Neurobiological and Microbiota Alterations After Bariatric Surgery: Implications for Hunger, Appetite, Taste, and Long-Term Metabolic Health

Bariatric surgery (BS) is an effective intervention for obesity, inducing significant neurobiological and gut microbiota changes that influence hunger, appetite, taste perception, and long-term metabolic health. This narrative review examines these alterations by analyzing recent findings from clinical and preclinical studies, including neuroimaging, microbiome sequencing, and hormonal assessments. BS modulates appetite-regulating hormones, reducing ghrelin while increasing glucagon-like peptide-1 (GLP-1) and peptide tyrosine-tyrosine (PYY), leading to enhanced satiety and decreased caloric intake. Neuroimaging studies reveal structural and functional changes in brain regions involved in reward processing and cognitive control, contributing to reduced cravings and altered food choices. Additionally, BS reshapes the gut microbiota, increasing beneficial species such as Akkermansia muciniphila, which influence metabolic pathways through short-chain fatty acid production and bile acid metabolism. These findings highlight the complex interplay between the gut and the brain in post-surgical metabolic regulation. Understanding these mechanisms is essential for optimizing post-operative care, including nutritional strategies and behavioral interventions. Future research should explore how these changes impact long-term outcomes, guiding the development of targeted therapies to enhance the recovery and quality of life for BS patients.

Selective increases in taste sensitivity to glucose as a function of hunger status

Glucose is critical for normal metabolic function in humans. Accordingly, the ability to sense glucose and glucose-containing saccharides is crucial for maintenance of energy homeostasis. Here, we report the evidence that glucose is perceived relatively stronger compared to fructose or sucralose when subjects are hungry. In the initial experiment, we measured the relative sensitivities between glucose and fructose when subjects were fasted vs. fed. Overnight fasted subjects (n = 22) completed a series of 3-AFC tests comparing one target (glucose from a range of concentrations) and two constants (200 mM fructose) before and after consuming mild-tasting breakfast sandwiches until satiated (738 ± 60 kcal). We found that the relative sensitivity to glucose as compared to fructose was significantly higher when individuals were hungry vs. satiated (p < 0.001). We replicated this finding by comparing the same range of glucose concentrations to a constant sucralose concentration (0.04 mM) (N = 19, p < 0.001). Importantly, when we compared a fixed concentration of sucralose (0.4 mM) to a range of fructose concentrations, we saw no difference in iso-intense concentration before and after eating (N = 19, p > 0.05). These findings support the hypothesis that hunger selectively increases taste sensitivity of glucose compared to other sweeteners.

Determining the sweet detection threshold of COVID-19 patients during infection and recovery periods

BACKGROUND

The loss of taste and smell is a common symptom of COVID-19, affecting individuals' quality of life and nutritional status. Detecting sweet thresholds during infection and recovery periods can assist in implementing dietary modifications and nutritional strategies for these patients.

OBJECTIVE

To investigate the changes and differences in sweet detection thresholds of confirmed COVID-19 patients on Day 1, Day 10, and Day 14 of the infection and recovery periods.

METHODS

The demographic factors such as gender, smoking status, BMI, and age group were abstracted on Excel sheet from the medical health records for confirmed COVID-19 patients, who were admitted to King Fahad General Hospital in Jeddah, Saudi Arabia, a COVID-19 care facility, from September 2021 to July 2022. Sweet detection thresholds were determined using a pair-wise comparison procedure and sugar solutions with varying concentrations, arranged in ascending order and presented to participants until the lowest detected concentration was noted after three consecutive positive detections, with the median just noticeable difference (JND) value calculated as the population average threshold. Sensory tests were conducted on COVID-19 patients during their infection and recovery periods to evaluate their taste sensation thresholds. The demographic factors of gender, smoking status, BMI, and age group were considered in the analysis.

RESULTS

A total of 37 patients who met the inclusion criteria of the study were enrolled as participants. Significant variances in sweet detection thresholds were observed among the COVID-19 patients, with consistent decreases over the three testing days, indicating increasing sucrose sensitivity. Infected men showed significant returns to sweet detection thresholds on Day 14 compared to women, while infected smokers exhibited greater recoveries than non-smokers. Overweight patients had consistently elevated thresholds and recovery rates that were comparable to those of normal-weight patients by Day 14, while younger patients had lower thresholds than their older counterparts. On Day 14, the thresholds had significantly recovered to a level comparable to that of healthy individuals (approximately 0.23%).

CONCLUSION

These findings suggest that sweet detection thresholds can be used as a marker for assessing the progression and recovery of COVID-19 patients. These findings highlight the importance of recognizing and managing alterations in sweet detection thresholds promptly in COVID-19 patients, as this could positively impact dietary management, nutritional recommendations, and interventions during infection and recovery periods.

Impact of 4-week of a restricted Mediterranean diet on taste perception, anthropometric, and blood parameters in subjects with severe obesity

Introduction

The study of taste functionality and its relation to human health is receiving growing attention. Obesity has been reported to cause alterations in sensory perception regarding system functionality and preferences. However, a small body of research addresses tastes perception and its modification with the achievement of body mass reduction through surgical intervention. Much fewer efforts have been made to evaluate the impact of mild restrictive nutritional intervention on gustatory functions. Thus, the objectives of this study were to determine if a dietary intervention of 4 weeks following a restricted balanced Mediterranean diet would affect the sweet and salty taste thresholds of subjects with severe obesity and could influence their anthropometric and blood parameters.

Methods

Fifty-one patients with severe obesity (F: 31; age: 43.7 ± 12.5; BMI = 47.6 ± 1.0) were enrolled in the study. The recognition threshold for sweet and salty taste and anthropometric and blood parameters were assessed before and after the 4-week weight loss program.

Results and Discussion

The Mediterranean diet has proven to be an effective treatment, significantly improving all anthropometric and blood parameters (p < 0.05) after 4 weeks of intervention. Moreover, the hypo-sodium treatment associated with the diet significantly improved the salty threshold (p < 0.001). No changes were detected for the sweet threshold. Collectively, these data highlight that dietary treatment might impact taste perception differently. Therefore, a taste-oriented nutritional intervention could represent a novel approach to developing more individualized, taste-oriented follow-up interventions to maintain sustainable and long-term weight loss.

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.

Body Fat Moderates the Association of Olfactory Dysfunction with Dietary Intake in U.S. Middle-Aged and Older Adults: A Cross-Sectional Analysis of NHANES 2013-2014

Background: Obesity relates to impaired olfactory function. Abnormal olfactory function is also associated with poor diet; however, whether obesity-related markers shape this relationship is unknown. Methods: Cross-sectional analysis (n = 1415, age > 40 years) of NHANES 2013−2014 examined body fat percent (BF%) and waist circumference (WC) as moderators of the relationship between olfactory function and diet. The olfactory function test identified adults with olfactory dysfunction (OD) or normal olfaction (NO). Validated 24 h recall captured nutrient intake and Healthy Eating Index-2010 scores. BF% and WC were measured. We tested adjusted linear regression models, with an interaction term between olfactory function and BF%/WC, for each nutrient or HEI score, and reported coefficients (β), standard errors (SE), and p-values for significant interaction terms. Results: In OD (9.5%; mean age 50.9 years, 95% CI 49.6, 52.2) compared with NO (mean age 49.3 years, 95% CI 48.8, 49.9), higher BF% was associated with higher intake of saturated fat (β (SE): 0.2 (0.1) g; p = 0.06) and percent of total calories from total fat (0.2 (0.1); p = 0.07), saturated (0.1 (0.004); p = 0.02), and monounsaturated fat (0.1 (0.1); p = 0.08); lower percent of total calories from carbohydrates (−0.2 (0.1); p = 0.09) and mg of sodium (−17.8 (09.6); p = 0.08); and a higher (healthier) refined grain score (0.1 (0.1); p = 0.04). Higher WC was associated with higher refined grain scores (0.01 (0.02); p = 0.01) in OD. Conclusion: BF% may shape dietary intake and quality in OD. Longitudinal studies are needed to elucidate the directionality of these relationships and develop strategies to improve dietary intake among OD.

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.

Potential Effects of Prolonged Water-Only Fasting Followed by a Whole-Plant-Food Diet on Salty and Sweet Taste Sensitivity and Perceived Intensity, Food Liking, and Dietary Intake

The overconsumption of calorie-dense foods high in added salt, sugar, and fat is a major contributor to current rates of obesity, and methods to reduce consumption are needed. Prolonged water-only fasting followed by an exclusively whole-plant-food diet free of added salt, oil, and sugar may reduce the consumption of these hyper-palatable foods, but such effects have not been quantified. Therefore, we conducted a preliminary study to estimate the effects of this intervention on salty and sweet taste detection and recognition thresholds and perceived taste intensity after at least five days of fasting and at refeed day three. We also assessed the effects on sweet, salty, and fatty food preference and overall dietary consumption 30 days after the day three refeed visit. Based on this data, we estimated that 10 days after the start of the fasting, salty taste recognition, sweet taste detection, and sweet taste recognition thresholds decreased significantly, salty taste intensity ratings increased significantly, and sweet taste intensity ratings decreased significantly. We also have preliminary data that prolonged water-only fasting followed by refeeding on an exclusively whole-food-plant diet may reduce salty/fatty and sweet/fatty food liking, reduce sugar intake, and increase vegetable intake. These results support further research into the effects of fasting and diet on taste function and food likability and consumption.

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.

Impact of aerobic exercises on taste perception for sucrose in patients with type 2 diabetes mellitus; A randomized controlled trial

BACKGROUND

Regular exercise is a key element in the management of type 2 diabetes mellitus (T2DM). Although the importance of regular exercises on glycemic control in people with diabetes is studied extensively, evidence is lacking on its impact on sweet taste perception. Thus, the aim of this study was to determine the impact of aerobic exercises on taste perception for sucrose in people with diabetes.

METHODS

A sample of 225 people with diabetes aged 35-60 years was assigned randomly into 3 groups; aerobic exercise, combined exercise and a control group. The outcomes of the combined exercise group is not reported. The aerobic exercise group performed brisk walking 30min/day, 4-5days/week for 6 months. The primary outcome measures were supra-threshold intensity ratings and preference for sucrose assessed at baseline, at 3 and 6 months using 'general Labeled Magnitude Scale' and 'Monell 2-series-forced choice method' respectively. Glycated haemoglobin (HbA1c) level was assessed at baseline and at 6 months to determine glycemic control.

RESULTS

Aerobic exercise group showed significantly increased ratings (mm) for higher sucrose concentrations at 3 months (mean difference for 2.02M; +6.63±2.50, p=0.048 and for 0.64M; +7.26±2.76, p=0.026) and at 6 months (mean difference for 0.64M; +7.79±4.49, p= 0.044) compared to baseline and also when compared to controls (mean difference for 2.02M between baseline and 3 months; intervention: +6.63±2.50, control: -4.01±1.79, p=0.02 and between baseline and 6 months for 2.02M; intervention: +3.15±0.57, control: -7.96±0.40, p=0.022 and for 0.64M; intervention: +7.79±4.49, control: -8.98±0.99, p=0.003). A significantly reduced preference (mol/L) was seen both at 3 (mean difference; -0.03±0.02, p= 0.037) and at 6 months (mean difference; -0.05±0.12, p=0.011) compared to baseline within the intervention group. Also, a significant reduction was seen in the intervention group compared to controls at 6 months (mean difference; intervention: -0.05±0.12, control: 0.01±0.03, p=0.044). HbA1c was significantly reduced in the intervention group compared to controls at 6 months (mean difference; intervention -0.43±1.6%, control +0.33±1.8%, p=0.018).

CONCLUSION

Regular aerobic exercises increase the sweet taste sensitivity, especially for higher concentrations of sucrose and decrease sweet taste preference in people with diabetes . These alterations in sweet taste perception, are likely to contribute to a better glycemic control in people with diabetes.

TRIAL REGISTRATION

This trial was registered at the Sri Lanka Clinical Trial registry on 16/12/2015. (Trial registration number- SLCTR/2015/029 , https://slctr.lk/trials/slctr-2015-029).

Impact of Nutritional Intervention on Taste Perception-A Scoping Review

The aim of the present scoping review was to evaluate the impact of experimental meal loads or observational diet changes/habits on taste tests in both healthy subjects and patients. A systematic search performed in PubMed, Scopus, and Institute for Scientific Information (ISI) Web of Science electronic databases retrieved, respectively 2981, 6258, and 7555 articles from January 2000 to December 2020. A total of 17 articles were included for full-text review. Literature results were stratified according to the observational/interventional approach, the involvement of healthy subjects or patients, the taste test, and the meal/dietary changes. The present scoping review reinforced the notions postulating that certain taste tests (for example focusing on fatty acid, salt, or sugar) might be specifically influenced by the nutritional intervention and that other ones might be susceptible to a wide span of changes beyond the extent of tastant included in the specific food changes. This could also depend on the inhomogeneity of literature trend: The short duration of the intervention or the random type of meal load, unsuitability of the taste test chosen, and the presence of underlying disorders. Future studies for a better comprehension of taste tests reliability in relation to specific food changes are thus to be fostered.

Is sonic hedgehog expression in saliva related to taste sensitivity in adults?

Recent studies have demonstrated the critical role of the sonic hedgehog in the sensory perception of taste. Salivary sonic hedgehog stimulates taste bud stem cells, also acts as a taste bud growth factor, and contributes to the receptors' development and longevity in the taste buds. This study's objective was to investigate the possible relationship between taste sensitivity and sonic hedgehog expression in saliva in normal-weight and pre-obese/obese participants (totally 46 male (47.8%) and female (52.2%) aged 19-44 were recruited). Thresholds for the six tastes (sweet, salty, bitter, sour, umami and fat) were investigated using 3-Alternate Forced Choice Methodology. Saliva was collected with the draining method for sonic hedgehog expression analysis. The results indicated significantly higher thresholds for sweet, bitter and fat in pre-obese /obese adults than normal-weight adults (p<0.05). The sonic hedgehog expression was also lower in pre-obese /obese participants than normal-weight participants (p<0.05). Furthermore, sonic hedgehog expression was higher in hypersensitive participants than hyposensitive participants (p<0.05) only among normal-weight individuals, with no significant difference in sonic hedgehog expression level by taste sensitivity in pre-obese/obese individuals (p>0.05). Sonic hedgehog expression level was negatively correlated with body mass index, sweet, salty, bitter and fat taste threshold. The study results indicated that sonic hedgehog expression level acted on taste sensitivity in normal-weight participants, with greater expression in hypersensitive individuals than hyposensitive individuals.

Gustatory Function Can Improve after Multimodal Lifestyle Intervention: A Longitudinal Observational Study in Pediatric Patients with Obesity

Introduction: Obesity is a major health burden in children and adolescents. One influential factor is the choice of food, which is partly determined by gustatory perception. Cross-sectional studies have provided evidence that gustatory function is reduced in patients with obesity compared to individuals with normal weight. This longitudinal study was aimed at investigating potential effects of a multimodal lifestyle intervention program on gustatory function in pediatric patients with obesity. Methods: Gustatory perception of five different taste qualities (sweet, sour, salty, bitter, and umami) was assessed in n = 102 patients (age 6-18) with obesity (BMI >97th percentile). Testing was performed before (T0) and after (T1) a residential multimodal weight reduction program between June and December 2015 using well-established taste strips. Results: Overall, identification performance increased between T0 and T1. Patients were most successful at identifying the taste quality sweet at both time points and reached higher scores at identifying umami and bitter at T1 compared to T0. Moreover, patients rated the highest concentration of sweet significantly sweeter at T1 compared to T0. Conclusion: Gustatory function can improve after a multimodal lifestyle intervention program in pediatric patients with obesity. This may lead to a modified choice of food, possibly resulting in a long-term therapeutic success. Therefore, these findings underline the importance of professional nutritional counseling as part of treatment for obesity.

Phosphatidylinositol-3 kinase mediates the sweet suppressive effect of leptin in mouse taste cells

Leptin is known to selectively suppress neural and taste cell responses to sweet compounds. The sweet suppressive effect of leptin is mediated by the leptin receptor Ob-Rb, and the ATP-gated K⁺ (K_ATP ) channel expressed in some sweet-sensitive, taste receptor family 1 member 3 (T1R3)-positive taste cells. However, the intracellular transduction pathway connecting Ob-Rb to K_ATP channel remains unknown. Here we report that phosphoinositide 3-kinase (PI3K) mediates leptin's suppression of sweet responses in T1R3-positive taste cells. In in situ taste cell recording, systemically administrated leptin suppressed taste cell responses to sucrose in T1R3-positive taste cells. Such leptin's suppression of sucrose responses was impaired by co-administration of PI3K inhibitors (wortmannin or LY294002). In contrast, co-administration of signal transducer and activator of transcription 3 inhibitor (Stattic) or Src homology region 2 domain-containing phosphatase-2 inhibitor (SHP099) had no effect on leptin's suppression of sucrose responses, although signal transducer and activator of transcription 3 and Src homology region 2 domain-containing phosphatase-2 were expressed in T1R3-positive taste cells. In peeled tongue epithelium, phosphatidylinositol (3,4,5)-trisphosphate production and phosphorylation of AKT by leptin were immunohistochemically detected in some T1R3-positive taste cells but not in glutamate decarboxylase 67-positive taste cells. Leptin-induced phosphatidylinositol (3,4,5)-trisphosphate production was suppressed by LY294002. Thus, leptin suppresses sweet responses of T1R3-positive taste cells by activation of Ob-Rb-PI3K-K_ATP channel pathway.

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.

Effect of Physical Exercise on Taste Perceptions: A Systematic Review

The effect of physical exercise on nutrition has gained substantial interest in the last decade. Meaningful results have been produced concerning the effect of physical exercise on different appetite hormones and food choice/preference. While it is well known that taste and nutrition are related, the relation between taste and physical activity has not yet been fully explored. This systematic review aims to provide a detailed view of the literature on physical exercise and its effect on taste perceptions. Five tastes were included in this review: sweet, salty, bitter, sour, and umami. Sweet taste intensity, sensitivity, and preference were increased by acute physical exercise, but sweet preference was reduced by chronic physical activity. Perceived intensity and sensitivity decreased overall for salty taste, but an increased preference was noted during/following exercise. Sour taste intensity ratings were decreased following exercise and preference was enhanced. Umami taste intensity and sensitivity increased following exercise and preference was decreased. No significant results were obtained for bitter taste. While evidence regarding the effect of exercise on taste has arisen from this review, the pre-testing nutrition, testing conditions, type of test, and exercise modality must be standardized in order to produce meaningful and reproducible results in the future.

Consequences of Obesity on the Sense of Taste: Taste Buds as Treatment Targets?

Premature obesity-related mortality is caused by cardiovascular and pulmonary diseases, type 2 diabetes mellitus, physical disabilities, osteoarthritis, and certain types of cancer. Obesity is caused by a positive energy balance due to hyper-caloric nutrition, low physical activity, and energy expenditure. Overeating is partially driven by impaired homeostatic feedback of the peripheral energy status in obesity. However, food with its different qualities is a key driver for the reward driven hedonic feeding with tremendous consequences on calorie consumption. In addition to visual and olfactory cues, taste buds of the oral cavity process the earliest signals which affect the regulation of food intake, appetite and satiety. Therefore, taste buds may play a crucial role how food related signals are transmitted to the brain, particularly in priming the body for digestion during the cephalic phase. Indeed, obesity development is associated with a significant reduction in taste buds. Impaired taste bud sensitivity may play a causal role in the pathophysiology of obesity in children and adolescents. In addition, genetic variation in taste receptors has been linked to body weight regulation. This review discusses the importance of taste buds as contributing factors in the development of obesity and how obesity may affect the sense of taste, alterations in food preferences and eating behavior.

Bariatric Surgery Leads to Short-Term Effects on Sweet Taste Sensitivity and Hedonic Evaluation of Fatty Food Stimuli

OBJECTIVE

The aim of this study was to investigate the effect of bariatric surgery on sweet taste sensitivity and the hedonic evaluation of sweet, savory, and fatty food stimuli as well as associations with weight loss and food preferences assessed at a buffet meal test.

METHODS

The detection and recognition threshold for sweet taste and the hedonic rating of sweet, savory, and fatty food stimuli were assessed before and after a preoperative diet-induced weight loss and 6 weeks, 6 months, and 18 months after Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) (n = 29).

RESULTS

The detection threshold for sweet taste decreased after the diet-induced weight loss and 6 weeks after RYGB (both P ≤ 0.03). The hedonic rating of high-fat food stimuli decreased 6 weeks after RYGB and SG (all P ≤ 0.02). Changes in the hedonic rating of high-fat food stimuli were associated with increased preferences for high-fat foods at the buffet meal (P = 0.03) and tended to be associated with weight loss (P = 0.05). No changes were detected for sweet and savory food stimuli.

CONCLUSIONS

RYGB increased sweet taste sensitivity; however, this effect was already seen after the diet-induced weight-loss. RYGB and SG decreased the hedonic evaluation of high-fat food stimuli, but this effect did not translate into decreased preferences for high-fat food.

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.

Food Intake and Eating Behavior After Bariatric Surgery

Obesity is an escalating global chronic disease. Bariatric surgery is a very efficacious treatment for obesity and its comorbidities. Alterations to gastrointestinal anatomy during bariatric surgery result in neurological and physiological changes affecting hypothalamic signaling, gut hormones, bile acids, and gut microbiota, which coalesce to exert a profound influence on eating behavior. A thorough understanding of the mechanisms underlying eating behavior is essential in the management of patients after bariatric surgery. Studies investigating candidate mechanisms have expanded dramatically in the last decade. Herein we review the proposed mechanisms governing changes in eating behavior, food intake, and body weight after bariatric surgery. Additive or synergistic effects of both conditioned and unconditioned factors likely account for the complete picture of changes in eating behavior. Considered application of strategies designed to support the underlying principles governing changes in eating behavior holds promise as a means of optimizing responses to surgery and long-term outcomes.

Being born small-for-gestational-age is associated with an unfavourable dietary intake in Danish adolescent girls: findings from the Danish National Birth Cohort

Individuals born small have an increased risk for developing type 2 diabetes. Altered food preferences in these subjects seem to play a role; however, limited evidence is available on the association between being born small-for-gestational-age (SGA) at term and food intake in adolescence. Alterations in leptin, ghrelin and dopamine levels are suggested mechanisms linking SGA with later food intake. From a large prospective Danish National Birth Cohort, we compared dietary intake of adolescents being born SGA with normal-for-gestational-age (NGA) adolescents. Intake of foods and nutrients was assessed by a validated food frequency questionnaire in a subsample of 15,607 14-year-old individuals born at term. SGA was defined by birth weight (BW) &lt;10th percentile (n = 1470) and NGA as BW between 10 and 90th percentile (n = 14,137) according to sex and gestational age-specific BW standard curves. Girls born SGA had a 7% (95% CI: 3-12%, P = 0.002) higher intake of added sugar and a 2-8% lower intake of dietary fibre, vegetables, polyunsaturated fatty acids, and total n-6, compared with NGA girls (P &lt; 0.05). Adjusting for parental socio-occupational status, maternal smoking and diet in pregnancy did not substantially change the differences in dietary intake, except from dietary fibre, which were no longer statistically significant. No significant differences in dietary intake between SGA and NGA boys were found. In summary, girls born SGA had an unfavourable dietary intake compared with NGA girls. These differences persisted after controlling for potential confounders, thus supporting a fetal programming effect on dietary intake in girls born SGA at term. However, residual confounding by other factors operating early in childhood cannot be excluded.

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

Sweet taste is associated with food reward and energy source in the form of carbohydrate. Excessive sweet consumption is blamed for the prevalence of obesity. However, evidence for the potential of sweet taste to influence food intake and bodyweight regulation in humans remains unclear. The purpose of this review was to examine the physiological responses relevant to sweet taste mechanisms and the impact on appetite control. The literature was examined for studies that assessed the effects of non-nutritive sweeteners and natural sugars on hormonal secretions and neural activations via oral and gastrointestinal pathways. The findings indicated that a network of sweet taste signalling pathways in the oral cavity and the gut seem to mediate hormonal responses and some metabolism differences in neural circus that orchestrating the hunger-satiety cycle. Individual variations of sweet taste perception which is modulated by hormonal and genetic factors have been associated with dietary nutrient and sugar consumption.

Inflammation arising from obesity reduces taste bud abundance and inhibits renewal

Despite evidence that the ability to taste is weakened by obesity and can be rescued with weight loss intervention, few studies have investigated the molecular effects of obesity on the taste system. Taste bud cells undergo continual turnover even in adulthood, exhibiting an average life span of only a few weeks, tightly controlled by a balance of proliferation and cell death. Recent data reveal that an acute inflammation event can alter this balance. We demonstrate that chronic low-grade inflammation brought on by obesity reduces the number of taste buds in gustatory tissues of mice-and is likely the cause of taste dysfunction seen in obese populations-by upsetting this balance of renewal and cell death.

Nutrition and taste and smell dysfunction

Food selection plays a pivotal role in maintaining adequate nutrient intake, thus elucidating drivers of food choice is a meaningful strategy to maintain health and manage disease. Taste and smell are key determinants of food choice and warrant careful consideration. In this review, we first discuss how sensory stimulation influences food selection and metabolism. We then review the evidence regarding the relationship between taste and smell dysfunction and food preferences and selection, with attention given to contexts of certain chronic diseases. We conclude with brief recommendations for the management of chemosensory disorders. While sensory abilities influence food selection, the effect of taste and smell dysfunction on long-term consumption patterns and health status must be considered in light of environment, exposure, and culture.

Salivary leptin and TAS1R2/TAS1R3 polymorphisms are related to sweet taste sensitivity and carbohydrate intake from a buffet meal in healthy young adults

The influence of sweet taste sensitivity on food intake is not well understood. We investigated the involvement of salivary leptin and SNP of the sweet taste receptor genes (TAS1R2/TAS1R3) on sweet taste sensitivity, sensory-specific satiety (SSS) and macronutrient intake in healthy human adults. In all, nineteen high sweet sensitivity (HS) and eleven low sweet sensitivity (LS) subjects were classified based on the sweetness perception of one solution (9 mm sucrose) forced-choice triangle test. All participants completed a randomised crossover design experiment where they consumed one of three iso-energetic soup preloads differing in primary taste quality (sweet, non-sweet taste-control or no-taste energy-control). A period of 1 h after the preload, participants were offered a buffet meal consisting of foods varying in taste (sweet or non-sweet) and fat content. Subjective measures included hunger/fullness and SSS for sweetness. Saliva and buccal cells were collected to measure leptin level and to study the TAS1R2/TAS1R3 specific SNP, respectively. Salivary leptin concentrations were significantly higher in LS than HS participants (P<0·05). In addition, HS showed stronger sweet SSS compared with LH participants (P<0·05), and consumed less carbohydrate (% energy) and more non-sweet foods than LS (P<0·01 and P<0·05, respectively). Alleles from each TAS1R2 locus (GG compared with AA alleles of rs12033832, and CT/CC compared with TT alleles of rs35874116) were related to higher consumption of carbohydrates (% energy) and higher amount of sweet foods, respectively (P<0·05). In contrast, no associations were found for the TAS1R3 alleles. These results contribute to understand the links between taste sensitivity, macronutrient appetite and food consumption.

Low Dose Yeast Hydrolysate in Treatment of Obesity and Weight Loss

The anti-obesity effects of yeast hydrolysate (YH) supplementation (1.0 g/d) have already been demonstrated. We investigated whether a low dose of YH (0.5 g/d, YH-500) also has the anti-obesity effects. Thirty obese women were randomly assigned to the control or YH-500 groups. After 8 weeks, weight and body mass index were significantly reduced by the YH treatment (0.5 g/d) (P<0.05). The YH-500 group lost a significant amount of body fat after the 8-week treatment: fat mass 25.9 kg (baseline) versus 23.8 kg (8th week), P<0.01; fat mass ratio 38.8% (baseline) versus 36.5% (8th week), P<0.05. The YH-500 group showed a significant reduction in calorie intake during the 8-week treatment (P<0.001). The control group wanted to eat much more food (P<0.05) and sometimes thought about eating more often compared with the YH-500 group (P<0.05). Whereas the control group showed a slightly increased sweet preference, the YH-500 group showed a significant reduction in sweet preference (P<0.05). In conclusion, low dose YH supplementation (0.5 g/d) may induce a reductions in weight and body fat in obese women via the reduction of calorie intake.

Changes in Gustatory Function and Taste Preference Following Weight Loss

OBJECTIVE

To investigate taste changes of obese children during an inpatient weight reduction treatment in comparison with normal weight children.

STUDY DESIGN

Obese (n = 60) and normal weight (n = 27) children aged 9-17 years were assessed for gustatory functions using taste strips (taste identification test for the taste qualities sour, salty, sweet, and bitter), taste preferences, and experienced taste sensitivity. Obese children were examined upon admission (T1) and before discharge (T2). Normal weight children served as the control group.

RESULTS

Irrespective of taste quality, obese children exhibited a lower ability to identify taste (total taste score) than normal weight children (P < .01); this overall score remained stable during inpatient treatment in obese children. Group and treatment effects were seen when evaluating individual taste qualities. In comparison with normal weight children, obese children exhibited poorer sour taste identification performance (P < .01). Obese children showed improvement in sour taste identification (P < .001) and deterioration in sweet taste identification (P < .001) following treatment. Subjective reports revealed a lower preference for sour taste in obese children compared with normal weight children (P < .05). The sweet and bitter taste ability at T1 predicted the body mass index z score at T2 (R² = .23, P < .01).

CONCLUSIONS

We identified differences in the ability to discriminate tastes and in subjective taste perception between groups. Our findings of increased sour and reduced sweet taste discrimination after the intervention in obese children are indicative of an exposure-related effect on taste performance, possibly mediated by increased acid and reduced sugar consumption during the intervention. Because the sweet and bitter taste ability at T1 predicted weight loss, addressing gustatory function could be relevant in individualized obesity treatment approaches.

TRIAL REGISTRATION

Germanctr.de: DRKS00005122.

An increase in visceral fat is associated with a decrease in the taste and olfactory capacity

Introduction

Sensory factors may play an important role in the determination of appetite and food choices. Also, some adipokines may alter or predict the perception and pleasantness of specific odors. We aimed to analyze differences in smell–taste capacity between females with different weights and relate them with fat and fat-free mass, visceral fat, and several adipokines.

Materials and methods

179 females with different weights (from low weight to morbid obesity) were studied. We analyzed the relation between fat, fat-free mass, visceral fat (indirectly estimated by bioelectrical impedance analysis with visceral fat rating (VFR)), leptin, adiponectin and visfatin. The smell and taste assessments were performed through the "Sniffin’ Sticks" and "Taste Strips" respectively.

Results

We found a lower score in the measurement of smell (TDI-score (Threshold, Discrimination and Identification)) in obese subjects. All the olfactory functions measured, such as threshold, discrimination, identification and the TDI-score, correlated negatively with age, body mass index (BMI), leptin, fat mass, fat-free mass and VFR. In a multiple linear regression model, VFR mainly predicted the TDI-score. With regard to the taste function measurements, the normal weight subjects showed a higher score of taste functions. However a tendency to decrease was observed in the groups with greater or lesser BMI. In a multiple linear regression model VFR and age mainly predicted the total taste scores.

Discussion

We show for the first time that a reverse relationship exists between visceral fat and sensory signals, such as smell and taste, across a population with different body weight conditions.

Laparoscopic Sleeve Gastrectomy Improves Olfaction Sensitivity in Morbidly Obese Patients

BACKGROUND

Olfactory abilities of the patients are known to be altered by eating and metabolic disorders, including obesity. There are only a number of studies investigating the effect of obesity on olfaction, and there is limited data on the changes in olfactory abilities of morbidly obese patients after surgical treatment. Here we investigated the changes in olfactory abilities of 54 morbidly obese patients (M/F, 22/32; age range 19-57 years; body mass index (BMI) range 30.5-63.0 kg/m(2)) after laparoscopic sleeve gastrectomy.

METHOD

A laparoscopic sleeve gastrectomy was performed by the same surgeon using five-port technique. Olfactory abilities were tested preoperatively and 1, 3, and 6 months after the surgery using a standardized Sniffin' Sticks Extended Test kit.

RESULTS

Analyses of variance indicated statistically significant improvement in T, D, and I scores of morbidly obese patients within time factors (preoperative vs. 1, 3, and 6 months; 1 vs. 3 and 6 months; and 3 vs. 6 months; p < 0.001 for all). There was a statistically significant improvement in overall TDI scores with an increase from 25 to 41 during the 6 months follow-up period (p < 0.001 for all).

CONCLUSIONS

Here, for the first time in literature, we were able to show the significant improvement in olfactory abilities of morbidly obese patients after laparoscopic sleeve gastrectomy.

Sweet taste preferences before and after an intensive medical weight loss intervention

OBJECTIVE

Medical weight loss could change sweet taste threshold and preferences. The decrease in sweet taste preferences may, in turn, help in the maintenance of weight loss. This study examined the association between sweet taste preferences at baseline and weight change during a medical weight management programme and the impact of diet-induced weight loss on sweet taste preferences.

METHODS

Adult patients with body mass index ≥32 kg m-2 were recruited from a medical weight management clinic. Sweet taste preference was assessed using a forced-choice, paired-comparison tracking method before and after a very-low-calorie diet (VLCD).

RESULTS

Twenty participants were included in the analysis: mean age was 53.1 (standard deviation [SD]: 11.4) years, and 14 were female. The mean body mass index was 41.4 (SD: 7.5) kg m-2. The median preferred sucrose concentration before VLCD was 0.45 M. Following VLCD, mean change in weight was -13.3 (SD: 6.6) kg, and percentage weight change was -11.3% (SD: 5.9%). Based on mixed models with and without adjustment for demographic factors, diabetes status and smoking history, preferred sucrose concentration at baseline did not predict change in longer-term body weight. The change of preferred sucrose concentration following 12 weeks of VLCD was not significant (P-value 0.95).

CONCLUSIONS

Change in weight during and after VLCD was not associated with sweet taste preferences at baseline. After diet-induced weight loss, sweet taste preferences did not change.

Extremes of eating are associated with reduced neural taste discrimination

OBJECTIVE

Eating disorders are severe psychiatric disorders of unknown etiology. Understanding how neuronal function affects food choices could help personalize treatment based on brain function. Here we wanted to determine whether disordered eating behavior is associated with alterations in the primary taste cortex's ability to classify taste stimuli, which could interfere with taste reward processing.

METHOD

One-hundred and six women, 27 healthy comparison (age 26.15 ± 6.95 years), 21 with restricting-type anorexia nervosa (AN; age 23.10 ± 6.14 years), 19 recovered from restricting-type AN (recovered AN; age 26.95 ± 5.31 years), 20 with bulimia nervosa (BN; age 25.15 ± 5.31 years), and 19 with obesity (age 28.16 ± 8.13 years), received sucrose, control solution or no taste stimulation during functional magnetic resonance brain imaging. Multivariate Bayesian pattern analysis (decoding) and cross-validation tested taste classification accuracy (adjusted for comorbidity, medication use, taste perception, interoception, and brain activation volume).

RESULTS

For sucrose versus control solution, classification accuracy differed (F = 2.53, P < 0.041). Post hoc tests indicated higher classification accuracy in healthy comparison compared to women with AN (P < 0.016) or obesity (P < 0.027), and in recovered AN as compared to AN (P < 0.016) or obesity (P < 0.047) groups. Taste stimulation resulted in sparse insula voxel activation across all groups.

DISCUSSION

Reduced classification accuracy across stimuli in women with AN or obesity could indicate low brain encoding discrimination of stimulus quality, which could contribute to altered reward activation and eating drive that is not adjusted to nutritional needs. This deficit appears to normalize with recovery from AN, but adjusting food flavor intensity could aid in the treatment of individuals with AN or obesity. © 2016 Wiley Periodicals, Inc.(Int J Eat Disord 2016; 49:603-612).

The Association between Sweet Taste Function, Anthropometry, and Dietary Intake in Adults

Variation in ability to detect, recognize, and perceive sweetness may influence food consumption, and eventually chronic nutrition-related conditions such as overweight and obesity. The aim of this study was to investigate the associations between sweet taste function, anthropometry, and dietary intake in adults. Participants’ (n = 60; mean age in years = 26, SD = ±7.8) sweet taste function for a range of sweeteners (glucose, fructose, sucrose, sucralose, erythritol, and Rebaudioside A) was assessed by measuring detection and recognition thresholds and sweetness intensity. Height, weight, and waist circumference were also measured, and participants also completed a Food Frequency Questionnaire. There was large inter-individual variation in detection, recognition and sweetness intensity measures. Pearson’s correlation coefficient revealed no robust correlations between measures of sweet taste function, anthropometry, and dietary intake, with the exception of suprathreshold intensity, which was moderately correlated with total energy intake (r = 0.23–0.40). One-way analysis of variance revealed no significant differences between the most and least sensitive participants in terms of BMI, waist circumference, and dietary intake for all measures of sweet taste function and sweeteners (all p > 0.01). When stratified into BMI categories, there were no significant differences in any measure of sweet taste function between the normal weight and overweight/obese participants (all p > 0.01). Results show that that sweet taste function is not associated with anthropometry and sweetness intensity measures are the most appropriate measure when assessing links between sweet taste and food consumption.

Improved Gustatory Sensitivity in Morbidly Obese Patients After Laparoscopic Sleeve Gastrectomy

Introduction:

The reduction in the preferences for sweet and fat containing tastes in obese patients who underwent bariatric surgery was relatively well shown; however, there are only limited data on the changes in the sensitivity of other tastes like sour, salty, and bitter.

Methods:

We investigated the changes in gustatory sensitivity of 52 morbidly obese patients (M/F, 22/30; age range, 19-60 years; BMI range, 32.5-63.0 kg/m2) after laparoscopic sleeve gastrectomy. The surgery was performed by the same surgeon using 5 ports technique. Gustatory sensitivity was tested preoperatively and 1 and 3 months after the surgery using standardized Taste Strips test.

Results:

There was a statistically significant improvement in the taste acuity to sweet, sour, salty, and bitter tastants in morbidly obese patients after the laparoscopic sleeve gastrectomy during the follow-up period of 3 months. Median whole test scores of the patients were increased from 11.5 preoperatively to 14 in the first and third months.

Conclusion:

In this study, we were able to show the significant improvement in gustatory sensitivity of morbidly obese patients after laparoscopic sleeve gastrectomy for the first time in literature.

Leptin Suppresses Mouse Taste Cell Responses to Sweet Compounds

Leptin is known to selectively suppress neural and behavioral responses to sweet-tasting compounds. However, the molecular basis for the effect of leptin on sweet taste is not known. Here, we report that leptin suppresses sweet taste via leptin receptors (Ob-Rb) and KATP channels expressed selectively in sweet-sensitive taste cells. Ob-Rb was more often expressed in taste cells that expressed T1R3 (a sweet receptor component) than in those that expressed glutamate-aspartate transporter (a marker for Type I taste cells) or GAD67 (a marker for Type III taste cells). Systemically administered leptin suppressed taste cell responses to sweet but not to bitter or sour compounds. This effect was blocked by a leptin antagonist and was absent in leptin receptor-deficient db/db mice and mice with diet-induced obesity. Blocking the KATP channel subunit sulfonylurea receptor 1, which was frequently coexpressed with Ob-Rb in T1R3-expressing taste cells, eliminated the effect of leptin on sweet taste. In contrast, activating the KATP channel with diazoxide mimicked the sweet-suppressing effect of leptin. These results indicate that leptin acts via Ob-Rb and KATP channels that are present in T1R3-expressing taste cells to selectively suppress their responses to sweet compounds.

Modulation of sweet taste sensitivities by endogenous leptin and endocannabinoids in mice

KEY POINTS

Potential roles of endogenous leptin and endocannabinoids in sweet taste were examined by using pharmacological antagonists and mouse models including leptin receptor deficient (db/db) and diet-induced obese (DIO) mice. Chorda tympani (CT) nerve responses of lean mice to sweet compounds were increased after administration of leptin antagonist (LA) but not affected by administration of cannabinoid receptor antagonist (AM251). db/db mice showed clear suppression of CT responses to sweet compounds after AM251, increased endocannabinoid levels in the taste organ, and enhanced expression of a biosynthesizing enzyme of endocannabinoids in taste cells. The effect of LA was gradually decreased and that of AM251 was increased during the course of obesity in DIO mice. These findings suggest that circulating leptin, but not local endocannabinoids, is a dominant modulator for sweet taste in lean mice and endocannabinoids become more effective modulators of sweet taste under conditions of deficient leptin signalling.

ABSTRACT

Leptin is an anorexigenic mediator that reduces food intake by acting on hypothalamic receptor Ob-Rb. In contrast, endocannabinoids are orexigenic mediators that act via cannabinoid CB1 receptors in hypothalamus, limbic forebrain, and brainstem. In the peripheral taste system, leptin administration selectively inhibits behavioural, taste nerve and taste cell responses to sweet compounds. Opposing the action of leptin, endocannabinoids enhance sweet taste responses. However, potential roles of endogenous leptin and endocannabinoids in sweet taste remain unclear. Here, we used pharmacological antagonists (Ob-Rb: L39A/D40A/F41A (LA), CB1 : AM251) and examined the effects of their blocking activation of endogenous leptin and endocannabinoid signalling on taste responses in lean control, leptin receptor deficient db/db, and diet-induced obese (DIO) mice. Lean mice exhibited significant increases in chorda tympani (CT) nerve responses to sweet compounds after LA administration, while they showed no significant changes in CT responses after AM251. In contrast, db/db mice showed clear suppression of CT responses to sweet compounds after AM251, increased endocannabinoid (2-arachidonoyl-sn-glycerol (2-AG)) levels in the taste organ, and enhanced expression of a biosynthesizing enzyme (diacylglycerol lipase α (DAGLα)) of 2-AG in taste cells. In DIO mice, the LA effect was gradually decreased and the AM251 effect was increased during the course of obesity. Taken together, our results suggest that circulating leptin, but not local endocannabinoids, may be a dominant modulator for sweet taste in lean mice; however, endocannabinoids may become more effective modulators of sweet taste under conditions of deficient leptin signalling, possibly due to increased production of endocannabinoids in taste tissue.

Intense Sweeteners, Appetite for the Sweet Taste, and Relationship to Weight Management

High intensity, low-energy sweeteners (LES) are used by many consumers in order to limit energy intake and possibly facilitate body weight control. These beneficial effects are often questioned in the scientific and lay media. LES are frequently accused of stimulating and/or maintaining a liking for sweetness which in turn would be deleterious for adequate body weight control. Evidence for the specific effects of LES use on appetite for sweet products will be extracted from observational studies, experimental laboratory studies, randomized controlled trials, and finally brain imaging studies. While many of the existing studies cannot identify any causal links between use of LES and appetite for sweetness, randomized trials in children and adults suggest that use of LES tends to reduce rather than increase the intake of sugar-containing foods and to facilitate, rather than impair, weight loss.

The role of sweet taste in satiation and satiety

Increased energy consumption, especially increased consumption of sweet energy-dense food, is thought to be one of the main contributors to the escalating rates in overweight individuals and obesity globally. The individual’s ability to detect or sense sweetness in the oral cavity is thought to be one of many factors influencing food acceptance, and therefore, taste may play an essential role in modulating food acceptance and/or energy intake. Emerging evidence now suggests that the sweet taste signaling mechanisms identified in the oral cavity also operate in the gastrointestinal system and may influence the development of satiety. Understanding the individual differences in detecting sweetness in both the oral and gastrointestinal system towards both caloric sugar and high intensity sweetener and the functional role of the sweet taste system may be important in understanding the reasons for excess energy intake. This review will summarize evidence of possible associations between the sweet taste mechanisms within the oral cavity, gastrointestinal tract and the brain systems towards both caloric sugar and high intensity sweetener and sweet taste function, which may influence satiation, satiety and, perhaps, predisposition to being overweight and obesity.

Sweet taste sensitivity in pre-diabetics, diabetics and normoglycemic controls: a comparative cross sectional study

BACKGROUND

Increasing prevalence of pre-diabetes is an emerging public health problem. Decrease in sweet taste sensitivity which can lead to an increase in sugar intake might be a factor driving them to overt diabetes. The aim of the present study was to assess the sweet taste sensitivity in pre-diabetics in comparison with diabetics and with normoglycemic controls.

METHODS

Forty pre-diabetics, 40 diabetics and 34 normoglycemic controls were studied. The three groups were matched for age, sex and BMI. The division into groups was based on their glycated hemoglobin levels. The detection and recognition thresholds were determined by the multiple forced-choice method using sucrose solutions prepared in ¼ log dilutions. The intensities of perceived sensations for a series of suprathreshold concentrations of sucrose solutions prepared in ½ log dilution were determined by rating on a visual analogue scale. Statistical analyses were performed by SPSS version 21.

RESULTS

The mean (SD) detection thresholds of diabetic, pre-diabetic and normoglycemic groups were 0.025 (0.01), 0.018 (0.01) and 0.015 (0.01) respectively with a significant increase in diabetic group compared to normoglycemic group (p = 0.03). The mean recognition thresholds were not different among the three groups. When the intensity ratings for suprathreshold concentrations of sucrose were compared between the three groups, for all suprathreshold concentrations tested, significant differences were observed across the four concentrations (p < 0.001) and between groups in suprathreshold ratings (p < 0.05). Further analysis showed that the diabetic group had significantly lower suprathreshold ratings than the normoglycemic group (p < 0.001). Although all mean suprathreshold intensity ratings of the pre-diabetic group were between the normoglycemic and diabetic groups, the differences were not significant.

CONCLUSIONS

This is the first study to demonstrate the sweet taste sensitivity in pre-diabetics. The findings of the present study do not support the hypothesis of decreased sweet taste sensitivity of pre-diabetics. However, the results confirm the previous findings of blunted taste response in diabetics. The observation of pre-diabetics having intermediate values for all taste thresholds and suprathreshold ratings warrants a future investigation with a larger pre-diabetic sample recruited with more specific screening criteria to test this hypothesis further.

Longitudinal analysis of calorie restriction on rat taste bud morphology and expression of sweet taste modulators

Calorie restriction (CR) is a lifestyle intervention employed to reduce body weight and improve metabolic functions primarily via reduction of ingested carbohydrates and fats. Taste perception is highly related to functional metabolic status and body adiposity. We have previously shown that sweet taste perception diminishes with age; however, relatively little is known about the effects of various lengths of CR upon taste cell morphology and function. We investigated the effects of CR on taste bud morphology and expression of sweet taste-related modulators in 5-, 17-, and 30-month-old rats. In ad libitum (AL) and CR rats, we consistently found the following parameters altered significantly with advancing age: reduction of taste bud size and taste cell numbers per taste bud and reduced expression of sonic hedgehog, type 1 taste receptor 3 (T1r3), α-gustducin, and glucagon-like peptide-1 (GLP-1). In the oldest rats, CR affected a significant reduction of tongue T1r3, GLP-1, and α-gustducin expression compared with age-matched AL rats. Leptin receptor immunopositive cells were elevated in 17- and 30-month-old CR rats compared with age-matched AL rats. These alterations of sweet taste-related modulators, specifically during advanced aging, suggest that sweet taste perception may be altered in response to different lengths of CR.

Modulation of taste responsiveness by the satiation hormone peptide YY

It has been hypothesized that the peripheral taste system may be modulated in the context of an animal's metabolic state. One purported mechanism for this phenomenon is that circulating gastrointestinal peptides modulate the functioning of the peripheral gustatory system. Recent evidence suggests endocrine signaling in the oral cavity can influence food intake (FI) and satiety. We hypothesized that these hormones may be affecting FI by influencing taste perception. We used immunohistochemistry along with genetic knockout models and the specific reconstitution of peptide YY (PYY) in saliva using gene therapy protocols to identify a role for PYY signaling in taste. We show that PYY is expressed in subsets of taste cells in murine taste buds. We also show, using brief-access testing with PYY knockouts, that PYY signaling modulates responsiveness to bitter-tasting stimuli, as well as to lipid emulsions. We show that salivary PYY augmentation, via viral vector therapy, rescues behavioral responsiveness to a lipid emulsion but not to bitter stimuli and that this response is likely mediated via activation of Y2 receptors localized apically in taste cells. Our findings suggest distinct functions for PYY produced locally in taste cells vs. that circulating systemically.

Metabolic hormones in saliva: origins and functions

The salivary proteome consists of thousands of proteins, which include, among others, hormonal modulators of energy intake and output. Although the functions of this prominent category of hormones in whole body energy metabolism are well characterized, their functions in the oral cavity, whether as a salivary component, or when expressed in taste cells, are less studied and poorly understood. The respective receptors for the majority of salivary metabolic hormones have been also shown to be expressed in salivary glands (SGs), taste cells, or other cells in the oral mucosa. This review provides a comprehensive account of the gastrointestinal hormones, adipokines, and neuropeptides identified in saliva, SGs, or lingual epithelium, as well as their respective cognate receptors expressed in the oral cavity. Surprisingly, few functions are assigned to salivary metabolic hormones, and these functions are mostly associated with the modulation of taste perception. Because of the well-characterized correlation between impaired oral nutrient sensing and increased energy intake and body mass index, a conceptually provocative point of view is introduced, whereupon it is argued that targeted changes in the composition of saliva could affect whole body metabolism in response to the activation of cognate receptors expressed locally in the oral mucosa.

Peptide regulators of peripheral taste function

The peripheral sensory organ of the gustatory system, the taste bud, contains a heterogeneous collection of sensory cells. These taste cells can differ in the stimuli to which they respond and the receptors and other signaling molecules they employ to transduce and encode those stimuli. This molecular diversity extends to the expression of a varied repertoire of bioactive peptides that appear to play important functional roles in signaling taste information between the taste cells and afferent sensory nerves and/or in processing sensory signals within the taste bud itself. Here, we review studies that examine the expression of bioactive peptides in the taste bud and the impact of those peptides on taste functions. Many of these peptides produced in taste buds are known to affect appetite, satiety or metabolism through their actions in the brain, pancreas and other organs, suggesting a functional link between the gustatory system and the neural and endocrine systems that regulate feeding and nutrient utilization.