The sweet taste signalling pathways in the oral cavity and the gastrointestinal tract affect human appetite and food intake: a review

The influence of different flavor peptides on brain perception via scalp electroencephalogram and development of a taste model

Traditional taste evaluation methods often rely on subjective assessments, introducing biases. To address this, we propose using electroencephalography (EEG) to explore the link between brain activity and taste perception. Our EEG analysis showed significant activity differences in specific brain regions, particularly at electrodes Pz, FT7, F7, and TP7, highlighting their role in taste signal processing. Consistent activity at Pz across various tastes supports the development of a mathematical model and sensory evaluation system. We used wavelet packet transform for EEG signal preprocessing, followed by feature extraction and classification with the Common Spatial Pattern (CSP) and Support Vector Machine (SVM) algorithms. Testing five taste categories-sour, sweet, bitter, salty, and umami-resulted in an overall prediction accuracy of 0.7613, with the highest accuracy of 0.8235 for "sweet" taste. Despite challenges in predicting "sour" and "salty" tastes, our study demonstrates the potential of combining wavelet packet transform, CSP, and SVM for EEG-based taste classification.

Impact of Some Natural and Artificial Sweeteners Consumption on Different Hormonal Levels and Inflammatory Cytokines in Male Rats: In Vivo and In Silico Studies

Substituting sugar with noncaloric sweeteners prevents overweight and diabetes development. They come in two types: artificial, like aspartame and sucralose, and natural, such as sorbitol. This research aimed to assess the effects of sucrose and these sweeteners on nutritional parameters, hematological parameters, hormones, and anti- and pro-inflammatory cytokines in male rats. Thirty rats had been separated into five groups. The results showed the highest significant increase in body weight gain, total food intake, and feed efficiency noticed in the aspartame group followed by sucralose, sucrose, and sorbitol, respectively. In contrast to RBCs and platelets, all sweeteners significantly reduced the hemoglobin level, Hct %, and WBC count. The aspartame group showed the highest decline in glycoproteins, steroids, and T3, and T4 hormones and a dramatic elevation in thyroid stimulating hormone, eicosanoid, and amine hormones compared with the control group. A vigorous elevation in anti- and proinflammatory cytokine levels was observed in the aspartame group, followed by sucralose, sucrose, and sorbitol groups. Aspartame has the highest docking scores when studying the interactions of sweeteners and a target protein associated with hormones or cytokines using in silico molecular docking, with the best absorption, distribution, metabolism, elimination, and toxicity properties compared to the remaining sweeteners.

The dawning era of oral thin films for nutraceutical delivery: From laboratory to clinic

Oral thin films (OTFs) are innovative dosage forms that have gained tremendous attention for the delivery of nutraceuticals. They are ultra-thin, flexible sheets that can be easily placed on the tongue, sublingual or buccal mucosa (inner lining of the cheek). These thin films possess several advantages for nutraceutical delivery including ease of administration, rapid disintegration, fast absorption, rapid onset of action, bypass first-pass hepatic metabolism, accurate dosing, enhanced stability, portability, discreetness, dose flexibility and most importantly consumer acceptance. This review highlights the utilization OTFs for nutraceutical delivery, their composition, criteria for excipient selection, methods of development and quality-based design (QbD) approach to achieve quality product. We have also provided recent case studies representing OTFs as promising platform in delivery of nutraceuticals (plant extracts, bioactive molecules, vitamins, minerals and protein/peptides) and probiotics. Finally, we provided advancement in technologies, recent patents, market analysis, challenges and future perspectives associated with this unique dosage form.

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.

Suppression of sweet taste-related responses by plant-derived bioactive compounds and eating. Part I: A systematic review in humans

The taste of food plays a crucial role in determining what and how much we eat. Thus, interventions that temporarily block sweet taste receptors offer a promising approach to addressing unhealthy behaviours associated with sugary foods. However, the relationship between reduced sweet taste response and food consumption remains unclear, with contradictory findings. Certain studies suggest that a diminished perception of sweetness leads to a sense of fullness and results in reduced food intake, while others suggest the opposite effect. To shed some light, our systematic review looked into the relationship between diminished sweet taste response and food consumption by examining the effects of bioactive compounds that experimentally inhibit sweetness in healthy individuals. This review was registered in the International Prospective Register of Systematic Reviews and conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and the Scottish Intercollegiate Guidelines Network, and covered original papers included in Web of Science, PubMed, Scopus, Food Science Source and Food Science and technology abstracts. We identified 33 peer-reviewed English-language studies that fit the topic and met the inclusion criteria. The current literature predominantly focuses on the immediate impact of oral gymnemic acids, failing to provide preliminary evidence in support of the specific threshold hypothesis, above which food consumption decreases and below which the opposite effect occurs. Additionally, there was inconsistency in the findings regarding the short-term desire to eat following sweetness inhibition. Considering the downstream effects on energy intake and their clinical applications, further research is needed to clarify both the acute within-session effects (i.e., not wanting any more now) and the longer-term effects (i.e., deciding not to start eating) linked to oral sweet-taste-suppressing compounds.

Taste Function in Adult Humans from Lean Condition to Stage II Obesity: Interactions with Biochemical Regulators, Dietary Habits, and Clinical Aspects

Differences in gustatory sensitivity, nutritional habits, circulating levels of modulators, anthropometric measures, and metabolic assays may be involved in overweight (OW) development. The present study aimed at evaluating the differences in these aspects between 39 OW (19 female; mean age = 53.51 ± 11.17), 18 stage I (11 female; mean age = 54.3 ± 13.1 years), and 20 II (10 female; mean age = 54.5 ± 11.9) obesity participants when compared with 60 lean subjects (LS; 29 female; mean age = 54.04 ± 10.27). Participants were evaluated based on taste function scores, nutritional habits, levels of modulators (leptin, insulin, ghrelin, and glucose), and bioelectrical impedance analysis measurements. Significant reductions in total and subtests taste scores were found between LS and stage I and II obesity participants. Significant reductions in total and all subtests taste scores were found between OW and stage II obesity participants. Together with the progressive increase in plasmatic leptin levels, insulin, and serum glucose, decrease in plasmatic ghrelin levels, and changes in anthropometric measures and nutritional habits along with body mass index, these data for the first time demonstrated that taste sensitivity, biochemical regulators, and food habits play a parallel, concurring role along the stages evolving to obesity.

The effect of regular consumption of four low- or no-calorie sweeteners on glycemic response in healthy women: A randomized controlled trial

OBJECTIVES

The aim of this study was to determine the effects of regular exposure to certain low- or no-calorie sweeteners (LNCS) on glucose tolerance and glucagon-like peptide 1 (GLP-1) release in healthy individuals.

METHODS

It was designed as a randomized, single-blinded, controlled study. Healthy and normoglycemic adults who did not have regular consumption of LNCS were recruited. Participants underwent a 75-g oral glucose tolerance test (OGTT) at baseline and were randomly assigned to consume 330 mL water sweetened with saccharine, sucralose, or aspartame + acesulfame-K (Asp+Ace-K), or plain water for the control group, daily for 4 wk. Fasting plasma glucose, insulin, GLP-1, and glycated hemoglobin A_1c (HbA_1c) levels and 1-h, 2-h, and 3-h plasma glucose and insulin levels during OGTT were obtained at baseline. The change in insulin sensitivity was assessed by both the Homeostatic Model Assessment Insulin Resistance (HOMA-IR) Index and the Matsuda Index. Anthropometric measurements and dietary intakes were determined at baseline. Baseline measurements were repeated at week 4.

RESULTS

Of the participants enrolled in the study, 42 (age, 21.24 ± 2.26 y; body mass index, 20.65 ± 2.88 kg/m²) completed the 4-wk intervention period. There were no differences for glucose, insulin, GLP-1, or HbA_1c levels or HOMA-IR scores at baseline or at week 4 when compared with the control group. The area under the curve of mean glucose and insulin values during OGTT were also found to be similar between groups at baseline and week 4. There were also no effects of LNCS intake on body weight, body composition, and waist circumference.

CONCLUSIONS

These results suggest that regular consumption of LNCS-sweetened water similar to doses consumed in daily life over 4 wk had no significant effect on glycemic response, insulin sensitivity, GLP-1 release, and body weight in healthy individuals. This trial was registered at www.

CLINICALTRIALS

gov as NCT04904133.

Sweet Chestnut (Castanea sativa Mill.) Nutritional and Phenolic Composition Interactions with Chestnut Flavor Physiology

The European chestnut (Castanea sativa Mill.), is an environmentally and economically important species in Europe, mainly for fruit production. The chestnut fruit is well-known for its nutritional properties, namely its high concentration of carbohydrates (starch) and its low-fat content, as well as being one of the few fruits that do not contain gluten. Due to its chemical and nutritional characteristics beneficial to health, the sweet chestnut is a food recommended at different levels. The biochemistry of the mouth and nose of a human being is very complex. However, understanding the different interactions between the biochemistry of our sensory organs and food helps us to comprehend certain concepts, such as flavor and how it is involved in the sensory evaluation of the chestnuts. For the selection of high-quality products, it is necessary to develop reliable methods both from a qualitative and sensory point of view, and chestnut is a fruit with unique sensory characteristics that can be used in various gastronomic dishes, from main courses to desserts.

Recent advance in technological innovations of sugar-reduced products

Sugar is crucial as an essential nutrient for humans as well as for providing texture, sweetness and so on to food. But with the rise in people's pursuit of health, it is becoming increasingly clear that excessive consumption of sugar can locate a load on the body. It has been that excessive sugar is associated with many diseases, such as dental caries, obesity, diabetes, and coronary heart disease. Therefore, researchers and industries are trying to reduce or substitute sugar in food without affecting the sensory evaluation. Substituting sugar with sweeteners is alternatively becoming the most traditional way to minimize its use. So far, the sweeteners such as stevia and xylitol have been are commercially applied. Several studies have shown that technological innovation can partially compensate for the loss in sweetness as a result of sugar reduction, such as cross-modal interactions that stimulate sweetness with aroma, nanofiltration that filters disaccharides and above, enzyme-catalyzed sugar hydrolysis, and microbial fermentation that turns sugar into sugar alcohol. This review summarizes these studies to enhance the safety and quality of sugar-reduced products, and will provide some theoretical frameworks for the food industry to reduce sugar in foods, meet consumers' needs, and promote human health.

Mapping the Homeostatic and Hedonic Brain Responses to Stevia Compared to Caloric Sweeteners and Water: A Double-Blind Randomised Controlled Crossover Trial in Healthy Adults

Non-nutritive sweeteners have potential effects on brain function. We investigated neural correlates of responses to beverages differing in sweetness and calories. Healthy participants completed 4 randomised sessions: water vs. water with stevia, glucose, or maltodextrin. Blood-oxygenation level-dependent (BOLD) contrast was monitored for 30 min post-ingestion by functional Magnetic Resonance Imaging. A food visual probe task at baseline was repeated at 30 min. A significant interaction of taste-by-calories-by-time was demonstrated mainly in motor, frontal, and insula cortices. Consumption of the stevia-sweetened beverage resulted in greater BOLD decrease, especially in the 20-30 min period, compared to other beverages. There was a significant interaction of taste-by-time in BOLD response in gustatory and reward areas; sweet beverages induced greater reduction in BOLD compared to non-sweet. The interaction calories-by-time showed significantly greater incremental area under the curve in thalamic, visual, frontal, and parietal areas for glucose and maltodextrin 10-20 min post-consumption only, compared to water. In the visual cue task, the water demonstrated an increased response in the visual cortex to food images post-consumption; however, no difference was observed for the three sweet/caloric beverages. In conclusion, both sweet taste and calories exert modulatory effects, but stevia showed a more robust and prolonged effect.

The Effect of Artificial Sweeteners Use on Sweet Taste Perception and Weight Loss Efficacy: A Review

Excessive consumption of sugar-rich foods is currently one of the most important factors that has led to the development of the global pandemic of obesity. On the other hand, there is evidence that obesity contributes to reduced sensitivity to sweet taste and hormonal changes affecting appetite, leading to an increased craving for sweets. A high intake of sugars increases the caloric value of the diet and, consequently, leads to weight gain. Moreover, attention is drawn to the concept of the addictive properties of sugar and sugary foods. A potential method to reduce the energy value of diet while maintaining the sweet taste is using non-nutritive sweeteners (NNS). NNS are commonly used as table sugar substitutes. This wide group of chemical compounds features high sweetness almost without calories due to its high sweetening strength. NNS include aspartame, acesulfame-K, sucralose, saccharin, cyclamate, neohesperidin dihydrochalcone (neohesperidin DC), neotame, taumatin, and advantame. The available evidence suggests that replacing sugar with NNS may support weight control. However, the effect of NNS on the regulation of appetite and sweet taste perception is not clear. Therefore, the review aimed to summarize the current knowledge about the use of NNS as a potential strategy for weight loss and their impact on sweet taste perception. Most studies have demonstrated that consumption of NNS-sweetened foods does not increase sweetness preference orenergy intake. Nonetheless, further research is required to determine the long-term effects of NNS on weight management.

Effect of Obesity Surgery on Taste

Obesity surgery is a highly efficacious treatment for obesity and its comorbidities. The underlying mechanisms of weight loss after obesity surgery are not yet fully understood. Changes to taste function could be a contributing factor. However, the pattern of change in different taste domains and among obesity surgery operations is not consistent in the literature. A systematic search was performed to identify all articles investigating gustation in human studies following bariatric procedures. A total of 3323 articles were identified after database searches, searching references and deduplication, and 17 articles were included. These articles provided evidence of changes in the sensory and reward domains of taste following obesity procedures. No study investigated the effect of obesity surgery on the physiological domain of taste. Taste detection sensitivity for sweetness increases shortly after Roux-en-Y gastric bypass. Additionally, patients have a reduced appetitive reward value to sweet stimuli. For the subgroup of patients who experience changes in their food preferences after Roux-en-Y gastric bypass or vertical sleeve gastrectomy, changes in taste function may be underlying mechanisms for changing food preferences which may lead to weight loss and its maintenance. However, data are heterogeneous; the potential effect dilutes over time and varies significantly between different procedures.

Taste of Fat and Obesity: Different Hypotheses and Our Point of View

Obesity results from a temporary or prolonged positive energy balance due to an alteration in the homeostatic feedback of energy balance. Food, with its discriminative and hedonic qualities, is a key element of reward-based energy intake. An alteration in the brain reward system for highly palatable energy-rich foods, comprised of fat and carbohydrates, could be one of the main factors involved in the development of obesity by increasing the attractiveness and consumption of fat-rich foods. This would induce, in turn, a decrease in the taste of fat. A better understanding of the altered reward system in obesity may open the door to a new era for the diagnosis, management and treatment of this disease.

Sweet Taste Is Complex: Signaling Cascades and Circuits Involved in Sweet Sensation

Sweetness is the preferred taste of humans and many animals, likely because sugars are a primary source of energy. In many mammals, sweet compounds are sensed in the tongue by the gustatory organ, the taste buds. Here, a group of taste bud cells expresses a canonical sweet taste receptor, whose activation induces Ca²⁺ rise, cell depolarization and ATP release to communicate with afferent gustatory nerves. The discovery of the sweet taste receptor, 20 years ago, was a milestone in the understanding of sweet signal transduction and is described here from a historical perspective. Our review briefly summarizes the major findings of the canonical sweet taste pathway, and then focuses on molecular details, about the related downstream signaling, that are still elusive or have been neglected. In this context, we discuss evidence supporting the existence of an alternative pathway, independent of the sweet taste receptor, to sense sugars and its proposed role in glucose homeostasis. Further, given that sweet taste receptor expression has been reported in many other organs, the physiological role of these extraoral receptors is addressed. Finally, and along these lines, we expand on the multiple direct and indirect effects of sugars on the brain. In summary, the review tries to stimulate a comprehensive understanding of how sweet compounds signal to the brain upon taste bud cells activation, and how this gustatory process is integrated with gastro-intestinal sugar sensing to create a hedonic and metabolic representation of sugars, which finally drives our behavior. Understanding of this is indeed a crucial step in developing new strategies to prevent obesity and associated diseases.

The metabolic impact of small intestinal nutrient sensing

The gastrointestinal tract maintains energy and glucose homeostasis, in part through nutrient-sensing and subsequent signaling to the brain and other tissues. In this review, we highlight the role of small intestinal nutrient-sensing in metabolic homeostasis, and link high-fat feeding, obesity, and diabetes with perturbations in these gut-brain signaling pathways. We identify how lipids, carbohydrates, and proteins, initiate gut peptide release from the enteroendocrine cells through small intestinal sensing pathways, and how these peptides regulate food intake, glucose tolerance, and hepatic glucose production. Lastly, we highlight how the gut microbiota impact small intestinal nutrient-sensing in normal physiology, and in disease, pharmacological and surgical settings. Emerging evidence indicates that the molecular mechanisms of small intestinal nutrient sensing in metabolic homeostasis have physiological and pathological impact as well as therapeutic potential in obesity and diabetes.

The gastrointestinal tract participates in maintaining metabolic homeostasis in part through nutrient-sensing and subsequent gut-brain signalling. Here the authors review the role of small intestinal nutrient-sensing in regulation of energy intake and systemic glucose metabolism, and link high-fat diet, obesity and diabetes with perturbations in these pathways.

The Impact of Artificial Sweeteners on Body Weight Control and Glucose Homeostasis

A poor diet is one of the leading causes for non-communicable diseases. Due to the increasing prevalence of overweight and obesity, there is a strong focus on dietary overconsumption and energy restriction. Many strategies focus on improving energy balance to achieve successful weight loss. One of the strategies to lower energy intake is refraining from sugars and replacing them with artificial sweeteners, which maintain the palatability without ingesting calories. Nevertheless, the safety and health benefits of artificial sweeteners consumption remain a topic of debate within the scientific community and society at large. Notably, artificial sweeteners are metabolized differently from each other due to their different properties. Therefore, the difference in metabolic fate of artificial sweeteners may underlie conflicting findings that have been reported related to their effects on body weight control, glucose homeostasis, and underlying biological mechanisms. Thus, extrapolation of the metabolic effects of a single artificial sweetener to all artificial sweeteners is not appropriate. Although many rodent studies have assessed the metabolic effects of artificial sweeteners, long-term studies in humans are scarce. The majority of clinical studies performed thus far report no significant effects or beneficial effects of artificial sweeteners on body weight and glycemic control, but it should be emphasized that the study duration of most studies was limited. Clearly, further well-controlled, long-term human studies investigating the effects of different artificial sweeteners and their impact on gut microbiota, body weight regulation and glucose homeostasis, as well as the underlying mechanisms, are warranted.

A rational review on the effects of sweeteners and sweetness enhancers on appetite, food reward and metabolic/adiposity outcomes in adults

Numerous strategies have been investigated to overcome the excessive weight gain that accompanies a chronic positive energy balance. Most approaches focus on a reduction of energy intake and the improvement of lifestyle habits. The use of high intensity artificial sweeteners, also known as non-caloric sweeteners (NCS), as sugar substitutes in foods and beverages, is rapidly developing. NCS are commonly defined as molecules with a sweetness profile of 30 times higher or more that of sucrose, scarcely contributing to the individual's net energy intake as they are hardly metabolized. The purpose of this review is first, to assess the impact of NCS on eating behaviour, including subjective appetite, food intake, food reward and sensory stimulation; and secondly, to assess the metabolic impact of NCS on body weight regulation, glucose homeostasis and gut health. The evidence reviewed suggests that while some sweeteners have the potential to increase subjective appetite, these effects do not translate in changes in food intake. This is supported by a large body of empirical evidence advocating that the use of NCS facilitates weight management when used alongside other weight management strategies. On the other hand, although NCS are very unlikely to impair insulin metabolism and glycaemic control, some studies suggest that NCS could have putatively undesirable effects, through various indirect mechanisms, on body weight, glycemia, adipogenesis and the gut microbiota; however there is insufficient evidence to determine the degree of such effects. Overall, the available data suggests that NCS can be used to facilitate a reduction in dietary energy content without significant negative effects on food intake behaviour or body metabolism, which would support their potential role in the prevention of obesity as a complementary strategy to other weight management approaches. More research is needed to determine the impact of NCS on metabolic health, in particular gut microbiota.

An alternative pathway for sweet sensation: possible mechanisms and physiological relevance

Sweet substances are detected by taste-bud cells upon binding to the sweet-taste receptor, a T1R2/T1R3 heterodimeric G protein-coupled receptor. In addition, experiments with mouse models lacking the sweet-taste receptor or its downstream signaling components led to the proposal of a parallel "alternative pathway" that may serve as metabolic sensor and energy regulator. Indeed, these mice showed residual nerve responses and behavioral attraction to sugars and oligosaccharides but not to artificial sweeteners. In analogy to pancreatic β cells, such alternative mechanism, to sense glucose in sweet-sensitive taste cells, might involve glucose transporters and K_ATP channels. Their activation may induce depolarization-dependent Ca²⁺ signals and release of GLP-1, which binds to its receptors on intragemmal nerve fibers. Via unknown neuronal and/or endocrine mechanisms, this pathway may contribute to both, behavioral attraction and/or induction of cephalic-phase insulin release upon oral sweet stimulation. Here, we critically review the evidence for a parallel sweet-sensitive pathway, involved signaling mechanisms, neural processing, interactions with endocrine hormonal mechanisms, and its sensitivity to different stimuli. Finally, we propose its physiological role in detecting the energy content of food and preparing for digestion.

Sugar Reduction in Dairy Food: An Overview with Flavoured Milk as an Example

Owing to the public health concern associated with the consumption of added sugar, the World Health Organization recommends cutting down sugar in processed foods. Furthermore, due to the growing concern of increased calorie intake from added sugar in sweetened dairy foods, the present review provides an overview of different types and functions of sugar, various sugar reduction strategies, and current trends in the use of sweeteners for sugar reduction in dairy food, taking flavoured milk as a central theme where possible to explore the aforementioned aspects. The strength and uniqueness of this review are that it brings together all the information on the available types of sugar and sugar reduction strategies and explores the current trends that could be applied for reducing sugar in dairy foods without much impact on consumer acceptance. Among different strategies for sugar reduction, the use of natural non-nutritive sweeteners (NNSs), has received much attention due to consumer demand for natural ingredients. Sweetness imparted by sugar can be replaced by natural NNSs, however, sugar provides more than just sweetness to flavoured milk. Sugar reduction involves multiple technical challenges to maintain the sensory properties of the product, as well as to maintain consumer acceptance. Because no single sugar has a sensory profile that matches sucrose, the use of two or more natural NNSs could be an option for food industries to reduce sugar using a holistic approach rather than a single sugar reduction strategy. Therefore, achieving even a small sugar reduction can significantly improve the diet and health of an individual.

Oral and pre-absorptive sensing of amino acids relates to hypothalamic control of food intake in rainbow trout

To assess the putative role of taste and pre-absorptive sensing of amino acids in food intake control in fish, we carried out an oral administration with l-leucine, l-valine, l-proline or l-glutamic acid in rainbow trout (Oncorhynchus mykiss). Treatment with proline significantly reduced voluntary food intake at 2 h and 3 h after oral administration, while glutamic acid showed a less pronounced satiating effect at 3 h. The mRNA expression of taste receptor subunits tas1r1, tas1r2a, tas1r2b and tas1r3 was measured in the epithelium overlying the bony basihyal of the fish (analogous to the tetrapod tongue) at 10, 20 or 30 min following treatment. No significant changes were observed, except for a tas1r down-regulation by valine at 30 min. Of the downstream taste signalling genes that were analysed in parallel, plcb2 and possibly trpm5 (non-significant trend) were down-regulated 20 min after proline and glutamic acid treatment. The signal originated in the oropharyngeal and/or gastric cavity presumably relays to the brain as changes in genes involved in the regulation of food intake occurred in hypothalamus 10-30 min after oral treatment with amino acids. In particular, proline induced changes consistent with an increased anorexigenic potential in the hypothalamus. We have therefore demonstrated, for the first time in fish, that the peripheral (pre-absorptive) detection of an amino acid (l-proline), presumably by taste-related mechanisms, elicits a satiety signal that in hypothalamus is translated into changes in cellular signalling and neuropeptides regulating food intake, ultimately resulting in decreased food intake.

The Evolution of Neuroscience as a Research Field Relevant to Dentistry

The field of neuroscience did not exist as such when the Journal of Dental Research was founded 100 y ago. It has emerged as an important scientific field relevant to dentistry in view of the many neurally based functions manifested in the orofacial area (e.g., pain, taste, chewing, swallowing, salivation). This article reviews many of the novel insights that have been gained through neuroscience research into the neural basis of these functions and their clinical relevance to the diagnosis and management of pain and sensorimotor disorders. These include the neural pathways and brain circuitry underlying each of these functions and the role of nonneural as well as neural processes and their "plasticity" in modulating these functions and allowing for adaptation to tissue injury and pain and for learning or rehabilitation of orofacial functions.

Fructose vs glucose decreased liking/wanting and subsequent intake of high-energy foods in young women

Recent research on the health impacts of added sugar has prompted the comparison of the effects of its 2 major components: glucose and fructose. Fructose was identified as a risk factor for obesity and metabolic syndrome. However, because of the differences in metabolic responses and responsivity of reward circuitry to palatable food, it is unknown if glucose and fructose induce similar appetite-related responses in humans with varying weights. This study compared the behavioral responses to food in young women of a healthy weight (n = 31) and with excess weight (n = 28). We hypothesized that (1) the inhibitory effect of glucose (vs fructose) on food-related responses would be greater in subjects of a healthy weight than in those with overweight/obesity and (2) subjects with overweight/obesity would exhibit a stronger preference for food than subjects with a healthy weight. After an overnight fast, the subjects ingested a glucose or equienergetic fructose beverage on 2 separate days, respectively. Then, they completed liking and wanting ratings and 2 decision-making tasks followed by ad libitum food intake. The results revealed that fructose reduced both liking and wanting for food in subjects with overweight/obesity and also decreased energy intake in all subjects. Relative to the healthy-weight group, subjects with overweight/obesity preferred the immediate reward. Moreover, only in the healthy-weight group were liking and wanting scores for food positively associated with actual food consumption. Overall, fructose (vs glucose) showed an acute inhibitory effect on appetite-related responses in subjects with excess weight.

Intense Sweeteners, Taste Receptors and the Gut Microbiome: A Metabolic Health Perspective

Intense sweeteners (IS) are often marketed as a healthier alternative to sugars, with the potential to aid in combating the worldwide rise of diabetes and obesity. However, their use has been counterintuitively associated with impaired glucose homeostasis, weight gain and altered gut microbiota. The nature of these associations, and the mechanisms responsible, are yet to be fully elucidated. Differences in their interaction with taste receptors may be a potential explanatory factor. Like sugars, IS stimulate sweet taste receptors, but due to their diverse structures, some are also able to stimulate bitter taste receptors. These receptors are expressed in the oral cavity and extra-orally, including throughout the gastrointestinal tract. They are involved in the modulation of appetite, glucose homeostasis and gut motility. Therefore, taste genotypes resulting in functional receptor changes and altered receptor expression levels may be associated with metabolic conditions. IS and taste receptors may both interact with the gastrointestinal microbiome, and their interactions may potentially explain the relationship between IS use, obesity and metabolic outcomes. While these elements are often studied in isolation, the potential interactions remain unexplored. Here, the current evidence of the relationship between IS use, obesity and metabolic outcomes is presented, and the potential roles for interactions with taste receptors and the gastrointestinal microbiota in modulating these relationships are explored.

Contribution of macronutrients to obesity: implications for precision nutrition

The specific metabolic contribution of consuming different energy-yielding macronutrients (namely, carbohydrates, protein and lipids) to obesity is a matter of active debate. In this Review, we summarize the current research concerning associations between the intake of different macronutrients and weight gain and adiposity. We discuss insights into possible differential mechanistic pathways where macronutrients might act on either appetite or adipogenesis to cause weight gain. We also explore the role of dietary macronutrient distribution on thermogenesis or energy expenditure for weight loss and maintenance. On the basis of the data discussed, we describe a novel way to manage excessive body weight; namely, prescribing personalized diets with different macronutrient compositions according to the individual's genotype and/or enterotype. In this context, the interplay of macronutrient consumption with obesity incidence involves mechanisms that affect appetite, thermogenesis and metabolism, and the outcomes of these mechanisms are altered by an individual's genotype and microbiota. Indeed, the interactions of the genetic make-up and/or microbiota features of a person with specific macronutrient intakes or dietary pattern consumption help to explain individualized responses to macronutrients and food patterns, which might represent key factors for comprehensive precision nutrition recommendations and personalized obesity management.

Alteration Pattern of Taste Perception After Bariatric Surgery: a Systematic Review of Four Taste Domains

BACKGROUND

Efforts continue to understand the underlying mechanism of weight loss after bariatric surgery. Taste perception has shown to be a contributing factor. However, the alteration pattern in different taste domains and among bariatric procedures has not been sufficiently investigated.

OBJECTIVES

To study the alteration pattern in the perception of four taste domains after different bariatric procedures.

SETTINGS

Private Research Institute, USA.

METHODS

A systematic review was conducted to pool available data in the literature on post-operative changes in the perception of sensitivity to four taste domains after Roux-en-Y gastric bypass (RYGB), laparoscopic sleeve gastrectomy (LSG), and adjustable gastric banding (AGB).

RESULTS

Our study showed that bariatric surgery is associated with significant change in sensitivity to all four taste domains especially salt taste, sweetness, and sourness. LSG patients showed an increased sensitivity to all four taste domains. However, RYGB patients had a variable alteration pattern of taste perception but more commonly a decreased sensitivity to sweetness and an increased sensitivity to salt taste and sourness. Additionally, AGB patients had a decreased sensitivity to sweetness, salt taste, and sourness.

CONCLUSION

Bariatric surgery is associated with taste change in a way which results in less preference for high-calorie food and possibly reduced calorie intake. This may explain one of the mechanisms by which bariatric surgery produces weight loss. However, data are heterogeneous, the potential effect dilutes over time, and the alteration varies significantly between different procedures.

How Lifestyle Factors Affect Cognitive and Executive Function and the Ability to Learn in Children

In today's research environment, children's diet, physical activity, and other lifestyle factors are commonly studied in the context of health, independent of their effect on cognition and learning. Moreover, there is little overlap between the two literatures, although it is reasonable to expect that the lifestyle factors explored in the health-focused research are intertwined with cognition and learning processes. This thematic review provides an overview of knowledge connecting the selected lifestyle factors of diet, physical activity, and sleep hygiene to children's cognition and learning. Research from studies of diet and nutrition, physical activity and fitness, sleep, and broader influences of cultural and socioeconomic factors related to health and learning, were summarized to offer examples of research that integrate lifestyle factors and cognition with learning. The literature review demonstrates that the associations and causal relationships between these factors are vastly understudied. As a result, current knowledge on predictors of optimal cognition and learning is incomplete, and likely lacks understanding of many critical facts and relationships, their interactions, and the nature of their relationships, such as there being mediating or confounding factors that could provide important knowledge to increase the efficacy of learning-focused interventions. This review provides information focused on studies in children. Although basic research in cells or animal studies are available and indicate a number of possible physiological pathways, inclusion of those data would distract from the fact that there is a significant gap in knowledge on lifestyle factors and optimal learning in children. In a climate where childcare and school feeding policies are continuously discussed, this thematic review aims to provide an impulse for discussion and a call for more holistic approaches to support child development.

Non-Nutritive Sweeteners and Their Implications on the Development of Metabolic Syndrome

Individuals widely use non-nutritive sweeteners (NNS) in attempts to lower their overall daily caloric intake, lose weight, and sustain a healthy diet. There are insufficient scientific data that support the safety of consuming NNS. However, recent studies have suggested that NNS consumption can induce gut microbiota dysbiosis and promote glucose intolerance in healthy individuals that may result in the development of type 2 diabetes mellitus (T2DM). This sequence of events may result in changes in the gut microbiota composition through microRNA (miRNA)-mediated changes. The mechanism(s) by which miRNAs alter gene expression of different bacterial species provides a link between the consumption of NNS and the development of metabolic changes. Another potential mechanism that connects NNS to metabolic changes is the molecular crosstalk between the insulin receptor (IR) and G protein-coupled receptors (GPCRs). Here, we aim to highlight the role of NNS in obesity and discuss IR-GPCR crosstalk and miRNA-mediated changes, in the manipulation of the gut microbiota composition and T2DM pathogenesis.

Bitter, Sweet, Salty, Sour and Umami Taste Perception Decreases with Age: Sex-Specific Analysis, Modulation by Genetic Variants and Taste-Preference Associations in 18 to 80 Year-Old Subjects

There is growing interest in relating taste perception to diet and healthy aging. However, there is still limited information on the influence of age, sex and genetics on taste acuity as well as on the relationship between taste perception and taste preferences. We have analysed the influence of age on the intensity rating of the five basic tastes: sweet, salty, bitter, sour and umami (separately and jointly in a “total taste score”) and their modulation by sex and genetics in a relatively healthy population (men and women) aged 18–80 years (n = 1020 Caucasian European participants). Taste perception was determined by challenging subjects with solutions of the five basic tastes using standard prototypical tastants (6-n-propylthiouracil (PROP), NaCl, sucrose, monopotassium glutamate and citric acid) at 5 increasing concentrations (I to V). We also measured taste preferences and determined the polymorphisms of the genes taste 2 receptor member 38 (TAS2R38), taste 1 receptor member 2 (TAS2R38) and sodium channel epithelial 1 beta subunit (SCNN1B), as TAS2R38-rs713598, TAS1R2-rs35874116 and SCNN1B-rs239345 respectively. We found a statistically significant decrease in taste perception (“total taste score”) with increasing age for all the concentrations analysed. This association was stronger for the higher concentrations (p = 0.028; p = 0.012; p = 0.005; p = 4.20 × 10⁻⁵ and p = 1.48 × 10⁻⁷, for I to V in the multivariable-adjusted models). When we analysed taste qualities (using concentration V), the intensity rating of all the 5 tastes was diminished with age (p < 0.05 for all). This inverse association differed depending on the test quality, being higher for bitter (PROP) and sour. Women perceived taste significantly more intense than men (p = 1.4 × 10⁻⁸ for total taste score). However, there were differences depending on the taste, umami being the lowest (p = 0.069). There was a complex association between the ability to perceive a taste and the preference for the same. Significant associations were, nevertheless, found between a higher perception of sour taste and a higher preference for it in women. In contrast, the higher perception of sweet was significantly associated with a higher preference for bitter in both, men and women. The TAS2R38-rs713598 was strongly associated with bitter (PROP) taste (p = 1.38 × 10⁻⁵⁰), having a significant interaction with sex (p = 0.030). The TAS1R2-rs35874116 was not significantly associated with sweet, whereas the SCNN1B-rs239345 was associated (p = 0.040) with salty taste. In conclusion, the inverse association between age and perceived taste intensity as well as the additional influence of sex and some genetic polymorphisms give rise to large inter-individual differences in taste perception and taste preferences that should be taken into account in future studies and for applications in precision nutrition for healthy aging.