Integrative Hedonic and Homeostatic Food Intake Regulation by the Central Nervous System: Insights from Neuroimaging

Impact of ultra-processed foods on hedonic and homeostatic appetite regulation: A systematic review

The rapid rise in ultra-processed foods (UPF) consumption correlates with the growing global obesity prevalence. Investigating the hedonic and homeostatic mechanisms affected by UPF may provide insights for obesity prevention and appetite regulation. This systematic review aimed to examine the current understanding of the potential effects of UPF on appetite regulation and food intake, examining both hedonic and homeostatic pathways. A search was performed in PubMed, Scopus, Web of Science, and EMBASE databases, and studies published in English language were selected. Study selection and inclusion/exclusion criteria were determined based on PECOS framework. The quality of the studies was evaluated using appropriate Cochrane Risk of Bias tools and all articles were found to have low risk of bias. Of the 11 studies included, three were randomized controlled trials, one was cross-over study, one was non-randomized controlled study, and six were observational studies. Results indicated that UPF consumption may influence to hedonic appetite by promoting faster eating rates, enhancing palatability, activating brain reward circuits, and potentially increasing food addiction behaviors. Additionally, UPF intake may disrupt homeostatic appetite regulation by altering gut-brain axis signaling and modulating peripheral peptides such as ghrelin, GLP-1, GIP, and PYY. However, findings on both hedonic and homeostatic mechanisms remain inconclusive due to heterogeneous study designs, general characteristics of participants, and varying baseline UPF intake. These findings suggest that reducing UPF consumption could be a relevant target for appetite and weight management strategies, highlighting the need for more mechanistic and longitudinal research.

Accumbal serotonin hypofunction and dopamine hyperfunction due to chronic stress and palatable food intake in rats

ABSTRACTFeeding is regulated by energy homeostatic and pleasure-induced rewarding signals. Palatable food intake modifies serotonergic (5-HT) and dopaminergic (DA) pathways in nucleus accumbens, inducing neuronal maladaptations that favor hyperphagia for high-energy dense food and consequent obesity. Chronic stress is an environmental condition that increases the preference for palatable food by modulating brain DA and 5-HT metabolism. Objective: To evaluate the association between changes in accumbal 5-HT and DA metabolism and the effects of chronic stress, palatable food intake and their interaction with satiety/hunger condition. Methods: Wistar rats were housed in pairs (non-stressed) or individually (stressed), fed with chow or chocolate milk plus chow (Ch) for 2 weeks (4 groups); then 6 animals/group were 48 h fasted or maintained ad libitum; the rest were fasted and re-fed for 2 h either with chow or Ch. Results: Rats with prolonged high-energy density food intake and re-fed with chow showed reduced 5-HT metabolism, although there was no association with animals' feeding behavior. In contrast, after re-fed with palatable food, stressed chow-fed rats had increased 5-HT turnover, which decreased in Ch re-fed rats, supporting that palatable food might induce positive mood changes related to high extracellular 5-HT in limbic regions. Discussion: Rats with prolonged palatable food intake exhibited high accumbal DA turnover independently of stress exposure, supporting its relation with the development of high-energy dense food hyperphagia. As accumbal 5-HT and DA metabolism changed due to fasting or re-feeding, alterations could represent the interaction of energy homeostatic and hedonic feeding signaling in animals.

Examining the biological causes of eating disorders to inform treatment strategies

Despite their prevalence, eating disorders (EDs) are under-researched and often misunderstood. A recent focus of research on the biological underpinnings of EDs has helped to reframe our understanding of their origins, but there remain a lack of effective treatment options, high rates of relapse and, unfortunately, high mortality and morbidity. In this Review, we highlight the many facets of normal and pathological feeding behaviour and body weight regulation and suggest that these provide a framework with which to develop integrative methods to study, and ultimately treat, EDs. We propose that a better understanding of the biological causes of ED, and their crucial interactions with psychological and environmental factors, is necessary to progress the field. This can be achieved through a combination of preclinical and clinical investigations, which provide complementary information on these highly complex disorders. In the era of individualized medicine and with the advent of artificial intelligence tools that allow the amalgamation of multimodal data, we hope that a better understanding of the biology of EDs may hold the answer to effectively overcoming the debilitating effects of these conditions.

Association between brain resting-state functional activities and obesity: A bidirectional Mendelian randomization study

BACKGROUND

Investigations revealed significant changes in brain activity between people with obesity or overweight and people with normal weight. The causal relationship between body weight and brain functional activity remains unclear and warrants further investigation.

METHODS

We conducted a bidirectional two-sample Mendelian randomization (MR) study. We gathered summary statistics from genome-wide association studies for 191 resting-state functional magnetic resonance imaging phenotypes and obesity traits (body mass index, body fat percentage, waist-to-hip ratio). Inverse variance weighting, the weighted median, MR Egger, and the weighted mode were employed. We conducted pleiotropy and heterogeneity analyses to evaluate robustness and reliability.

RESULTS

Forward analysis revealed that the intensity of spontaneous brain activity in the calcarine, lingual, or cuneus gyri within the visual network (beta = -0.076; 95 % CI: -0.11 to -0.04; p = 6.97 × 10-5) had a causal effect on body weight. The reverse analysis revealed that body weight has a causal effect on the intensity of spontaneous brain activity in the precuneus, angular, and cingulate gyri (beta = 0.209; 95 % CI: 0.11 to 0.31; p = 2.41 × 10-5), and the angular and temporal gyri (beta = 0.215; 95 % CI: 0.11 to 0.32; p = 3.87 × 10-5) within the default mode and central executive network.

CONCLUSIONS

Genetic evidence proves a causal relationship between body weight and brain functional activity.

Neurovascular decoupling of frontoparietal cortex-putamen-cerebellum network in type 2 diabetes patient: Potential biomarker for abnormal eating patterns

AIM

High rates of dropout and binge eating triggered by restrictive diet limit the effectiveness of dietary interventions in type 2 diabetes mellitus (T2DM). However, it remains unclear what the potential central underpinnings of T2DM-specific dietary behavior characteristics are.

METHODS

41 T2DM patients and 43 matched healthy controls (HC) who underwent resting state functional MRI were enrolled to screen for the suspicious network by effective connectivity (EC) analysis and to explore its dynamic temporal and neurovascular coupling properties. Additionally, the timeline of neuropathological changes during T2DM progression was evaluated.

RESULTS

Increased uncontrolled eating, internal and external loci of hunger were found in T2DM. EC of the frontoparietal cortex-putamen-cerebellum network was significantly higher in T2DM patients (P = 0.023). The fractional windows (P = 0.009) and mean dwell time (P = 0.009) of the densest state were significantly higher in T2DM patients. Neurovascular decoupling of the frontoparietal cortex-putamen-cerebellum network was correlated with these T2DM-specific eating behavior characteristics. Neurovascular decoupling coefficient of right putamen (Putamen_R) changed at the very beginning of T2DM.

CONCLUSION

The frontoparietal cortex-putamen-cerebellum network was the suspicious T2DM-related abnormal eating pattern network. Neurovascular decoupling of the network, especially that of Putamen_R, occurred early and might serve as a biomarker for abnormal eating patterns in T2DM patients.

Smoking, Obesity, and Post-Cessation Weight Gain: Neurobiological Intersection and Treatment Recommendations

In the US, 28.8 million adults currently smoke cigarettes, and approximately 1.25 billion people use tobacco globally. Unfortunately, post-cessation weight gain is a substantial barrier to smoking cessation and sustained abstinence. Among people who smoke, 36% meet the body mass index (BMI) criteria for obesity and over 50% meet the waist circumference criteria for central obesity. Despite this, primary care providers currently have limited guidance on how to best treat their patients who want to quit smoking without post-cessation weight gain. There are common neurobiologic and endocrine dysregulations in nicotine dependence and weight gain. For example, nicotine dependence and obesity are both associated with dysregulation in hypothalamic neuropeptide systems and dopaminergic pathways. Medications for nicotine dependence act on dopaminergic pathways and hypothalamic pro-opiomelanocortin (POMC) cells. Similarly, medications for obesity may increase dopamine and norepinephrine signaling and stimulate POMC activity. A unique medication, the fixed-dose extended-release combination of naltrexone and bupropion, supports both smoking cessation and weight loss by increasing dopamine and norepinephrine signaling and stimulating POMC-producing cells. This narrative review outlines neurobiologic mechanisms common to smoking and obesity and compares the effects of available pharmacotherapies on dopaminergic system and neuroendocrine dysregulation. Finally, this review outlines factors that primary care professionals should consider when treating people who want to stop smoking but are at risk of post-cessation weight gain.

Early overfeeding and adult anhedonia: Impact of neonatal nutrition on hedonic food regulation in male rats

The aim of our study was to analyze the impact of early-life overnutrition and the exposure in adulthood to a cafeteria diet (CAF) on eating behavior and on the expression of key genes involved in the regulation of food intake. Male Wistar rats were raised in small (SL, 4 pups/dam) or normal litters (NL, 10 pups/dam), fed a control diet (CON) until postnatal day (PND) 90. Then, they received CON or CAF for 11 weeks (NL-CON, NL-CAF, SL-CON, SL-CAF; 12±2 rats/group). Body weight, food intake and behavioral tests (Elevated Plus Maze: EPM, Sensory-specific satiety: SSS) were assessed. At PND167, the rats were euthanized to obtain brain, blood and fat pads. Ventral tegmental area (VTA), Nucleus Accumbens (NAc) and Arcuate Nucleus (Arc), were isolated by micropunch technique for qPCR analysis. Early overfeeding alone had the ability to alter long-term SSS. CAF groups showed increased body weight, adiposity and energy intake; sweet food preference and altered SSS. SL-CAF showed hypophagia, basal hyperglycemia, altered SSS and anxiety-like behavior. Both NL-CAF and SL-CAF showed antidopaminergic effects, but through different pathways: NL-CAF reduced dopamine (DA) production in VTA via decreased tyrosine hydroxylase (TH) expression, while SL-CAF exhibited an increase in dopamine active transporter (DAT) expression in NAc enhancing clearance. SL decreased Neuropeptide Y (NPY) expression in the Arc in adulthood, which has been proposed to be the link between homeostatic and hedonic systems. Our research reveals a key link between early-life overnutrition and adult hedonic feeding control, emphasizing its lasting impact on eating behavior and the potential for innovative therapeutics to combat obesity.

Comfort Foods in the Twenty-First Century: Friend or Foe?

The comfort food (CF) concept emerged during the latter half of the twentieth century. Although not well defined, CF can be described as familiar foods that elicit feelings of well-being and play a role in social interactions and psychological health. These foods are often calorically dense and nutrient-poor, and overconsumption of some CF may contribute to negative metabolic health outcomes. This is particularly relevant when considering the global increase in obesity, leading to the development of therapeutics for improved weight control and metabolic health. In this review, we aim to (a) provide a historical perspective of the CF concept, (b) detail some genetic, developmental, and cultural factors that determine food preference, (c) discuss the influence of diet on the gut-brain connection, hormones, nutrient absorption, and microbiome diversity, and (d) provide a perspective detailing possible future directions in which food technology may enable a new generation of CF with enhanced palatability and nutrient profiles while contributing to well-being and environmental sustainability.

Treating obesity in patients with depression: a narrative review and treatment recommendation

The high morbidity of obesity and depression pose significant public health concerns, with the prevalence of obesity doubling in the US between 1990 and 2022 and patients frequently presenting with both. Untreated obesity and depression can greatly impact patient health and well-being, as both obesity and depression are associated with a number of comorbidities including sleep apnea, type 2 diabetes mellitus, metabolic syndrome, metabolic dysfunction-associated steatotic liver disease, and cardiovascular disease. This narrative review aims to provide a comprehensive and current overview of the overlapping etiologies between obesity and depression as well as the available treatment options that may be recommended by primary care professionals to treat these patients with concomitant obesity and depression. With the considerable overlap in the population of patients with obesity and depression, as well as the overlap in the neurobiological, hormonal, and inflammatory pathways underlying both diseases, primary care professionals should consider screening patients presenting with obesity for depression. Holistic treatment options, including lifestyle and behavioral modifications, and pharmacotherapy for both depression and obesity and bariatric surgery for obesity are critical to manage both conditions simultaneously. Therefore, due to the overlapping neurobiological pathways and mechanisms responsible for the incidence and progression of both obesity and depression, a holistic treatment plan including strategies with efficacy for both conditions and any additional comorbidities may improve the clinical approach for patients with concomitant obesity and depression.

Novel model of childhood appetitive traits in children with obesity

BACKGROUND/OBJECTIVES

Appetitive traits have a central role in energy intake and development of obesity. Child Eating Behavior Questionnaire (CEBQ) is a validated psychometric tool to measure appetitive traits in children. This study sought to assess the CEBQ factor structure in children with obesity. We hypothesized that hedonic traits are more prominent with obesity and in older children.

SUBJECTS/METHODS

This cross-sectional observational study used CEBQ data from three geographically diverse centers in children with obesity. Eight known CEBQ subscales and the established factor model were compared by severity of obesity, age and sex. Exploratory factor analysis (EFA) to define the appetitive trait factor structure was undertaken in a training dataset and validated in a test set.

RESULTS

Children with obesity (n = 814) showed higher food response, enjoyment of food, emotional overeating and desire to drink compared to population-based controls (p < 0.001) that correlated with obesity severity. The EFA identified a novel six-factor model with a new "Food avidity" factor that explained 15.8% of the variance. Satiety responsiveness (p < 0.001) and emotional undereating (p = 0.03) were lower in youth over 6 years compared to younger, while food fussiness and food avidity were the same, without any sex differences.

CONCLUSIONS

CEBQ is useful to assess appetitive traits in children with obesity. The novel factor structure in youth with obesity suggests that temporal or phenotypic differences necessitate a revision of the established factor model. The new factor structure may be used to develop a hyperphagia questionnaire.

Precision medicine for obesity: current evidence and insights for personalization of obesity pharmacotherapy

Obesity is a chronic and complex disease associated with increased morbidity, mortality, and financial burden. It is expected that by 2030 one of two people in the United States will have obesity. The backbone for obesity management continues to be lifestyle interventions, consisting of calorie deficit diets and increased physical activity levels, however, these interventions are often insufficient to achieve sufficient and maintained weight loss. As a result, multiple patients require additional interventions such as antiobesity medications or bariatric interventions in order to achieve clinically significant weight loss and improvement or resolution of obesity-associated comorbidities. Despite the recent advances in the field of obesity pharmacotherapy that have resulted in never-before-seen weight loss outcomes, comorbidity improvement, and even reduction in cardiovascular mortality, there is still a significant interindividual variability in terms of response to antiobesity medications, with a subset of patients not achieving a clinically significant weight loss. Currently, the trial-and-error paradigm for the selection of antiobesity medications results in increased costs and risks for developing side effects, while also reduces engagement in weight management programs for patients with obesity. The implementation of a precision medicine framework to the selection of antiobesity medications might help reduce heterogeneity and optimize weight loss outcomes by identifying unique subsets of patients, or phenotypes, that have a better response to a specific intervention. The detailed study of energy balance regulation holds promise, as actionable behavioral and physiologic traits could help guide antiobesity medication selection based on previous mechanistic studies. Moreover, the rapid advances in genotyping, multi-omics, and big data analysis might hold the key to discover additional signatures or phenotypes that might respond better to a certain intervention and might permit the widespread adoption of a precision medicine approach for obesity management.

Moderate-to-vigorous and light-intensity aerobic exercise yield similar effects on food reward, appetitive responses, and energy intake in physically inactive adults

OBJECTIVE

To examine the effect of acute aerobic exercise at moderate-to-vigorous and light intensity on food reward, appetite sensation, and energy intake (EI) in physically inactive adults.

METHODS

Twenty inactive, healthy adults (mean age: 21 ± 3 years) completed two trials (i.e. moderate-to-vigorous and light-intensity exercise) in a randomised, crossover design. Participants performed a 40-min cycling bout at either 50% or 20% peak power output in a counterbalanced order. Before and after exercise bouts, liking and wanting for fat and sweet/savoury categories of food were assessed by the Leeds Food Preference Questionnaire, along with subjective ratings of appetite and state food cravings. EI was evaluated by ad libitum meals following exercise bouts.

RESULTS

Results showed increased implicit wanting for high-fat relative to low-fat foods (p = .04, drm = 0.50) and savoury relative to sweet foods following exercise bouts (p = .04, drm = -0.49) without intensity-specific effects. Exercise bouts also led to increased subjective appetite (p < 0.001, η2p = 0.60) and state food cravings (p = 0.001, η2p = 0.44) without intensity-specific differences. There was no difference between exercise intensities on absolute EI, whereas relative EI was lower after moderate-to-vigorous exercise relative to light exercise (p < 0.001, drm = -1.56).

CONCLUSION

Acute aerobic exercise, regardless of intensity, may lead to increased wanting for high-fat relative to low-fat and savoury relative to sweet-tasting foods, as well as enhanced appetite sensation and food cravings in physically inactive adults. Moderate-to-vigorous exercise does not induce additional energy intake relative to light exercise.

Neural mechanisms and health implications of food cravings during pregnancy

Food cravings, an intense desire to consume specific foods, are a complex interplay of cognitive, emotional, behavioral, physiological, and cultural factors. Although prevalent across genders, food cravings are more frequent and intense in women, with hormonal fluctuations-particularly during the menstrual cycle and pregnancy-playing a significant role. Pregnancy, marked by profound hormonal and physiological shifts, often heightens cravings, likely as a response to the increased metabolic needs of both mother and fetus. However, the tendency to crave high-calorie, palatable foods during this time can lead to excessive weight gain, presenting potential risks to both maternal and fetal health. This chapter examines the neural mechanisms underlying altered eating behaviors during pregnancy and their role in triggering food cravings. We discuss the health implications of disrupted eating patterns in pregnancy, emphasizing the need for further research to advance understanding of female-specific neurobiology and to develop targeted interventions that support healthy eating behaviors, ultimately improving maternal and offspring health outcomes.

Investigating the impact of microbiome-changing interventions on food decision-making: MIFOOD study protocol

BACKGROUND

Obesity is a multifactorial disease reaching pandemic proportions with increasing healthcare costs, advocating the development of better prevention and treatment strategies. Previous research indicates that the gut microbiome plays an important role in metabolic, hormonal, and neuronal cross-talk underlying eating behavior. We therefore aim to examine the effects of prebiotic and neurocognitive behavioral interventions on food decision-making and to assay the underlying mechanisms in a Randomized Controlled Trial (RCT).

METHOD

This study uses a parallel arm RCT design with a 26-week intervention period. We plan to enroll 90 participants (male/diverse/female) living with overweight or obesity, defined as either a Waist-to-Hip Ratio (WHR) ≥ 0.9 (male)/0.85 (diverse, female) or a Body Mass Index (BMI) ≥ 25 kg/m2. Key inclusion criteria are 18-60 years of age and exclusion criteria are type 2 diabetes, psychiatric disease, and Magnetic Resonance Imaging (MRI) contraindications. The interventions comprise either a daily supplementary intake of 30 g soluble fiber (inulin), or weekly neurocognitive behavioral group sessions, compared to placebo (equicaloric maltodextrin). At baseline and follow-up, food decision-making is assessed utilizing task-based MRI. Secondary outcome measures include structural MRI, eating habits, lifestyle factors, personality traits, and mood. Further, we obtain fecal and blood samples to investigate gut microbiome composition and related metabolites.

DISCUSSION

This study relies on expanding research suggesting that dietary prebiotics could improve gut microbiome composition, leading to beneficial effects on gut-brain signaling and higher-order cognitive functions. In parallel, neurocognitive behavioral interventions have been proposed to improve unhealthy eating habits and metabolic status. However, causal evidence on how these "bottom-up" and "top-down" processes affect food decision-making and neuronal correlates in humans is still scarce. In addition, microbiome, and gut-brain-axis-related mediating mechanisms remain unclear. The present study proposes a comprehensive approach to assess the effects of these gut-brain-related processes influencing food decision-making in overweight and obesity.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05353504. Retrospectively registered on 29 April 2022.

Bioactive compounds regulate appetite through the melanocortin system: a review

Obesity, a significant health crisis, arises from an imbalance between energy intake and expenditure. Enhancing appetite regulation has garnered substantial attention from researchers as a novel and effective strategy for weight management. The melanocortin system, situated in the hypothalamus, is recognized as a critical node in the regulation of appetite. It integrates long-term and short-term hormone signals from the periphery as well as nutrients, forming a complex network of interacting feedback mechanisms with the gut-brain axis, significantly contributing to the regulation of energy homeostasis. Appetite regulation by bioactive compounds has been a focus of intensive research due to their favorable safety profiles and easy accessibility. These bioactive compounds, derived from a variety of plant and animal sources, modulate the melanocortin system and influence appetite and energy homeostasis through multiple pathways: central nervous system, peripheral hormones, and intestinal microbiota. Here, we review the anatomy, function, and receptors of the melanocortin system, outline the long-term and short-term regulatory hormones that act on the melanocortin system, and discuss the bioactive compounds and their mechanisms of action that exert a regulatory effect on appetite by targeting the melanocortin system. This review contributes to a better understanding of how bioactive compounds regulate appetite via the melanocortin system, thereby providing nutritional references for citizens' dietary preferences.

Amelioration impact of gut-brain communication on obesity control by regulating gut microbiota composition through the ingestion of animal-plant-derived peptides and dietary fiber: can food reward effect as a hidden regulator?

Various roles of intestinal flora in the gut-brain axis response pathway have received enormous attention because of their unique position in intestinal flora-derived metabolites regulating hormones, inducing appetite, and modulating energy metabolism. Reward pathways in the brain play a crucial role in gut-brain communications, but the mechanisms have not been methodically understood. This review outlined the mechanisms by which leptin, ghrelin, and insulin are influenced by intestinal flora-derived metabolites to regulate appetite and body weight, focused on the significance of the paraventricular nucleus and ventromedial prefrontal cortex in food reward. The vagus nerve and mitochondria are essential pathways of the intestinal flora involved in the modulation of neurotransmitters, neural signaling, and neurotransmission in gut-brain communications. The dynamic response to nutrient intake and changes in the characteristics of feeding activity requires the participation of the vagus nerve to transmit messages to be completed. SCFAs, Bas, BCAAs, and induced hormones mediate the sensory information and reward signaling of the host in the complex regulatory mechanism of food selection, and the composition of the intestinal flora significantly impacts this process. Food reward in the process of obesity based on gut-brain communications expands new ideas for the prevention and treatment of obesity.

Impact of excessive sucrose intake on mouse behavior across different developmental stages

This study aimed to elucidate the effects of sucrose (SUC) consumption on neurodevelopmental processes through behavioral changes in rodents and determine whether these effects could be because of sweet taste, energy supply, or both. Mice were divided into five groups based on the time of SUC or sucralose (SUR, a noncaloric sweetener) administration: for 6 days from gestation day (GTD) 7, to birth from GTD13 and for 15 days from postnatal day (PND) 21, PND38, and PND56. SUC and SUR administration did not impact body weight. However, food intake in the PND56 group and water intake in the GTD13 and PND56 groups were increased by SUC and SUR administration. Amphetamine (0.5, 1, 2, and 3 mg/kg), a dopamine reuptake inhibitor, administration to assess alterations in the dopaminergic system induced increases in distance traveled after SUC administration in the GTD13 and PND21 groups compared with that in the control (vehicle administration) group. In contrast, the SUR group showed a decrease in the distance traveled in the PND56 group. Although there were no differences in locomotor activity and foraging behavior, SUC preference increased in the SUC group regarding the GTD13 and PND38 groups. The correlations between SUC preference and foraging behavior and between SUC preference and amphetamine response varied in both groups according to the developmental stage. Excessive SUC consumption might affect neural function at different developmental stages, as it could affect brain function through complex mechanisms involving sweet taste and energy supply and influence the dopaminergic system.

The gut-brain axis in appetite, satiety, food intake, and eating behavior: Insights from animal models and human studies

The gut-brain axis plays a pivotal role in the finely tuned orchestration of food intake, where both homeostatic and hedonic processes collaboratively control our dietary decisions. This interplay involves the transmission of mechanical and chemical signals from the gastrointestinal tract to the appetite centers in the brain, conveying information on meal arrival, quantity, and chemical composition. These signals are processed in the brain eventually leading to the sensation of satiety and the termination of a meal. However, the regulation of food intake and appetite extends beyond the realms of pure physiological need. Hedonic mechanisms, including sensory perception (i.e., through sight, smell, and taste), habitual behaviors, and psychological factors, exert profound influences on food intake. Drawing from studies in animal models and human research, this comprehensive review summarizes the physiological mechanisms that underlie the gut-brain axis and its interplay with the reward network in the regulation of appetite and satiety. The recent advancements in neuroimaging techniques, with a focus on human studies that enable investigation of the neural mechanisms underpinning appetite regulation are discussed. Furthermore, this review explores therapeutic/pharmacological strategies that hold the potential for controlling food intake.

Tackling Cravings in Medical Weight Management: An Update on Pathophysiology and an Integrated Approach to Treatment

Background/Objectives: Food cravings involve a strong drive to consume palatable foods irrespective of nutritional status. Importantly, cravings contribute substantially to the obesity epidemic. Managing hunger alone is insufficient for weight management as this relates only to homeostatic eating and does not address the complex aetiology of hedonic eating and its crucial role in food cravings. Medical weight management clinics and anti-obesity medication trials do not routinely identify and address food cravings. Methods: We conducted a narrative review of the literature consisting of 115 peer-reviewed articles (original articles and reviews). We included articles focused on food craving pathophysiology, assessment, and management strategies providing contrasts against the current medical model of weight management seen in obesity pharmacotherapy trials as well as the current standard of practise. Results: We outline the neurohormonal and psychological drivers of cravings, which lead to a spectrum of eating behaviours, from comfort food eating to binge eating disorders. We provide an overview of ways of identification and measurement options, including their strengths and weaknesses, and an overview of management strategies and their cravings control efficacy, spanning lifestyle modifications like nutrition and sleep, psychological therapies (i.e., cognitive behavioural therapy [CBT], acceptance-based therapies such as mindfulness) and, last but not least, medications that not only are approved for weight reduction but reduce cravings. Finally, based on these findings, we provide a proposed integrated and iterative model that is able to evolve and adapt to the individual over time in tackling cravings for long-term weight loss maintenance. Conclusions: The findings emphasise the importance of cravings management and provide a synthesis on how cravings can be identified in a medical weight management setting, which can be practically implemented in an integrated iterative model spanning anti-obesity medications that have craving control data to evidence-based lifestyle and psychological interventions.

Reward for fat and sweet dimensions of food are altered by an acute bout of running in healthy young men

Acute moderate- to high-intensity exercise, primarily aerobic exercise, has been reported to decrease food reward in brain regions via the hedonic pathways and reduce preference for high-energy or high-fat foods. However, studies examining food reward responses to acute exercise have been limited to measuring food reward only after exercise and less frequently before and after exercise. Therefore, the changes in food reward in response to acute exercise remain unclear. This study investigated the effect of acute running on food reward in healthy young men. Fourteen young healthy men (mean ± standard deviation, age; 23 ± 2 years, body mass index; 21 ± 2 kg/m2) completed two trials (i.e., exercise and control) in a randomised, crossover design. Participants performed a 30-min running bout at 70% of maximal oxygen uptake or sitting rest before and after food reward evaluation with a computer-based food choice behaviour task tool. Food reward was assessed for foods varying in fat content and sweet taste, and there were four assessment parameters: explicit liking, explicit wanting, implicit wanting and frequency of choice of each food category (relative preference). Explicit and implicit wanting, and relative preference for high-fat relative to low-fat foods were reduced after the exercise trial compared to the control trial (trial-by-time interaction, all p ≤ 0.02). Implicit wanting and relative preference for sweet relative to savoury foods were increased after the exercise trial compared to the control trial (trial-by-time interaction, all p ≤ 0.003). These findings indicate that moderate-intensity acute running alters the reward bias away from high fat towards low fat foods and away from savoury towards sweet foods in healthy young men.

Association between hedonic hunger and body mass index in adults: A systematic review and meta-analysis

Hedonic hunger has been proposed as one of the important causes of obesity in recent years. In the present study, we systematically reviewed and meta-analyzed the relationship between hedonic hunger and body mass index (BMI) in healthy adults. PubMed, Web of Science, and Scopus were searched until January 19, 2023. All English-language original observational studies conducted on healthy adult subjects, which used the Power of Food Scale (PFS) to evaluate hedonic hunger were included. Quality assessment was done using the Joanna Briggs Institute checklist, and StataMP-17 software was used for the meta-analysis. After screening, 25 observational studies with a total of 14457 participants were included. Twenty-four studies were cross-sectional, and one was a cohort study. Twenty-two studies examined both sexes, two studies were conducted only on women, and one study conducted analysis separately on men and women. The results of the meta-analysis showed a positive and significant association between hedonic hunger and BMI with a small effect size (r = 0.13, 95% CI: 0.08, 0.18). In addition, a positive significant association was observed between subscales of PFS ("food available", "food present", and "food tasted") and BMI. The association between hedonic hunger and BMI was not affected by the results of meta-regression analysis of %female, mean age & BMI, and sample size. In conclusion, there was a positive significant association between hedonic hunger and BMI, but the effect size was weak. Considering the low quality of included studies, we need longitudinal design studies considering the association between these two variables as a primary outcome for a more accurate conclusion.

Post-COVID-19 Changes in Appetite-An Exploratory Study

In this analysis, we aimed to investigate the effect of COVID-19 disease on eating behavior. A total of 55 right-handed adults, <50 years of age, without overweight or obesity, from two cross-sectional studies were included. The first one enrolled subjects between September 2018 and December 2019 (non-COVID-19 group). The second one included subjects enrolled between March 2022 and May 2023; for this analysis, 28 with a history of COVID-19 (COVID-19 group) were retained. Hunger, TFEQ-18, plasma ghrelin, neuropeptide Y (NPY) and resting-state fMRI were assessed during fasting. Intraregional neuronal synchronicity and connectivity were assessed by voxel-based regional homogeneity (ReHo) and degree of centrality (DC). Significantly higher ghrelin and NPY levels were observed in the COVID-19 group than in the non-COVID-19 group (ghrelin 197.5 pg/mL vs. 67.1 pg/mL, p < 0.001; NPY 128.0 pg/mL vs. 84.5 pg/mL, p = 0.005). The NPY levels positively correlated with the DC and ReHo in the left lingual (r = 0.67785 and r = 0.73604, respectively). Similar scores were noted for cognitive restraint, uncontrolled eating and emotional eating in both groups according to the TFEQ-18 questionnaire results (p > 0.05 for all). Our data showed increased levels of appetite-related hormones, correlated with activity in brain regions involved in appetite regulation, persisting long after COVID-19 infection.

Food addiction and the physical and mental health status of adults with overweight and obesity

Background

Overweight and obesity now affect more than a third of the world's population. They are strongly associated with somatic diseases, in particular increasing the risk of many metabolic and cardiovascular diseases, but also with mental disorders. In particular, there is a strong association between obesity and depression. As a result, more attention is paid to the neurobiological, behavioural, and psychological mechanisms involved in eating. One of these is food addiction (FA). Research comparing lifestyle elements, physical and mental health problems of excess body weight and individuals with FA is limited and has focused on younger people, mainly students. There is also a lack of studies that relate actual metabolic parameters to FA. To better understand the problem of FA also in older adults, it is important to understand the specific relationships between these variables.

Methods

A cross-sectional survey was conducted with 172 adults with overweight and obesity (82% female) aged 23-85 years. The mean age of all subjects was M = 59.97 years (SD = 11.93), the mean BMI was M = 32.05 kg/m2 (SD = 4.84), and the mean body fat was M = 39.12% (SD = 6.48). The following questionnaires were used: Food Frequency Questionnaire-6 (FFQ-6), Global Physical Activity Questionnaire (GPAQ), Three Factor Eating Questionnaire-R18 (TFEQ-R18), Yale Food Addiction Scale 2. 0 (YFAS 2.0), Zung Self-Rating Depression Scale (SDS). Body composition, anthropometry, fasting glucose, lipid profile, and blood pressure were measured.

Results

A total of 22.7% of participants with overweight and obesity had symptoms of depression according to the SDS, and 18.6% met the criteria for FA according to YFAS 2.0. FA was statistically significantly more common among people up to 50 years. BMI, body fat mass, diastolic blood pressure and sedentary behaviour were statistically significantly higher in people with FA symptoms. Those who were sedentary for 301-450 min per day were significantly more likely to have depressive symptoms, and those who were sedentary for more than 450 min per day were significantly more likely to have FA symptoms.

Conclusions

Our findings complement the current literature on FA, particularly in older adults and metabolic parameters, and suggest further research directions. Although our cross-sectional study design does not allow causal interpretations, increasing physical activity appears to be particularly important in the management of people with overweight or obesity and FA. This may be even more important than for people with depression alone, but future research is needed to explore these relationships further.

Exploring the Potential Impact of GLP-1 Receptor Agonists on Substance Use, Compulsive Behavior, and Libido: Insights from Social Media Using a Mixed-Methods Approach

Glucagon-like peptide-1 (GLP-1) is involved in a range of central and peripheral pathways related to appetitive behavior. Hence, this study explored the effects of glucagon-like peptide-1 receptor agonists (GLP-1 RAs) on substance and behavioral addictions, including alcohol, caffeine, nicotine, cannabis, psychostimulants, compulsive shopping, and sex drive/libido. Data were collected from various social platforms. Keywords related to GLP-1 RAs and substance/behavioral addiction were used to extract relevant comments. The study employed a mixed-methods approach to analyze online discussions posted from December 2019 to June 2023 and collected using a specialized web application. Reddit entries were the focus here due to limited data from other platforms, such as TikTok and YouTube. A total of 5859 threads and related comments were extracted from six subreddits, which included threads about GLP-1 RAs drugs and associated brand names. To obtain relevant posts, keywords related to potential substance use and compulsive behavior were selected. Further analysis involved two main steps: (1) manually coding posts based on users' references to the potential impact of GLP-1 RAs on substance use and non-substance habits, excluding irrelevant or unclear comments; (2) performing a thematic analysis on the dataset of keywords, using AI-assisted techniques followed by the manual revision of the generated themes. Second, a thematic analysis was performed on the keyword-related dataset, using AI-assisted techniques followed by the manual revision of the generated themes. In total, 29.75% of alcohol-related; 22.22% of caffeine-related; and 23.08% of nicotine-related comments clearly stated a cessation of the intake of these substances following the start of GLP-1 RAs prescription. Conversely, mixed results were found for cannabis intake, and only limited, anecdotal data were made available for cocaine, entactogens, and dissociative drugs' misuse. Regarding behavioral addictions, 21.35% of comments reported a compulsive shopping interruption, whilst the sexual drive/libido elements reportedly increased in several users. The current mixed-methods approach appeared to be a useful tool in gaining insight into complex topics such as the effects of GLP-1 RAs on substance and non-substance addiction-related disorders; some GLP-1 RA-related mental health benefits could also be inferred from here. Overall, it appeared that GLP-1 RAs may show the potential to target both substance craving and maladaptive/addictive behaviors, although further empirical research is needed.

Could Insulin Be a Better Regulator of Appetite/Satiety Balance and Body Weight Maintenance in Response to Glucose Exposure Compared to Sucrose Substitutes? Unraveling Current Knowledge and Searching for More Appropriate Choices

BACKGROUND

Insulin exerts a crucial impact on glucose control, cellular growing, function, and metabolism. It is partially modulated by nutrients, especially as a response to the intake of foods, including carbohydrates. Moreover, insulin can exert an anorexigenic effect when inserted into the hypothalamus of the brain, in which a complex network of an appetite/hunger control system occurs. The current literature review aims at thoroughly summarizing and scrutinizing whether insulin release in response to glucose exposure may be a better choice to control body weight gain and related diseases compared to the use of sucrose substitutes (SSs) in combination with a long-term, well-balanced diet.

METHODS

This is a comprehensive literature review, which was performed through searching in-depth for the most accurate scientific databases and applying effective and relevant keywords.

RESULTS

The insulin action can be inserted into the hypothalamic orexigenic/anorexigenic complex system, activating several anorexigenic peptides, increasing the hedonic aspect of food intake, and effectively controlling the human body weight. In contrast, SSs appear not to affect the orexigenic/anorexigenic complex system, resulting in more cases of uncontrolled body weight maintenance while also increasing the risk of developing related diseases.

CONCLUSIONS

Most evidence, mainly derived from in vitro and in vivo animal studies, has reinforced the insulin anorexigenic action in the hypothalamus of the brain. Simultaneously, most available clinical studies showed that SSs during a well-balanced diet either maintain or even increase body weight, which may indirectly be ascribed to the fact that they cannot cover the hedonic aspect of food intake. However, there is a strong demand for long-term longitudinal surveys to effectively specify the impact of SSs on human metabolic health.

The role of central neurotransmitters in appetite regulation of broilers and layers: similarities and differences

The importance of feeding as a vital physiological function, on the one hand, and the spread of complications induced by its disorder in humans and animals, on the other hand, have led to extensive research on its regulatory factors. Unfortunately, despite many studies focused on appetite, only limited experiments have been conducted on avian, and our knowledge of this species is scant. Considering this, the purpose of this review article is to examine the role of central neurotransmitters in regulating food consumption in broilers and layers and highlight the similarities and differences between these two strains. The methodology of this review study includes a comprehensive search of relevant literature on the topic using appropriate keywords in reliable electronic databases. Based on the findings, the central effect of most neurotransmitters on the feeding of broilers and laying chickens was similar, but in some cases, such as dopamine, ghrelin, nitric oxide, and agouti-related peptide, differences were observed. Also, the lack of conducting a study on the role of some neurotransmitters in one of the bird strains made it impossible to make an exact comparison. Finally, it seems that although there are general similarities in appetite regulatory mechanisms in meat and egg-type chickens, the long-term genetic selection appropriate to breeding goals (meat or egg production) has caused differences in the effect of some neurotransmitters. Undoubtedly, conducting future studies while completing the missing links can lead to a comprehensive understanding of this process and its manipulation according to the breeding purposes of chickens.

The effects of environmental changes on the endocrine regulation of feeding in fishes

Fishes are exposed to natural and anthropogenic changes in their environment, which can have major effects on their behaviour and their physiology, including feeding behaviour, food intake and digestive processes. These alterations are owing to the direct action of environmental physico-chemical parameters (i.e. temperature, pH, turbidity) on feeding physiology but can also be a consequence of variations in food availability. Food intake is ultimately regulated by feeding centres of the brain, which receive and process information from endocrine signals from both brain and peripheral tissues such as the gastrointestinal tract. These endocrine signals stimulate or inhibit food intake, and interact with each other to maintain energy homeostasis. Changes in environmental conditions might change feeding habits and rates, thus affecting levels of energy stores, and the expression of endocrine appetite regulators. This review provides an overview of how environmental changes and food availability could affect feeding and these endocrine networks in fishes. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.

Neurohormonal response patterns to hunger, satiation, and postprandial fullness in normal weight, anorexia nervosa, and obesity

BACKGROUND

Food intake is regulated by homeostatic and hedonic systems that interact in a complex neuro-hormonal network. Dysregulation in energy intake can lead to obesity (OB) or anorexia nervosa (AN). However, little is known about the neurohormonal response patterns to food intake in normal weight (NW), OB, and AN.

MATERIAL & METHODS

During an ad libitum nutrient drink (Ensure®) test (NDT), participants underwent three pseudo-continuous arterial spin labeling (pCASL) MRI scans. The first scan was performed before starting the NDT after a > 12 h overnight fast (Hunger), the second after reaching maximal fullness (Satiation), and the third 30-min after satiation (postprandial fullness). We measured blood levels of ghrelin, cholecystokinin (CCK), glucagon-like peptide (GLP-1), and peptide YY (PYY) with every pCASL-MRI scan. Semiquantitative cerebral blood flow (CBF) maps in mL/100 gr brain/min were calculated and normalized (nCBF) with the CBF in the frontoparietal white matter. The hypothalamus (HT), nucleus accumbens [NAc] and dorsal striatum [DS] were selected as regions of interest (ROIs).

RESULTS

A total of 53 participants, 7 with AN, 17 with NW (body-mass index [BMI] 18.5-24.9 kg/m2 ), and 29 with OB (BMI ≥30 kg/m2 ) completed the study. The NW group had a progressive decrease in all five ROIs during the three stages of food intake (hunger, satiation, and post-prandial fullness). In contrast, participants with OB showed a minimal change from hunger to postprandial fullness in all five ROIs. The AN group had a sustained nCBF in the HT and DS, from hunger to satiation, with a subsequent decrease in nCBF from satiation to postprandial fullness. All three groups had similar hormonal response patterns with a decrease in ghrelin, an increase in GLP-1 and PYY, and no change in CCK.

CONCLUSION

Conditions of regulated (NW) and dysregulated (OB and AN) energy intake are associated with distinctive neurohormonal activity patterns in response to hunger, satiation, and postprandial fullness.

Neuroendocrinological and Clinical Aspects of Leptin

Obesity is characterized by an abnormal increase in adipose tissue mass and is regarded as a neurobehavioral as well as a metabolic disorder. Increases in body fat are caused by even slight, long-term discrepancies between energy intake and energy expenditure. It is a chronic condition linked to the metabolic syndrome, a spectrum of risky conditions, such as diabetes, high blood pressure, and heart disease. With a swiftly rising prevalence, obesity has emerged as a significant global health concern. Leptin influences the brain's neuroendocrine and metabolic processes, which is important for maintaining energy homeostasis. White adipose tissue secretes the majority of leptin, and there is a positive correlation between leptin levels in the blood and body fat percentages. The central nervous system is also modulated by leptin levels to modify energy intake and usage. The idea of an obesity cure sparked excitement after it was discovered more than 25 years ago. However, the leptin medication only effectively reduces weight in patients with congenital leptin insufficiency and not in patients with typical obesity who may also have leptin resistance. Recent research has focused on the role of leptin in managing weight reduction and preventing "yo-yo dieting". This review concentrates on the neurological effects of leptin with a focus on therapeutic and diagnostic applications, particularly for childhood obesity.

Causes of obesity: a review

Obesity research is advancing swiftly, but the increase in obesity prevalence is faster. Over the past three decades, researchers have found that biopsychosocial factors determine weight gain much more than personal choices and responsibility. Various genes have found to predispose people to obesity by interacting with our obesogenic environment. In this review, we discuss the impact of physical inactivity, excessive caloric intake, intrauterine environment, postnatal influences, insufficient sleep, drugs, medical conditions, socioeconomic status, ethnicity, psychosocial stress, endocrine disrupting chemicals and the gastrointestinal microbiome, on the occurrence of obesity.

Effects of Essential Oils and Fragrant Compounds on Appetite: A Systematic Review

Appetite dysregulation is one of the factors contributing to anorexia, bulimia nervosa, obesity, and diabetes. Essential oils or fragrant compounds have been proven to regulate food intake and energy expenditure; hence, this study aimed to summarize their effects on appetite and the underlying mechanisms. The PubMed and Web of Science databases were searched until July 2022. Only two of the 41 studies were performed clinically, and the remaining 39 used animal models. Oral administration was the most common route, and a dosage range of 100-2000 mg/kg for mice or 2-32 mg/kg for rats was applied, with a duration of 12 days to 4 weeks, followed by inhalation (10^-6-10^-3 mg/cage or 10^-9-10^-2 mg/cm³ within 1 h). Approximately 11 essential oil samples and 22 fragrant compounds were found to increase appetite, while 12 essential oils and seven compounds decreased appetite. These fragrant components can exert appetite-regulating effects via leptin resistance, the activity of sympathetic/parasympathetic nerves, or the mRNA expression of neuropeptide Y (NPY)/agouti-related protein (AgRP), cocaine- and amphetamine-regulated transcript (CART)/proopiomelanocortin (POMC) in the hypothalamus. Fragrance memory and cognitive processes may also play roles in appetite regulation. The findings of this study accentuate the potential of essential oils and fragrant compounds to regulate appetite and eating disorders.

Hypothalamic Reactivity and Connectivity following Intravenous Glucose Administration

Dysfunctional glucose sensing in homeostatic brain regions such as the hypothalamus is interlinked with the pathogenesis of obesity and type 2 diabetes mellitus. However, the physiology and pathophysiology of glucose sensing and neuronal homeostatic regulation remain insufficiently understood. To provide a better understanding of glucose signaling to the brain, we assessed the responsivity of the hypothalamus (i.e., the core region of homeostatic control) and its interaction with mesocorticolimbic brain regions in 31 normal-weight, healthy participants. We employed a single-blind, randomized, crossover design of the intravenous infusion of glucose and saline during fMRI. This approach allows to investigate glucose signaling independent of digestive processes. Hypothalamic reactivity and connectivity were assessed using a pseudo-pharmacological design and a glycemia-dependent functional connectivity analysis, respectively. In line with previous studies, we observed a hypothalamic response to glucose infusion which was negatively related to fasting insulin levels. The observed effect size was smaller than in previous studies employing oral or intragastric administration of glucose, demonstrating the important role of the digestive process in homeostatic signaling. Finally, we were able to observe hypothalamic connectivity with reward-related brain regions. Given the small amount of glucose employed, this points toward a high responsiveness of these regions to even a small energy stimulus in healthy individuals. Our study highlights the intricate relationship between homeostatic and reward-related systems and their pronounced sensitivity to subtle changes in glycemia.

Obesity and diabetes: the final frontier

INTRODUCTION

Obesity is a key target in the treatment and prevention of diabetes and independently to reduce the burden of cardiovascular disease. We reviewed the options now available and anticipated to deal with obesity.

AREAS COVERED

We considered the epidemiology, genetics, and causation of obesity and the relationship to diabetes, and the dietary, pharmaceutical, and surgical management of the condition. The literature search covered both popular media via Google Search and the academic literature as indexed on PubMed with search terms including obesity, childhood obesity, adipocytes, insulin resistance, mechanisms of satiety, bariatric surgery, GLP-1 receptor agonists, and SGLT2 inhibitors.

EXPERT OPINION

Although bariatric surgery has been the primary approach to treating obese individuals, the emergence of agents impacting the brain satiety centers now promises effective, non-invasive treatment of obesity for individuals with and without diabetes. The GLP-1 receptor agonists have assumed the primary role in treating obesity with significant weight loss. Long-term results with semaglutide and tirzepatide are now approaching the success seen with bariatric surgery. Future agents combining the benefits of satiety control and thermogenesis to dissipate caloric excess are under investigation.

Mucosal and hormonal adaptations after Roux-en-Y gastric bypass

The aim of this study was to perform a comprehensive literature review regarding the relevant hormonal and histologic changes observed after Roux-en-Y gastric bypass (RYGB). We aimed to describe the relevant hormonal (glucagon-like peptides 1 and 2 [GLP-1 and GLP-2], peptide YY [PYY], oxyntomodulin [OXM], bile acids [BA], cholecystokinin [CCK], ghrelin, glucagon, gastric inhibitory polypeptide [GIP], and amylin) profiles, as well as the histologic (mucosal cellular) adaptations happening after patients undergo RYGB. Our review compiles the current evidence and furthers the understanding of the rationale behind the food intake regulatory adaptations occurring after RYGB surgery. We identify gaps in the literature where the potential for future investigations and therapeutics may lie. We performed a comprehensive database search without language restrictions looking for RYGB bariatric surgery outcomes in patients with pre- and postoperative blood work hormonal profiling and/or gut mucosal biopsies. We gathered the relevant study results and describe them in this review. Where human findings were lacking, we included animal model studies. The amalgamation of physiologic, metabolic, and cellular adaptations following RYGB is yet to be fully characterized. This constitutes a fundamental aspiration for enhancing and individualizing obesity therapy.

Agouti-related protein as the glucose signaling sensor in the central melanocortin circuits in regulating fish food intake

Agouti-related protein (AgRP) is a neuropeptide synthesized by AgRP/NPY neurons and transcribed as 132 amino acids in humans and 142 amino acids (AgRP1) in Japanese seabass (Lateolabrax maculatus) fish. AgRP neurons are activated by hormonal signals of energy deficits and inhibited by signals of energy surpluses and have been demonstrated to have the ability to sense the dynamics of blood glucose concentrations as the "glucose sensor" in mammals. It is widely recognized that AgRP is an endogenous antagonist of the melanocortin-3 and -4 receptors (MC3R and MC4R) in the hypothalamus, exhibiting potent orexigenic activity and control of energy homeostasis. Most fish, especially carnivorous fish, cannot make efficient use of carbohydrates. When carbohydrates like corn or wheat bran are added as energy sources, they often cause feeding inhibition and metabolic diseases. When fishmeal is replaced by plant protein, this does not completely eliminate carbs, limiting the utilization of carbohydrates and plant proteins in aquaculture. Our previous study showed that AgRP, and not neuropeptide Y (NPY) is the principal protein molecule that correlates well with feeding behavior in Japanese seabass from anorexia to adaptation. The Ghrelin/Leptin-mTOR-S6K1-NPY/AgRP/POMC feed intake regulatory pathway responds to the plant-oriented protein which contains glucose. However, its regulatory function and mechanism are still not clear. This review offers an integrative overview of how glucose signals converge on a molecular level in AgRP neurons of the arcuate nucleus of the hypothalamus. This is in order to control fish food intake and energy homeostasis.