Taste Thresholds and Food Dislikes

Bitter taste receptors: Key target to understand the effects of polyphenols on glucose and body weight homeostasis. Pathophysiological and pharmacological implications

Experimental and clinical research has reported beneficial effects of polyphenol intake on high prevalent diseases such as type 2 diabetes and obesity. These phytochemicals are ligands of taste 2 receptors (T2Rs) that have been recently located in a variety of organs and extra-oral tissues. Therefore, the interaction between polyphenol and T2Rs in brain structures can play a direct effect on appetite/satiety regulation and food intake. T2Rs are also expressed along the digestive tract, and their interaction with polyphenols can induce the release of gastrointestinal hormones (e.g., ghrelin, GLP-1, CCK) influencing appetite, gastrointestinal functionally, and glycemia control. Intestinal microbiota can also influence on network effects of polyphenols-T2Rs interaction and vice versa, impacting innate immune responses and consequently on gut functionally. Furthermore, polyphenols binding to T2Rs present important effects on adipose tissue metabolism. Interestingly, T2R polymorphism could, at least partially, explain the inter-individual variability of the effects of polyphenols on glucose and body weight homeostasis. Together, these factors can contribute to understand the beneficial effects of polyphenol-rich diets but also might aid in identifying new pharmacological pathway targets for the treatment of diabetes and obesity.

Differential Activation of TAS2R4 May Recover Ability to Taste Propylthiouracil for Some TAS2R38 AVI Homozygotes

Bitterness from phenylthiocarbamide and 6-n-propylthiouracil (PROP) varies with polymorphisms in the TAS2R38 gene. Three SNPs form two common (AVI, PAV) and four rare haplotypes (AAI, AAV, PVI, and PAI). AVI homozygotes exhibit higher detection thresholds and lower suprathreshold bitterness for PROP compared to PAV homozygotes and heterozygotes, and these differences may influence alcohol and vegetable intake. Within a diplotype, substantial variation in suprathreshold bitterness persists, and some AVI homozygotes report moderate bitterness at high concentrations. A second receptor encoded by a gene containing a functional polymorphism may explain this. Early work has suggested that PROP might activate TAS2R4 in vitro, but later work did not replicate this. Here, we identify three TAS2R4 SNPs that result in three diplotypes-SLN/SLN, FVS/SLN, and FVS/FVS-which make up 25.1%, 44.9%, and 23.9% of our sample. These TAS2R4 haplotypes show minimal linkage disequilibrium with TAS2R38, so we examined the suprathreshold bitterness as a function of both. The participants (n = 243) rated five PROP concentrations in duplicate, interleaved with other stimuli. As expected, the TAS2R38 haplotypes explained ~29% (p < 0.0001) of the variation in the bitterness ratings, with substantial variation within the haplotypes (AVI/AVI, PAV/AVI, and PAV/PAV). Notably, the TAS2R4 diplotypes (independent of the TAS2R38 haplotypes) explained ~7-8% of the variation in the bitterness ratings (p = 0.0001). Given this, we revisited if PROP could activate heterologously expressed TAS2R4 in HEK293T cells, and calcium imaging indicated 3 mM PROP is a weak TAS2R4 agonist. In sum, our data are consistent with the second receptor hypothesis and may explain the recovery of the PROP tasting phenotype in some AVI homozygotes; further, this finding may potentially help explain the conflicting results on the TAS2R38 diplotype and food intake.

Generating Demand for Alternative Protein in Low- and Middle- Income Countries: Opportunities and Experiences from Nutritious and Sustainable Market Solutions

Protein consumption and the demand for high-value nutritional products is growing rapidly in emerging markets. The projected growth of the alternative protein industry may position it well to meet this demand while addressing environmental sustainability and ethical standards. However, adoption of alternative protein products over traditional animal-sourced proteins is not always a clear choice, with factors such as consumer preferences and habitual behaviors influencing consumer decisions. Insights and considerations associated with generating demand for alternative protein products in low- and middle-income countries (LMIC) were identified through 3 case studies: the OBAASIMA Project in Ghana, the Egg Initiative in Ethiopia, and the World Food Programme Farming Coalition project in Armenia. Key findings emphasize the importance of local sourcing, positive messaging, and integration within existing diets and behaviors. Therefore, these factors will be essential for the adoption of novel alternative protein products in LMIC.

Bitter taste sensitivity, cruciferous vegetable intake, obesity, and diabetes in American adults: a cross-sectional study of NHANES 2013-2014

Objective: To examine the associations between bitter taste sensitivity, cruciferous vegetable consumption, and likelihood of obesity and diabetes among American adults. Research design and method: Cross-section observation of 2129 adults aged 40-80 years of the National Health and Nutrition Examination Survey (NHANES) 2013-2014. Bitter taste sensitivity was estimated by the generalized labeled magnitude scale (gLMS) rating for bitterness (non-tasters: the lowest 25%, the others were tasters). Consumption of cruciferous vegetables was recorded by the 2 day 24 hours dietary records. Obesity was defined as body mass index (BMI) ≥30 kg m-2. Diabetes was defined as self-reported physician-diagnosed diabetes, or who reported taking diabetes medication or individuals with a fasting plasma glucose (FPG) ≥ 126 mg dL-1 or Hemoglobin A1c ≥ 6.5%. Results: The proportion of participants who ate cruciferous vegetables over the two days was 29.5% among bitter tasters, significantly lower than that (35.7%) among non-tasters (P = 0.04) after adjustment of age, gender, race/ethnicity, dietary energy intake, physical activity, education, smoking and income levels. Among participants who ate cruciferous vegetables, bitter tasters on average consumed 15.5 g (±7.0) grams less cruciferous vegetables per day compared to non-tasters. The multi-variates adjusted odds ratio of obesity was 1.29 (95% confident interval (CI): 0.76-2.17), 1.40 (95% CI: 0.90-2.18) and 1.68 (95% CI: 1.05-2.67) among bitter tasters who ate cruciferous vegetables, among non-tasters who did not ate cruciferous vegetables, and among bitter tasters who did not eat cruciferous vegetables, respectively, as compared with non-tasters who ate cruciferous vegetables. The prevalence of diabetes was 17.3% and 13.0% among bitter tasters and non-tasters, respectively, with a multi-adjusted odds ratio of 1.32 (95% CI: 1.02-1.69, P = 0.033) for diabetes comparing bitter tasters with non-tasters, which was attenuated to 1.26 (95% CI: 0.95-1.67, P = 0.108) by further adjustment of cruciferous vegetables consumption and obesity, with a mediation effect of 17.8% (95% CI: 2.9%-60.9%; P = 0.069). Conclusion: Bitter taste sensitivity was associated with less consumption of cruciferous vegetables and a high likelihood of obesity, which may mediate its association with diabetes.

What is the link between personality and food behavior?

A number of personality characteristics have been linked to various aspects of taste (gustation), trigeminal, and olfactory perception. In particular, personality traits have been linked to olfactory sensory thresholds and olfactory identification abilities, as well as to the sensory-discriminative aspects of taste/flavour perception. To date, much of the research in this area has focused on Sensation Seeking (including Experience Seeking, and Openness to Novel Experiences), with the latter being linked to a preference for spicy, and possibly also crunchy, sour, and bitter foods/drinks. Novelty-seeking has also been linked to a preference for salty foods, while anxious individuals appear to enjoy a much narrower range of foods. A bidirectional link has also been documented between taste and mood. Certain of the personality-based differences in taste/flavour perception and food behaviour have been linked to differences in circulating levels of neurotransmitters and hormones in both normal and clinical populations. Taken together, therefore, the evidence that has been published to date supports a number of intriguing connections between personality traits and taste perception/food behaviour.

Elevation of the Blood Glucose Level is Involved in an Increase in Expression of Sweet Taste Receptors in Taste Buds of Rat Circumvallate Papillae

The gustation system for sweeteners is well-known to be regulated by nutritional and metabolic conditions, but there is no or little information on the underlying mechanism. Here, we examined whether elevation of the blood glucose level was involved in alteration of the expression of sweet taste receptors in circumvallate papillae (CP) and sweet taste sensitivity in male Sprague-Dawley rats. Rats under 4 h-fed conditions following 18 h-fasting exhibited elevated blood glucose levels and decreased pancreatic T1R3 expression, compared to rats after 18 h-fasting treatment, and they exhibited increased protein expression of sweet taste receptors T1R2 and T1R3 in CP. Under streptozotocin (STZ)-induced diabetes mellites (DM) conditions, the protein expression levels of T1R2 and T1R3 in CP were higher than those under control conditions, and these DM rats exhibited increased lick ratios in a low sucrose concentration range in a brief access test with a mixture of sucrose and quinine hydrochloride (QHCl). These findings indicate that the elevation of blood glucose level is a regulator for an increase in sweet taste receptor protein expression in rat CP, and such alteration in STZ-induced DM rats is involved in enhancement of their sweet taste sensitivity.

Variation in the Ability to Taste Bitter Thiourea Compounds: Implications for Food Acceptance, Dietary Intake, and Obesity Risk in Children

The ability to taste bitter thiourea compounds, such as phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP), is inherited. Polymorphisms in the bitter-taste receptor TAS2R38 explain the majority of phenotypic variation in the PROP phenotype. It has been hypothesized that the PROP phenotype is a marker for perception of a variety of chemosensory experiences. In this review, we discuss studies that have investigated the relationship between bitter-taste response and dietary behaviors and chronic health in children. Investigators have hypothesized that children who are PROP tasters have lower liking and consumption of bitter foods, such as cruciferous vegetables. Additionally, several studies suggest that children who are unable to taste PROP (i.e., nontasters) like and consume more dietary fat and are prone to obesity. The relationship between the PROP phenotype and obesity is influenced by multiple confounders, including sex, food access, ethnicity, and socioeconomic status. Future studies that adjust for these variables are needed.

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.

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.

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.

Facial affective reactions to bitter-tasting foods and body mass index in adults

Differences in food consumption among body-weight statuses (e.g., higher fruit intake linked with lower body mass index (BMI) and energy-dense products with higher BMI) has raised the question of why people who are overweight or are at risk of becoming overweight eat differently from thinner people. One explanation, in terms of sensitivity to affective properties of food, suggests that palatability-driven consumption is likely to be an important contributor to food intake, and therefore body weight. Extending this approach to unpalatable tastes, we examined the relationship between aversive reactions to foods and BMI. We hypothesized that people who have a high BMI will show more negative affective reactions to bitter-tasting stimuli, even after controlling for sensory perception differences. Given that hedonic reactions may influence consumption even without conscious feelings of pleasure/displeasure, the facial expressions were included in order to provide more direct access to affective systems than subjective reports. Forty adults (28 females, 12 males) participated voluntarily. Their ages ranged from 18 to 46 years (M=24.2, SD=5.8). On the basis of BMI, participants were classified as low BMI (BMI<20; n=20) and high BMI (BMI>23; n=20). The mean BMI was 19.1 for low BMI (SD=0.7) and 25.2 for high BMI participants (SD=1.8). Each subject tasted 5 mL of a grapefruit juice drink and a bitter chocolate drink. Subjects rated the drinks' hedonic and incentive value, familiarity and bitter intensity immediately after each stimulus presentation. The results indicated that high BMI participants reacted to bitter stimuli showing more profound changes from baseline in neutral and disgust facial expressions compared with low BMI. No differences between groups were detected for the subjective pleasantness and familiarity. The research here is the first to examine how affective facial reactions to bitter food, apart from taste responsiveness, can predict differences in BMI.

Factors affecting food choice in relation to fruit and vegetable intake: a review

The present review provides an investigation into the food choice decisions made by individuals in relation to fruit and vegetable consumption. A comprehensive body of evidence now exists concerning the protective effect of fruit and vegetables against a number of diseases, particularly cardiovascular disease and certain forms of cancer. Current UK recommendations are to increase intakes of fruit and vegetables to 400 g/person per d. In the main body of the review the factors that affect food choice decisions of adults in relation to fruit and vegetable consumption are studied, following a suggested framework of food choice. Factors covered include sensory appeal, familiarity and habit, social interactions, cost, availability, time constraints, personal ideology, media and advertising and health. The content of the review shows just how complex the food choice process can be. Health promotion techniques can be better targeted towards certain groups of individuals, all holding similar sets of values, when making food choice decisions. Food choice, in relation to fruit and vegetable intake, needs to be studied in more depth, in order to provide effective nutrition education programmes, in particular the sets of priorities that different sub-groups of the population consider when making food choice decisions.

Variation in the gene TAS2R13 is associated with differences in alcohol consumption in patients with head and neck cancer

Variation in responsiveness to bitter-tasting compounds has been associated with differences in alcohol consumption. One strong genetic determinant of variation in bitter taste sensitivity is alleles of the TAS2R gene family, which encode chemosensory receptors sensitive to a diverse array of natural and synthetic compounds. Members of the TAS2R family, when expressed in the gustatory system, function as bitter taste receptors. To better understand the relationship between TAS2R function and alcohol consumption, we asked if TAS2R variants are associated with measures of alcohol consumption in a head and neck cancer patient cohort. Factors associated with increased alcohol intake are of strong interest to those concerned with decreasing the incidence of cancers of oral and pharyngeal structures. We found a single nucleotide polymorphism (SNP) located within the TAS2R13 gene (rs1015443 [C1040T, Ser259Asn]), which showed a significant association with measures of alcohol consumption assessed via the Alcohol Use Disorders Identification Test (AUDIT). Analyses with other SNPs in close proximity to rs1015443 suggest that this locus is principally responsible for the association. Thus, our results provide additional support to the emerging hypothesis that genetic variation in bitter taste receptors can impact upon alcohol consumption.

Development of eating behavior: biology and context

Eating is necessary for survival, gives great pleasure, and can be perturbed leading to undernutrition, overnutrition, and eating disorders. The development of feeding in humans relies on complex interplay between homeostatic mechanisms; neural reward systems; and child motor, sensory, and socioemotional capability. Furthermore, parenting, social influences, and the food environment influence the development of eating behavior. The rapid expansion of new knowledge in this field, from basic science to clinical and community-based research, is expected to lead to urgently needed research in support of effective, evidence-based prevention and treatment strategies for undernutrition, overnutrition, and eating disorders in early childhood. Using a biopsychosocial approach, this review covers current knowledge of the development of eating behavior from the brain to the individual child, taking into account important contextual influences.

Allelic variation in TAS2R bitter receptor genes associates with variation in sensations from and ingestive behaviors toward common bitter beverages in adults

The 25 human bitter receptors and their respective genes (TAS2Rs) contain unusually high levels of allelic variation, which may influence response to bitter compounds in the food supply. Phenotypes based on the perceived bitterness of single bitter compounds were first linked to food preference over 50 years ago. The most studied phenotype is propylthiouracil bitterness, which is mediated primarily by the TAS2R38 gene and possibly others. In a laboratory-based study, we tested for associations between TAS2R variants and sensations, liking, or intake of bitter beverages among healthy adults who were primarily of European ancestry. A haploblock across TAS2R3, TAS2R4, and TAS2R5 explained some variability in the bitterness of espresso coffee. For grapefruit juice, variation at a TAS2R19 single nucleotide polymorphism (SNP) was associated with increased bitterness and decreased liking. An association between a TAS2R16 SNP and alcohol intake was identified, and the putative TAS2R38-alcohol relationship was confirmed, although these polymorphisms did not explain sensory or hedonic responses to sampled scotch whisky. In summary, TAS2R polymorphisms appear to influence the sensations, liking, or intake of common and nutritionally significant beverages. Studying perceptual and behavioral differences in vivo using real foods and beverages may potentially identify polymorphisms related to dietary behavior even in the absence of known ligands.

Reliability of Threshold and Suprathreshold Methods for Taste Phenotyping: Characterization with PROP and Sodium Chloride

The present study aimed to compare the accuracy and reliability of four standard methods used for classification of people as taster or non-tasters based on their sensitivity to PROP (6-n-propylthiouracil). A panel consisting of 21 subjects was tested for threshold and suprathreshold sensitivity of sodium chloride, PROP, and genotyped for TAS2R38. Two threshold methods, staircase and modified Harris–Kalmus, were used to obtain detection and recognition thresholds and compared for accuracy and repeatability. Similarly, two suprathreshold techniques, the just noticeable differences (JND) and the general labeled magnitude scale (gLMS), were used to determine Weber fractions and individual psychophysical functions and compared for accuracy and repeatability. Results show both threshold methods have been able to correctly separate people into two groups of tasters and non-tasters, with the staircase method having a lower variability among subjects. On the suprathreshold front, we found differences in sensitivity between tasters and non-tasters when comparing Weber fractions and psychophysical functions; however, our data suggest that clustering people without previous knowledge of their taster status is less accurate when using Weber fractions. Intensity ratings are more reliable to classify people into tasters and non-tasters. Results show that the staircase for threshold measurement and the gLMS methods are more reliable methods than Harris–Kalmus and JND for phenotyping people and can be used in large-scale studies in the quest to discover new genotype–phenotype associations.

Variation in the gene TAS2R38 is associated with the eating behavior disinhibition in Old Order Amish women

Insensitivity to the bitter-tasting compound 6-n-propylthiouracil (PROP) has been proposed as a marker for individual differences in taste perception that influence food preference and intake. The principal genetic determinants of phenotypic variation in PROP taste sensitivity are alleles of the TAS2R38 gene, which encodes a chemosensory receptor sensitive to thiourea compounds including PROP and phenylthiocarbamide. Members of the TAS2R family are expressed in the gustatory system, where they function as bitter taste receptors, and throughout the gut, where their physiological roles in prandial, gut-derived hormone release are beginning to be elucidated. To better understand the relationship between TAS2R function and ingestive behaviors, we asked if TAS2R38 variants are associated with one or more of three eating behaviors: restraint, disinhibition, and hunger. We genotyped a single nucleotide polymorphism (SNP) located within the TAS2R38 gene, rs1726866 (T785C, Val262Ala) in 729 nondiabetic individuals (381 females, 348 males) within the Amish Family Diabetes Study. Eating behaviors were assessed using the Three-Factor Eating Questionnaire. An association analysis between rs1726866 and these three traits revealed a significant association of the PROP-insensitive "T" allele with increased disinhibition (p=0.03). Because eating behaviors differ substantially between males and females, we subsequently performed sex-stratified analyses, which revealed a strong association in females (p=0.0002) but not in males. Analyses with other SNPs in close proximity to rs1726866 suggest that this locus is principally responsible for the association. Therefore, our results indicate that a polymorphism in TAS2R38 is associated with differences in ingestive behavior.

Bitter taste receptors and their cells

The molecular basis of human bitter taste perception is an area of intense research. Only 25 G protein-coupled receptors belonging to the hTAS2R gene family face the challenge to detect thousands of structurally different bitter compounds, most of which are plant metabolites. Since many natural bitter compounds are highly toxic, whereas others are part of our daily diets, bitter taste was crucial during evolution and still most likely affects our food selection. The article presented here addresses biosynthesis, functional analyses of TAS2Rs and TAS2R variants, as well as gustatory expression of hTAS2R genes.

Nutritional implications of genetic taste variation: the role of PROP sensitivity and other taste phenotypes

Genetic sensitivity to the bitter taste of phenylthiocarbamide and 6-n-propylthiouracil (PROP) is a well-studied human trait. It has been hypothesized that this phenotype is a marker for individual differences in taste perception that influence food preferences and dietary behavior with subsequent links to body weight and chronic disease risk. Steady progress has been made over the past several decades in defining the involvement of this phenotype and its underlying gene, TAS2R38, in this complex behavioral pathway. However, more work needs to be done to fully determine its overall nutritional and health significance. The primary goal of this review is to assess our current understanding of the role of the PROP bitter taste phenotype in food selection and body weight in both children and adults. A brief history of the field is included and controversies surrounding the use of different PROP screening methods are addressed. The contribution of other receptors (both bitter and nonbitter) to human taste variation is also discussed.

Oral sensory phenotype identifies level of sugar and fat required for maximal liking

A half-century ago, Fischer and colleagues found correlations between food preference and genetic markers of taste [6-n-propylthiouracil (PROP), quinine]. Recently, a number of studies report differences in sweet liking/disliking with taste phenotype or genotype. Here we modeled optimal liking for milk/sugar mixtures using the response surface method among 79 mostly normal weight adults (36 women) who reported low dietary restraint. Two non-overlapping phenotype analyses were performed: a) discordance in PROP versus quinine bitterness and b) number of fungiform papillae (FP, taste papillae on the tongue tip). Although all phenotype groups liked highly sweet and creamy sensations (in liking by sensation models), the fat and sugar levels for hedonic optima varied (in liking by concentration models). Males generally liked higher fat (20 to 40%) and sugar levels, with females disliking unsweetened cream. In quinine/PROP groups, liking peaked at 30% fat/15% sucrose for men and women who tasted 0.32 mM quinine more bitter than 3.2 mM PROP (n=15); a group previously shown to have highest sugar intakes (Duffy et al., 2003). Those tasting PROP more bitter than quinine (n=14) reported greater creamy/sweet sensations, with peak liking at lower fat and sweet levels (3.3% fat/10% sucrose). Generally, those in the high FP group perceived more creamy/sweet sensations with level of liking more influenced by sugar level, especially among high FP females. At high sugar/high fat levels low FP males and females retained this liking while liking fell off for those in the high FP group. In summary, although most liked sweet/creamy sensations, perceptual differences in these sensations varied with oral phenotype, explaining some of the differences in the amount of sugar and fat required to reach hedonic optima. A high affinity for high sugar/high fat mixtures among oral phenotype subgroups has relevance for energy consumption and could explain the link previously observed between oral sensation and body weight.

Ability to taste 6-n-propylthiouracil and BMI in low-income preschool-aged children

BACKGROUND

Sensitivity to the bitter compound 6-n-propylthiouracil (PROP) is genetically mediated. Sensitivity to PROP has been associated with weight status in both adults and children.

OBJECTIVE

To determine whether there is an association between PROP sensitivity and BMI in low-income children of diverse race/ethnicity, among whom there is a high prevalence of obesity.

METHODS AND PROCEDURES

Eighty-one preschool-aged children attending Head Start tasted a solution of 560 micromol/l PROP and reported whether it tasted "like water" or "like something else". Mothers reported child's race, age, maternal education, maternal weight and height, child's reluctance to sample new foods via the Food Neophobia Scale (FNS), and child's dietary intake using a food frequency questionnaire. Child weight and height were measured. BMI was calculated and for children, expressed in z-scores. Regression analyses were used to evaluate the relationship between child's PROP taster status and BMI z-score, testing covariates child's age, gender, race, maternal education and BMI, and child's FNS score. Children's dietary intake was compared by PROP taster status.

RESULTS

PROP tasters, compared with nontasters, had significantly higher BMI z-scores (0.99 (s.d. 1.24) vs. 0.03 (1.12), P=0.004) and had a significantly higher prevalence of overweight (31.8% vs. 5.6%, P=0.025), but demonstrated no differences in reported dietary intake. The most parsimonious model predicting the child's BMI z-score included only maternal BMI and the child's PROP taster status (R(2)=22.3%).

DISCUSSION

A genetically mediated ability to taste bitter may contribute to obesity risk in low-income, preschool-aged children.

Associations of phenylthiocarbamide tasting to alcohol problems and family history of alcoholism differ by gender

Past research associating phenylthiocarbamide/propylthiouracil (PTC/PROP) taste status with alcoholism has produced equivocal results. Some have found higher proportions of nontasters among those with a family history of alcoholism than controls, whereas others have not. The purpose of this study was to investigate the relationship between PTC taste status, alcohol problems, and family history of alcoholism. A total of 244 undergraduate students participated in this study, with a gender distribution of 75% female and 25% male. We found support for our hypothesis that male supertasters would report fewer problems with alcohol and a less significant family history of alcoholism. Interestingly, we also found that female supertasters had a greater family history of alcoholism and more current problems associated with alcohol use. Implications for the genetic link between PTC taste status and alcoholism are discussed.

The relationship between phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP) taster status and taste thresholds for sucrose and quinine

OBJECTIVE

The aim of this study was to investigate the relationship of taster status with taste detection and recognition thresholds for sucrose and quinine.

DESIGN

Sixty-nine subjects (35 men and 34 women; mean age, 23.9+/-1.2 years) were included. Stimulus fluids were prepared, one each for phenylthiocarbamide (PTC), 6-n-propylthiouracil (PROP), sucrose and quinine HCl. In each series, successive solutions, which comprised a total of 15 grades, differed by 0.25log units of the molar concentration. Two concentrations of NaCl (0.32 and 1.0 M) were prepared. The subjects were classified as nontasters and tasters using their PTC and PROP perceptions. Tasters were classified as medium-tasters and supertasters by the ratio of perceived bitterness of above-threshold PROP relative to the perceived saltiness of NaCl (PROP ratio). Taste detection and recognition thresholds for sucrose and quinine were determined by standard two-alternative forced choice trials. A Student's t-test, a Pearson's correlation analysis and linear contrasts in a one-way analysis of variance (ANOVA) were used.

RESULTS

The percentages of nontaster, medium-taster and supertaster were 13, 70 and 17%, respectively. There were no significant gender differences in the taste detection and recognition thresholds for sucrose and quinine. The threshold for PTC and PROP showed significant correlations with taste threshold for quinine. Linear contrast in one-way ANOVA showed that the greater the value of PROP ratio, the more sensitive to sweet and bitter tastes (p<0.001).

CONCLUSION

The PTC and PROP taster status is closely related with taste detection and recognition thresholds for sucrose and quinine.

Sensitivity to allyl isothiocyanate, dimethyl trisulfide, sinigrin, and cooked cauliflower consumption

The consumption of cauliflower consumers has been related to the olfactory and gustatory sensitivities to potentially objectionable flavor compounds in this vegetable. Based on the ascending concentration series method of limits, a first experiment was designed to develop rapid tests dedicated to estimate individuals' olfactory thresholds for allyl isothiocyanate (AITC) and dimethyl trisulfide (DMTS) and gustatory thresholds for sinigrin (SIN). The best compromise between rapidity and reliability was obtained with two replications of a four-alternative forced choice (AFC) at six ascending concentrations (6x2x4-AFC) for both AITC and DMTS, and with a 6x1x4-AFC for SIN. In a second experiment, sensitivity to SIN, AITC and DMTS was determined on 267 participants divided into three cauliflower consumer target groups: non-, medium- or high consumers. The non-consumers were significantly more sensitive to SIN and AITC than were the medium and high consumers. No effect of consumer's sensitivity to DMTS was observed.

Modeling the human PTC bitter-taste receptor interactions with bitter tastants

We employed the first principles computational method MembStruk and homology modeling techniques to predict the 3D structures of the human phenylthiocarbamide (PTC) taste receptor. This protein is a seven-transmembrane-domain G protein-coupled receptor that exists in two main forms worldwide, designated taster and nontaster, which differ from each other at three amino-acid positions. 3D models were generated with and without structural similarity comparison to bovine rhodopsin. We used computational tools (HierDock and ScanBindSite) to generate models of the receptor bound to PTC ligand to estimate binding sites and binding energies. In these models, PTC binds at a site distant from the variant amino acids, and PTC binding energy was equivalent for both the taster and nontaster forms of the protein. These models suggest that the inability of humans to taste PTC is due to a failure of G protein activation rather than decreased binding affinity of the receptor for PTC. Amino-acid substitutions in the sixth and seventh transmembrane domains of the nontaster form of the protein may produce increased steric hindrance between these two alpha-helices and reduce the motion of the sixth helix required for G protein activation.

The relationship between PTC taster status and taste thresholds in young adults

OBJECTIVE

The aim of this study was to compare taste detection and recognition thresholds of young males and females, and young phenylthiocarbamide (PTC) "tasters" and "nontasters" for stimuli representing sweet, sour, bitter, salty, and umami classes of taste sensations.

STUDY DESIGN

Thirty-eight men and 37 women (mean [SD] age = 24.5 [2.5] years) were classified as PTC tasters and nontasters according to their PTC recognition thresholds. Detection and recognition thresholds for the non-PTC stimuli were determined using a 2-alternative, forced choice procedure.

RESULTS

The detection thresholds for quinine-HCl and sucrose and the recognition threshold for quinine-HCl were significantly higher in the PTC nontasters than in the tasters. The PTC threshold showed significant correlations with detection or recognition thresholds for sucrose, sodium chloride, quinine-HCl, and monosodium glutamate. The sucrose recognition threshold was lower in women than in men.

CONCLUSION

In this study, gender and PTC taster status were found to be associated with thresholds for sucrose and quinine-HCl.

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

Intake of vegetables falls short of recommendations to lower risk of chronic diseases. Most research addresses bitterness as a sensory deterrent to consuming vegetables. We examined bitter and sweet sensations from vegetables as mediators of vegetable preference and intake as well as how these tastes vary with markers of genetic variation in taste (3.2 mM 6-n-propylthiouracil bitterness) and taste pathology (1.0 mM quinine bitterness, chorda tympani nerve relative to whole mouth). Seventy-one females and 39 males (18-60 years) reported prototypical tastes from and preference for Brussels sprouts, kale and asparagus as well as servings of vegetables consumed, excluding salad and potatoes. Intensity and hedonic ratings were made with the general Labeled Magnitude Scale. Data were analyzed with multiple linear regression and structural equation modeling. Vegetable sweetness and bitterness were independent predictors of more or less preference for sampled vegetables and vegetable intake, respectively. Those who taste PROP as most bitter also tasted the vegetables as most bitter and least sweet. The spatial pattern of quinine bitterness, suggestive of insult to chorda tympani taste fibers, was associated with less bitterness and sweetness from vegetables. Via structural equation modeling, PROP best explained variability in vegetable preference and intake via vegetable bitterness whereas the quinine marker explained variability in vegetable preference and intake via vegetable bitterness and sweetness. In summary, bitterness and sweetness of sampled vegetables varied by taste genetic and taste function markers, which explained differences in preference for vegetables tasted in the laboratory as well as overall vegetable intake outside the laboratory.

Association between 6-n-propylthiouracil (PROP) bitterness and colonic neoplasms

Inadequate vegetable intake appears to increase colon cancer risk. Since genetic variation in taste influences vegetable preference, we tested associations between bitterness of 6-n-propylthiouracil (PROP), a measure of taste genetics, and number of colonic polyps, a measure of colon cancer risk, in 251 men who underwent screening lower endoscopy. Patients used the general Labeled Magnitude Scale to rate bitterness of 1.6 mg PROP delivered via filter paper. A subset of 86 patients reported weekly vegetable intakes, excluding salad or potatoes. PROP bitterness correlated significantly with polyp number, an effect separate from age-associated increases in polyp number. The PROP-polyp relationship was strongest in men over 66 years, and older men with polyps were most likely to be overweight or obese. In the subset reporting vegetable intake, men who tasted PROP as more bitter consumed fewer vegetables. These preliminary findings suggest that taste genetics may influence colon cancer risk, possibly through intake of vegetables.

Role of parents in the determination of the food preferences of children and the development of obesity

The role of parental behaviour in the development of food preferences is considered. Food preferences develop from genetically determined predispositions to like sweet and salty flavours and to dislike bitter and sour tastes. Particularly towards the second year of life, there is a tendency to avoid novel foods (neophobia). Food aversions can be learnt in one trial if consumption is followed by discomfort. There is a predisposition to learn to like foods with high-energy density. However, from birth genetic predispositions are modified by experience and in this context during the early years parents play a particularly important role. Parental style is a critical factor in the development of food preferences. Children are more likely to eat in emotionally positive atmospheres. Siblings, peers and parents can act as role models to encourage the tasting of novel foods. Repeated exposure to initially disliked foods can breakdown resistance. The offering of low-energy-dense foods allows the child to balance energy intake. Restricting access to particular foods increases rather than decreases preference. Forcing a child to eat a food will decrease the liking for that food. Traditionally, educational strategies have typically involved attempts to impart basic nutritional information. Given the limited ability of information to induce changes in behaviour, an alternative strategy would be to teach parents about child development in the hope that an understanding of the characteristic innate tendencies and developmental stages can be used to teach healthy food preferences.

Phenylthiocarbamide tasting and family history of depression, revisited: low rates of depression in families of supertasters

Past studies suggest that phenylthiocarbamide (PTC) taste status is related to vulnerability to depression, such that those sensitive to PTC are more vulnerable. We questioned this, reasoning that those insensitive to PTC may be more vulnerable (because they may have lower hedonic tone and higher risk for alcohol abuse). Forty-two volunteers responded to questionnaires regarding family history of depression, and were assigned to supertaster, taster, or non-taster categories based on taste reactions to a 3.80 x 1.43 cm piece of commercially prepared paper treated with PTC. Supertasters were significantly less likely to report first-degree relatives with a history of depression than were tasters and non-tasters. Supertasters may be afforded some protection from depression; elucidating the mechanisms of this protection is a potentially interesting avenue for future research.

Effects of caloric deprivation and satiety on sensitivity of the gustatory system

BACKGROUND

Sensitivity of the gustatory system could be modulated by a number of short-term and long-term factors such as body mass, gender, age, local and systemic diseases and pathological processes, excessive alcohol drinking, drug dependence, smoking, composition of oral fluid, state of oral hygiene, consumption of some foods among many others. A few studies have demonstrated the effects of hunger and caloric satiety on sensitivity of the gustatory system in obese humans and animals. The aim of the present study was to assess the effects of short-term caloric deprivation and satiety on recognition taste thresholds of healthy, non-smoking, non-drinking, non-obese young male subjects. The two-alternative forced-choice technique was used to measure taste threshold.

RESULTS

Recognition thresholds for sucrose and salt were significantly lower during fasting state than after a meal (t = 2.23, P < 0.05, and t = 2.86, P < 0.02, respectively) while the values of recognition thresholds for bitter substances in fasting state and after caloric loading did not differ significantly.

CONCLUSIONS

Short-term caloric deprivation in our study model was associated with increased taste sensitivity to sweet and salty substances compared to satiated state while taste sensitivity to bitter substances was not affected by the conditions of measurements. Selective modulation of sensitivity of the gustatory system might reflect the different biological importance of salty, sweet and bitter qualities of taste.

Relationships between threshold-based PROP sensitivity and food preferences of Tunisians

The extent to which taste responses--and notably the genetically determined sensitivity to 6-n-propylthiouracil (PROP)--influences food preferences and food use is still a matter of debate. We addressed the issue on the basis of a behavioural and anthropological study performed in Tunis in 1999. The working sample consists of 123 adults of both sexes (38 men, 85 women), aged 19-59, in various social categories. Taste recognition thresholds for sucrose, fructose, sodium chloride, quinine hydrochloride, citric acid, tannic acid, oak tannin and PROP were determined by presenting, in a semi-randomised order (blind-test), series of graded aqueous solutions of each product. Subjects also tasted and rated the pleasantness/unpleasantness of 4 supra-threshold solutions of NaCl and sucrose. All subjects completed a checklist of 43 food items representative of Tunisian diet, rated in terms of flavour, cost, effect on health and prestige on a labelled affective magnitude scale. According to the underlying distribution of PROP thresholds, the subjects were separated into three categories: "non-tasters", "medium-threshold tasters", and "low-threshold tasters". Results bring out the specificity of low-threshold tasters, as exhibiting a greater taste sensitivity for most tested substances. Low-threshold taster status is also linked to higher mean food preferences ratings irrespective of sex, age and socio-cultural influences. Tasters as a group (medium-threshold tasters + low-threshold tasters) do not exhibit a higher percentage of food dislikes; however PROP sensitivity is negatively correlated with hedonic responses to NaCl solutions. These results together with the evidence of a limited set of food actually used by low-threshold tasters suggest that these subjects might have difficulties at overcoming an inherent neophobia.

The genetics of phenylthiocarbamide perception

The ability to taste the bitter compound phenylthiocarbamide (PTC) and related chemicals is bimodal, and all human populations tested to date contain some people who can and some people who cannot taste PTC. Why this trait has been maintained in the population is uncertain but this polymorphism may influence food selection, nutritional status or thyroid metabolism. The gene product that gives rise to this phenotype is unknown, and its characterization would provide insight into the mechanism of bitter taste perception. Although this trait is often considered a simple Mendelian trait, i.e. one gene two alleles, a recent linkage study found a major locus on chromosome 5p15 and evidence for an additional locus on chromosome 7. The development of methods to identify these genes will provide a good stepping-stone between single-gene disorders and polygenic traits.

Food acceptance and genetic variation in taste

OBJECTIVE

To determine if individuals who taste 6-n-propylthiouracil (PROP), one marker of genetic variation in taste, as exceptionally bitter can also perceive sugars as sweeter, other bitters as more intense, and dietary fats as more creamy and/or viscous than do individuals who taste PROP as weakly bitter. This study examined the association between genetic variation in taste and acceptance for sweet, high-fat, and bitter foods and beverages.

DESIGN

Genetic variation was measured by perceived bitterness of PROP (influenced by genetic, hormonal, and pathologic factors) and density of fungiform papillae on the anterior portion of the tongue (influenced primarily by genetic factors). Four sweet, 3 fat, and 3 bitter groups were derived from principal components analyses of questionnaire items.

SUBJECTS

Convenience sample of healthy adults (24 women, 22 men; mean age +/- standard deviation = 21 +/- 6 years) who did not report high dietary restraint.

STATISTICAL ANALYSES

Pearson product moment correlations between genetic taste measures and food and beverage groups.

RESULTS

The sample showed diversity in genetic taste measures: perceived bitterness of 0.0032 mol/L PROP ranged from "weak" to well above "very strong"; fungiform papillae densities ranged from 33 to 156 papillae per square centimeter. Distribution of perceived bitterness of PROP and fungiform papillae density differed in women and men. The association between genetic taste measures and acceptance of sweet and high-fat groups differed in women and men. In women, liking of sweet and high-fat food and beverage groups decreased with increasing perceived bitterness of PROP. In men, liking of these foods and beverages increased but with increasing papillae densities. Genetic taste measures were not associated with a dislike of bitter food and beverage groups.

APPLICATIONS

The influence of genetic variation in taste on food intake depends on how perceptible sweet, fat, or bitter components are in foods and beverages, as well as the value of sensory factors vs other factors (e.g., health, convenience) on personal dietary choices. Female supertasters of PROP bitterness may avoid high-fat or sweet foods because these oral sensations are too intense and thus less pleasant. Supertasters may taste more bitterness in vegetables but still enjoy eating them because of their healthfulness and because condiments (especially those that are salt based) can block bitterness.

Young women's food preferences and taste responsiveness to 6-n-propylthiouracil (PROP)

This study examined links between taste responsiveness to 6-n-propylthiouracil (PROP), a heritable trait, and sensory responses to six common foods. Sixty-three young women subjects were divided into PROP tasters (n = 25) and nontasters (n = 25), based on their responses to PROP-impregnated filter paper and mean bitterness intensity ratings for seven PROP solutions. Thirteen subjects were excluded as unclassifiable. The 50 subjects sampled Brussels sprouts, broccoli, spinach, black coffee, soy milk, and soybean tofu. Sensory ratings for bitter intensity; pleasantness of taste, odor, and texture, and overall food acceptability scores were obtained using nine-point category scales. All subjects completed a food-preference checklist and a modified food-frequency questionnaire. PROP tasters rated Brussels sprouts as more bitter than did nontasters (p<0.05). Subjects who perceived the foods as more bitter also rated them as less pleasant and less acceptable. Taste preferences and food preferences were linked. Self-reported food preferences and self-reported frequencies of consumption for the same foods were also linked. Taste factors and food preferences may impact dietary choices and the frequency of food consumption.

Development of food preferences

Using a developmental systems perspective, this review focuses on how genetic predispositions interact with aspects of the eating environment to produce phenotypic food preferences. Predispositions include the unlearned, reflexive reactions to basic tastes: the preference for sweet and salty tastes, and the rejection of sour and bitter tastes. Other predispositions are (a) the neophobic reaction to new foods and (b) the ability to learn food preferences based on associations with the contexts and consequences of eating various foods. Whether genetic predispositions are manifested in food preferences that foster healthy diets depends on the eating environment, including food availability and child-feeding practices of the adults. Unfortunately, in the United States today, the ready availability of energy-dense foods, high in sugar, fat, and salt, provides an eating environment that fosters food preferences inconsistent with dietary guidelines, which can promote excess weight gain and obesity.

Heritable variation in food preferences and their contribution to obesity

What an animal chooses to eat can either induce or retard the development of obesity; this review summarizes what is known about the genetic determinants of nutrient selection and its impact on obesity in humans and rodents. The selection of macronutrients in the diet appears to be, in part, heritable. Genes that mediate the consumption of sweet-tasting carbohydrate sources have been mapped and are being isolated and characterized. Excessive dietary fat intake is strongly tied to obesity, and several studies suggest that a preference for fat and the resulting obesity are partially genetically determined. Identifying genes involved in the excess consumption of dietary fat will be an important key to our understanding of the genetic disposition toward common dietary obesity.

Fat perception is related to PROP taster status

Individuals who are sensitive to the bitter compounds phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP) are also more sensitive to selected bitter and sweet substances, to sharp-tasting foods, and to the trigeminal irritant capsaicin. PTC/PROP tasters have a greater density of fungiform taste papillae and it is speculated that PTC/PROP tasters also have more trigeminal innervation. Because oral texture perception is also mediated, in part, by trigeminal fibers, it has been proposed that individual differences in fat perception might also be linked to PTC/PROP taster status and taste bud density. This work tests the hypothesis that individuals who are PROP tasters: 1. have a higher density of fungiform papillae; 2. are more sensitive to capsaicin; and 3. have increased ability to discriminate differences in fat content in salad dressing. Individual subjects were classified as PROP nontasters, medium tasters, or supertasters (n = 25 per group) by comparing their psychophysical function for PROP to that of NaCl. Papillae densities (papillae/cm2) were significantly different among the 3 taster groups (p < or = 0.0001), and were highest among the supertasters. Both medium tasters and supertasters perceived more oral burn from capsaicin than did nontasters at concentrations of 50, 70, and 100 ppm (p < or = 0.0001). Medium tasters and supertasters could also discriminate differences in fat content between 40% fat and 10% fat salad dressings (p < or = 0.005), but the nontasters could not. These data provide the first published evidence that fat perception can be linked to genetic and anatomical differences between individuals.

Taste preferences and food intake

Sensory responses to the taste, smell, and texture of foods help determine food preferences and eating habits. However, sensory responses alone do not predict food consumption. The view that a "sweet tooth" leads to obesity through excess sugar consumption is overly narrow. In reality, there are multiple links between taste perceptions, taste preferences, food preferences, and food choices and the amount of food consumed. Taste responses are influenced by a range of genetic, physiological, and metabolic variables. The impact of taste factors on food intake further depends on sex and age and is modulated by obesity, eating disorders, and other pathologies of eating behavior. Food preferences and food choices of populations are further linked to attitudinal, social, and--probably most important--economic variables such as income. Nutrition education and intervention strategies aimed at improving population diets ought to consider sensory pleasure response to foods, in addition to a wide range of demographic and sociocultural variables.

Influences on acceptance of bitter foods and beverages

Bitterness is generally viewed as an undesirable attribute of foods and beverages, yet segments of the population regularly ingest items with a prominent bitter taste. The influence of taste sensitivity, exposure, selected personality traits (i.e., neophobia, variety seeking, sensation seeking) and pharmacological reactivity on alcohol and caffeine consumption, two widely consumed bitter substances, was assessed in 20 healthy adults (10 male, 10 female). Self-reported alcohol use was positively correlated with measured ethanol taste detection threshold and pharmacological reactivity (self-reported behavioral effects). The latter accounted for 23% of the variance in alcohol intake. Caffeine intake was significantly associated with personality traits. Sensation seeking status and self-reported reactivity to caffeine accounted for 46% of the variance in caffeine intake. Pleasantness ratings for novel bitter and sour foods were unaffected by 10 exposures whereas increased ratings were given to sweet and salty items. Variation in the influence of these factors between individuals and across products may explain individual differences in the acceptability and use of foods and beverages containing alcohol, caffeine and other bitter compounds.

Evidence for a genetic influence on preference for some foods

OBJECTIVE

The purpose of this study was to evaluate genetic influence on preference for 17 foods. The relationship between preference and use of these foods was also examined. The study focused on frequently eaten foods and on foods consumed less frequently but promoted for good health.

DESIGN

Food preferences were investigated in young monozygotic and same-sex dizygotic twin pairs living at home and sharing the same environment. Subjects provided preference ratings after testing each food. A food frequency questionnaire was used to determine whether the genetic component of preference is associated with food use.

SUBJECTS

Subjects were 14 pairs of monozygotic twins and 21 pairs of same-sex dizygotic twins, aged 9 to 18 years. They were recruited on a volunteer basis from public schools in Cincinnati, Ohio.

MAIN OUTCOME MEASURES

We found a greater similarity in food preference between members of monozygotic twin pairs than between dizygotic twin pairs, which suggests an important role for genetics in accounting for individual differences in food preference.

STATISTICAL ANALYSES PERFORMED

Food preference data were analyzed using Pearson correlation coefficients and Fischer z scores. Additional estimates of heritability were obtained by applying the Mann-Whitney nonparametric t test and the Holzinger index. Food use was correlated with preference using Pearson correlation coefficients.

RESULTS

Significant differences in intrapair correlations for monozygotic and dizygotic twins were found for orange juice (z = 5.39; P < .05), broccoli (z = 2.60; P < .05), cottage cheese (z = 2.54; P < .05), chicken (z = 2.54; P < .05), sweetened cereal (z = 2.00; P < .05), and hamburger (z = 1.95; P < .10). The genetic component of preference was correlated with use for only two foods.

APPLICATIONS/CONCLUSIONS

It is important for nutritionists to realize that heritable factors may influence selection of a range of foods, including some that are promoted for good health. If health-promoting foods are to be included in the diet, accessibility and exposure to these foods must be increased.

Co-evolution of glucose-6-phosphate dehydrogenase deficiency and quinine taste sensitivity

We hypothesized that 'quinine' taste sensitivity functions to regulate the intake of bitter-tasting, naturally occurring antimalarial substances of plant origin, and that this genetic trait has co-evolved with the G6PD locus. This hypothesis was tested by evaluating taste sensitivity to quinine sulphate and sodium chloride among 17 G6PD-deficient and 25 G6PD-normal African American subjects 14-40 years of age. There was no significant difference in mean 'quinine' taste sensitivity between the two groups, although there was a trend towards greater 'quinine' taste acuity among the G6PD-deficient subjects. A larger study sample would provide a fairer test of the hypothesis.