the Solution?

Obesity is a complex disorder, and the number of people affected is growing every day. In recent years, research has confirmed the hypothesis that food addiction is a determining factor in obesity. Food addiction is a behavioral disorder characterized by disruptions in the reward system in response to hedonic eating. The endocannabinoid system (ECS) plays an important role in the central and peripheral control of food intake and reward-related behaviors. Moreover, both obesity and food addiction have been linked to impairments in the ECS function in various brain regions integrating peripheral metabolic signals and modulating appetite. For these reasons, targeting the ECS could be a valid pharmacological therapy for these pathologies. However, targeting the cannabinoid receptors with inverse agonists failed when used in clinical contexts as a consequence of the induction of affective disorders. In this context, new classes of drugs acting either on CB1 and/or CB2 receptors or on synthetic and degradation enzymes of endogenous cannabinoids are being studied. However, further investigation is necessary to find safe and effective treatments that can exert anti-obesity effects, normalizing reward-related behaviors without causing important adverse mood effects.

Evaluation and Management of Early Onset Genetic Obesity in Childhood

One in five children and adolescents in the United States are diagnosed with obesity and nearly 6% of them are being classified under the severe obesity category. With over 7% of severe obesity being attributed to genetic disorders, in this review we aim to focus on monogenic and syndromic obesity: its etiology, wide spectrum of clinical presentation, criticalness of early identification, and limited management options. Advanced genetic testing methods including microarray and whole genome sequencing are imperative to identify the spectrum of mutations and develop targeted treatment strategies including personalized multidisciplinary care, use of investigational drugs, and explore surgical options in this unique subset of severe pediatric obesity.

Complexity and Stigma of Pediatric Obesity

Weight stigma is rooted in a fundamental misunderstanding of the origins of obesity, wherein the interplay of behavioral, environmental, genetic, and metabolic factors is deemphasized. Instead, the widespread societal and cultural presence of weight stigma fosters misconceptions of obesity being solely a result of unhealthy personal choices. Weight stigma is pervasive in childhood and adolescence and can affect individuals throughout their life. Although the prevalence of pediatric obesity remains high throughout the world, it becomes increasingly important to understand how weight stigma affects weight and health outcomes in children and adolescents with overweight or obesity, including in those with rare genetic diseases of obesity. We identified and reviewed recent literature (primarily published since 2000) on weight stigma in the pediatric setting. Articles were identified with search terms including pediatric obesity, weight bias, weight stigma, weight-based teasing and bullying, and weight bias in health care. In this narrative review, we discuss the stigma of pediatric obesity as it relates to the complex etiology of obesity as well as describe best practices for avoiding bias and perpetuating stigma in the health care setting.

Dietary Management of Obesity: A Review of the Evidence

Obesity is a multi-factorial disease and its prevention and management require knowledge of the complex interactions underlying it and adopting a whole system approach that addresses obesogenic environments within country specific contexts. The pathophysiology behind obesity involves a myriad of genetic, epigenetic, physiological, and macroenvironmental factors that drive food intake and appetite and increase the obesity risk for susceptible individuals. Metabolically, food intake and appetite are regulated via intricate processes and feedback systems between the brain, gastrointestinal system, adipose and endocrine tissues that aim to maintain body weight and energy homeostasis but are also responsive to environmental cues that may trigger overconsumption of food beyond homeostatic needs. Under restricted caloric intake conditions such as dieting, these processes elicit compensatory metabolic mechanisms that promote energy intake and weight regain, posing great challenges to diet adherence and weight loss attempts. To mitigate these responses and enhance diet adherence and weight loss, different dietary strategies have been suggested in the literature based on their differential effects on satiety and metabolism. In this review article, we offer an overview of the literature on obesity and its underlying pathological mechanisms, and we present an evidence based comparative analysis of the effects of different popular dietary strategies on weight loss, metabolic responses and diet adherence in obesity.

Exploring Patterns of Disturbed Eating in Psychosis: A Scoping Review

Disturbed eating behaviours have been widely reported in psychotic disorders since the early 19th century. There is also evidence that antipsychotic (AP) treatment may induce binge eating or other related compulsive eating behaviours. It is therefore possible that abnormal eating patterns may contribute to the significant weight gain and other metabolic disturbances observed in patients with psychosis. In this scoping review, we aimed to explore the underlying psychopathological and neurobiological mechanisms of disrupted eating behaviours in psychosis spectrum disorders and the role of APs in this relationship. A systematic search identified 35 studies that met our eligibility criteria and were included in our qualitative synthesis. Synthesizing evidence from self-report questionnaires and food surveys, we found that patients with psychosis exhibit increased appetite and craving for fatty food, as well as increased caloric intake and snacking, which may be associated with increased disinhibition. Limited evidence from neuroimaging studies suggested that AP-naïve first episode patients exhibit similar neural processing of food to healthy controls, while chronic AP exposure may lead to decreased activity in satiety areas and increased activity in areas associated with reward anticipation. Overall, this review supports the notion that AP use can lead to disturbed eating patterns in patients, which may contribute to AP-induced weight gain. However, intrinsic illness-related effects on eating behaviors remain less well elucidated, and many confounding factors as well as variability in study designs limits interpretation of existing literature in this field and precludes firm conclusions from being made.

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.

A latent class analysis of dietary behaviours associated with metabolic syndrome: a retrospective observational cross-sectional study

BACKGROUND

Obesity defined solely by the Body Mass Index (BMI) may not reflect the true heterogeneity of the obese population. This study aimed to classify the dietary behaviours of overweight and obese individuals and to explore the relationship between patterns of dietary behaviour and cardiometabolic risk factors.

METHODS

A total of 259 patients who visited an outpatient weight management clinic at a tertiary hospital and underwent a dietary behaviour assessment between January 2014 and February 2019 were enrolled in the study. Dietary behaviours were assessed in three domains with nine categories, including choice of food (frequently eating out and consumption of instant/fast/takeaway food), eating behaviour (irregular meals; frequent snacking, including eating at night; emotional eating; and overeating/binge eating), and nutrient intake (high-fat/high-calorie foods, salty food, and poorly balanced diet). Latent class analysis (LCA) was used to classify the subjects according to these categories. Associations between latent class and metabolic syndrome were assessed by logistic regression.

RESULTS

The subjects were classified into three LCA-driven classes, including a referent class of healthy but unbalanced eaters (n = 118), a class of emotional eaters (n = 53), and a class of irregular unhealthy eaters (n = 88). Compared with the referent class, emotional eaters had a significantly higher BMI (beta = 3.40, P < 0.001) accompanied by metabolic syndrome (odds ratio 2.88, 95% confidence interval 1.16-7.13).

CONCLUSIONS

Our three LCA-driven obesity phenotypes could be useful for assessment and management of obesity and metabolic syndrome. The association between emotional eaters and higher BMI and metabolic syndrome was stronger than that with other eaters. Thus, emotional regulation strategies might have benefit for emotional eater's diet.

Identification of ALK in Thinness

There is considerable inter-individual variability in susceptibility to weight gain despite an equally obesogenic environment in large parts of the world. Whereas many studies have focused on identifying the genetic susceptibility to obesity, we performed a GWAS on metabolically healthy thin individuals (lowest 6th percentile of the population-wide BMI spectrum) in a uniquely phenotyped Estonian cohort. We discovered anaplastic lymphoma kinase (ALK) as a candidate thinness gene. In Drosophila, RNAi mediated knockdown of Alk led to decreased triglyceride levels. In mice, genetic deletion of Alk resulted in thin animals with marked resistance to diet- and leptin-mutation-induced obesity. Mechanistically, we found that ALK expression in hypothalamic neurons controls energy expenditure via sympathetic control of adipose tissue lipolysis. Our genetic and mechanistic experiments identify ALK as a thinness gene, which is involved in the resistance to weight gain.

Four main barriers to weight loss maintenance? A quantitative analysis of difficulties experienced by obese patients after successful weight reduction

BACKGROUND

Weight maintenance remains to be a challenge for patients in a reduced obese state and it has been recommended to provide them more individualized support. For this purpose it is crucial to understand the barriers patients are experiencing after weight loss. Many have been identified by qualitative studies. We evaluated if a quantitative assessment of patient perspective during weight maintenance can help identify major barriers that refer to actual regain.

METHODS

Follow-up data were analyzed from patients attempting weight maintenances after successful completion of a nonsurgical weight loss and lifestyle intervention for morbid obesity. The data were acquired at mandatory follow-up assessments and included rating of 26 probable difficulties. A principal component analysis was carried out to explore whether these difficulties could be grouped into meaningful factors. Associations with socio-demographics, follow-up time, and weight changes were evaluated.

RESULTS

Data from 88 out of 102 patients were available (baseline BMI 49.5 ± 7.4 kg/m²; 12-month weight loss 24.3 ± 9.6%; follow-up time 1.48 ± 0.6 years). Four solid factors, composed of 21 items and explaining 56% of the variance were extracted and interpreted as 'Hedonic Hunger', 'Mental Distress', 'Binge Eating', and 'Demoralization'. Weight regain (12.4 ± 12%) was correlated with each factor, most closely with 'Mental Distress' (r = 0.38). When controlling for age and follow-up time, 'Binge Eating' was the most important predictor (adj. R² = 0.297).

CONCLUSIONS

A quantitative assessment of patient perspective during the first years after weight loss can help identify valid barriers to weight loss maintenance.

Sugar Promotes Feeding in Flies via the Serine Protease Homolog scarface

A balanced diet of macronutrients is critical for animal health. A lack of specific elements can have profound effects on behavior, reproduction, and lifespan. Here, we used Drosophila to understand how the brain responds to carbohydrate deprivation. We found that serine protease homologs (SPHs) are enriched among genes that are transcriptionally regulated in flies deprived of carbohydrates. Stimulation of neurons expressing one of these SPHs, Scarface (Scaf), or overexpression of scaf positively regulates feeding on nutritious sugars, whereas inhibition of these neurons or knockdown of scaf reduces feeding. This modulation of food intake occurs only in sated flies while hunger-induced feeding is unaffected. Furthermore, scaf expression correlates with the presence of sugar in the food. As Scaf and Scaf neurons promote feeding independent of the hunger state, and the levels of scaf are positively regulated by the presence of sugar, we conclude that scaf mediates the hedonic control of feeding.

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The fly brain responds to specific macronutrients via distinct signaling pathways

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Serine protease homologs act as neuromodulators under sugar deprivation

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Sugar is both necessary and sufficient to maintain expression levels of scarface

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Scarface and Scarface neurons mediate hedonic control of feeding in flies

Reconceptualizing anorexia nervosa

Anorexia nervosa (AN) has one of the highest mortality rates of any psychiatric disorder. Treatments are often ineffective and relapse is common. Most research attempting to understand the underlying causes and maintenance factors of AN has focused on environmental contributions, yet there is much to be explored in terms of biological risk and maintenance factors. In this paper, we focus primarily on AN research related to genetics and the complex microbial community in the gut (intestinal microbiota), and how these impact our conceptualization of this disorder. Emerging research identifying significant negative genetic correlations between AN and obesity suggests that the conditions may represent 'metabolic bookends'. The identification of underlying biological mechanisms may provide both insight into extreme weight dysregulation on both ends of the spectrum and new possible points of entry for AN treatment. Additionally, the reported microbial imbalance (dysbiosis) in the gut microbiota in AN patients, potentially due to a nutrient- and energy-deprived gut environment, implies alterations in functional and metabolic capacity of the gut microbiome. The extent to which AN and obesity can also be considered to be 'microbiome bookends' requires further investigation. Finally, we discuss ongoing and future AN projects exploring the interplay between host genomics, the environment, and cumulative microbial genomes (microbiome) as well as interventions at the microbial and gut level.

Transgenerational effects of obesogens

Obesity and associated disorders are now a global pandemic. The prevailing clinical model for obesity is overconsumption of calorie-dense food and diminished physical activity (the calories in-calories out model). However, this explanation does not account for numerous recent research findings demonstrating that a variety of environmental factors can be superimposed on diet and exercise to influence the development of obesity. The environmental obesogen model proposes that exposure to chemical obesogens during in utero and/or early life can strongly influence later predisposition to obesity. Obesogens are chemicals that inappropriately stimulate adipogenesis and fat storage, in vivo either directly or indirectly. Numerous obesogens have been identified in recent years and some of these elicit transgenerational effects on obesity as well as a variety of health end-points after exposure of pregnant F0 females. Prenatal exposure to environmental obesogens can produce lasting effects on the exposed animals and their offspring to at least the F4 generation. Recent results show that some of these transgenerational effects of obesogen exposure can be carried across the generations via alterations in chromatin structure and accessibility. That some chemicals can have permanent effects on the offspring of exposed animals suggests increased caution in the debate about whether and to what extent exposure to endocrine-disrupting chemicals and obesogens should be regulated.

Role of eating disorders-related polymorphisms in obesity pathophysiology

Human biological system provides innumerable neuroendocrine inputs for food intake control, with effects on appetite's modulation and the satiety signs. Its regulation is very complex, engaging several molecular interactions with many tissues, hormones, and neural circuits. Thus, signaling molecules that control food intake are critical for normal energy homeostasis and a deregulation of these pathways can lead to eating disorders and obesity. In line of this, genetic factors have a significantly influence of the regulation of neural circuits controlling the appetite and satiety pathways, as well as the regulation of brain reward systems. Single Nucleotide Polymorphisms (SNPs) in genes related to hypothalamic appetite and satiety mechanisms, further in multiple neurotransmitter systems may contribute to the development of major Eating Disorders (EDs) related to obesity, among them Binge Eating Disorder (BED) and Bulimia Nervosa (BN), which are discussed in this review.

The renin-angiotensin system as a target to solve the riddle of endocrine pancreas homeostasis

Local renin-angiotensin system (RAS) in the pancreas is linked to the modulation of glucose-stimulated insulin secretion (GSIS) in beta cells and insulin sensitivity in target tissues, emerging as a promising tool in the prevention and/or treatment of obesity, diabetes, and systemic arterial hypertension. Insulin resistance alters pancreatic islet cell distribution and morphology and hypertrophied islets exhibit upregulated angiotensin II type 1 receptor, which drives oxidative stress, apoptosis, and fibrosis, configuring beta cell dysfunction and diminishing islet lifespan. Pharmacological modulation of RAS has shown beneficial effects in diet-induced obesity model, mainly related to the translational potential that angiotensin receptor blockers and ECA2/ANG (1-7)/MAS receptor axis modulation have when it comes to islet preservation and type 2 diabetes prevention and/or treatment. This review describes the existing evidence for different approaches to blocking RAS elements in the management of insulin resistance and diabetes and focuses on islet remodeling and GSIS in rodents and humans.

Effects of Estrogens on Central Nervous System Neurotransmission: Implications for Sex Differences in Mental Disorders

Nearly one of every five US individuals aged 12 years old or older lives with certain types of mental disorders. Men are more likely to use various types of substances, while women tend to be more susceptible to mood disorders, addiction, and eating disorders, all of which are risks associated with suicidal attempts. Fundamental sex differences exist in multiple aspects of the functions and activities of neurotransmitter-mediated neural circuits in the central nervous system (CNS). Dysregulation of these neural circuits leads to various types of mental disorders. The potential mechanisms of sex differences in the CNS neural circuitry regulating mood, reward, and motivation are only beginning to be understood, although they have been largely attributed to the effects of sex hormones on CNS neurotransmission pathways. Understanding this topic is important for developing prevention and treatment of mental disorders that should be tailored differently for men and women. Studies using animal models have provided important insights into pathogenesis, mechanisms, and new therapeutic approaches of human diseases, but some concerns remain to be addressed. The purpose of this chapter is to integrate human and animal studies involving the effects of the sex hormones, estrogens, on CNS neurotransmission, reward processing, and associated mental disorders. We provide an overview of existing evidence for the physiological, behavioral, cellular, and molecular actions of estrogens in the context of controlling neurotransmission in the CNS circuits regulating mood, reward, and motivation and discuss related pathology that leads to mental disorders.

Pharmaceutical interventions for weight-loss maintenance: no effect from cabergoline

BACKGROUND

Weight regain is a major limitation to successful weight maintenance following weight loss. Observational studies suggest that stimulation of dopamine receptors in the central nervous system is associated with weight loss and inhibition of weight gain. Our objective was to test the hypothesis that dopamine agonist treatment would prevent weight regain following acute weight loss in individuals with obesity.

METHODS

We conducted a 2-year double blind randomised controlled trial comparing the effect of a dopamine agonist, cabergoline, with placebo on weight regain in obese individuals who had lost at least 5% of their body weight using an 800 kcal/day commercial meal replacement programme. The primary outcome measure was the difference in mean weight between the treatment and control groups over the 2-year period following randomisation.

RESULTS

At 24 months, there was no difference in body weight between cabergoline and placebo treatment after adjustment for age, gender and baseline values (0.6 kg (95% CI: -1.5, 2.6), p = 0.58). The mean (±SD) baseline body weight of the randomised participants was 101.8 kg, the mean (±SD) weight loss with the 800 kcal/day diet was 7.1 ± 1.8 kg and the mean (±SD) weight regain at 24 months was 5.1 ± 7.5 kg. There were no significant differences in BMI, percent weight loss, waist circumference, resting energy expenditure, blood pressure or metabolic parameters at 24 months between the two groups.

CONCLUSIONS

Treatment with the dopamine agonist cabergoline does not prevent weight regain in obese individuals following weight loss.

Ecological momentary assessment of food perceptions and eating behavior using a novel phone application in adults with or without obesity

We developed a smart phone application to measure participants' food-reward perceptions and eating behavior in their naturalistic environment. Intensity ratings (0 - not at all to 10 - very strongly) of perceived anticipation of food (wanting) and food enjoyment at endpoint of intake (liking) were recorded as they occurred over a period of 14 days. Moreover, food craving trait, implicit and explicit attitude towards healthy food, and body composition were assessed. 53 participants provided complete data. Participants were classified by percentage of body fat; 33 participants with lower body fat (L-group) and 20 with higher body fat (H-group; ≥25% body fat for males and ≥32% for females). L-group participants reported 6.34 (2.00) food wanting events per day, whereas H-group participants recorded significantly fewer food wanting events (5.07 (1.42)); both groups resisted about the same percentage of wanting events (L-group: 29.2 (15.5)%; H-group 27.3 (12.8)%). Perceived intensity ratings were significantly different within the L-group in the order liking (7.65 (0.81)) > un-resisted wanting (leading to eating) (7.00 (1.01)) > resisted wanting (not leading to eating) (6.02 (1.72)) but not in the H-group. Liking scores (L-group: 7.65 (0.81); H-group: 7.14 (1.04)) were significantly higher in L-group than in H-group after controlling for age. Our results show that individuals with higher percentage of body fat show less food enjoyment after intake and reveal no differentiation in intensity ratings of perceived anticipatory and consummatory food reward. These results are consistent with a hypothesized reward deficiency among individuals with higher percentage of body fat.

Environmental Obesogens: Mechanisms and Controversies

Obesity is a worldwide pandemic in adults as well as children and adds greatly to health care costs through its association with type 2 diabetes, metabolic syndrome, cardiovascular disease, and cancers. The prevailing medical view of obesity is that it results from a simple imbalance between caloric intake and energy expenditure. However, numerous other factors are important in the etiology of obesity. The obesogen hypothesis proposes that environmental chemicals termed obesogens promote obesity by acting to increase adipocyte commitment, differentiation, and size by altering metabolic set points or altering the hormonal regulation of appetite and satiety. Many obesogens are endocrine disrupting chemicals that interfere with normal endocrine regulation. Endocrine disrupting obesogens are abundant in our environment, used in everyday products from food packaging to fungicides. In this review, we explore the evidence supporting the obesogen hypothesis, as well as the gaps in our knowledge that are currently preventing a complete understanding of the extent to which obesogens contribute to the obesity pandemic.

Recent advances in understanding body weight homeostasis in humans

Presently, control of body weight is assumed to exist, but there is no consensus framework of body weight homeostasis. Three different models have been proposed, with a "set point" suggesting (i) a more or less tight and (ii) symmetric or asymmetric biological control of body weight resulting from feedback loops from peripheral organs and tissues (e.g. leptin secreted from adipose tissue) to a central control system within the hypothalamus. Alternatively, a "settling point" rather than a set point reflects metabolic adaptations to energy imbalance without any need for feedback control. Finally, the "dual intervention point" model combines both paradigms with two set points and a settling point between them. In humans, observational studies on large populations do not provide consistent evidence for a biological control of body weight, which, if it exists, may be overridden by the influences of the obesogenic environment and culture on personal behavior and experiences. To re-address the issue of body weight homeostasis, there is a need for targeted protocols based on sound concepts, e.g. lean rather than overweight subjects should be investigated before, during, and after weight loss and weight regain. In addition, improved methods and a multi-level-multi-systemic approach are needed to address the associations (i) between masses of individual body components and (ii) between masses and metabolic functions in the contexts of neurohumoral control and systemic effects. In the future, simplifications and the use of crude and non-biological phenotypes (i.e. body mass index and waist circumference) should be avoided. Since changes in body weight follow the mismatch between tightly controlled energy expenditure at loosely controlled energy intake, control (or even a set point) is more likely to be about energy expenditure rather than about body weight itself.

Maternal Overnutrition Programs Central Inflammation and Addiction-Like Behavior in Offspring

Obesity or maternal overnutrition during pregnancy and lactation might have long-term consequences in offspring health. Fetal programming is characterized by adaptive responses to specific environmental conditions during early life stages. Programming alters gene expression through epigenetic modifications leading to a transgenerational effect of behavioral phenotypes in the offspring. Maternal intake of hypercaloric diets during fetal development programs aberrant behaviors resembling addiction in offspring. Programming by hypercaloric surplus sets a gene expression pattern modulating axonal pruning, synaptic signaling, and synaptic plasticity in selective regions of the reward system. Likewise, fetal programming can promote an inflammatory phenotype in peripheral and central sites through different cell types such as microglia and T and B cells, which contribute to disrupted energy sensing and behavioral pathways. The molecular mechanism that regulates the central and peripheral immune cross-talk during fetal programming and its relevance on offspring's addictive behavior susceptibility is still unclear. Here, we review the most relevant scientific reports about the impact of hypercaloric nutritional fetal programming on central and peripheral inflammation and its effects on addictive behavior of the offspring.

Food for Thought: Reward Mechanisms and Hedonic Overeating in Obesity

PURPOSE OF REVIEW

This review examines the food addiction model and the role of food hedonic pathways in the pathogenesis and treatment of obesity.

RECENT FINDINGS

The hedonic pathway interacts with the obesogenic environment to override homeostatic mechanisms to cause increase in body weight. Weight gain sustained over time leads to "upward setting" of defended level of body-fat mass. There are neurobiological and phenotypic similarities and differences between hedonic pathways triggered by food compared with other addictive substances, and the entity of food addiction remains controversial. Treatment for obesity including pharmacotherapy and bariatric surgery impacts on neural pathways governing appetite and hedonic control of food intake. The food addiction model may also have significant impact on public health policy, regulation of certain foods, and weight stigma and bias. Recent rapid progress in delineation of food hedonic pathways advances our understanding of obesity and facilitates development of effective treatment measures against the disease.

Weight loss in the healthy elderly might be a non-cognitive sign of preclinical Alzheimer's disease

Weight loss has been proposed as a sign of pre-clinical Alzheimer Disease (AD). To test this hypothesis, we have evaluated the association between longitudinal changes in weight trajectories, cognitive performance, AD biomarker profiles and brain structure in 363 healthy controls from the Alzheimer´s Disease Neuroimaging Initiative (mean follow-up 50.5±30.5 months). Subjects were classified according to body weight trajectory into a weight loss group (WLG; relative weight loss ≥ 5%) and a non-weight loss group (non-WLG; relative weight loss < 5%). Linear mixed effects models were used to estimate the effect of body weight changes on ADAS-Cognitive score across time. Baseline CSF tau/AΔ₄₂ ratio and AV45 PET uptake were compared between WLG and non-WLG by analysis of covariance. Atrophy maps were compared between groups at baseline and longitudinally at a 2-year follow-up using Freesurfer. WLG showed increased baseline levels of cerebrospinal fluid tau/AΔ₄₂ ratio, increased PET amyloid uptake and diminished cortical thickness at baseline. WLG also showed faster cognitive decline and faster longitudinal atrophy. Our data support weight loss as a non-cognitive manifestation of pre-clinical AD.

Significant Locus and Metabolic Genetic Correlations Revealed in Genome-Wide Association Study of Anorexia Nervosa

OBJECTIVE

The authors conducted a genome-wide association study of anorexia nervosa and calculated genetic correlations with a series of psychiatric, educational, and metabolic phenotypes.

METHOD

Following uniform quality control and imputation procedures using the 1000 Genomes Project (phase 3) in 12 case-control cohorts comprising 3,495 anorexia nervosa cases and 10,982 controls, the authors performed standard association analysis followed by a meta-analysis across cohorts. Linkage disequilibrium score regression was used to calculate genome-wide common variant heritability (single-nucleotide polymorphism [SNP]-based heritability [h2SNP]), partitioned heritability, and genetic correlations (rg) between anorexia nervosa and 159 other phenotypes.

RESULTS

Results were obtained for 10,641,224 SNPs and insertion-deletion variants with minor allele frequencies >1% and imputation quality scores >0.6. The h2SNP of anorexia nervosa was 0.20 (SE=0.02), suggesting that a substantial fraction of the twin-based heritability arises from common genetic variation. The authors identified one genome-wide significant locus on chromosome 12 (rs4622308) in a region harboring a previously reported type 1 diabetes and autoimmune disorder locus. Significant positive genetic correlations were observed between anorexia nervosa and schizophrenia, neuroticism, educational attainment, and high-density lipoprotein cholesterol, and significant negative genetic correlations were observed between anorexia nervosa and body mass index, insulin, glucose, and lipid phenotypes.

CONCLUSIONS

Anorexia nervosa is a complex heritable phenotype for which this study has uncovered the first genome-wide significant locus. Anorexia nervosa also has large and significant genetic correlations with both psychiatric phenotypes and metabolic traits. The study results encourage a reconceptualization of this frequently lethal disorder as one with both psychiatric and metabolic etiology.

Reduced brain response to a sweet taste in Hispanic young adults

Hispanics have an increased risk for metabolic disorders, which evidence suggests may be due to interactions between lifespan biological, genetic, and lifestyle factors. Studies show the diet of many U.S. Hispanic groups have high sugar consumption, which has been shown to influence future preference for and consumption of high-sugar foods, and is associated with increased risk for insulin-related disorders and obesity. Taste is a primary determinant of food preference and selection. Differences in neural response to taste have been associated with obesity. Understanding brain response to sweet taste stimuli in healthy Hispanic adults is an important first step in characterizing the potential neural mechanisms for this behavior. We used fMRI to examine brain activation during the hedonic evaluation of sucrose as a function of ethnicity in Hispanic and non-Hispanic young adults. Taste stimuli were administered orally while subjects were scanned at 3T. Data were analyzed with AFNI via 3dROIstats and 3dMEMA, a mixed effects multi-level analysis of whole brain activation. The Hispanic group had significantly lower ROI activation in the left amygdala and significantly lower whole brain activation in regions critical for reward processing, and hedonic evaluation (e.g. frontal, orbitofrontal, and anterior cingulate cortices) than the non-Hispanic group. Differences in processing of sweet tastes have important clinical and public health implications, especially considering increased risk of metabolic syndrome and cognitive decline in Hispanic populations. Future research to better understanding relationships between health risk and brain function in Hispanic populations is warranted to better conceptualize and develop interventions for these populations.

Making sense of metabolic obesity and hedonic obesity

Body weight is neither stationary nor does it change unidirectionally. Rather, body weight usually oscillates up and down around a set point. Two types of forces determine the direction of weight changes. Forces that push body weight away from the set point are defined as non-homeostatic and are governed by multiple mechanisms, including, but not limited to, hedonic regulation of food intake. Forces that restore the set point weight are defined as homeostatic, and they operate through mechanisms that regulate short-term energy balance driven by hunger and satiation and long-term energy balance driven by changes in adiposity. In the normal physiological state, the deviation of body weight from the set point is usually small and temporary, and is constantly corrected by homeostatic forces. Metabolic obesity develops when body weight set point is shifted to an abnormally high level and the obese body weight becomes metabolically defended. In hedonic obesity, the obese body weight is maintained by consistent overeating due to impairments in the reward system, although the set point is not elevated. Adaptive increases in energy expenditure are elicited in hedonic obesity because body weight is elevated above the set point. Neither subtype of obesity undergoes spontaneous resolution unless the underlying disorders are corrected. In this review, the need for both appropriate patient stratification and tailored treatments is discussed in the context of the new framework of metabolic and hedonic obesity.

From the past to future: from energy expenditure to energy intake to energy expenditure

Although most recent research on energy balance focusses on energy intake (EI) there is still need to think about both sides of the energy balance. Current research on energy expenditure (EE) relates to metabolic adaptation to negative energy balance, mitochondrial metabolism associated with aging, obesity and type 2 diabetes mellitus, the role of EE in hunger and appetite control, non-shivering thermogenesis and brown adipose tissue activity, cellular bioenergetics as a target of obesity treatment and the evolutionary and ecological determinants of EE in humans and other primates. As far as regulation of energy balance is concerned there is recent evidence that EE rather than body weight is under tight control. Biologically, EE is maintained within a narrow physiological range. An EE-set point has been proposed as the width between the upper and lower boundaries of the individual EE range. Regulation of EE may fail in very obese patients with an EI above their upper boundary and after drastic weight loss when patients may go far below their lower EE boundary and thus are loosing control. In population studies, fat-free mass (FFM) and its composition (that is, the proportion of high to low metabolic rate organs) are major determinants of EE. It is tempting to speculate that tight biologic control of EE is related to brain energy need, which is preserved at the cost of peripheral metabolism. There is a moderate heritability of EE, which is independent of the heritability of FFM. In future, metabolic phenotyping should focus on the EE-FFM relationship rather than on EE-values alone.

Weight Perturbation Alters Leptin Signal Transduction in a Region-Specific Manner throughout the Brain

Diet-induced obesity (DIO) resulting from consumption of a high fat diet (HFD) attenuates normal neuronal responses to leptin and may contribute to the metabolic defense of an acquired higher body weight in humans; the molecular bases for the persistence of this defense are unknown. We measured the responses of 23 brain regions to exogenous leptin in 4 different groups of weight- and/or diet-perturbed mice. Responses to leptin were assessed by quantifying pSTAT3 levels in brain nuclei 30 minutes following 3 mg/kg intraperitoneal leptin. HFD attenuated leptin sensing throughout the brain, but weight loss did not restore central leptin signaling to control levels in several brain regions important in energy homeostasis, including the arcuate and dorsomedial hypothalamic nuclei. Effects of diet on leptin signaling varied by brain region, with results dependent on the method of weight loss (restriction of calories of HFD, ad lib intake of standard mouse chow). High fat diet attenuates leptin signaling throughout the brain, but some brain regions maintain their ability to sense leptin. Weight loss restores leptin sensing to some degree in most (but not all) brain regions, while other brain regions display hypersensitivity to leptin following weight loss. Normal leptin sensing was restored in several brain regions, with the pattern of restoration dependent on the method of weight loss.

The Role of Brain in Energy Balance

Energy homeostasis is regulated by homeostatic and nonhomeostatic reward circuits which are closely integrated and interrelated. Before, during, and after meals, peripheral nutritional signals, through hormonal and neuronal pathways, are conveyed to selective brain areas, namely the hypothalamic nuclei and the brainstem, the main brain areas for energy balance regulation. These orexigenic and anorexigenic centers are held responsible for the integration of those signals and for an adequate output to peripheral organs involved in metabolism and energy homeostasis.Feeding includes also a hedonic behavior defined as food intake for pleasure independently of energy requirement. This nonhomeostatic regulation of energy balance is based on food reward properties, unrelated to nutritional demands, and involves areas like mesolimbic reward system, such as the ventral tegmental area and the nucleus accumbens, and also opioid, endocannabinoid, and dopamine systems.Herein, focus will be put on the brain circuits of homeostatic and nonhomeostatic regulation of food intake and energy expenditure.

Homeostatic responses to palatable food consumption in satiated rats

OBJECTIVE

Energy intake is regulated by overlapping homeostatic and hedonic systems. Consumption of palatable foods has been implicated in weight gain, but this assumes that homeostatic control systems do not accurately detect this hedonically driven energy intake. This study tested this assumption, hypothesizing that satiated rats would reduce their voluntary food intake and maintain a stable body weight after consuming a palatable food.

METHODS

Lean rats or rats previously exposed to an obesogenic diet were schedule-fed with fixed or varying amounts of palatable sweetened condensed milk (SCM) daily, and their voluntary energy intake and body weight were monitored.

RESULTS

During scheduled feeding of SCM, rats voluntarily reduced bland food consumption and maintained a stable body weight. This behavior was also seen in rats with access to an obesogenic diet and was independent of the predictability of SCM access. However, lean rats offered large amounts of SCM showed an increase in total energy intake. To test whether a nutrient deficiency drove this under-compensatory behavior, SCM was enriched with protein. However, no effect was seen on voluntary energy intake.

CONCLUSIONS

In schedule-fed rats, compensatory reductions in voluntary energy intake were seen, but under-compensation was observed if large amounts of SCM were consumed.

Leptin Substitution in Patients With Lipodystrophy: Neural Correlates for Long-term Success in the Normalization of Eating Behavior

Lipodystrophy (LD) is a rare disease with a paucity of subcutaneous adipocytes and leptin deficiency. Patients often develop severe diabetes and, additionally, show a disturbed eating behavior with reduced satiety. The disturbed eating behavior can be restored by substitution with the leptin analog metreleptin. Long-term effects of metreleptin on resting state brain connectivity in treatment-naive patients with LD have not been assessed. In this study, resting state functional MRI scans and extensive behavioral testing assessing changes in hunger/satiety regulation were performed during the first 52 weeks of metreleptin treatment in nine patients with LD. Resting state connectivity significantly increased over the course of metreleptin treatment in three brain areas (i.e., hypothalamus, insula/superior temporal gyrus, medial prefrontal cortex). Behavioral tests demonstrated that perceived hunger, importance of eating, eating frequencies, and liking ratings of food pictures significantly decreased during metreleptin therapy. Taken together, leptin substitution was accompanied by long-term changes of hedonic and homeostatic central nervous networks regulating eating behavior as well as decreased hunger feelings and diminished incentive value of food. Future studies need to assess whether metreleptin treatment in LD restores physiological processes important for the development of satiety.

Precision Bariatrics: Toward a New Paradigm of Personalized Devices in Obesity Therapeutics

The prevalence and complexity of obesity and its associated metabolic complications highlight the importance of building a rigorous investigative framework for the development of novel weight loss therapies. Device-based interventions in particular constitute a market poised for rapid expansion in the coming years. Optimizing outcomes for this new class of therapies requires attention to an evolving taxonomy of subdivisions within the broader obesity phenotype and a means for stratifying patients toward maximally effective interventions. Extant bariatric devices implicitly prioritize anatomic variables as surrogates for physiology, a somewhat arbitrary assumption that merits empiric validation. Utilizing the governing principles of systems biology and recent innovations in clinical trial design, a robust and precise research infrastructure can and should be developed to more effectively mitigate this contemporary epidemic.

Requirements for multi-level systems pharmacology models to reach end-usage: the case of type 2 diabetes

We are currently in the middle of a major shift in biomedical research: unprecedented and rapidly growing amounts of data may be obtained today, from in vitro, in vivo and clinical studies, at molecular, physiological and clinical levels. To make use of these large-scale, multi-level datasets, corresponding multi-level mathematical models are needed, i.e. models that simultaneously capture multiple layers of the biological, physiological and disease-level organization (also referred to as quantitative systems pharmacology-QSP-models). However, today's multi-level models are not yet embedded in end-usage applications, neither in drug research and development nor in the clinic. Given the expectations and claims made historically, this seemingly slow adoption may seem surprising. Therefore, we herein consider a specific example-type 2 diabetes-and critically review the current status and identify key remaining steps for these models to become mainstream in the future. This overview reveals how, today, we may use models to ask scientific questions concerning, e.g., the cellular origin of insulin resistance, and how this translates to the whole-body level and short-term meal responses. However, before these multi-level models can become truly useful, they need to be linked with the capabilities of other important existing models, in order to make them 'personalized' (e.g. specific to certain patient phenotypes) and capable of describing long-term disease progression. To be useful in drug development, it is also critical that the developed models and their underlying data and assumptions are easily accessible. For clinical end-usage, in addition, model links to decision-support systems combined with the engagement of other disciplines are needed to create user-friendly and cost-efficient software packages.

FNDC5/irisin, a molecular target for boosting reward-related learning and motivation

Interventions focusing on the prevention and treatment of chronic non-communicable diseases are on rise. In the current article, we propose that dysfunction of the mesocortico-limbic reward system contributes to the emergence of the WHO-identified risk behaviors (tobacco use, unhealthy diet, physical inactivity and harmful use of alcohol), behaviors that underlie the evolution of major non-communicable diseases (e.g. cardiovascular diseases, cancer, diabetes and chronic respiratory diseases). Given that dopaminergic neurons of the mesocortico-limbic system are tightly associated with reward-related processes and motivation, their dysfunction may fundamentally influence behavior. While nicotine and alcohol alter dopamine neuron function by influencing some receptors, mesocortico-limbic system dysfunction was associated with elevation of metabolic set-point leading to hedonic over-eating. Although there is some empirical evidence, precise molecular mechanism for linking physical inactivity and mesocortico-limbic dysfunction per se seems to be missing; identification of which may contribute to higher success rates for interventions targeting lifestyle changes pertaining to physical activity. In the current article, we compile evidence in support of a link between exercise and the mesocortico-limbic system by elucidating interactions on the axis of muscle - irisin - brain derived neurotrophic factor (BDNF) - and dopaminergic function of the midbrain. Irisin is a contraction-regulated myokine formed primarily in skeletal muscle but also in the brain. Irisin stirred considerable interest, when its ability to induce browning of white adipose tissue parallel to increasing thermogenesis was discovered. Furthermore, it may also play a role in the regulation of behavior given it readily enters the central nervous system, where it induces BDNF expression in several brain areas linked to reward processing, e.g. the ventral tegmental area and the hippocampus. BDNF is a neurotropic factor that increases neuronal dopamine content, modulates dopamine release relevant for neuronal plasticity and increased neuronal survival as well as learning and memory. Further linking BDNF to dopaminergic function is BDNF's ability to activate tropomyosin-related kinase B receptor that shares signalization with presynaptic dopamine-3 receptors in the ventral tegmental area. Summarizing, we propose that the skeletal muscle derived irisin may be the link between physical activity and reward-related processes and motivation. Moreover alteration of this axis may contribute to sedentary lifestyle and subsequent non-communicable diseases. Preclinical and clinical experimental models to test this hypothesis are also proposed.