Modulation of taste responsiveness and food preference by obesity and weight loss

Taste Plasticity in Nutrition and Health: A Scoping Review

Taste sensation is at the intersection of nutrition and health. Our food choices are shaped by the foods we like, but our dietary habits can, in turn, influence how we sense food. This phenomenon, known as diet-induced taste plasticity, has received renewed attention as a tool for designing healthier foods and retraining eating habits. This review synthesizes emerging data from humans and model organisms to characterize how dietary environments shape taste sensation while exploring its underlying molecular and physiological mechanisms. Although there is still so much to discover about this phenomenon, accumulating evidence suggests an inverse relationship between a tastant concentration and the ability of the organism to respond to it. The effects largely depend on diet, but body weight changes play a role in specific dietary settings. Several mechanisms are at play, including receptor abundance and function, neuroendocrine signaling, gene expression, and neuroinflammation. Many open questions on mechanisms remain, including the concentration and times of exposure for effects to manifest and the consequences for nutrition and health. Beyond mechanisms, future research should explore strategies to leverage taste adaptation for healthier food design.

Modulation of sweet preference by neurosteroid-sensitive, δ-GABAA receptors in adult mouse gustatory insular cortex

Taste preference is a fundamental driver of feeding behavior, influencing dietary choices and eating patterns. Extensive experimental evidence indicates that the gustatory cortex (GC) is engaged in taste perception, palatability, and preference. However, our knowledge of the neural and neurochemical signals regulating taste preference is limited. Neuromodulators can affect preferences, though their effects on neural circuits for taste are incompletely understood. Neurosteroids are of particular interest, as systemic administration of the neurosteroid allopregnanolone (ALLO), a positive allosteric modulator of extrasynaptic GABAA receptors containing the delta subunit (δ-GABAARs), induces hyperphagia and increases intake of energy-rich food in humans and animals. The δ-GABAARs receptors produce a tonic inhibitory current and are widely distributed in the brain. However, information regarding their expression within gustatory circuits is lacking, and their role in taste preference has not been investigated. Here, we focused on GC to investigate whether activation of δ-GABAARs affects sweet taste preference in adult mice. Our data reveal that δ-GABAARs are expressed in multiple cell types within GC, mediate an ALLO-sensitive tonic current, decrease the behavioral sensitivity to sucrose, and reduce the preference for sweet taste in a cell-type-specific manner. Our findings demonstrate a fundamental role for δ-GABAAR-mediated currents within GC in regulating taste sensitivity and preference in the adult mammalian brain.

Chemosensory and cardiometabolic improvements after a fasting-mimicking diet: A randomized cross-over clinical trial

Obesity is associated with a decrease in chemosensory perception acuity and increased disease risk, pointing to the need for feasible interventions that affect smell, taste, and cardiometabolic markers. Here, subjects with overweight/obesity are treated with six monthly cycles of a fasting-mimicking diet (FMD) lasting 5 days followed by a normal diet for the rest of the month to determine their effects on chemosensory function and cardiometabolic risk factors. Both arms of the 102 randomized cross-over trial participants indicate FMD-dependent improvements in a wide range of taste and smell chemosensory functions. The portion of hyposmic subjects is reduced from 38.1% at baseline to 6.4% at the end of 6 FMD cycles. FMD cycles also reduce cardiometabolic and inflammatory markers and drug use in diabetic patients. This trial provides evidence for the effect of periodic FMD cycles in improving chemosensory function while reducing cardiometabolic risk factors without requiring long-term lifestyle changes. The trial is registered at ClinicalTrials.gov (NCT04529161).

Research progress of GLP-1RAs in the treatment of type 2 diabetes mellitus

Glucagon-like peptide-1 (GLP-1) is a 30-amino acid intestinal insulin-stimulating factor, which is mainly secreted by L cells in the distal ileum and colon. It has various physiological functions, such as promoting insulin secretion and synthesis, stimulating β-cell proliferation, inducing islet regeneration, inhibiting β-cell apoptosis and glucagon release, delaying gastric emptying and controlling appetite, etc. It plays a role through a specific GLP-1 receptor (GLP-1R) distributed in many organs or tissues and participates in the regulation of glucose homeostasis in the body. GLP-1 receptor agonists (GLP-1RAs) has the similar physiological function of GLP-1. Because of its structural difference from natural GLP-1, it is not easy to be degraded by dipeptidyl peptidase-4 (DPP-4), thus prolonging the action time. GLP-1RAs have been recognized as a new type of hypoglycemic drugs and widely used in the treatment of type 2 diabetes mellitus (T2DM). Compared with other non-insulin hypoglycemic drugs, it can not only effectively reduce blood glucose and glycosylated hemoglobin (HbA1c), but also protect cardiovascular system, nervous system and kidney function without causing hypoglycemia and weight gain. Therefore, GLP-1RAs has good application prospects and potential for further development.

Distinct network patterns emerge from Cartesian and XOR epistasis models: a comparative network science analysis

BACKGROUND

Epistasis, the phenomenon where the effect of one gene (or variant) is masked or modified by one or more other genes, significantly contributes to the phenotypic variance of complex traits. Traditionally, epistasis has been modeled using the Cartesian epistatic model, a multiplicative approach based on standard statistical regression. However, a recent study investigating epistasis in obesity-related traits has identified potential limitations of the Cartesian epistatic model, revealing that it likely only detects a fraction of the genetic interactions occurring in natural systems. In contrast, the exclusive-or (XOR) epistatic model has shown promise in detecting a broader range of epistatic interactions and revealing more biologically relevant functions associated with interacting variants. To investigate whether the XOR epistatic model also forms distinct network structures compared to the Cartesian model, we applied network science to examine genetic interactions underlying body mass index (BMI) in rats (Rattus norvegicus).

RESULTS

Our comparative analysis of XOR and Cartesian epistatic models in rats reveals distinct topological characteristics. The XOR model exhibits enhanced sensitivity to epistatic interactions between the network communities found in the Cartesian epistatic network, facilitating the identification of novel trait-related biological functions via community-based enrichment analysis. Additionally, the XOR network features triangle network motifs, indicative of higher-order epistatic interactions. This research also evaluates the impact of linkage disequilibrium (LD)-based edge pruning on network-based epistasis analysis, finding that LD-based edge pruning may lead to increased network fragmentation, which may hinder the effectiveness of network analysis for the investigation of epistasis. We confirmed through network permutation analysis that most XOR and Cartesian epistatic networks derived from the data display distinct structural properties compared to randomly shuffled networks.

CONCLUSIONS

Collectively, these findings highlight the XOR model's ability to uncover meaningful biological associations and higher-order epistasis derived from lower-order network topologies. The introduction of community-based enrichment analysis and motif-based epistatic discovery emphasize network science as a critical approach for advancing epistasis research and understanding complex genetic architectures.

Healthy dietary choices involve prefrontal mechanisms associated with long-term reward maximization but not working memory

Taste and health are critical factors to be considered when choosing foods. Prioritizing healthiness over tastiness requires self-control. It has also been suggested that self-control is guided by cognitive control. We then hypothesized that neural mechanisms underlying healthy food choice are associated with both self-control and cognitive control. Human participants performed a food choice task and a working memory task during functional MRI scanning. Their degree of self-control was assessed behaviorally by the value discount of delayed monetary rewards in intertemporal choice. Prioritizing healthiness in food choice was associated with greater activity in the superior, dorsolateral, and medial prefrontal cortices. Importantly, the prefrontal activity was greater in individuals with smaller delay discounting (i.e. high self-control) who preferred a delayed larger reward to an immediate smaller reward in intertemporal choice. On the other hand, working memory activity did not show a correlation with delay discounting or food choice activity, which was further supported by supplementary results that analyzed data from the Human Connectome Project. Our results suggest that the prefrontal cortex plays a critical role in healthy food choice, which requires self-control, but not working memory, for maximization of reward attainments in a remote future.

Changes in Food Preferences Before and After Intragastric Balloon Placement

BACKGROUNDS

In recent years, numerous studies have tried to decode the way bariatric surgery works toward weight reduction by the use of food preference questionnaires. The intragastric balloon has gained popularity, mainly due to its limited invasiveness, in patients with obesity not fulfilling criteria for bariatric surgery. However, there is no study assessing the changes in food preferences [FP]. We decided to analyze the FP of individuals prior to intragastric balloon insertion and following its removal, on the strict condition that participants must complete the 6-month treatment period and attend at least 4 of the 7 follow-up interviews.

METHODS

Patients were asked to rate the frequency of consumption of 63 food items before balloon insertion, at monthly intervals and after balloon removal. The food categories were protein, carbohydrates, fruit and vegetables, and sweets and fats.

RESULTS

The questionnaires of 320 participants were analyzed. A reduced frequency in consumption of meat and meat products, high-fat, and high-carbohydrate/sugary products and an increase in raw vegetables and fruit was found in all individuals.

CONCLUSION

The intragastric balloon seems to exert analogically similar mechanisms to bariatric surgery for weight loss, both functioning through alterations in FP. These are dictated by the anatomical re-configuration of the stomach, but mainly by counseling of dieticians and the self-education of the patient after experiencing unpleasant postprandial discomfort.

Distinct Network Patterns Emerge from Cartesian and XOR Epistasis Models: A Comparative Network Science Analysis

Background

Epistasis, the phenomenon where the effect of one gene (or variant) is masked or modified by one or more other genes, can significantly contribute to the observed phenotypic variance of complex traits. To date, it has been generally assumed that genetic interactions can be detected using a Cartesian, or multiplicative, interaction model commonly utilized in standard regression approaches. However, a recent study investigating epistasis in obesity-related traits in rats and mice has identified potential limitations of the Cartesian model, revealing that it only detects some of the genetic interactions occurring in these systems. By applying an alternative approach, the exclusive-or (XOR) model, the researchers detected a greater number of epistatic interactions and identified more biologically relevant ontological terms associated with the interacting loci. This suggests that the XOR model may provide a more comprehensive understanding of epistasis in these species and phenotypes. To further explore these findings and determine if different interaction models also make up distinct epistatic networks, we leverage network science to provide a more comprehensive view into the genetic interactions underlying BMI in this system.

Results

Our comparative analysis of networks derived from Cartesian and XOR interaction models in rats (Rattus norvegicus) uncovers distinct topological characteristics for each model-derived network. Notably, we discover that networks based on the XOR model exhibit an enhanced sensitivity to epistatic interactions. This sensitivity enables the identification of network communities, revealing novel trait-related biological functions through enrichment analysis. Furthermore, we identify triangle network motifs in the XOR epistatic network, suggestive of higher-order epistasis, based on the topology of lower-order epistasis.

Conclusions

These findings highlight the XOR model's ability to uncover meaningful biological associations as well as higher-order epistasis from lower-order epistatic networks. Additionally, our results demonstrate that network approaches not only enhance epistasis detection capabilities but also provide more nuanced understandings of genetic architectures underlying complex traits. The identification of community structures and motifs within these distinct networks, especially in XOR, points to the potential for network science to aid in the discovery of novel genetic pathways and regulatory networks. Such insights are important for advancing our understanding of phenotype-genotype relationships.

Indirect Effects of Body Mass Index and Sweet Taste Responsiveness on E-Cigarette Dependence: The Role of E-Cigarette Motives

Background: Recent research has shown obesity to be associated with e-cigarette use and appeal, but models have yet to examine how weight status may be related to e-cigarette dependence among e-cigarette users. Objectives: To increase our understanding of pathways from body mass index (BMI) to e-cigarette dependence, the present cross-sectional observational study investigated a model in which BMI, sweet taste responsiveness, and the interaction of BMI and sweet taste responsiveness are associated with e-cigarette dependence indirectly via seven conceptually-distinct motives for e-cigarette use. Data from several e-cigarette clinical laboratory research studies were pooled and analyzed; only current e-cigarette users were included in the analyses (N=330). Structural equation modeling was used to analyze the hypothesized model. Results: BMI was positively associated with lower social/environmental goad motives and higher weight control motives, and BMI x sweet taste interaction terms found that sweet taste responsiveness strengthened the association of BMI and weight control motives. BMI was not directly or indirectly associated with e-cigarette dependence nor was there a bivariate association between BMI and e-cigarette dependence. Sweet taste responsiveness was positively associated with greater affiliative attachment motives, cognitive enhancement motives, cue exposure-associative process motives, weight control motives, and affect enhancement motives. Sweet taste responsiveness was bivariately associated with e-cigarette dependence and mediation paths show indirect relations to e-cigarette dependence via three of the seven motives. Conclusions: The findings suggest that sweet taste responsiveness, opposed to BMI, is associated with a wider range of e-cigarette use motives and indirectly relates to e-cigarette dependence via several e-cigarette use motives.

Smell, taste and food habits changes along body mass index increase: an observational study

PURPOSE

To evaluate the changes in gustatory and olfactory sensitivity and dietary habits between healthy lean subjects (LS) and participants affected by overweight (OW), stage I and II obesity and to estimate possible impact of these factors on body mass index (BMI).

METHODS

After a general and ear-nose-throat evaluation, taste and olfactory function testing by means of taste strips and sniffin' stick tests, respectively, and food habits analysis by means of food frequency questionnaire (FFQ), 221 participants (68 LS [33 female; mean age = 53.01 ± 7.54 years]; 51 OW [26 female; mean age = 51.5 ± 12.16 years]; 50 stage I obesity [24 female; mean age = 50.78 ± 13.71 years] and 52 stage II obesity [24 female; mean age = 52.21 ± 13.35 years]) were enrolled in the study.

RESULTS

Significant (p < 0.008) reductions in total and subtest taste and smell scores were found in stage I and II obesity when compared to LS and OW participants. FFQ depicted a progressive intake increase of nutrients along the BMI stages. Significant associations were found between BMI and taste/smell subtests sugar taste carbs, saturated, monounsaturated and polyunsaturated fatty acids.

CONCLUSIONS

These data demonstrated for the first time a parallel impairment in smell and taste in a large sample size of participants from lean to stage II obesity and could reinforce those previous theories claiming that the greater the ability in taste or smell qualities perception, the lower the preference for them, resulting in a lower intake of specific foods.

Impact of a Food Rebalancing Program Associated with Plant-Derived Food Supplements on the Biometric, Behavioral, and Biological Parameters of Obese Subjects

Between 2021 and 2023, the Scientific Council of Dietplus®, a group specialized in overweight and obesity management, conducted a clinical study on 170 volunteer subjects with a BMI > 29 Kg/m2 consecutively recruited. The Dietplus® program comprises nutritional education, intensive, personalized coaching, and consuming food supplements rich in plant derivatives. The aim of this study was to assess the effect of the Dietplus® program on biometric, behavioral, and biological parameters. A control group of 30 obese patients was followed for a similar 12-week period. Mean weight loss reached 9 ± 2.1 kg in the Dietplus® test group versus a 1 ± 0.1 kg weight gain in the control group. Excess weight loss reached 33 ± 13%, and fat mass loss was 7.6% (p < 0.001); waist circumference was reduced by 30%. Quality of Life, Nutriscore, and Prochaska di Clemente scale significantly improved (p < 0.001). Biological parameters showed substantial improvements in the carbohydrate profile and insulin resistance (HOMA index) and in the lipid profile with lower plasma triglyceride (p < 0.01) and VLDL (p < 0.01) concentrations. Inflammatory parameters (orosomucoid, ultrasensitive C-reactive protein, and PINI indices) were also substantially reduced. These results indicate a substantial benefit in subjects who followed the Dietplus® program. (Dietplus® 116 Rue Robert Bunsen, 57460 Behren-lès-Forbach, France is active in France Belgium and Spain. Plant Derived Food Supplements are produced in France). Indeed, improvements were observed in all biometric, behavioral, and metabolic parameters.

Effects of weight change on taste function; a systematic review

BACKGROUND

The aim of this review is to evaluate the relationship between weight status and taste perception and preference of sweet, salt, fat, bitter, and sour through reviewing observational and interventional studies with objective methods.

METHODS

A comprehensive literature search was performed in 6 online databases of PubMed, Scopus, Web of Science, Cochrane, Embase, and Google Scholar up to October 2021. The following keywords were used in the search strategy: (Taste OR "Taste Perception" OR "Taste Threshold" OR "Taste preference" OR "Taste sensitivity" OR "Taste changes") AND (weight OR "Weight gain" OR "weight loss" OR "weight change").

RESULTS

Most observational studies indicate that four taste sensitivities or perceptions (especially sweet and salt taste perception) are lower in subjects with overweight and obesity. The longitudinal studies reported that sweet and fat preference is increased along with weight gain in adults. It is concluded that taste perceptions are decreased in individuals with overweight and obesity, especially in men. Also, taste perception and preference change after weight loss but not significantly.

CONCLUSION

It is suggested that the results of the interventional studies are not conclusive and need further studies with the same and standard design adjusting cofounding variables including genetic, gender, age and food condition of subjects.

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.

Nutritional geometry framework of sucrose taste in Drosophila

Dietary protein (P) and carbohydrate (C) have a major impact on sweet taste sensation. However, it remains unclear whether the balance of P and C influences sweet taste sensitivity. Here, we use the nutritional geometry framework (NGF) to address the interaction of protein and carbohydrates and on sweet taste using Drosophila as a model. Our results reveal that high-protein, low-carbohydrate (HPLC) diets sensitize to sweet taste and low-protein, high-carbohydrate (LPHC) diets desensitize sweet taste in both male and female flies. We further investigate the underlying mechanisms of these two diets' effect on sweet taste using RNA sequencing. When compared to the LPHC diet, the mRNA expression of genes involved in the metabolism of glycine, serine, and threonine is significantly upregulated in the HPLC diet, suggesting these amino acids may mediate sweet taste perception. We further find that sweet sensitization occurs in flies fed with the LPHC diet supplemented with serine and threonine. Our study demonstrates that sucrose taste sensitivity is affected by the balance of dietary protein and carbohydrates possibly through changes in serine and threonine.

Sleeve Gastrectomy-Induced Body Mass Index Reduction Increases the Intensity of Taste Perception's and Reduces Bitter-Induced Pleasantness in Severe Obesity

Background: The sense of taste is involved in food behavior and may drive food choices, likely contributing to obesity. Differences in taste preferences have been reported in normal-weight as compared to obese subjects. Changes in taste perception with an increased sweet-induced sensitivity have been reported in surgically treated obese patients, but data regarding the perception of basic tastes yielded conflicting results. We aimed to evaluate basic taste identification, induced perception, and pleasantness in normal-weight controls and obese subjects before and after bariatric surgery. Methods: Severe obese and matched normal weight subjects underwent a standardized spit test to evaluate sweet, bitter, salty, umami, and sour taste identification, induced perception, and pleasantness. A subset of obese subjects were also studied before and 12 months after sleeve gastrectomy. Results: No significant differences in basic taste-induced perceptions were observed, although a higher number of controls correctly identified umami than did obese subjects. Sleeve-gastrectomy-induced weight loss did not affect the overall ability to correctly identify basic tastes but was associated with a significant increase in taste intensities, with higher scores for sour and bitter, and a significantly reduced bitter-induced pleasantness. Conclusions: The perception of basic tastes is similar in normal-weight and severely obese subjects. Sleeve-gastrectomy-induced weight loss significantly increases basic taste-induced intensity, and selectively reduces bitter-related pleasantness without affecting the ability to identify the tastes. Our findings reveal that taste perception is influenced by body mass index changes, likely supporting the hypothesis that centrally mediated mechanisms modulate taste perception in severe obesity.

Changes in Food Choice, Taste, Desire, and Enjoyment 1 Year after Sleeve Gastrectomy: A Prospective Study

Obesity is a well-recognized global health problem, and bariatric surgery (BS)-induced weight reduction has been demonstrated to improve survival and obesity-related conditions. Sleeve gastrectomy (SG) is actually one of the most performed bariatric procedures. The underlying mechanisms of weight loss and its maintenance after SG are not yet fully understood. However, changes to the taste function could be a contributing factor. Data on the extent of the phenomenon are limited. The primary objective was to assess, through validated questionnaires, the percentage of patients who report an altered perception of post-SG taste and compare the frequency of intake of the different food classes before SG and after 1 year follow-up. The secondary objective was to evaluate the total body weight change. Materials and Methods: We prospectively investigated the changes in food choice and gustatory sensitivity of 52 patients (55.8% females) 12 months after SG. The mean initial weight and body mass index (BMI) were 130.9 ± 24.7 kg and 47.4 ± 7.1 kg/m2, respectively. The frequency of food intake was assessed by food-frequency questionnaire, while changes in taste perception were assessed using the taste desire and enjoyment change questionnaire. The change in total body weight was also assessed. Results: A significant decrease in the intake frequency of bread and crackers (p < 0.001), dairy products and fats (p < 0.001), sweets and snacks (p < 0.001) and soft drinks (p < 0.001), and a significant increase in the frequency of vegetable and fruit consumption (p < 0.001) were observed at 12 months after SG in both genders. On the contrary, we found no significant changes in the frequency of meat and fish intake in females (p = 0.204), whereas a significant change was found in males (p = 0.028). Changes in perceived taste intensity of fatty foods (p = 0.021) and tart foods (p = 0.006) for females and taste of bitter foods for females and males (p = 0.002; p = 0.017) were found. Regarding the change in food desire for both genders, there was a decrease in the desire for sweet, fatty, and salty foods, whereas there was an increasing trend in the desire for tart foods, especially for females. Significant reduction in total body weight and BMI was observed in both genders at the time of follow-up. Conclusions: Based on our findings, we are able to support the evidence that changes in taste, desire, and enjoyment of taste are very common after SG, with a reduced preference for food with high sugar and fat content and an increased postoperative preference for low-sugar and -fat foods. However, further investigation is needed to clarify this issue. The molecular, hormonal, and central mechanisms underlying these changes in taste perception need to be further elucidated, as they could identify new targets able to modify obesogenic eating behavior, opening up a novel personalized therapeutic approach to obesity.

The Influence of Roux-en-Y Gastric Bypass and Diet on NaCl and Sucrose Taste Detection Thresholds and Number of Circumvallate and Fungiform Taste Buds in Female Rats

Roux-en-Y gastric bypass (RYGB) in rats attenuates preference for, and intake of, sugar solutions. Additionally, maintenance on a high-fat diet (HFD) reportedly alters behavioral responsiveness to sucrose in rodents in short-term drinking tests. Due to the fact that the behavioral tests to date rely on the hedonic value of the stimulus to drive responsiveness, we sought to determine whether taste detection thresholds to sucrose and NaCl are affected by these manipulations as measured in an operant two-response signal detection paradigm. Female rats were maintained on HFD or chow for 10 weeks, at which point animals received either RYGB or SHAM surgery followed by a gel-based diet and then powdered chow. Upon recovery, half of the rats that were previously on HFD were switched permanently to chow, and the other rats were maintained on their presurgical diets (n = 5–9/diet condition x surgery group for behavioral testing). The rats were then trained and tested in a gustometer. There was a significant interaction between diet condition and surgery on NaCl threshold that was attributable to a lower value in RYGB vs. SHAM rats in the HFD condition, but this failed to survive a Bonferroni correction. Importantly, there were no effects of diet condition or surgery on sucrose thresholds. Additionally, although recent evidence suggests that maintenance on HFD alters taste bud number in the circumvallate papillae (CV) of mice, in a subset of rats, we did not find that diet significantly influenced taste pores in the anterior tongue or CV of female rats. These results suggest that any changes in sucrose responsiveness in intake/preference or hedonically oriented tests in rats as a function of HFD maintenance or RYGB are not attributable to alterations in taste sensitivity.

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.

The Influence of Common Noncommunicable Diseases on Chemosensory Perception and Clinical Implications in Children and Adolescents

An increased incidence of noninfectious chronic diseases, such as obesity, diabetes, and allergies, has been noted in the last century, especially in the last 2 to 3 generations. Evidence suggested that the interrelation among these chronic conditions in pediatric age (e.g., children and adolescents aged 4-16 y) is complex and still unknown, reinforcing the interest of pediatricians in these diseases. Of interest is the need to better understand the link between these pathologies and sensory perception, since the chemical senses of taste and smell, together with chemesthesis, are reported to have a role in food choices and may provide a novel target for intervention in the treatment of these pathologies. This review aims to explore the current evidence on the link between these chronic conditions and chemosensory perception (i.e., taste and smell). In addition, the putative role that chemosensory perception may have on food choices and eating behavior of children and adolescents affected by these diseases are highlighted. Furthermore, the review addresses the unexplored issues that need to be investigated in this area. The literature data search suggested that no clear relation between taste and smell perception and the aforementioned diseases in young population yet exists. However, some possible trends have been highlighted in the adult population, in whom the duration of disease might have affected the relation. There is a need for further, high-quality, hypothesis-led research, with robust measures of taste and smell functions as the primary outcomes, to strengthen or deny this evidence.

Phenotyping of Drosophila Melanogaster-A Nutritional Perspective

The model organism Drosophila melanogaster was increasingly applied in nutrition research in recent years. A range of methods are available for the phenotyping of D. melanogaster, which are outlined in the first part of this review. The methods include determinations of body weight, body composition, food intake, lifespan, locomotor activity, reproductive capacity and stress tolerance. In the second part, the practical application of the phenotyping of flies is demonstrated via a discussion of obese phenotypes in response to high-sugar diet (HSD) and high-fat diet (HFD) feeding. HSD feeding and HFD feeding are dietary interventions that lead to an increase in fat storage and affect carbohydrate-insulin homeostasis, lifespan, locomotor activity, reproductive capacity and stress tolerance. Furthermore, studies regarding the impacts of HSD and HFD on the transcriptome and metabolome of D. melanogaster are important for relating phenotypic changes to underlying molecular mechanisms. Overall, D. melanogaster was demonstrated to be a valuable model organism with which to examine the pathogeneses and underlying molecular mechanisms of common chronic metabolic diseases in a nutritional context.

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.

Cellular and Molecular Mechanisms of Fat Taste Perception

During the last couples of years, a number of studies have increasingly accumulated on the gustatory perception of dietary fatty acids in rodent models and human beings in health and disease. There is still a debate to coin a specific term for the gustatory perception of dietary fatty acids either as the sixth basic taste quality or as an alimentary taste. Indeed, the psycho-physical cues of orosensory detection of dietary lipids are not as distinctly perceived as other taste qualities like sweet or bitter. The cellular and molecular pharmacological mechanisms, triggered by the binding of dietary long-chain fatty acids (LCFAs) to tongue taste bud lipid receptors like CD36 and GPR120, involve Ca²⁺ signaling as other five basic taste qualities. We have not only elucidated the role of Ca²⁺ signaling but also identified different components of the second messenger cascade like STIM1 and MAP kinases, implicated in fat taste perception. We have also demonstrated the implication of Calhm1 voltage-gated channels and store-operated Ca²⁺ (SOC) channels like Orai1, Orai1/3, and TRPC3 in gustatory perception of dietary fatty acids. We have not only employed siRNA technology in vitro and ex vivo on tissues but also used animal models of genetic invalidation of STIM1, ERK1, Orai1, Calhm1 genes to explore their implications in fat taste signal transduction. Moreover, our laboratory has also demonstrated the importance of LCFAs detection dysfunction in obesity in animal models and human beings.

Taste perception in children with different caries activity

PURPOSE

The aim of the study was to investigate whether caries-active and caries-free children differ in terms of their taste perception for sweet, sour, salty and bitter.

METHODS

The study group consisted of 100 children aged 5-10 years: 50 caries-free children and 50 children with at least four untreated carious lesions. Taste perception was analysed using two test systems. First, filter paper strips impregnated with four taste qualities (sweet, sour, salty, and bitter) at four defined intensities were used ("taste strips"). Then a tasting spray in suprathreshold concentration of the respective taste was applied. The children were asked to name the perceived taste. The parents answered a questionnaire about the children's dietary habits.

RESULTS

The children with high caries activity scored lower on average on the taste strips than the caries-free participants. For the taste sprays, the perception of the taste quality "bitter" was significantly worse in the children with caries than in caries-free children (Mann-Whitney U test p < 0.05).

CONCLUSION

The results of this study suggest that taste preferences in children are associated with increased susceptibility to tooth decay.

Chronic exposure to cafeteria-style diet in rats alters sweet taste preference and reduces motivation for, but not 'liking' of sucrose

Obesity is associated with changes to taste perception and brain reward circuitry. It is important to understand how these effects alter the preference for palatable foods and drinks, given that these are widely consumed, and leading risk factors for obesity. This study examined the effects of diet-induced obesity on sweet taste preference by analysing the microstructure of licking for sugar solutions and assessing pERK expression in the nucleus accumbens shell and insula. Adult male Sprague-Dawley rats were fed standard chow (Control; n = 16) or a varied, palatable cafeteria diet (Caf; n = 16) for 12 weeks. Two-choice preference tests between 2%, 8% and 32% sucrose solutions were conducted at baseline and in weeks 11-12 of the diet. Rats in the Caf group trebled energy intake and doubled weight gain relative to controls. In tests held under water restriction after 11 weeks of diet, the Control group reliably preferred higher sucrose concentrations (i.e., 32% > 8% > 2%). Relative to controls, the Caf group showed a stronger preference for 32% vs. 2% sucrose, lower preference for 32% vs. 8% sucrose, and were indifferent to 8% vs. 2% sucrose. Testing without water restriction increased preference for higher sucrose concentrations in both groups. Chronic Caf diet increased the latency to lick, decreased total licks and reduced alternations between spouts, but did not alter lick cluster size, a measure of hedonic appraisal, on any test. Following a final exposure to a novel sucrose concentration, neuronal activity (pERK) in the insula and nucleus accumbens shell was significantly reduced in the Caf group. Results indicate that differences in 'liking' do not underlie obesity-induced changes to sweet taste preference.

Glucagon-like peptide-1, a matter of taste?

Understanding of gustatory coding helps to predict, and perhaps even modulate the ingestive decision circuitry, especially when eating behaviour becomes dysfunctional. Preclinical research demonstrated that glucagon like peptide 1 (GLP-1) is locally synthesized in taste bud cells in the tongue and that GLP-1 receptor exists on the gustatory nerves in close proximity to GLP-1 containing taste bud cells. In humans, the tongue has not yet been addressed as clinically relevant target for GLP-1 based therapies. The primary aim of the current review was to elaborate on the role of GLP- 1 in mammalian gustatory system, in particular in the perception of sweet. Secondly, we aimed to explore what modulates gustatory coding and whether the GLP-1 based therapies might be involved in regulation of taste perception. We performed a series of PubMed, Medline and Embase databases systemic searches. The Population-Intervention-Comparison-Outcome (PICO) framework was used to identify interventional studies. Based on the available data, GLP-1 is specifically involved in the perception of sweet. Aging, diabetes and obesity are characterized by diminished taste and sweet perception. Calorie restriction and bariatric surgery are associated with a diminished appreciation of sweet food. GLP-1 receptor agonists (RAs) modulate food preference, yet its modulatory potential in gustatory coding is currently unknown. Future studies should explore whether GLP-1 RAs modulate taste perception to the extent that changes of food preference and consumption ensue.

Post-oral sensing of fat increases food intake and attenuates body weight defense

In mammals, changes in weight elicit responses that favor a return to one's previous weight and promote weight stability. It has been hypothesized that palatable sweet and high-fat foods disturb the defense of body weight, leading to weight gain. We find that increasing sweetness or percent calories from fat increases diet palatability but that only increases in nutritive fat content increase caloric intake and body weight. In a mouse model of overfeeding that activates weight defense, high-fat diets, but not sweetened diets, attenuate the defense of body weight, leading to weight gain. The ability of a palatable, high-fat diet to increase food intake does not require tasting or smelling the food. Instead, the direct infusion of a high-fat diet into the stomach increases the ad libitum intake of less palatable, low-fat food. Post-oral sensing of percent calories from fat modulates feeding behavior to alter weight stability.

C-section birth increases offspring obesity risk dependent on maternal diet and obesity status in rats

OBJECTIVE

The gut microbiota is a complex ecosystem that shapes host metabolism, especially in early life. Maternal vaginal and gut microbiota is vertically transmitted to offspring during natural birth. Offspring born by cesarean section (CS) do not receive these bacteria and exhibit higher obesity risk later in life. The objective of this study was to examine differences in obesity risk between offspring born naturally (NB) or by CS to lean/obese dams.

METHODS

Lean and obese rat dams gave birth to offspring naturally or by CS. Offspring obesity risk was analyzed via body weight/composition, food intake, sucrose preference, gut microbiota, and gene expression in gut and brain tissues.

RESULTS

Obese (O)+CS offspring showed greater weight gain and caloric intake but a reduction in hypothalamic agouti related neuropeptide, neuropeptide Y, and interleukin 1β expression compared with O+NB offspring. Lean (L)+CS offspring had higher serum corticosterone concentration and reduced liver peroxisome proliferator-activated receptor γ expression compared with L+NB. O+CS offspring had long-term alterations to gut microbiota, including increased relative abundance of Faecalibaculum and reduced Muribaculaceae.

CONCLUSIONS

Overall, CS alters obesity risk differentially based on maternal obesity status. Further studies looking at the risks of obesity associated with CS are needed, with special attention paid to maternal obesity status and gut microbiota.

The prevalence of constipation and its relation to sweet taste preference among patients receiving methadone maintenance treatment

BACKGROUND

Preference for sweet-tasting foods, weight gain, and constipation characterize patients receiving methadone maintenance treatment (MMT). The prevalence of constipation in MMT and its relation to preference for sweet taste and body mass index (BMI) are undetermined.

METHODS

A random sample of 83 patients was interviewed for constipation with the Patient Assessment Constipation Quality of Life (PAC-QOL) questionnaire. They rated taste intensity and reward of sweet, salty, and sour solutions by means of a nine-point Likert scale. Data on their BMI, drugs in urine, methadone dose, and serum levels were analyzed.

RESULTS

Forty-two patients reported minimum to severe constipation. They characterized as having longer durations of opioid usage before MMT and worse sleep quality than non-constipated patients (logistic regression). Constipation intensity was inversely correlated with duration in MMT and linearly correlated with the Patient Assessment Constipation Quality of Life score. Patients with constipation rated reward to sweet taste significantly higher with no differences in taste intensity compared to non-constipated patients. Patients with high methadone serum levels (≥750 ng/mL) rated taste intensity significantly lower compared to those with normal methadone serum levels (<750 ng/mL), and the lowest rates were reported among patients with no constipation and high methadone serum levels.

CONCLUSIONS

Constipation was highly prevalent among MMT patients and associated with poor sleep and lower quality of life. The relation to preference for sweets, as reflected by higher reward rating, strongly supports the need for nutritional intervention to alleviate constipation symptoms and improve quality of life and sleep.

Do Gut Microbes Taste?

Gut microbiota has emerged as a major metabolically active organ with critical functions in both health and disease. The trillions of microorganisms hosted by the gastrointestinal tract are involved in numerous physiological and metabolic processes including modulation of appetite and regulation of energy in the host spanning from periphery to the brain. Indeed, bacteria and their metabolic byproducts are working in concert with the host chemosensory signaling pathways to affect both short- and long-term ingestive behavior. Sensing of nutrients and taste by specialized G protein-coupled receptor cells is important in transmitting food-related signals, optimizing nutrition as well as in prevention and treatment of several diseases, notably obesity, diabetes and associated metabolic disorders. Further, bacteria metabolites interact with specialized receptors cells expressed by gut epithelium leading to taste and appetite response changes to nutrients. This review describes recent advances on the role of gut bacteria in taste perception and functions. It further discusses how intestinal dysbiosis characteristic of several pathological conditions may alter and modulate taste preference and food consumption via changes in taste receptor expression.

Does intervention with GLP-1 receptor agonist semaglutide modulate perception of sweet taste in women with obesity: study protocol of a randomized, single-blinded, placebo-controlled clinical trial

Background

Preclinical studies demonstrated that glucagon-like peptide 1 (GLP-1) is locally synthesized in taste bud cells and that GLP-1 receptor exists on the gustatory nerves in close proximity to GLP-1-containing taste bud cells. This local paracrine GLP-1 signalling seems to be specifically involved in the perception of sweets. However, the role of GLP-1 in taste perception remains largely unaddressed in clinical studies. Whether any weight-reducing effects of GLP-1 receptor agonists are mediated through the modulation of taste perception is currently unknown.

Methods and analysis

This is an investigator-initiated, randomized single-blind, placebo-controlled clinical trial. We will enrol 30 women with obesity and polycystic ovary syndrome (PCOS). Participants will be randomized in a 1:1 ratio to either semaglutide 1.0 mg or placebo for 16 weeks. The primary endpoints are alteration of transcriptomic profile of tongue tissue as changes in expression level from baseline to follow-up after 16 weeks of treatment, measured by RNA sequencing, and change in taste sensitivity as detected by chemical gustometry. Secondary endpoints include change in neural response to visual food cues and to sweet-tasting substances as assessed by functional MRI, change in body weight, change in fat mass and change in eating behaviour and food intake.

Discussion

This is the first study to investigate the role of semaglutide on taste perception, along with a neural response to visual food cues in reward processing regions. The study may identify the tongue and the taste perception as a novel target for GLP-1 receptor agonists.

Ethics and disseminations

The study has been approved by the Slovene National Medical Ethics Committee and will be conducted in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines. Results will be submitted for publication in an international peer-reviewed scientific journal.

Trial registration

ClinicalTrials.govNCT04263415. Retrospectively registered on 10 February 2020

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-021-05442-y.

To Detect and Reject, Parallel Roles for Taste and Immunity

PURPOSE OF REVIEW

From single cells to entire organisms, biological entities are in constant communication with their surroundings, deciding what to 'allow' in, and what to reject. In very different ways, the immune and taste systems both fulfill this function, with growing evidence suggesting a relationship between the two, through shared signaling pathways, receptors, and feedback loops. The purpose of this review was to explore recent reports on taste and immunity in model animals and in humans to explore our understanding of the interplay between these systems.

RECENT FINDINGS

Acute infections in the upper airway, as with SARS-CoV-2, are associated with a proinflammatory state, and blunted taste perception. Further, recent findings highlight taste receptors working as immune sentinels throughout the body. Work in humans and mice also points to inflammation from obesity impacting taste, altering taste bud abundance and composition. There is accumulating evidence that taste cells, and particularly their receptors, play a role in airway and gut immunity, responsive to invading organisms. Inflammation itself may further act on taste buds and other taste receptor expressing cells throughout the body as a form of homeostatic control.

Food Preferences and Obesity

Obesity is a multifactorial disease with several potential causes that remain incompletely understood. Recent changes in the environment, which has become increasingly obesogenic, have been found to interact with individual factors. Evidence of the role of taste responsiveness and food preference in obesity has been reported, pointing to a lower taste sensitivity and a higher preference and intake of fat and, to a lesser extent, sweet foods in obese people. Studies in the last decades have also suggested that individual differences in the neurophysiology of food reward may lead to overeating, contributing to obesity. However, further studies are needed to confirm these findings. In fact, only a limited number of studies has been conducted on large samples, and several studies were conducted only on women. Larger balanced studies in terms of sex/gender and age are required in order to control the confounding effect of these variables. As many factors are intertwined in obesity, a multidisciplinary approach is needed. This will allow a better understanding of taste alteration and food behaviours in obese people in order to design more effective strategies to promote healthier eating and to prevent obesity and the related chronic disease risks.

Confection Confusion: Interplay Between Diet, Taste, and Nutrition

Although genetics shapes our sense of taste to prefer some foods over others, taste sensation is plastic and changes with age, disease state, and nutrition. We have known for decades that diet composition can influence the way we perceive foods, but many questions remain unanswered, particularly regarding the effects of chemosensory plasticity on feeding behavior. Here, we review recent evidence on the effects of high-nutrient diets, especially high dietary sugar, on sweet taste in vinegar flies, rodents, and humans, and discuss open questions about molecular and neural mechanisms and research priorities. We also consider ways in which diet-dependent chemosensory plasticity may influence food intake and play a role in the etiology of obesity and metabolic disease. Understanding the interplay between nutrition, taste sensation, and feeding will help us define the role of the food environment in mediating chronic disease and design better public health strategies to combat it.

What Role Does the Endocannabinoid System Play in the Pathogenesis of Obesity?

The endocannabinoid system (ECS) is an endogenous signaling system formed by specific receptors (cannabinoid type 1 and type 2 (CB₁ and CB₂)), their endogenous ligands (endocannabinoids), and enzymes involved in their synthesis and degradation. The ECS, centrally and peripherally, is involved in various physiological processes, including regulation of energy balance, promotion of metabolic process, food intake, weight gain, promotion of fat accumulation in adipocytes, and regulation of body homeostasis; thus, its overactivity may be related to obesity. In this review, we try to explain the role of the ECS and the impact of genetic factors on endocannabinoid system modulation in the pathogenesis of obesity, which is a global and civilizational problem affecting the entire world population regardless of age. We also emphasize that the search for potential new targets for health assessment, treatment, and the development of possible therapies in obesity is of great importance.

Glucagon-Like Peptide 1 and Taste Perception: From Molecular Mechanisms to Potential Clinical Implications

Preclinical studies provided some important insights into the action of glucagon-like peptide 1 (GLP-1) in taste perception. This review examines the literature to uncover some molecular mechanisms and connections between GLP-1 and the gustatory coding. Local GLP-1 production in the taste bud cells, the expression of GLP-1 receptor on the adjacent nerves, a functional continuum in the perception of sweet chemicals from the gut to the tongue and an identification of GLP-1 induced signaling pathways in peripheral and central gustatory coding all strongly suggest that GLP-1 is involved in the taste perception, especially sweet. However, the impact of GLP-1 based therapies on gustatory coding in humans remains largely unaddressed. Based on the molecular background we encourage further exploration of the tongue as a new treatment target for GLP-1 receptor agonists in clinical studies. Given that pharmacological manipulation of gustatory coding may represent a new potential strategy against obesity and diabetes, the topic is of utmost clinical relevance.

Microbiota-gut-brain axis as a regulator of reward processes

Our gut harbours trillions of microorganisms essential for the maintenance of homeostasis and host physiology in health and disease. In the last decade, there has been a growing interest in understanding the bidirectional pathway of communication between our microbiota and the central nervous system. With regard to reward processes there is accumulating evidence from both animal and human studies that this axis may be a key factor in gating reward valence. Focusing on the mesocorticolimbic pathway, we will discuss how the intestinal microbiota is involved in regulating brain reward functions, both in natural (i.e. eating, social or sexual behaviours) and non-natural reinforcers (drug addiction behaviours including those relevant to alcohol, psychostimulants, opioids and cannabinoids). We will integrate preclinical and clinical evidence suggesting that the microbiota-gut-brain axis could be implicated in the development of disorders associated with alterations in the reward system and how it may be targeted as a promising therapeutic strategy. Cover Image for this issue: https://doi.org/10.1111/jnc.15065.

Glucagon-like peptide-1, a matter of taste?

Understanding of gustatory coding helps to predict, and perhaps even modulate the ingestive decision circuitry, especially when eating behaviour becomes dysfunctional. Preclinical research demonstrated that glucagon like peptide 1 (GLP-1) is locally synthesized in taste bud cells in the tongue and that GLP-1 receptor exists on the gustatory nerves in close proximity to GLP-1 containing taste bud cells. In humans, the tongue has not yet been addressed as clinically relevant target for GLP-1 based therapies. The primary aim of the current review was to elaborate on the role of GLP- 1 in mammalian gustatory system, in particular in the perception of sweet. Secondly, we aimed to explore what modulates gustatory coding and whether the GLP-1 based therapies might be involved in regulation of taste perception. We performed a series of PubMed, Medline and Embase databases systemic searches. The Population-Intervention-Comparison-Outcome (PICO) framework was used to identify interventional studies. Based on the available data, GLP-1 is specifically involved in the perception of sweet. Aging, diabetes and obesity are characterized by diminished taste and sweet perception. Calorie restriction and bariatric surgery are associated with a diminished appreciation of sweet food. GLP-1 receptor agonists (RAs) modulate food preference, yet its modulatory potential in gustatory coding is currently unknown. Future studies should explore whether GLP-1 RAs modulate taste perception to the extent that changes of food preference and consumption ensue.

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

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

Administration of small-molecule guanabenz acetate attenuates fatty liver and hyperglycemia associated with obesity

Nonalcoholic fatty liver disease (NAFLD) is characterized by excessive accumulation of hepatic triglycerides (TG) and hyperglycemia arising due to persistent insulin resistance, and is profoundly linked to obesity. However, there is currently no established treatment for NAFLD in obese human subjects. We previously isolated Helz2, the expression of which was upregulated in human and mouse NAFLD, and its deletion activated the hepatic expression of functional leptin receptor long form (Leprb) and suppressed NAFLD development and body weight (BW) gain in obese mice. A high-throughput assay of small-molecule drugs revealed that guanabenz acetate (Ga), originally used to treat hypertension, possesses a high affinity constant against HELZ2, and its administration activates LEPRB expression in HepG2 cells in vitro. The chronic oral administration of Ga shows the selective leptin sensitization in the liver via upregulation of hepatic Leprb expression, which affects expression of genes involved in lipogenesis and fatty acid β-oxidation and diminishes hepatocyte hypertrophy with droplets enriched in TG in high-fat diet-induced obese mice. This activity significantly improves insulin resistance to decrease hyperglycemia and hepatocyte and adipocyte weights, resulting in BW reduction without reducing food intake. Regarding drug repositioning, Ga has the potential to effectively treat NAFLD and hyperglycemia in obese patients.

High Dietary Sugar Reshapes Sweet Taste to Promote Feeding Behavior in Drosophila melanogaster

Recent studies find that sugar tastes less intense to humans with obesity, but whether this sensory change is a cause or a consequence of obesity is unclear. To tackle this question, we study the effects of a high sugar diet on sweet taste sensation and feeding behavior in Drosophila melanogaster. On this diet, fruit flies have lower taste responses to sweet stimuli, overconsume food, and develop obesity. Excess dietary sugar, but not obesity or dietary sweetness alone, caused taste deficits and overeating via the cell-autonomous action of the sugar sensor O-linked N-Acetylglucosamine (O-GlcNAc) transferase (OGT) in the sweet-sensing neurons. Correcting taste deficits by manipulating the excitability of the sweet gustatory neurons or the levels of OGT protected animals from diet-induced obesity. Our work demonstrates that the reshaping of sweet taste sensation by excess dietary sugar drives obesity and highlights the role of glucose metabolism in neural activity and behavior.

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.

GLP-1 Analog Modulates Appetite, Taste Preference, Gut Hormones, and Regional Body Fat Stores in Adults with Obesity

PURPOSE

Obesity is associated with alterations in appetite, gastrointestinal hormone levels and excessive fat mass. We previously published a double-blind, placebo-controlled, randomized, 16-week trial on effects of once-daily glucagon-like peptide-1 (GLP-1) analog, liraglutide on weight, satiation, and gastric functions in obese volunteers. The aim of this substudy is to compare to placebo the effects of liraglutide on appetite, taste preference, regional body fat stores, and anthropometric measurements.

METHODS

Forty obese adults received standard instruction for weight management, monthly behavioral intervention utilizing motivational interviews, and 16-week treatment of once-daily liraglutide (escalated to 3 mg SQ daily). At baseline and 16 weeks, the following were measured: appetite and taste preferences rated every 30 min for 5 h after ingesting 300 mL Ensure®; maximal tolerated volume (MTV) with a nutrient drink test; fasting and postprandial bioactive GLP-1 (7-36) and peptide YY (PYY) levels; total and regional body fat with dual-energy X-ray absorptiometry, and waist and hip circumference.

RESULTS

Thirty-five participants (17 liraglutide; 18 placebo) completed the trial. Compared to placebo group, liraglutide group had significant reductions in MTV; prospective food consumption score; desire to eat something sweet, salty, savory or fatty; and an increase in perceived fullness. Postprandial plasma levels of GLP-1 decreased and PYY levels increased with liraglutide relative to baseline. Significant reductions in total body, trunk, and upper and lower body fat without reduction in lean body mass were observed.

CONCLUSION

Liraglutide 3 mg SQ modulates appetite, taste preference, gut hormones, and regional body fat stores in adults with obesity without reduction in lean body mass.

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.

The Microbiota-Gut-Brain Axis

The importance of the gut-brain axis in maintaining homeostasis has long been appreciated. However, the past 15 yr have seen the emergence of the microbiota (the trillions of microorganisms within and on our bodies) as one of the key regulators of gut-brain function and has led to the appreciation of the importance of a distinct microbiota-gut-brain axis. This axis is gaining ever more traction in fields investigating the biological and physiological basis of psychiatric, neurodevelopmental, age-related, and neurodegenerative disorders. The microbiota and the brain communicate with each other via various routes including the immune system, tryptophan metabolism, the vagus nerve and the enteric nervous system, involving microbial metabolites such as short-chain fatty acids, branched chain amino acids, and peptidoglycans. Many factors can influence microbiota composition in early life, including infection, mode of birth delivery, use of antibiotic medications, the nature of nutritional provision, environmental stressors, and host genetics. At the other extreme of life, microbial diversity diminishes with aging. Stress, in particular, can significantly impact the microbiota-gut-brain axis at all stages of life. Much recent work has implicated the gut microbiota in many conditions including autism, anxiety, obesity, schizophrenia, Parkinson’s disease, and Alzheimer’s disease. Animal models have been paramount in linking the regulation of fundamental neural processes, such as neurogenesis and myelination, to microbiome activation of microglia. Moreover, translational human studies are ongoing and will greatly enhance the field. Future studies will focus on understanding the mechanisms underlying the microbiota-gut-brain axis and attempt to elucidate microbial-based intervention and therapeutic strategies for neuropsychiatric disorders.

Effects of Weight Loss on Sweet Taste Preference and Palatability following Cognitive Behavioral Therapy for Women with Obesity

OBJECTIVE

Current evidence suggests that obesity is associated with alteration of sweet taste perception. The purpose of this study was to determine if nonsurgical cognitive behavioral therapy (CBT)-based weight loss can cause a change in sweet taste perception.

METHODS

This case-control study consisted of 51 women aged 21-64 years. Twenty-seven with obesity or overweight were assigned to an obesity (OB) group (BMI: 29.8 ± 0.5 kg/m2) and 24 to a normal control (NC) group (BMI: 20.9 ± 0.3 kg/m2). The OB group underwent a 30-week weight loss intervention using CBT-based group therapy. The results of measurement of detection threshold, suprathreshold perceived intensity, preference, and palatability, elements of sweet taste perception, were compared before and after the intervention. Psychological variables and appetite-related hormonal levels were measured.

RESULTS

Twenty-three patients and 22 controls completed the study. The OB group showed a 14.6% weight loss after the intervention. At baseline, the OB group preferred significantly higher sucrose concentrations than did the NC group; however, this difference was no longer significant after intervention. In the OB group, persistent pleasure and reduced desire for other taste, measured by repeated exposure to sweetness, normalized after weight loss to levels comparable to those seen in the NC group. No significant difference in discriminative perception of the threshold concentration or the suprathreshold sensory value was found between the two groups before or after intervention. A significant correlation was found between the basal preferred sucrose concentration and the serum leptin level of the OB group after adjusting for confounding factors, such as BMI, depressive symptom score, and trait-anxiety scores.

CONCLUSIONS

Weight loss induced by CBT-based nonsurgical intervention resulted in the normalization of the sucrose preference and palatability of women with obesity. Leptin activity may be associated with the altered sweet taste preference of people with obesity.

Different and Unequal: A Qualitative Evaluation of Salient Factors Influencing Energy Intake in Adults with Overweight and Obesity

Environmental factors such as food availability and variety can function as cues for overeating in individuals susceptible to overweight or obesity, but relatively little is known about other types of environmental factors that may also be important. This qualitative study compared and contrasted categories of internal and external cues through focus groups and key informant interviews with 24 adults (26 to 77 years old) in the United States who had a body mass index within the healthy range (21.6 ± 2.5 kg/m²) or had overweight or obesity (29.1 ± 3.6 kg/m²). Five domains of external factors influencing food intake were identified: (a) Environmental cues including food availability and variety; (b) normative expectations for dietary intake; (c) food palatability; (d) overt social pressures to overeat; and (e) perceived social expectations around eating. All external domains were noted by participants with overweight or obesity to be challenging, and solutions to avoid overeating were lacking; however, overt social pressures and perceived social expectations appeared to be especially problematic. By explicitly defining different domains of external factors that challenge healthy weight regulation, this study identifies specific targets to address in interventions for healthy weight management.