Participants with pharmacologically impaired taste function seek out more intense, higher calorie stimuli

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

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

Oral Exposure to Sodium Chloride without Subsequent Consumption Does Not Alter Salt Taste Function in Adults: A Cross-Over Intervention Study

BACKGROUND

Reduction in dietary sodium increases salt taste sensitivity; however, non-oral sodium supplementation does not, suggesting that oral exposure is more important for modulating taste perception than consumption without tasting.

OBJECTIVE

Using psychophysical methods, we assessed the effect of a two-week intervention involving oral exposure to a tastant without consumption on modulating taste function.

METHODS

In a cross-over intervention study, n = 42 adults (age, mean ± SD: 29.7 ± 8.0 years) completed 4 intervention treatments requiring participants to rinse their mouths with 30 mL of a tastant, 3 times daily for 2 weeks. Treatments included oral exposure to 400 mM sodium chloride (NaCl), monosodium glutamate (MSG), monopotassium glutamate, and sucrose. Participants' taste function for salty, umami, and sweet [detection threshold (DT), recognition threshold (RT), and suprathreshold (ST)], and the glutamate-sodium discrimination status was evaluated before and after the tastant treatments. Effects of the interventions on taste function were assessed by using linear mixed models including treatment, time, and treatment x time interactions as fixed effects; significance was set at P > 0.05.

RESULTS

There was no treatment × time interaction on DT and RT for all tastes assessed (P > 0.05). The only change in ST was following the NaCl intervention, participants' salt ST decreased at the highest concentration (400 mM) compared with the pre-NaCl treatment taste assessment (mean difference (MD): -0.052 [95% CI: -0.093, -0.010] labeled magnitude scale, P = 0.016). Compared with the pre-MSG treatment taste assessment, participants improved their ability to perform the glutamate-sodium discrimination task after the MSG intervention (MD:1.64 [95% CI: 0.395, 2.878] correct discrimination tasks, P = 0.010).

CONCLUSION

Saltiness of an adult's free-living diet is unlikely to influence salt taste function, as oral exposure without consumption to a salt concentration greater than normally found in food, only attenuated taste responses to highly salty stimuli. This provides preliminary evidence that regulating salt taste function may require a coordinated response between oral activation and consumption of sodium.

Plasma LEAP-2 Following a Low-Calorie Diet with or without Interval Exercise in Women with Obesity

Liver-expressed antimicrobial peptide-2 (LEAP-2) is associated with caloric intake and glucose metabolism. Purpose: Assess if a low-calorie diet with interval exercise (LCD+INT) raises LEAP-2 more than LCD in relation to appetite and cardiometabolic health. Methods: Women with obesity were randomized to either 2 weeks of LCD (n = 13, ~1200 kcal/d) or LCD+INT (n = 12; 60 min/d) of INT at 3 min of 90% and 50% HRpeak, respectively. LEAP-2 and acylated ghrelin (AG) were measured at 0, 30, and 60 min, while glucose, insulin, C-peptide, and free fatty acids (FFA) were obtained up to 180 min of a 75 g OGTT. Fasting and 120 min OGTT appetite were assessed via visual analog scales. Results: LCD reduced the BMI (p < 0.001) compared with LCD+INT, but only LCD+INT increased the VO2 max (p = 0.04). Treatments reduced fasting LEAP-2 (p = 0.05), but only LCD increased LEAP-2 iAUC60 min (p = 0.06) and post-prandial LEAP-2 stimulation (p = 0.02). Higher post-LEAP-260 min tended to relate to a lower desire to eat 120 min of sweet (r = 0.40, p = 0.07) and salty foods (r = 0.41, p = 0.06), as well as lower AG30 min (r = -0.51, p = 0.01) and higher FFA iAUC180 min (r = 0.56, p = 0.007) post-treatment. Conclusion: LCD, with or without INT, reduced fasting LEAP-2, but only LCD raised post-prandial LEAP-2. How diet and exercise impact LEAP-2 for lower chronic disease risk awaits further investigation.

Reduced Fat Taste Sensitivity in Obese Japanese Patients and Its Recovery after a Short-Term Weight Loss Program

Fat taste has recently attracted attention as the 'sixth taste.' However, the relationship between fat and sweet taste in Japanese obesity has not yet been examined, and no reports have ascertained whether improvement of fat taste can be obtained by weight loss. Patients were recruited into obesity group (BMI≥30 kg/m²; n=15) or control group (BMI<25 kg/m²; n=11). They answered a questionnaire on smoking, eating behavior, lifestyle, and food frequency, and their taste thresholds were measured (fat, umami, and sweet). The obesity group was tested twice (on admission and before discharge). They showed several eating behavior abnormalities, higher total energy intake, and less physical activity. There were some gender differences: physical inactivity was more prominent in females, and high total energy intake in males, which correlates with fat taste rank. Fat taste rank was significantly higher in obesity group, whereas taste rank of umami and sweet were not significantly different. Gender-specific analysis of fat taste rank revealed only male obesity showed significant difference. Reduced sensitivity of fat may be specific to male gender or obesity by overeating, but not by physical inactivity. Multiple logistic regression analysis revealed that fat taste was a factor relevant to obesity. Fat taste significantly improved after a weight loss program, with average duration of 11.3 d. Japanese obese people, especially males and those who are obese by overeating, have reduced sensitivity to fat taste. This can be recovered by even a short-term weight loss program.

Dysgeusia: A review in the context of COVID-19

Background

Taste disorders in general, and dysgeusia in particular, are relatively common disorders that may be a sign of a more complex acute or chronic medical condition. During the COVID-19 pandemic, taste disorders have found their way into the realm of general as well as specialty dentistry, with significance in screening for patients who potentially may have the virus.

Types of Studies Reviewed

The authors searched electronic databases (PubMed, Embase, Web of Science, Google Scholar) for studies focused on dysgeusia, ageusia, and other taste disorders and their relationship to local and systemic causes.

Results

The authors found pertinent literature explaining the normal physiology of taste sensation, proposals for suggested new tastes, presence of gustatory receptors in remote tissues of the body, and etiology and pathophysiology of taste disorders, in addition to the valuable knowledge gained about gustatory disorders in the context of COVID-19. Along with olfactory disorders, taste disorders are one of the earliest suggestive symptoms of COVID-19 infection.

Conclusions

Gustatory disorders are the result of local or systemic etiology or both. Newer taste sensations, such as calcium and fat tastes, have been discovered, as well as taste receptors that are remote from the oropharyngeal area. Literature published during the COVID-19 pandemic to date reinforces the significance of early detection of potential patients with COVID-19 by means of screening for recent-onset taste disorders.

Practical Implications

Timely screening and identification of potential gustatory disorders are paramount for the dental care practitioner to aid in the early diagnosis of COVID-19 and other serious systemic disorders.

Assessment of gustatory function in aging people using event-related potentials

Gustatory dysfunctions are more frequent than other chemosensory dysfunctions in aging people. Gustatory event-related potentials (ERPs) has been suggested as a reliable and effective approach for assessing gustatory functions in young and middle subjects, but has rarely been investigated in aging people, leaving influencing factors of ERPs in that population not completely understood. In this study, we analyzed gustatory ERPs results of aging participants and characterized potential impacting factors, including age, sex, BMI, drinking, smoking, hypertension, diabetes, cognition and psychophysical test scores of gustation and olfaction. Our results revealed three components (P1, N1 and P2) in gustatory ERPs upon salty stimulation. Significant differences between responses collected from different recording electrodes were observed: minimum latencies and maximum amplitudes of P1 were detected at frontal electrode, and maximum amplitudes of N1 and P2 were detected at central and centro-parietal electrodes, respectively. Major cortical sources of components P1, N1 and P2 were located at bilateral insula, frontal operculum, and orbitofrontal cortex. Diabetes was positively associated with latencies of P1. Sex was positively associated with amplitudes of P1, N1 and P2. Hypertension was negatively associated with amplitudes of P1 and P2. In conclusion, gustatory ERPs in aging people exhibited a specific topographical distribution, represented by sex-related differences and negative impacts of diabetes and hypertension.

Obesity-induced taste dysfunction, and its implications for dietary intake

The incidence of obesity has dramatically increased in recent years, and poses a public health challenge for which an effective and scalable intervention strategy is yet to be found. Our food choices are one of the primary drivers of obesity, where the overconsumption of energy from foods high in fat and sugar can be particularly problematic. Unfortunately, these same foods also tend to be highly palatable. We select foods more on their sensory properties than on any other factor, such as price, convenience, or healthfulness. Previous evidence from human sensory studies has suggested a depressed sense of taste in panelists with obesity. Evidence from animal models also demonstrates a clear deficiency in taste buds occurring with obesity, suggesting that damage to the taste system may result from an obese state. In this review only taste, as opposed to smell, will be examined. Here we seek to bring together evidence from a diverse array of human and animal studies into taste response, dietary intake, and physiology, to better understand changes in taste with obesity, with the goal of understanding whether taste may provide a novel target for intervention in the treatment of obesity.

What is the relations between dysgeusia and alterations of the nutritional status? A metanarrative analysis of integrative review

BACKGROUND AND AIM

Dysgeusia is  an altered or damaged tasting perception of a multifactorial etiology, from polypharmacy, infections to chemotherapy and radiotherapy. Approximately 5% of the population suffer from a diminished taste sensation, which unfortunately remains underestimated by the affected person, creating the conditions for a dramatic underestimation of the incidence of the symptom. The aim of this study is to summarize the evidences present in literature on the relations between Dysgeusia and alterations of the nutritional status Methods: an integrative review with metanarrative analysis of the articles included was carried out in August 2020. PubMed, Scopus, Embase and CINAHL databases were examined with keywords and methodological strings. PRISMA flow-chart along with a qualitative evaluation grid (JBI-QARI) were applied in the selection of the studies with a time limitation to the last ten years.

RESULTS

10 articles resulted from the literature review process were divided into two macro-categories. Eight articles reported dysgeusia linked to weight loss. The second macro-category showed two studies relating to dysgeusia in patients with altered nutritional status associated with body weight gain.

CONCLUSIONS

this review represents an initial contribution to summarize the best evidence and knowledge in relation to dysgeusia, with the aim of enabling the identification and treatment of this symptom and facilitating targeted educational interventions.

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.

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.

Chronic Effects of a High Sucrose Diet on Murine Gastrointestinal Nutrient Sensor Gene and Protein Expression Levels and Lipid Metabolism

The gastrointestinal tract (GIT) plays a key role in regulating nutrient metabolism and appetite responses. This study aimed to identify changes in the GIT that are important in the development of diet related obesity and diabetes. GIT samples were obtained from C57BL/6J male mice chronically fed a control diet or a high sucrose diet (HSD) and analysed for changes in gene, protein and metabolite levels. In HSD mice, GIT expression levels of fat oxidation genes were reduced, and increased de novo lipogenesis was evident in ileum. Gene expression levels of the putative sugar sensor, slc5a4a and slc5a4b, and fat sensor, cd36, were downregulated in the small intestines of HSD mice. In HSD mice, there was also evidence of bacterial overgrowth and a lipopolysaccharide activated inflammatory pathway involving inducible nitric oxide synthase (iNOS). In Caco-2 cells, sucrose significantly increased the expression levels of the nos2, iNOS and nitric oxide (NO) gas levels. In conclusion, sucrose fed induced obesity/diabetes is associated with changes in GI macronutrient sensing, appetite regulation and nutrient metabolism and intestinal microflora. These may be important drivers, and thus therapeutic targets, of diet-related metabolic disease.

Decrease in sweet taste response and T1R3 sweet taste receptor expression in pregnant mice highlights a potential mechanism for increased caloric consumption in pregnancy

While much is known on how the maternal diet affects offspring fitness, less is known on the role of taste in guiding and promoting food intake during this crucial period. Women have intense food cravings and exhibit altered taste preferences during pregnancy, however the mechanistic details underlying these changes are presently unclear. We performed longitudinal brief-access taste testing in female mice before, during, and after pregnancy, along with quantitative PCR on taste buds and morphological analysis of taste tissues from pregnant and non-pregnant mice. Sucrose licking response decreased progressively during pregnancy compared to that prior to mating, with partial recovery in the post-partum period. No change in taste morphology was evident between pregnant and non-pregnant mice, however a notable decrease in T1R3 sweet taste receptor mRNA expression was recorded in pregnant dams. We conclude that altered taste preferences during pregnancy likely result from changes in the expression profile of taste buds in the mother, which may promote a less healthy diet while expecting.

Offspring of obese mice display enhanced intake and sensitivity for palatable stimuli, with altered expression of taste signaling elements

Maternal body mass index and gestational weight gain predict future obesity status of the offspring. In studies of both rodents and non-human primates, maternal obesity also predicts a preference for palatable foods in the offspring. In this study, we used C57BL/6J mice to investigate whether an underlying cause for an increase in palatable food consumption in the offspring of obese mice was a change in taste function. Adult female mice were fed a normal chow (NC) or a high fat diet (HFD) for 5 weeks before mating, then also during the gestation (3 weeks) and lactation (3 weeks) periods, with offspring always maintained on a normal chow diet; thus the only experience offspring had with high fat food was via maternal exposure. Offspring exhibited similar weight, blood glucose levels and baseline water and chow intake in adulthood. Taste response was assessed after reaching maturity, using brief-access taste testing, with female offspring of obese dams showing an enhanced response to sucrose, and both sexes consuming more sucrose, sucralose and high fat diet if from obese mothers. Offspring also exhibited increased taste bud expression of mRNA for sweet receptor subunits T1R (Taste receptor type) 2 and 3, as well as other markers associated with taste signaling. Taste morphology in both groups appeared similar. Results indicate that obesity in the mother may lead to unhealthy feeding behavior in the offspring, correlating with altered expression of taste signaling elements, which likely drive increased avidity for palatable foods.

Suppression of Oral Sweet Sensations during Consumption of Sweet Food in Humans: Effects on Gastric Emptying Rate, Glycemic Response, Appetite, Food Satisfaction and Desire for Basic Tastes

Suppression of oral sweet sensation (OSS) acutely reduces intake of sweet-tasting food due to lower liking. However, little is known about other physiological responses during both the prandial and postprandial phase. Here, we explored the effects of Gymnema sylvestre (GS)-based suppression of OSS of several types of sweet-tasting food (muffin, sweet yogurt, banana) on gastric emptying, blood glucose (BG), plasma insulin (PI), appetite indices (hunger, fullness and prospective consumption), satisfaction and desire for tastes. Fifteen healthy subjects (22 ± 3 years, 9 women) took part in the study. Subjects rinsed their mouth with either GS solution or distilled water before eating the sweet-tasting food. Subjects felt decreased sweet taste intensity and reduced taste liking associated with GS rinsing after consuming each food, compared with rinsing with distilled water (p < 0.05). Gastric emptying, BG, PI and appetite indices during and after the prandial phase did not significantly change with GS rinsing compared to rinsing with distilled water (p > 0.05). Higher desire for sweet taste as well as lower satisfaction (p < 0.05) in the postprandial phase were observed with GS rinsing. These results suggest that the suppression of OSS does not affect gastric emptying, glycemic response and appetite during and after consumption of sweet-tasting food.

Consuming Gymnema sylvestre Reduces the Desire for High-Sugar Sweet Foods

Background. Gymnemic acids, from the plant Gymnema sylvestre (GS), selectively suppress taste responses to sweet compounds without affecting the perception of other taste elements. The aim of this study was to investigate the effect of consuming a GS-containing mint on the desire to consume high-sugar sweet foods directly thereafter. Methods. This study utilized a single-blind, crossover design comparing the consumption of a mint (dissolving tablet) containing 4 mg of gymnemic acids with an isocaloric placebo in 56 healthy young men and women. Participants were given samples of their favourite chocolate (varied between 14–18 g; energy varied between 292–370 kJ) and were directed to rate on their hunger on 100-mm visual analogue scales 30 s prior to consuming high-sugar sweet food (chocolate). They then consumed the GS mint or placebo mint and rated their perceived pleasantness and desire for more chocolate on separate visual analogue scales immediately following consumption of the high-sugar sweet food before being offered up to five additional servings (and asked to rate hunger, pleasantness and desire to eat more chocolate between each ingestion period). Results. The number of chocolate bars eaten decreased by 0.48 bars (21.3%) within a 15-min period of consumption of the GS mint (p = 0.006). Desire to eat more of the high-sugar sweet food (p = 0.011) and pleasantness of the high-sugar sweet food (p < 0.001) was reduced after GS mint intake. Those who reported having a ‘sweet tooth’ had a greater reduction in the pleasantness of chocolate (p = 0.037) and desire to eat more (p = 0.004) after consuming the GS mint for the first serving of a high-sugar sweet food following the mint. Conclusion. Consuming gymnema-containing mints compared to placebo significantly reduced the quantity of chocolate eaten mainly due to a decrease in the desire and pleasantness of consuming it.

Impact of Common Food Labels on Consumer Liking in Vanilla Yogurt

As competition on super market shelves is higher than ever, the importance of product concepts, communicated through labels, can dictate a product’s success or failure. However, it is possible for labels to affect a consumer’s experience, changing the overall response to the product. In this study, we tested samples of vanilla yogurt with one of four commonly used labeling concepts (high-protein, low-fat, made with stevia and all-natural) on sensory perception, consumer liking, expected consumption amount, and willingness to pay (WTP) in a consumer test (n = 108). Each participant evaluated five samples of the same vanilla yogurt identified with one of the labels, or an unlabeled control. Results showed panelists liked the samples labeled with low-fat and high-protein to the greatest degree, with all-natural scoring the lowest. Those more concerned with protein content found the samples less satiating, dependent on sex. Sweetness was also perceived more highly in younger panelists, with panelists WTP dependent on their liking of the labels. Results highlight the importance of labeling as an extrinsic cue affecting liking ratings, with potential ramification for ultimate product success. Understanding consumers’ response to labels, as well as their attitudes, has broad implications for food marketing, as well as public health and the study of eating habits.

Oral adverse effects of drugs: Taste disorders

Objective

Oral healthcare professionals are frequently confronted with patients using drugs on a daily basis. These drugs can cause taste disorders as adverse effect. The literature that discusses drug‐induced taste disorders is fragmented. This article aims to support oral healthcare professionals in their decision making whether a taste disorder can be due to use of drugs by providing a comprehensive overview of drugs with taste disorders as an adverse effect.

Materials and methods

The national drug information database for Dutch pharmacists, based on scientific drug information, guidelines, and summaries of product characteristics, was analyzed for drug‐induced taste disorders. “MedDRA classification” and “Anatomic Therapeutical Chemical codes” were used to categorize the results.

Results

Of the 1,645 drugs registered in the database, 282 (17%) were documented with “dysgeusia” and 61 (3.7%) with “hypogeusia.” Drug‐induced taste disorders are reported in all drug categories, but predominantly in “antineoplastic and immunomodulating agents,” “antiinfectives for systemic use,” and “nervous system.” In ~45%, “dry mouth” coincided as adverse effect with taste disorders.

Conclusion

Healthcare professionals are frequently confronted with drugs reported to cause taste disorders. This article provides an overview of these drugs to support clinicians in their awareness, diagnosis, and treatment of drug‐induced taste disorders.

Taste loss with obesity in mice and men

BACKGROUND

Our sense of taste is critical in defining our food choices and habits. Located primarily in our tongue, taste buds are small assemblies of constantly renewing sensory cells, tasked with evaluating oral stimuli before the food we eat is consumed.

METHODS

Using both mice and a free-living human population, we tracked taste papilla abundancy with weight gain, to test for deficiencies in the taste system of obese mice and humans with increased adiposity.

RESULTS

Mice fed a high-fat diet for 8 weeks expressed markers for all subtypes of taste cells at a lower level than chow-fed counterparts. This came alongside the loss of markers for taste cell proliferation (Ki-67) and development (β-catenin), as well as lower fungiform papillae density, consistent with earlier results showing lower circumvallate taste bud abundance in obese mice. Likewise, in a population of college students tracked through 4 years of college attendance, the change in density of fungiform papillae, which house taste buds in the anterior tongue, was negatively correlated with change in neck circumference, a marker of adiposity.

CONCLUSIONS

These results highlight changes in taste during weight gain as a potentially important consideration in the study of obesity.

Taste Responses in the Nucleus of the Solitary Tract of Awake Obese Rats Are Blunted Compared With Those in Lean Rats

Taste perception changes with obesity but the underlying neural changes remain poorly understood. To address this issue, we recorded taste responses from single cells in the nucleus tractus solitarius (NTS, the first synapse in the central gustatory circuit) in awake, diet-induced obese [(DIO; ≥ 8 weeks on a high-energy diet (45%fat, 17% sugar; HED)], and lean rats. Rats were implanted with a bundle of microelectrodes in the NTS and allowed to recover. Water-deprived rats were allowed to freely lick various tastants in an experimental chamber. Taste stimuli included an array of sapid stimuli dissolved in artificial saliva (AS). Each taste trial consisted of five consecutive licks followed by five AS licks presented on a VR5 schedule. Results showed that taste responses (n = 49 for DIO; n = 74 for lean rats) in NTS cells in DIO rats were smaller in magnitude, shorter in duration, and longer in latency that those in lean rats. However, there were proportionately more taste-responsive cells in DIO than in lean rats. Lick coherence in DIO rats was significantly lower than in lean rats, both in taste-responsive, and lick-related cells (n = 172 in lean; n = 65 in DIO). Analyses of temporal coding showed that taste cells in DIO rats conveyed less information about taste quality than cells in lean rats. Collectively, results suggest that a HED produces blunted, but more prevalent, responses to taste in the NTS, and a weakened association of taste responses with ingestive behavior. These neural adaptations may represent both negative effects and compensatory mechanisms of a HED that may underlie deficits in taste-related behavior associated with obesity.

Association between taste perception and adiposity in overweight or obese older subjects with metabolic syndrome and identification of novel taste-related genes

BACKGROUND

The relation between taste perception, diet, and adiposity remains controversial. Additionally, there is a lack of knowledge on the polymorphisms influencing taste given the scarcity of genome-wide association studies (GWASs) published.

OBJECTIVES

We studied the relation between perception of the basic tastes, i.e., sweet, salty, bitter, sour, and umami (separately and jointly in a "taste score"), and anthropometric measurements in older subjects with metabolic syndrome (MetS). GWASs were undertaken to identify genes associated with basic tastes and their score.

METHODS

Taste perception was cross-sectionally determined by challenging subjects (381 older individuals with MetS) with solutions (5 concentrations) of the basic tastes with the use of standard prototypical tastants (phenylthiocarbamide and 6-n-propylthiouracil, NaCl, sucrose, monopotassium glutamate, and citric acid, for bitter, salt, sweet, umami, and sour, respectively). Taste perception intensities were expressed on a scale. A total taste score was derived.

RESULTS

The total taste score was inversely associated with body weight, body mass index, and waist circumference (P < 0.05). Subjects having a total taste score higher than or equal to the median (11 points for concentration V) were less likely to be classified as obese than subjects below the median (OR: 0.36; 95% CI: 0.22, 0.59; P < 0.001). Associations were similar, albeit less strong, for some taste qualities. In the GWASs, the highest associations were for bitter taste (rs1726866-TAS2R38, with P = 7.74 × 10-18 for phenylthiocarbamide and P = 3.96 × 10-19 for 6-n-propylthiouracil). For other tastes, several single-nucleotide polymorphisms (SNPs) exceeded the P threshold of 1 × 10-5. However, the top-ranked SNPs independently explained a low percentage of taste variability, hence their use as single proxies for the association between taste perception and adiposity is limited.

CONCLUSIONS

We found a strong inverse association between greater taste perception and body weight, body mass index, and waist circumference in older subjects with MetS and identified some taste-related SNPs. It would be advantageous to identify additional genetic proxies for taste and to develop polygenic scores. Data used in this study were derived from the clinical trial PREDIMED PLUS at baseline, registered at http://www.isrctn.com as ISRCTN89898870.

Exploring Associations between Interindividual Differences in Taste Perception, Oral Microbiota Composition, and Reported Food Intake

The role of taste perception, its relationship with oral microbiota composition, and their putative link with eating habits and food intake were the focus of the present study. A sample of 59 reportedly healthy adults (27 male, 32 female; age: 23.3 ± 2.6 years) were recruited for the study and taste thresholds for basic tastes, food intake, and oral microbiota composition were evaluated. Differences in taste perception were associated with different habitual food consumption (i.e., frequency) and actual intake. Subjects who were orally hyposensitive to salty taste reported consuming more bakery and salty baked products, saturated-fat-rich products, and soft drinks than hypersensitive subjects. Subjects hyposensitive to sweet taste reported consuming more frequently sweets and desserts than the hypersensitive group. Moreover, subjects hypersensitive to bitter taste showed higher total energy and carbohydrate intakes compared to those who perceived the solution as less bitter. Some bacterial taxa on tongue dorsum were associated with gustatory functions and with vegetable-rich (e.g., Prevotella) or protein/fat-rich diets (e.g., Clostridia). Future studies will be pivotal to confirm the hypothesis and the potential exploitation of oral microbiome as biomarker of long-term consumption of healthy or unhealthy diets.

The pathogenesis of obesity

Body fat mass increases when energy intake exceeds energy expenditure. In the long term, a positive energy balance will result in obesity. The worldwide prevalence of obesity has increased dramatically, posing a serious threat to human health. Therefore, insight in the pathogenesis of obesity is important to identify novel prevention and treatment strategies. This review describes the physiology of energy expenditure and energy intake in the context of body weight gain in humans. We focus on the components of energy expenditure and the regulation of energy intake. Finally, we describe rare monogenetic causes leading to an impairment in central regulation of food intake and obesity.

Environmental Immersion's Influence on Hedonics, Perceived Appropriateness, and Willingness to Pay in Alcoholic Beverages

The eating experience is multimodal. As we consume a dish, we perceive much more than that which initially activates the senses, including influences from our surroundings. Foods sampled in experimental settings are largely evaluated within a sensory booth, an environment designed to be devoid of such external or non-standardized stimuli, so that participants can focus solely on the sample itself. In natural experiences, we rarely consume food in such isolation—context is actually key to many dining experiences and can have an integral role in how we perceive the foods we eat. Using virtual reality to artificially provide this context, we tested how the setting in which a beverage was consumed influenced perception of two different samples. Virtual environments were formed by processing custom-recorded 360 degree videos and overlaying audio, text, and sensory scales to simulate a typical sensory evaluation. Participants were asked to taste two alcoholic beverages, a beer and a sparkling wine, in two virtual contexts, a bar and a winery. The results indicated that participants’ willingness to pay for, and overall enjoyment of the sparkling wine increased when placed in the winery context, with no change between the two virtual contexts for the beer sample. This occurred without alteration of the samples’ sensory properties or the ability of panelists to identify the beverage they were drinking; however, perceived appropriateness of the samples for the setting was strongly influenced by the context in which they were sampled, suggesting that perceived appropriateness for a surrounding may play a role in the degree to which we enjoy a food. Results provide further proof that artificially-applied context, such as that provided by virtual reality, can further the sensory testing of foods.

Evaluating All Potential Oral Complications of Diabetes Mellitus

Diabetes mellitus (DM) is associated with several microvascular and macrovascular complications, such as retinopathy, nephropathy, neuropathy, and cardiovascular diseases. The pathogenesis of these complications is complex, and involves metabolic and hemodynamic disturbances, including hyperglycemia, insulin resistance, dyslipidemia, hypertension, and immune dysfunction. These disturbances initiate several damaging processes, such as increased reactive oxygen species (ROS) production, inflammation, and ischemia. These processes mainly exert their damaging effect on endothelial and nerve cells, hence the susceptibility of densely vascularized and innervated sites, such as the eyes, kidneys, and nerves. Since the oral cavity is also highly vascularized and innervated, oral complications can be expected as well. The relationship between DM and oral diseases has received considerable attention in the past few decades. However, most studies only focus on periodontitis, and still approach DM from the limited perspective of elevated blood glucose levels only. In this review, we will assess other potential oral complications as well, including: dental caries, dry mouth, oral mucosal lesions, oral cancer, taste disturbances, temporomandibular disorders, burning mouth syndrome, apical periodontitis, and peri-implant diseases. Each oral complication will be briefly introduced, followed by an assessment of the literature studying epidemiological associations with DM. We will also elaborate on pathogenic mechanisms that might explain associations between DM and oral complications. To do so, we aim to expand our perspective of DM by not only considering elevated blood glucose levels, but also including literature about the other important pathogenic mechanisms, such as insulin resistance, dyslipidemia, hypertension, and immune dysfunction.

Receptor Regulation in Taste: Can Diet Influence How We Perceive Foods?

Taste buds are the dedicated sensory end organs of taste, comprising a complex and evolving profile of signaling elements. The sensation and ultimate perception of taste depends on the expression of a diverse array of receptors and channels that sense their respective tastes. Receptor regulation is a recognized and well-studied phenomenon in many systems, observed in opioid addiction, insulin resistance and caffeine tolerance. Results from human sensory studies suggest that receptor sensitivity or expression level may decrease after chronic exposure to respective tastants through diet. We review data supporting the theory that taste receptors may become downregulated with exposure to a specific tastant, along with presenting data from a small pilot study, showing the impact of long-term tastant exposure on taste receptor expression in mice. Mice treated with monosodium salt monohydrate (MSG), saccharin and NaCl (typically appetitive tastes) all displayed a significant decrease in mRNA expression for respective umami, sweet and salty receptors/sensory channels. Reduced sensitivity to appetitive tastes may promote overconsumption of foods high in such stimuli.

Impaired taste sensation in type 2 diabetic patients without chronic complications: a case-control study

PURPOSE

Few and contradictory data suggest changes in taste perception in type 2 diabetes (T2DM), potentially altering food choices. We, therefore, analyzed taste recognition thresholds in T2DM patients with good metabolic control and free of conditions potentially impacting on taste, compared with age-, body mass index-, and sex-matched normoglycemic controls.

METHODS

An ascending-concentration method was used, employing sucrose (sweet), sodium chloride (salty), citric acid (sour), and quinine hydrochloride (bitter), diluted in increasing concentration solutions. The recognition threshold was the lowest concentration of correct taste identification.

RESULTS

The recognition thresholds for the four tastes were higher in T2DM patients. In a multiple regression model, T2DM [β = 0.95; 95% CI 0.32-1.58; p = 0.004 (salty); β = 0.61; 0.19-1.03; p = 0.006 (sweet); β = 0.78; 0.15-1.40; p = 0.016 (sour); β = 0.74; 0.22-1.25; p = 0.006 (bitter)] and waist circumference [β = 0.05; 0.01-0.08; p = 0.012 (salty); β = 0.03; 0.01-0.05; p = 0.020 (sweet); β = 0.04; 0.01-0.08; p = 0.020 (sour); β = 0.04; 0.01-0.07; p = 0.007 (bitter)] were associated with the recognition thresholds. Age was associated with salty (β = 0.06; 0.01-0.12; p = 0.027) and BMI with sweet thresholds (β = 0.06; 0.01-0.11; p = 0.019).

CONCLUSIONS

Taste recognition thresholds were higher in uncomplicated T2DM, and central obesity was significantly associated with this impairment. Hypogeusia may be an early sign of diabetic neuropathy and be implicated in the poor compliance of these patients to dietary recommendations.

Prolonged Exposure to Monosodium Glutamate in Healthy Young Adults Decreases Perceived Umami Taste and Diminishes Appetite for Savory Foods

Background

Research suggests that increased consumption of sweet, salt, or fat is associated with diminished perceived taste intensity and shifted preferences for the respective stimulus. It is unknown whether a similar effect occurs with the consumption of umami.

Objective

The aim of the study was to investigate the influence of habitual exposure to umami stimuli on umami taste perception, hedonics, and satiety.

Methods

Fifty-eight healthy men (n = 16) and women (n = 42) participated in a parallel-group, randomized controlled study. The normal-weight [mean ± SD body mass index (kg/m2): 21.8 ± 2.2] group of young adults (mean ± SD age: 22.7 ± 6.2 y) consumed vegetable broth daily for 4 wk. The broth for the treatment group (n = 28) was supplemented with 3.8 g monosodium glutamate (MSG), whereas the control group (n = 30) consumed a sodium-matched broth without MSG. Perceived umami taste intensity and discrimination in MSG solutions; liking, wanting, and preference of a variety of umami-rich foods; satiation and satiety from an ad libitum meal; and anthropometric measures were evaluated at baseline and at week 4. General linear models assessed the effect of treatment on change from baseline for all outcomes and tested for effect modification of sex.

Results

Relative to controls, increased consumption of MSG for 4 wk diminished umami taste in women (8.4 units on generalized Labeled Magnitude Scale; 95% CI: -13.8, -3.1 units; P = 0.013). The desire for and intake of savory foods decreased after MSG treatment in both sexes with an ad libitum meal (desire: -7.7 units; 95% CI: -13.7, -1.7 units; P = 0.04; intake: -36 g; 95% CI: -91, 19 g; P = 0.04).

Conclusion

Our results highlight that a month-long diet high in umami stimuli attenuates perceived umami taste and appetite for savory foods in a young, healthy population. Our findings contribute to the understanding of food choice, a factor in the development and maintenance of obesity, as well as the etiology of protein-related health conditions such as osteoporosis and kidney disease. This study is registered at www.clinicaltrials.gov as NCT03010930.

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.

Sleep, food cravings and taste

OBJECTIVE

Taste is influenced by factors from our environment, psychology, and from our own physiological state. The objective of the study was to determine whether sleep influences our sense of taste or our cravings for food.

METHOD

57 healthy panelists, predominantly of college age, submitted to sleep tracking, and subsequently underwent a series of sensory tests, using basic prototypic tastants, as well as real foods. Panelists were also evaluated to quantify food cravings, using both the Leeds Food Preference Questionnaire, and the Control of Eating Questionnaire.

RESULTS

Umami (p = 0.025, F = 5.301) and sour (p = 0.037, F = 4.591) taste were intensified in those rating sleepiness higher, while this group also reported higher implicit wanting for high fat sweet foods (p = 0.011, Wald chi-sq = 14.937). Craving for sweet or savory also associated with a number of measures of taste response to real foods.

CONCLUSIONS

Results imply that a lack of sleep may induce cravings for unhealthy foods, and that foods high in umami or sour taste may be experienced differently due to alterations in taste function. Results imply that feeding behavior may be influenced by a lack of sleep, acting at least partially through our sense of taste.

Is Sweet Taste Perception Associated with Sweet Food Liking and Intake?

A range of psychophysical taste measurements are used to characterize an individual’s sweet taste perception and to assess links between taste perception and dietary intake. The aims of this study were to investigate the relationship between four different psychophysical measurements of sweet taste perception, and to explore which measures of sweet taste perception relate to sweet food intake. Forty-four women aged 20–40 years were recruited for the study. Four measures of sweet taste perception (detection and recognition thresholds, and sweet taste intensity and hedonic liking of suprathreshold concentrations) were assessed using glucose as the tastant. Dietary measurements included a four-day weighed food record, a sweet food-food frequency questionnaire and a sweet beverage liking questionnaire. Glucose detection and recognition thresholds showed no correlation with suprathreshold taste measurements or any dietary intake measurement. Importantly, sweet taste intensity correlated negatively with total energy and carbohydrate (starch, total sugar, fructose, glucose) intakes, frequency of sweet food intake and sweet beverage liking. Furthermore, sweet hedonic liking correlated positively with total energy and carbohydrate (total sugar, fructose, glucose) intakes. The present study shows a clear link between sweet taste intensity and hedonic liking with sweet food liking, and total energy, carbohydrate and sugar intake.