Bitter taste markers explain variability in vegetable sweetness, bitterness, and intake

New chemosensory component in the U.S. National Health and Nutrition Examination Survey (NHANES): first-year results for measured olfactory dysfunction

The U.S. NHANES included chemosensory assessments in the 2011-2014 protocol. We provide an overview of this protocol and 2012 olfactory exam findings. Of the 1818 NHANES participants aged ≥40 years, 1281 (70.5 %) completed the exam; non-participation mostly was due to time constraints. Health technicians administered an 8-item, forced-choice, odor identification task scored as normosmic (6-8 odors identified correctly) versus olfactory dysfunction, including hyposmic (4-5 correct) and anosmic/severe hyposmic (0-3 correct). Interviewers recorded self-reported smell alterations (during past year, since age 25, phantosmia), histories of sinonasal problems, xerostomia, dental extractions, head or facial trauma, and chemosensory-related treatment and changes in quality of life. Olfactory dysfunction was found in 12.4 % (13.3 million adults; 55 % males/45 % females) including 3.2 % anosmic/severe hyposmic (3.4 million; 74 % males/26 % females). Selected age-specific prevalences were 4.2 % (40-49 years), 12.7 % (60-69 years), and 39.4 % (80+ years). Among adults ≥70 years, misidentification rates for warning odors were 20.3 % for smoke and 31.3 % for natural gas. The highest sensitivity (correctly identifying dysfunction) and specificity (correctly identifying normosmia) of self-reported olfactory alteration was among anosmics/severe hyposmics (54.4 % and 78.1 %, respectively). In age- and sex-adjusted logistic regression analysis, risk factors of olfactory dysfunction were racial/ethnic minority, income-to-poverty ratio ≤ 1.1, education <high school, and heavy drinking. Moderate-to-vigorous physical activity reduced risk of impairment. Olfactory dysfunction is prevalent, particularly among older adults. Inexpensive, brief odor identification tests coupled with questions (smell problems past year, since age 25, phantosmia) could screen for marked dysfunction. Healthcare providers should be prepared to offer education on non-olfactory avoidance of hazardous events.

Exploring Ethnic Differences in Taste Perception

It is well known that nutritional intake can vary substantially as a function of demographic variables such as ethnicity and/or sex. Although a variety of factors are known to underlie the relationship between these demographic variables and nutritional intake, it is interesting to speculate that variation in food intake associated with ethnicity or sex may result, in part, from differences in the perceived taste of foods in these different populations. Thus, we initiated a study to evaluate taste responsiveness in different ethnic groups. Moreover, because of the known differences in taste responsiveness between males and females, analyses were stratified by sex. The ethnic groups tested differed significantly from one another in reported perceived taste intensity. Our results showed that Hispanics and African Americans rated taste sensations higher than non-Hispanic Whites and that these differences were more pronounced in males. Understanding the nature of these differences in taste perception is important, because taste perception may contribute to dietary health risk. When attempting to modify diet, individuals of different ethnicities may require personalized interventions that take into account the different sensory experience that these individuals may have when consuming foods.

Vegetable and Fruit Acceptance during Infancy: Impact of Ontogeny, Genetics, and Early Experiences

Many of the chronic illnesses that plague modern society derive in large part from poor food choices. Thus, it is not surprising that the Dietary Guidelines for Americans, aimed at the population ≥2 y of age, recommends limiting consumption of salt, fat, and simple sugars, all of which have sensory properties that we humans find particularly palatable, and increasing the variety and contribution of fruits and vegetables in the diet, to promote health and prevent disease. Similar recommendations may soon be targeted at even younger Americans: the B-24 Project, led by the US Department of Health and Human Services and the USDA, is currently evaluating evidence to include infants and children from birth to 2 y of age in the dietary guidelines. This article reviews the underinvestigated behavioral phenomena surrounding how to introduce vegetables and fruits into infants' diets, for which there is much medical lore but, to our knowledge, little evidence-based research. Because the chemical senses are the major determinants of whether young children will accept a food (e.g., they eat only what they like), these senses take on even greater importance in understanding the bases for food choices in children. We focus on early life, in contrast with many other studies that attempt to modify food habits in older children and thus may miss sensitive periods that modulate long-term acceptance. Our review also takes into consideration ontogeny and sources of individual differences in taste perception, in particular, the role of genetic variation in bitter taste perception.

Development of a molecular method for the rapid screening and identification of the three functionally relevant polymorphisms in the human TAS2R38 receptor gene in studies of sensitivity to the bitter taste of PROP

The objective of this work was to develop a rapid screening method to identify the three single nucleotide polymorphisms (SNPs) in the TAS2R38 gene, with the aim of providing a significant contribution to studies designed to assess sensitivity to the bitter taste of 6-n-propylthiouracil (PROP). Specifically, the objective of this study was to characterize the TAS2R38 gene haplotypes in a group of 60 subjects with variable sensitivity to PROP and preliminarily genotyped for the rs2274333 allele (A/G) of carbonic anhydrase isoform VI gene (CA6). The molecular characterization of the TAS2R38 gene was conducted using the PCR-restriction fragment length polymorphism technique after creating artificial restriction sites upstream or downstream of the SNPs, as none of the three polymorphisms contributes to the formation of a restriction site for a specific endonuclease. The results indicate that the method described in this paper could be a valid and simple experimental strategy to identify genetic differences related to taste sensitivity to bitter taste, and could be applied as a nutrigenetics test in studies aimed at understanding people’s eating behaviors.

Preschool-Adapted Liking Survey (PALS): A Brief and Valid Method To Assess Dietary Quality of Preschoolers

BACKGROUND

Feasible, valid, and reliable tools are needed to assess dietary quality among preschoolers. We aimed to test construct-/criterion-related validity and reliability of a dietary quality index generated from a liking survey and novel dietary patterns for characterizing food hedonism and parental feeding practices.

METHODS

Participants included 416 economically disadvantaged, diverse preschoolers (41% overweight/obese) from educational centers and their parents. Parents completed liking and frequency surveys; the liking survey took half as long to complete. Preschoolers' skin carotenoid status (measured by Resonance Raman spectroscopy) and BMI percentile (measured weight/height) were assessed. The Healthy Eating Preference Index (HEPI) was constructed from weighted averages of liking scores for food groups and healthy variety score and Healthy Eating Index 2010 (HEI) from nutrient analysis of the frequency survey.

RESULTS

The HEPI was normally distributed and showed construct validity and adequate internal reliability. In hierarchical regression analyses, the HEPI explained carotenoid status and adiposity as alternative or value-added predictors to HEI, supporting criterion-related validity of HEPI. Parental reporting of children's liking of high-fat/sweet/salty foods in excess of pleasurable activities (food hedonism) predicted heavier preschoolers, as did discord between HEI and HEPI (potential parental pressure toward healthy eating). HEPI alone or with HEI explained variability in carotenoid status and adiposity in path models with adequate to good fits.

CONCLUSIONS

With simple collection and processing, the liking survey can generate a valid/reliable dietary quality index in child care settings to identify preschoolers at risk for lower nutritional status. Using liking and frequency-based screeners could improve understanding of parental feeding behaviors and precision of predicting nutritional status.

Polymorphisms in sweet taste genes (TAS1R2 and GLUT2), sweet liking, and dental caries prevalence in an adult Italian population

The aim of the study was to assess the relationship between sweet taste genes and dental caries prevalence in a large sample of adults. In addition, the association between sweet liking and sugar intake with dental caries was investigated. Caries was measured by the decayed, missing, filled teeth (DMFT) index in 647 Caucasian subjects (285 males and 362 females, aged 18-65 years), coming from six villages in northeastern Italy. Sweet liking was assessed using a 9-point scale, and the mean of the liking given by each individual to specific sweet food and beverages was used to create a sweet liking score. Simple sugar consumption was estimated by a dietary history interview, considering both added sugars and sugar present naturally in foods. Our study confirmed that polymorphisms in TAS1R2 and GLUT2 genes are related to DMFT index. In particular, GG homozygous individuals for rs3935570 in TAS1R2 gene (p value = 0.0117) and GG homozygous individuals for rs1499821 in GLUT2 gene (p value = 0.0273) showed higher DMFT levels compared to both heterozygous and homozygous for the alternative allele. Furthermore, while the relationship sugar intake-DMFT did not achieve statistical significance (p value = 0.075), a significant association was identified between sweet liking and DMFT (p value = 0.004), independent of other variables. Our study showed that sweet taste genetic factors contribute to caries prevalence and highlighted the role of sweet liking as a predictor of caries risk. Therefore, these results may open new perspectives for individual risk identification and implementation of target preventive strategies, such as identifying high-risk patients before caries development.

The Taste and Smell Protocol in the 2011-2014 US National Health and Nutrition Examination Survey (NHANES): Test-Retest Reliability and Validity Testing

INTRODUCTION

The US NHANES 2011-2014 protocol includes a taste and smell questionnaire (CSQ) in home-based interviews and brief assessments in mobile exam centers. We report the short- and longer-term test-retest reliability and validity of this protocol against broader chemosensory measures.

METHODS

A convenience sample of 73 adults (age=39.5±20.8 years) underwent the NHANES protocol at baseline, 2 weeks and 6 months. For taste, participants rated intensities of two tastants (1 M NaCl, 1 mM quinine) applied to the tongue tip and three tastants (1 M NaCl, 1 mM quinine, 0.32 M NaCl) sampled with the whole mouth. Smell function was assessed with a Pocket Smell Test™ (PST; eight-item odor identification test). The CSQ asked about chemosensory problems, distortions, and age-related changes. Broader baseline measurements were a 40-item olfactometer-generated identification task and additional whole-mouth taste intensities (1 M sucrose, 32 mM citric acid, 3.2 mM propylthiouracil).

RESULTS

Intraclass correlations (ICCs) for NHANES taste measures showed moderate-to-good agreement after 2 weeks and 6 months (ICCs 0.42-0.71). Whole-mouth quinine intensity was significantly correlated with other taste intensities, supporting its utility as a marker for overall taste functioning. Olfactory classification from PSTs agreed for 98.5 % of participants across 2 weeks (κ=0.85; 95 % CI 0.71-0.99) and had good correspondence with the olfactometer task. CSQ items showed good-to-excellent agreement over 6 months (ICCs 0.66-0.90).

CONCLUSIONS

These findings further support that the NHANES chemosensory protocol has moderate-to-good test-retest reliability when administered to healthy, educated adults. Despite being a brief procedure with limited measures, the NHANES taste and smell assessments provided good information when compared to broader measures of taste and smell function.

Using Animal Models to Determine the Role of Gustatory Neural Input in the Control of Ingestive Behavior and the Maintenance of Body Weight

INTRODUCTION

Decades of research have suggested that nutritional intake contributes to the development of human disease, mainly by influencing the development of obesity and obesity-related conditions. A relatively large body of research indicates that functional variation in human taste perception can influence nutritional intake as well as body mass accumulation. However, there are a considerable number of studies that suggest that no link between these variables actually exists. These discrepancies in the literature likely result from the confounding influence of a variety of other, uncontrolled, factors that can influence ingestive behavior.

STRATEGY

In this review, the use of controlled animal experimentation to alleviate at least some of these issues related to the lack of control of experimental variables is discussed. Specific examples of the use of some of these techniques are examined.

DISCUSSION AND CONCLUSIONS

The review will close with some specific suggestions aimed at strengthening the link between gustatory neural input and its putative influence on ingestive behaviors and the maintenance of body weight.

The Measurement of Pleasure and Pain

Pleasure and pain are among our most salient experiences, and we want to know how our pleasures and pains stack up against those of others. Older psychophysical methods fail to provide valid comparisons of pleasure and pain across individuals or groups. We are making progress in measurement, but we still have a ways to go.

Bitter taste genetics--the relationship to tasting, liking, consumption and health

Bitter is the most complex of human tastes, and is arguably the most important. Aversion to bitter taste is important for detecting toxic compounds in food; however, many beneficial nutrients also taste bitter and these may therefore also be avoided as a consequence of bitter taste. While many polymorphisms in TAS2R genes may result in phenotypic differences that influence the range and sensitivity of bitter compounds detected, the full extent to which individuals differ in their abilities to detect bitter compounds remains unknown. Simple logic suggests that taste phenotypes influence food preferences, intake and consequently health status. However, it is becoming clear that genetics only plays a partial role in predicting preference, intake and health outcomes, and the complex, pleiotropic relationships involved are yet to be fully elucidated.

Consumer clusters in Denmark based on coarse vegetable intake frequency, explained by hedonics, socio-demographic, health and food lifestyle factors. A cross-sectional national survey

Vegetable intake seems to play a protective role against major lifestyle diseases. Despite this, the Danish population usually eats far less than the recommended daily intake. The present study focused on the intake of 17 coarse vegetables and the potential barriers limiting their intake. The present study drew upon a large Danish survey (n = 1079) to study the intake of coarse vegetables among Danish consumers. Four population clusters were identified based on their intake of 17 different coarse vegetables, and profiled according to hedonics, socio-demographic, health, and food lifestyle factors. The four clusters were characterized by a very low intake frequency of coarse vegetables ('low frequency'), a low intake frequency of coarse vegetables; but high intake frequency of carrots ('carrot eaters'), a moderate coarse vegetable intake frequency and high intake frequency of beetroot ('beetroot eaters'), and a high intake frequency of all coarse vegetables ('high frequency'). There was a relationship between reported liking and reported intake frequency for all tested vegetables. Preference for foods with a sweet, salty or bitter taste, in general, was also identified to be decisive for the reported vegetable intake, as these differed across the clusters. Each cluster had distinct socio-demographic, health and food lifestyle profiles. 'Low frequency' was characterized by uninvolved consumers with lack of interest in food, 'carrot eaters' vegetable intake was driven by health aspects, 'beetroot eaters' were characterized as traditional food consumers, and 'high frequency' were individuals with a strong food engagement and high vegetable liking. 'Low frequency' identified more barriers than other consumer clusters and specifically regarded low availability of pre-cut/prepared coarse vegetables on the market as a barrier. Across all clusters a low culinary knowledge was identified as the main barrier.

Relationship of 6-n-propylthiouracil taste intensity and chili pepper use with body mass index, energy intake, and fat intake within an ethnically diverse population

BACKGROUND

One of the weight-loss strategies that has attracted attention is the use of spicy foods. It has been suggested that spicy food preference is related to a genetically predetermined sensitivity to the bitter compound 6-n-propylthiouracil (PROP).

OBJECTIVE

Our aim was to examine the relationship of PROP taste intensity and hot chili pepper use with body mass index (BMI), energy intake, and fat intake.

DESIGN

This study utilized a cross-sectional design.

PARTICIPANTS/SETTING

The sample included 350 subjects (154 male, 196 female) ages 18 to 55 years living in the New York City area.

MAIN OUTCOME MEASURES

BMI was calculated by measuring weight and height, and the sensitivity to PROP was evaluated using the PROP filter paper method. Subjects also rated the frequency of usage and preference for hot chili pepper using a chili pepper questionnaire. Their daily energy and fat intake were assessed using a food frequency questionnaire.

STATISTICAL ANALYSES PERFORMED

An independent sample t-test compared subject characteristics between groups based on sex, PROP status, and hot chili pepper user status for the continuous variables, and the χ(2) test was used for categorical variables. One-way analysis variance examined the differences in subject characteristics across four ethnicities. To predict BMI, energy intake, and fat intake, multiple linear regression models were fit with the covariates of age, sex, ethnicity, chili pepper score, and PROP mean.

RESULTS

The values for BMI, energy intake, and fat intake of PROP tasters were significantly lower than those of PROP nontasters (P=0.03, P<0.001, and P<0.001, respectively). The energy intake of chili pepper nonusers was significantly lower than that of chili pepper users (P=0.02), while there was no significant difference in fat intake between chili pepper users and nonusers.

CONCLUSIONS

This study suggests that PROP taste sensitivity contributes more to the prediction of energy and fat intake than chili pepper use.

The impact of individual variations in taste sensitivity on coffee perceptions and preferences

Despite a few relationships between fungiform papillae (FP) density and 6-n-propylthiouracil (PROP) taster status have been reported for sensory qualities within foods, the impact on preferences remains relatively unclear. The present study investigated responses of FP number and PROP taster groups to different bitter compounds and how these affect coffee perception, consumption and liking. Subjects (Ss) with higher FP numbers (HFP) gave higher liking ratings to coffee samples than those with lower FP numbers (LFP), but only for sweetened coffee. Moreover, HFP Ss added more sugar to the samples than LFP Ss. Significant differences between FP groups were also found for the sourness of the coffee samples, but not for bitterness and astringency. However, HFP Ss rated bitter taste stimuli as stronger than did LFP Ss. While coffee liking was unrelated to PROP status, PROP non-tasters (NTs) added more sugar to the coffee samples than did super-tasters (STs). In addition, STs rated sourness, bitterness and astringency as stronger than NTs, both in coffee and standard solutions. These results confirm that FP density and PROP status play a significant role in taste sensitivity for bitter compounds in general and also demonstrate that sugar use is partly a function of fundamental individual differences in physiology.

The gustin (CA6) gene polymorphism, rs2274333 (A/G), is associated with fungiform papilla density, whereas PROP bitterness is mostly due to TAS2R38 in an ethnically-mixed population

PROP responsiveness is associated with TAS2R38 haplotypes and fungiform papilla density. Recently, we showed that a polymorphism in the gene coding for the salivary trophic factor, gustin (CA6), affects PROP sensitivity by acting on cell growth and fungiform papillae maintenance, in a genetically homogeneous cohort. Since population homogeneity can lead to over estimation of gene effects, the primary aim of the present work was to confirm gustin's role in PROP bitterness intensity and fungiform papillae density in a genetically diverse population. Eighty subjects were genotyped for both genes by PCR techniques. PROP responsiveness was assessed by a filter paper method and fungiform papilla density was determined in each subject. As expected, PROP bitterness ratings were lower in individuals with the AVI/AVI diplotype of TAS2R38 than in individuals with PAV/PAV and PAV/AVI diplotypes. However, no differences in PROP bitterness among genotypes of the gustin gene, and no differences in the density of fungiform papillae related to TAS2R38 diplotype were found. In contrast, the density of fungiform papillae decreased as the number of minor (G) alleles at the gustin locus increased. In addition, the distribution of TAS2R38 genotypes within each gustin genotype group showed that the occurrence of recessive alleles at both loci was infrequent in the present sample compared to other populations. These findings confirm that papillae density is associated with gustin gene polymorphism, rs2274333 (A/G), in an ancestrally heterogeneous population, and suggest that variations in the frequency of allele combinations for these two genes could provide a salient explanation for discrepant findings for gustin gene effects across populations.

Taste sensitivity, nutritional status and metabolic syndrome: Implication in weight loss dietary interventions

AIM: We investigated the relationship between taste sensitivity, nutritional status and metabolic syndrome and possible implications on weight loss dietary program.

METHODS: Sensitivity for bitter, sweet, salty and sour tastes was assessed by the three-Alternative-Forced-Choice method in 41 overweight (OW), 52 obese (OB) patients and 56 normal-weight matched controls. OW and OB were assessed also for body composition (by impedence), resting energy expenditure (by indirect calorimetry) and presence of metabolic syndrome (MetS) and were prescribed a weight loss diet. Compliance to the weight loss dietary program was defined as adherence to control visits and weight loss ≥ 5% in 3 mo.

RESULTS: Sex and age-adjusted multiple regression models revealed a significant association between body mass index (BMI) and both sour taste (P < 0.05) and global taste acuity score (GTAS) (P < 0.05), with lower sensitivity with increasing BMI. This trend in sensitivity for sour taste was also confirmed by the model refitted on the OW/OB group while the association with GTAS was marginally significant (P = 0.06). MetS+ subjects presented higher thresholds for salty taste when compared to MetS- patients while no significant difference was detected for the other tastes and GTAS. As assessed by multiple regression model, the association between salty taste and MetS appeared to be independent of sex, age and BMI. Patients continuing the program (n = 37) did not show any difference in baseline taste sensitivity when compared to drop-outs (n = 29). Similarly, no significant difference was detected between patients reporting and not reporting a weight loss ≥ 5% of the initial body weight. No significant difference in taste sensitivity was detected even after dividing patients on the basis of nutritional (OW and OB) or metabolic status (MetS+ and MetS-).

CONCLUSION: There is no cause-effect relationship between overweight and metabolic derangements. Taste thresholds assessment is not useful in predicting the outcome of a diet-induced weight loss program.

Genetic variation in the hTAS2R38 taste receptor and food consumption among Finnish adults

Genetic variation in bitter taste receptors, such as hTAS2R38, may affect food preferences and intake. The aim of the present study was to investigate the association between bitter taste receptor haplotypes and the consumption of vegetables, fruits, berries and sweet foods among an adult Finnish population. A cross-sectional design utilizing data from the Cardiovascular Risk in Young Finns cohort from 2007, which consisted of 1,903 men and women who were 30-45 years of age from five different regions in Finland, was employed. DNA was extracted from blood samples, and hTAS2R38 polymorphisms were determined based on three SNPs (rs713598, rs1726866 and rs10246939). Food consumption was assessed with a validated food frequency questionnaire. The prevalence of the bitter taste-sensitive (PAV/PAV) haplotype was 11.3 % and that of the insensitive (AVI/AVI) haplotype was 39.5 % among this Finnish population. PAV homozygotic women consumed fewer vegetables than did the AVI homozygotic women, 269 g/day (SD 131) versus 301 g/day (SD 187), respectively, p = 0.03 (multivariate ANOVA). Furthermore, the intake of sweet foods was higher among the PAV homozygotes of both genders. Fruit and berry consumption did not differ significantly between the haplotypes in either gender. Individuals perceive foods differently, and this may influence their patterns of food consumption. This study showed that the hTAS2R38 taste receptor gene variation was associated with vegetable and sweet food consumption among adults in a Finnish population.

Effects of sucrose detection threshold and weight status on intake of fruit and vegetables in children

Past research on the relationship between taste sensitivity and fruit and vegetable (FV) intake in children has focused on sensitivity to bitter taste. The effects of sensitivity to sweet taste on intake of FV have never been investigated. Furthermore, the effects of children's weight on intake of FV are inconclusive. This study measured the effects of Sucrose Detection Threshold (SDT) and weight status on intake of FV in children. The participants of this study were 99 children between 5-9 years old. Parents reported their own and their children's 24 hour intake of FV and completed a measure of children's sensory sensitivity. Children completed the triangle test with suprathreshold concentrations of sucrose ranging between 0.2% and 1.6%, in 0.2% increments. Two MANCOVAs showed that, controlling for parental intake and children's sensory sensitivity, there was a main effect of SDT on intake of fruit (p < 0.05), which was exclusive to non-astringent fruit (p < 0.05), and cruciferous vegetables (p < 0.01). Weight status had no effect on intake of FV. Mechanisms behind the effects of SDT are discussed in the context of past research on bitter taste sensitivity.

Genetic sensitivity to the bitter taste of 6-n-propylthiouracil (PROP) and its association with physiological mechanisms controlling body mass index (BMI)

Taste sensitivity to the bitter compound 6-n-propylthiouracil (PROP) is considered a marker for individual differences in taste perception that may influence food preferences and eating behavior, and thereby energy metabolism. This review describes genetic factors that may contribute to PROP sensitivity including: (1) the variants of the TAS2R38 bitter receptor with their different affinities for the stimulus; (2) the gene that controls the gustin protein that acts as a salivary trophic factor for fungiform taste papillae; and (3) other specific salivary proteins that could be involved in facilitating the binding of the PROP molecule with its receptor. In addition, we speculate on the influence of taste sensitivity on energy metabolism, possibly via modulation of the endocannabinoid system, and its possible role in regulating body composition homeostasis.

The association of taste with change in adiposity-related health measures

The relationship between taste-intensity patterns and 5-year change in adiposity-related health measures was determined. Participants were members of the Beaver Dam Offspring Study, a study of the adult children of participants in the population-based Epidemiology of Hearing Loss Study. There were 1,918 participants (mean baseline age=48.8 years; range=22 to 84 years) with baseline taste (2005 to 2008) and follow-up (2010 to 2013) data. Outcomes included 5-year change in body mass index, waist circumference, blood pressure, non-high-density lipoprotein cholesterol, and glycosylated hemoglobin A1c, and hedonic ratings of specific foods. Cluster analysis with Ward's minimum variance method identified the following 5 patterns of the suprathreshold taste intensities of salt, sweet, sour, and bitter: salt and sweet intensities slightly above population averages, average sour and bitter intensities; salt, sour, and bitter intensities above population average, average sweet intensity; salt, sour, and bitter intensities above population average, sweet intensity substantially above average; all intensities below population averages; and all intensities close to population average. The General Linear Model procedure was used for testing cluster differences in the outcomes. With covariate adjustment, the group with all intensities close to population averages had a significantly lower average increase in body mass index compared with the group with above-average intensities for salt, sour, and bitter (+0.4 vs +0.9), and in glycosylated hemoglobin A1c compared with the group with above-average intensities for all tastes (+0.20% vs +0.34%). Clusters differed in the hedonics of foods representing sweetness and saltiness. The study's findings provide evidence that perceived taste intensity might be related to changes in adiposity-related health.

Regional differences in suprathreshold intensity for bitter and umami stimuli

The sense of taste is often referred to as a 'nutritional gatekeeper', thought to have evolved to indicate energy sources and prevent ingestion of potential toxins. Fungiform papillae are structures on the anterior tongue in which taste buds are situated. They are concentrated at the tongue's tip and they can provide a useful estimate of overall taste bud density for taste research. Some reports suggest taste perception may differ subtly across tongue regions, irrespective of FP number. Other data show an association between taste intensity perception for the bitter compound 6-n-propylthiouracil (PROP) and FP density. However, contradictions exist in the literature, with more recent, larger studies suggesting little or no association between FP number and perceived taste intensity. Much research has examined the relation between FP density and PROP perception, while other tastes have been less thoroughly studied. Here, in a cohort of mainly Caucasian individuals, aged 18-45, recruited from the campus of a large rural university, we examined regional and whole-mouth taste intensities, and FP density using an updated method of a digital still photography method first described in 2005. We found regional differences in suprathreshold intensity. Although all taste sensations were experienced all over the tongue, once again disproving the mythical tongue map, we also observed bitter and umami taste perception to be significantly greater on the posterior tongue than on the anterior tongue. In contrast, there were no regional differences observed for sweet, salty or sour tastes. The relation of FP density to whole-mouth intensity of 6-n-propylthiouracil, and to the intensity of saltiness of NaCl, sweetness from sucrose or from Acesulfame-K, bitterness of quinine, or burning from capsaicin delivered to different regions of the tongue are also discussed.

A population-based approach to study the impact of PROP perception on food liking in populations along the Silk Road

Taste is one of the main factors determining food choices. Differences in PROP bitter taste perception have been implicated in individual differences in food preferences and selection. The present study examined associations between, PROP phenotypes, self-reported food liking and TAS2R38 polymorphisms, the major gene implicated in PROP bitterness, in six different populations of the Caucasus and Central Asia, located along the ancient Silk Road. Differences in the distribution of PROP phenotypes across populations were detected, with a higher frequency of super tasters in Tajikistan (31.3%) and Armenia (39.0%) and a higher frequency of non tasters in Georgia (50.9%). While no relationships were observed between PROP phenotypes and food liking using standard statistical tests, we used an approach based on comparison of distance matrices derived from these data. The first matrix compared the food liking ratings of each population to all others pairwise using the Kruskal-Wallis test (at p<0.00063), and the second one compared the distribution of PROP phenotypes across all populations in a similar manner calculating the chi-square statistic as a distance measure. A strong correlation between the two matrices was found (Mantel test: r = 0.67, p-value = 0.03), suggesting that the pattern of food liking across populations was closely related to the distribution of PROP phenotypes. This same relationship was not observed when TAS2R38 genotypes were substituted for PROP phenotypes in this analysis. Our data suggest that a population-based approach utilizing distance matrices is a useful technique for detecting PROP-related differences in food liking and can be applied to other taste phenotypes.

Exploring associations between taste perception, oral anatomy and polymorphisms in the carbonic anhydrase (gustin) gene CA6

Recent reports suggest that polymorphisms in the carbonic anhydrase gene CA6 (also known as gustin) may explain additional variation in the bitterness of 6-n-propylthiouracil beyond that explained by variation in the bitter receptor gene TAS2R38. CA6 (gustin) has been implicated in taste bud function and salivary buffer capacity. In the present study we examined associations between polymorphisms in the CA6 gene with salt and bitter taste perception, and oral anatomy. 243 subjects (146 female) aged 18-45 rated the intensity of five concentrations of 6-n-propylthiouracil and NaCl on a generalized Labeled Magnitude Scale (gLMS) in duplicate and one concentration of potassium chloride (KCl). Using salivary DNA, we examined 12 SNPs within CA6 in relation to taste intensity and number of fungiform papillae. We observed no difference in bitter taste perception from 6-n-propylthiouracil (PROP) or from potassium chloride for any of the SNPs examined. Perceived saltiness of NaCl on the other hand was significantly associated with a number of CA6 polymorphisms, and particularly rs3737665. Nonetheless, FP density did not vary between alleles of rs3737665, nor with any of the other CA6 SNPs. Also, we fail to find any evidence that CA6 effects on taste perception are due to differences in fungiform papilla number. Additional work is needed to confirm whether variations within the CA6 gene may be responsible for differences in salt taste perception.

Racial differences between African Americans and Asian Americans in the effect of 6-n-propylthiouracil taste intensity and food liking on body mass index

Taste intensity to 6-n-propylthiouracil (PROP) has been demonstrated to affect food acceptance and food intake. Because most PROP status research has been performed among predominantly white subjects, research is needed to test the effects of PROP taste intensity on food acceptance and body weight among racial minorities. This study was conducted to examine racial differences in the effect of PROP taste intensity and food liking on body mass index between African Americans and Asian Americans. A cross-sectional design with a sample of 50 African Americans (25 women, 25 men) and 50 Asian Americans (23 women, 27 men) in the New York City area aged 18 to 55 years was used in this study. Weight and height were measured and PROP intensity was assessed using PROP filter paper disks. Subjects rated the intensity of 171.15 g/L (0.5 mol/L) sucrose, 29.22 g/L (0.5 mol/L) sodium chloride, 4.8 g/L (0.025 mol/L) citric acid, and 0.127 g/L (3.2×10⁻⁴ mol/L) quinine solutions and completed a questionnaire to report their food liking/disliking for 19 food items. Characteristics were compared using analysis of variance or χ² test. A multiple linear regression model was fit with the covariates PROP mean, race, sex, age, fat-foods liking, and sweet-foods liking to predict body mass index score. The proportion of total nontasters was 22%. There were no significant differences in the PROP status distribution between African Americans and Asian Americans and in food likings between tasters and nontasters. Significant differences in fat foods, sugar, and black coffee liking were observed among the subracial groups (ie, African Caribbean, African black, East Asian, and South Asian). Race, sex, and age significantly contributed to predict body mass index score.

Do polymorphisms in chemosensory genes matter for human ingestive behavior?

In the last decade, basic research in chemoreceptor genetics and neurobiology have revolutionized our understanding of individual differences in chemosensation. From an evolutionary perspective, chemosensory variations appear to have arisen in response to different living environments, generally in the avoidance of toxins and to better detect vital food sources. Today, it is often assumed that these differences may drive variable food preferences and choices, with downstream effects on health and wellness. A growing body of evidence indicates chemosensory variation is far more complex than previously believed. However, just because a genetic polymorphism results in altered receptor function in cultured cells or even behavioral phenotypes in the laboratory, this variation may not be sufficient to influence food choice in free living humans. Still, there is ample evidence to indicate allelic variation in TAS2R38 predicts variation in bitterness of synthetic pharmaceuticals (e.g., propylthiouracil) and natural plant compounds (e.g., goitrin), and this variation associates with differential intake of alcohol and vegetables. Further, this is only one of 25 unique bitter taste genes (TAS2Rs) in humans, and emerging evidence suggests other TAS2Rs may also contain polymorphisms that a functional with respect to ingestive behavior. For example, TAS2R16 polymorphisms are linked to the bitterness of naturally occurring plant compounds and alcoholic beverage intake, a TAS2R19 polymorphism predicts differences in quinine bitterness and grapefruit bitterness and liking, and TAS2R31 polymorphisms associate with differential bitterness of plant compounds like aristolochic acid and the sulfonyl amide sweeteners saccharin and acesulfame-K. More critically with respect to food choices, these polymorphisms may vary independently from each other within and across individuals, meaning a monolithic one-size-fits-all approach to bitterness needs to be abandoned. Nor are genetic differences restricted to bitterness. Perceptual variation has also been associated with polymorphisms in genes involved in odors associated with meat defects (boar taint), green/grassy notes, and cilantro, as well as umami and sweet tastes (TAS1R1/2/3). Here, a short primer on receptor genetics is provided, followed by a summary of current knowledge, and implications for human ingestive behavior are discussed.

Energy intake and diet selection during buffet consumption in women classified by the 6-n-propylthiouracil bitter taste phenotype

BACKGROUND

Exposure to a variety of energy-dense foods promotes increased energy intake and adiposity. Taste blindness to the bitterness of 6-n-propylthiouracil (PROP) has been associated with increased adiposity in women and might be linked to an increased energy intake and greater selection of dietary fat.

OBJECTIVE

We investigated whether PROP nontaster (NT) women would consume more fat and energy in a buffet setting than medium taster (MT) or supertaster (ST) women.

DESIGN

Seventy-five non-diet-restrained, lean, young women [mean ± SEM BMI (in kg/m²): 21.5 ± 0.6; age: 26.1 ± 1.3 y) ate lunch and dinner in the laboratory for 3 consecutive days under the following 2 conditions: ad libitum control meals (CONTs) or high-variety buffet meals (BUFFs). A standard breakfast was consumed each day of the study (4 - d washout between conditions).

RESULTS

NTs and MTs consumed more energy and fat (as the percentage of energy) from BUFFs than did STs (P < 0.01), which contributed to higher daily energy intakes in these 2 groups of women during BUFFs (2149 ± 49 kcal/d for NTs and 2209 ± 48 kcal/d for MTs compared with 1933 ± 50 kcal/d for STs; P < 0.01). Together, NTs and MTs consumed an extra 246 kcal/d during BUFFs than during CONTs. In addition, compared with STs, NTs and MTs consumed more added fats and sweets (servings/d; P < 0.003) and more energy from snacks (P < 0.01) across all study days.

CONCLUSIONS

NT and MT women consume more daily energy than do ST women when eating in a buffet setting, which is a common type of dietary exposure. This increase in energy intake over time could contribute to a positive energy balance and increased adiposity previously reported in these women.

Quinine sensitivity influences the acceptance of sea-buckthorn and grapefruit juices in 9- to 11-year-old children

The acceptance of novel foods by children is related to a number of factors, and differences in taste sensitivity may form some specific challenges. High sensitivity might be a barrier to the acceptance of sour/bitter products by children. This study investigated the effect of sensitivity to bitter, sour, sweet, and salty tastes on the acceptance of Nordic juices in 9- to 11-year-old children. A total of 328 children were subjected to two taste sensitivity tests for quinine, citric acid, sucrose, and NaCl. Their acceptance of six juices (carrot, rosehip, sea-buckthorn, lingonberry, grapefruit, and aronia) was measured. Bitter sensitivity was found to be significantly correlated to the intake of the sweet sea-buckthorn and lingonberry juices; the most bitter-sensitive children exhibited the highest intake of these juices. The opposite relationship was found for bitter sensitivity and the intake of the bitter grapefruit juice. Sour, sweet, and salt sensitivities did not affect the intake of any of the juices. Liking scores were not affected by sensitivity. In conclusion, bitter sensitivity appears to influence food intake in children to a greater extent than sour, sweet, or salt sensitivity. Bitter-sensitive children exhibited a reduced intake of grapefruit juice and a higher intake of sucrose-sweetened juices. Thus, bitter sensitivity might be a challenge in the acceptance of certain bitter foods.

Early influences on the development of food preferences

The ability to perceive flavors begins in utero with the development and early functioning of the gustatory and olfactory systems. Because both amniotic fluid and breast milk contain molecules derived from the mother's diet, learning about flavors in foods begins in the womb and during early infancy. This early experience serves as the foundation for the continuing development of food preferences across the lifespan, and is shaped by the interplay of biological, social, and environmental factors. Shortly after birth, young infants show characteristic taste preferences: sweet and umami elicit positive responses; bitter and sour elicit negative responses. These taste preferences may reflect a biological drive towards foods that are calorie- and protein-dense and an aversion to foods that are poisonous or toxic. Early likes and dislikes are influenced by these innate preferences, but are also modifiable. Repeated exposure to novel or disliked foods that occurs in a positive, supportive environment may promote the acceptance of and eventually a preference for those foods. Alternatively, children who are pressured to eat certain foods may show decreased preference for those foods later on. With increasing age, the influence of a number of factors, such as peers and food availability, continue to mold food preferences and eating behaviors.

Variations in bitter-taste receptor genes, dietary intake, and colorectal adenoma risk

Genetic variants in bitter-taste receptor genes have been hypothesized to negatively impact health outcomes and/or influence dietary intake and, consequently, could increase the risk of colorectal neoplasia. Using a case-control study of 914 colorectal adenoma cases/1188 controls, we explored associations among colorectal adenoma risk, dietary intake, and genetic variation in 3 bitter-taste receptor genes: TAS2R38 (rs713598, rs1726866, rs10246939), TAS2R16 (rs846672), and TAS2R50 (rs1376251). Analysis of covariance was conducted to detect trends in dietary intake across TAS2R genotypes/haplotypes. Odds ratios and 95% confidence intervals were estimated by logistic regression to test gene-adenoma risk associations. No significant associations were observed between the TAS2R38 PAV/PAV diplotype or the TAS2R16 (rs846672) polymorphism with the selected diet variables. We observed weak inverse associations between the TAS2R50 (rs1376251) C allele and dietary fiber and vegetable intake (Ps < 0.015). Odds ratios for adenoma risk were not significantly different from the null. Our findings do not support a link between these TAS2R genotypes/haplotypes and dietary intake that could impact colorectal adenoma risk. However, given the paucity of data, we cannot dismiss the possibility that these genes may influence colorectal adenoma risk in other ways, such as through impaired gastrointestinal function, particularly in subgroups of the population.

The gustin (CA6) gene polymorphism, rs2274333 (A/G), as a mechanistic link between PROP tasting and fungiform taste papilla density and maintenance

Taste sensitivity to PROP varies greatly among individuals and is associated with polymorphisms in the bitter receptor gene TAS2R38, and with differences in fungiform papilla density on the anterior tongue surface. Recently we showed that the PROP non-taster phenotype is strongly associated with the G variant of polymorphism rs2274333 (A/G) of the gene that controls the salivary trophic factor, gustin. The aims of this study were 1) to investigate the role of gustin gene polymorphism rs2274333 (A/G), in PROP sensitivity and fungiform papilla density and morphology, and 2) to investigate the effect of this gustin gene polymorphism on cell proliferation and metabolic activity. Sixty-four subjects were genotyped for both genes by PCR techniques, their PROP sensitivity was assessed by scaling and threshold methods, and their fungiform papilla density, diameter and morphology were determined. In vitro experiments examined cell proliferation and metabolic activity, following treatment with saliva of individuals with and without the gustin gene mutation, and with isolated protein, in the two iso-forms. Gustin and TAS2R38 genotypes were associated with PROP threshold (p=0.0001 and p=0.0042), but bitterness intensity was mostly determined by TAS2R38 genotypes (p<0.000001). Fungiform papillae densities were associated with both genotypes (p<0.014) (with a stronger effect for gustin; p=0.0006), but papilla morphology was a function of gustin alone (p<0.0012). Treatment of isolated cells with saliva from individuals with the AA form of gustin or direct application of the active iso-form of gustin protein increased cell proliferation and metabolic activity (p<0.0135). These novel findings suggest that the rs2274333 polymorphism of the gustin gene affects PROP sensitivity by acting on fungiform papilla development and maintenance, and could provide the first mechanistic explanation for why PROP super-tasters are more responsive to a broad range of oral stimuli.

Validation of edible taste strips for assessing PROP taste perception

A novel delivery method is described that incorporates taste stimuli into edible strips for determining n-propylthiouracil (PROP) taster status. Edible strips that contained 400 or 600 nanomoles of PROP were prepared for psychophysical studies. Using these strips, we measured taste intensity, taste hedonics, and taste quality responses in a sample of healthy volunteers (n = 118). Participants were also asked to assess a single NaCl strip, a quinine strip, 3 NaCl solutions, and 3 PROP solutions. All psychophysical data were subsequently analyzed as a function of TAS2R38 genotype. The use of PROP strips for distinguishing between individuals with at least 1 PAV allele and individuals with other genotypes was assessed and compared with the use of PROP solutions for making this same distinction. For the 2 PROP strips and PROP solutions, individuals who expressed at least 1 PAV allele could perceive the bitter taste of PROP. Individuals who expressed 2 AVI alleles responded similarly to 400 nanomole PROP strips and blank strips. Furthermore, individuals with 2 AVI alleles responded to 0.032 and 0.32 mM PROP solutions at intensities that were similar to water, though intensity ratings to 3.2 mM PROP solution exceeded water. In general, those with at least 1 PAV allele rated the bitter taste of PROP as unpleasant in both delivery methods (strips or solutions). Psychophysical data from PROP strips and solutions were consistent with TAS2R38 genotype. These results support the validity of edible taste strips as a method for assessing PROP taste perception in humans.

Gustation assessment using the NIH Toolbox

The NIH Toolbox for Assessment of Neurological and Behavioral Function (NIH Toolbox) is a set of brief measures for the assessment of cognitive function, emotional health, motor function, and sensory function for use in clinical trials and in epidemiologic and longitudinal studies. Gustatory perception is assessed as 1 of 6 areas of sensory function. A team of 11 scientists with expertise in taste perception selected 2 gustatory measures, 1 of which can be used in young pediatric populations. The measure selected for young pediatric populations assesses sucrose (sweet) taste preference and can also be used across the age span of 5 to 85 years. For adult populations, the selected measure is a regional test, which assesses variability in perceived intensity of quinine hydrochloride (bitter) when applied to the tongue tip as well as perceived with the whole mouth. The team also recommends the regional test for assessing other tastants, such as sodium chloride (salty). Validation studies have demonstrated that the measures modified for the NIH Toolbox correlate with more traditional assessments, and can identify known population differences in gustation.

Bitterness of the non-nutritive sweetener acesulfame potassium varies with polymorphisms in TAS2R9 and TAS2R31

Demand for nonnutritive sweeteners continues to increase due to their ability to provide desirable sweetness with minimal calories. Acesulfame potassium and saccharin are well-studied nonnutritive sweeteners commonly found in food products. Some individuals report aversive sensations from these sweeteners, such as bitter and metallic side tastes. Recent advances in molecular genetics have provided insight into the cause of perceptual differences across people. For example, common alleles for the genes TAS2R9 and TAS2R38 explain variable response to the bitter drugs ofloxacin in vitro and propylthiouracil in vivo. Here, we wanted to determine whether differences in the bitterness of acesulfame potassium could be predicted by common polymorphisms (genetic variants) in bitter taste receptor genes (TAS2Rs). We genotyped participants (n = 108) for putatively functional single nucleotide polymorphisms in 5 TAS2Rs and asked them to rate the bitterness of 25 mM acesulfame potassium on a general labeled magnitude scale. Consistent with prior reports, we found 2 single nucleotide polymorphisms in TAS2R31 were associated with acesulfame potassium bitterness. However, TAS2R9 alleles also predicted additional variation in acesulfame potassium bitterness. Conversely, single nucleotide polymorphisms in TAS2R4, TAS2R38, and near TAS2R16 were not significant predictors. Using 1 single nucleotide polymorphism each from TAS2R9 and TAS2R31, we modeled the simultaneous influence of these single nucleotide polymorphisms on acesulfame potassium bitterness; together, these 2 single nucleotide polymorphisms explained 13.4% of the variance in perceived bitterness. These data suggest multiple polymorphisms within TAS2Rs contribute to the ability to perceive the bitterness from acesulfame potassium.

Greater energy reduction in 6-n-propylthiouracil (PROP) super-tasters as compared to non-tasters during a lifestyle intervention

Little is known as to how 6-n-propylthiouracil (PROP) taster status may influence changes in dietary intake in adults participating in a lifestyle intervention to assist with reducing weight. This secondary data analysis examined changes in energy, percent energy from macronutrients, and food group intake; physical activity; and body mass index (BMI) in super-tasters and non-tasters participating in two randomized controlled trials implementing a lifestyle obesity intervention. One trial focused on lowering energy density of the diet and the other trial focused on changing eating frequency. Overweight and obese participants (n = 57) who completed measures of dietary intake, physical activity, and anthropometrics at 0 and 3 months were included in the analyses. Taster status was determined at baseline: 46 non-tasters and 11 super-tasters. After controlling for condition assignment and baseline values, results indicated that a significantly greater reduction in energy intake occurred for super-tasters as compared to non-tasters (-1149 ± 561 kcal/day vs. -902 ± 660 kcal/day, p < 0.05). No other significant differences in changes in dietary intake, physical activity, or BMI were found. These results suggest that in situations of reducing energy intake, overweight and obese super-tasters may be more successful than overweight and obese non-tasters. More research is needed to understand the influence of taster-status on dietary change during a lifestyle intervention and how this may impact weight loss.

Marked increase in PROP taste responsiveness following oral supplementation with selected salivary proteins or their related free amino acids

The genetic predisposition to taste 6-n-propylthiouracil (PROP) varies among individuals and is associated with salivary levels of Ps-1 and II-2 peptides, belonging to the basic proline-rich protein family (bPRP). We evaluated the role of these proteins and free amino acids that selectively interact with the PROP molecule, in modulating bitter taste responsiveness. Subjects were classified by their PROP taster status based on ratings of perceived taste intensity for PROP and NaCl solutions. Quantitative and qualitative determinations of Ps-1 and II-2 proteins in unstimulated saliva were performed by HPLC-ESI-MS analysis. Subjects rated PROP bitterness after supplementation with Ps-1 and II-2, and two amino acids (L-Arg and L-Lys) whose interaction with PROP was demonstrated by (1)H-NMR spectroscopy. ANOVA showed that salivary levels of II-2 and Ps-1 proteins were higher in unstimulated saliva of PROP super-tasters and medium tasters than in non-tasters. Supplementation of Ps-1 protein in individuals lacking it in saliva enhanced their PROP bitter taste responsiveness, and this effect was specific to the non-taster group.(1)H-NMR results showed that the interaction between PROP and L-Arg is stronger than that involving L-Lys, and taste experiments confirmed that oral supplementation with these two amino acids increased PROP bitterness intensity, more for L-Arg than for L-Lys. These data suggest that Ps-1 protein facilitates PROP bitter taste perception and identifies a role for free L-Arg and L-Lys in PROP tasting.