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

Variation in the bitter-taste receptor gene TAS2R38, and adiposity in a genetically isolated population in Southern Italy

OBJECTIVE

Variation in the bitter-taste receptor gene, TAS2R38 confers the ability to taste 6-n-propylthiouracil (PROP). The objective of this study was to relate TAS2R38 haplotypes and PROP-tasting phenotypes to adiposity in a genetically isolated population. We hypothesized that the nontaster phenotype would be associated with higher BMI and waist circumference (WC) in females, and that dietary restraint would mediate this relationship.

METHODS AND PROCEDURES

Participants were 540 healthy inhabitants of the genetically isolated village of Carlantino in southern Italy who were 15-89 years of age at the time of the study. Haplotype analyses were performed and PROP tasting was assessed using a filter paper method. Height, weight, and WC were measured and restrained eating was assessed using a brief questionnaire.

RESULTS

Nontaster females had higher BMI and WC than females who were phenotypic tasters, and this relationship was specific to females with low dietary restraint. Regression analysis showed that BMI declined by 1.7 units across taster groups in females when the model included the PROP by restraint interaction. PROP phenotype was not significantly associated with WC in the regression models. Polymorphisms in TAS2R38 were not associated with BMI or WC in females. Neither TAS2R38 haplotype nor PROP phenotype was strongly related to BMI or WC in males.

DISCUSSION

These data support previous findings of a relation between the nontaster phenotype and higher BMI in females that is modified by dietary restraint. Assessment of PROP phenotypes might provide unique information about adiposity that is not captured by haplotype analysis alone.

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.

Genetic and environmental determinants of children's food preferences

Omnivores have the advantage of a variety of food options but face a challenge in identifying foods that are safe to eat. Not surprisingly, therefore, children show a relative aversion to new foods (neophobia) and a relative preference for familiar, bland, sweet foods. While this may in the past have promoted survival, in the modern food environment it could have an adverse effect on dietary quality. This review examines the evidence for genetic and environmental factors underlying individual differences in children's food preferences and neophobia. Twin studies indicate that neophobia is a strongly heritable characteristic, while specific food preferences show some genetic influence and are also influenced by the family environment. The advantage of the malleability of human food preferences is that dislike of a food can be reduced or even reversed by a combination of modelling and taste exposure. The need for effective guidance for parents who may be seeking to improve the range or nutritional value of foods accepted by their children is highlighted.

The taste transduction channel TRPM5 is a locus for bitter-sweet taste interactions

Ordinary gustatory experiences, which are usually evoked by taste mixtures, are determined by multiple interactions between different taste stimuli. The most studied model for these gustatory interactions is the suppression of the responses to sweeteners by the prototype bitter compound quinine. Here we report that TRPM5, a cation channel involved in sweet taste transduction, is inhibited by quinine (EC(50)=50 microM at -50 mV) owing to a decrease in the maximal whole-cell TRPM5 conductance and an acceleration of channel closure. Notably, quinine inhibits the gustatory responses of sweet-sensitive gustatory nerves in wild-type (EC(50)= approximately 1.6 mM) but not in Trpm5 knockout mice. Quinine induces a dose- and time-dependent inhibition of TRPM5-dependent responses of single sweet-sensitive fibers to sucrose, according to the restricted diffusion of the drug into the taste tissue. Quinidine, the stereoisomer of quinine, has similar effects on TRPM5 currents and on sweet-induced gustatory responses. In contrast, the chemically unrelated bitter compound denatonium benzoate has an approximately 100-fold weaker effect on TRPM5 currents and, accordingly, at 10 mM it does not alter gustatory responses to sucrose. The inhibition of TRPM5 by bitter compounds constitutes the molecular basis of a novel mechanism of taste interactions, whereby the bitter tastant inhibits directly the sweet transduction pathway.

Behavioral genetics and taste

This review focuses on behavioral genetic studies of sweet, umami, bitter and salt taste responses in mammals. Studies involving mouse inbred strain comparisons and genetic analyses, and their impact on elucidation of taste receptors and transduction mechanisms are discussed. Finally, the effect of genetic variation in taste responsiveness on complex traits such as drug intake is considered. Recent advances in development of genomic resources make behavioral genetics a powerful approach for understanding mechanisms of taste.

Genetic and environmental influences on children's food neophobia

BACKGROUND

Food neophobia in children has been associated with a low intake of fruit, vegetables, and protein foods. The design of effective interventions to improve children's diets would be facilitated by a better understanding of the determinants of neophobia.

OBJECTIVE

Our objective was to quantify the contribution of genetic and environmental differences to variation in child food neophobia.

DESIGN

Parents of twins aged 8-11 y (n = 5390 pairs) completed questionnaires about their children's eating habits, including a measure of food neophobia.

RESULTS

The results showed that neophobia is highly heritable. The heritability estimate from model fitting was 0.78 (95% CI: 0.76, 0.79). A further 22% of the variance was explained by nonshared environmental factors, with no influence of shared environmental factors.

CONCLUSIONS

Neophobia appears to be a heritable trait, but almost a quarter of the phenotypic variation is accounted for by nonshared environmental factors. An important aim for future research is the identification of influential aspects of the environment specific to individual children.

Psychosocial correlates of 6-n-propylthiouracil (PROP) ratings in a birth cohort

This study investigated the relation between ratings of 6-n-propylthiouracil (PROP) and two psychosocial constructs, socioeconomic status and IQ, which are related to health outcomes. A 3.2mM solution of PROP was rated by 922 32-year-old members of a birth cohort (450 women) relative to the strongest imaginable sensation of any kind using the generalised Labelled Magnitude Scale. Women had higher PROP ratings than men. Following normalisation of PROP ratings, multiple linear regression showed that higher ratings were independently associated with lower childhood socioeconomic status, lower childhood IQ scores and ratings of an imagined stimulus made on the same scale (r(2)=0.12). Results suggest that psychosocial variables, sex and scale use, in addition to established genetic determinants, may help explain variability in ratings of supra-threshold concentrations of PROP.

Influence of PROP taster status and maternal variables on energy intake and body weight of pre-adolescents

Genetic taste blindness to the bitterness of 6-n-propylthiouracil (PROP) may be a marker for increased energy intake and body weight. This hypothesis has not been tested in pre-adolescent children. This study determined if non-taster children would report higher energy intakes and maintain higher body weights than taster children. Maternal variables which are known to influence food intake and body weight during childhood were also considered including maternal weight, maternal restraint and disinhibition and child feeding practices. Sixty-five children with a mean age of 9.0+/-0.2 years participated. They completed a 3-day diet recall for the estimation of daily energy and macronutrient intakes. BMI (mothers) and BMI%-for-age (children) were calculated from measured heights and weights. Non-taster children reported higher daily energy intakes than super-taster children (p < or = 0.05), but no differences in macronutrient selection were observed. Also, children of disinhibited mothers reported higher daily energy intakes than children of mothers who were not disinhibited (p < or = 0.05). However, these variables did not predict children's body weight. Rather, regression modeling (R2 = 0.59; p < or = 0.0001) revealed that restriction, concern for child weight and maternal BMI were positive predictors of children's BMI%-for-age and pressure to eat was a strong negative predictor (p-value range = 0.02-0.004). PROP status was not a predictor of body weight in these children. These results suggest that in pre-adolescent children, current energy intakes were negatively related to children's PROP status and positively related to maternal disinhibition. However, BMI%-for-age, a measure of long-term energy balance, was related to child feeding practices and maternal BMI.

Variation in oral sensation: implications for diet and health

PURPOSE OF REVIEW

Important advances in our understanding of how taste, smell and somatosensation contribute to oral sensation are reviewed and the nutritional and health implications associated with variation in oral sensation are discussed.

RECENT FINDINGS

Oral sensation is a central integration of taste (salty, sweet, sour, bitter, umami), retronasal olfaction (i.e. smelling through the mouth), and somatosensation (touch, temperature, pain) by the orbitofrontal cortex. There is normal variation in oral sensation across individuals, ranging from those living in a neon orosensory world to those living in a pastel world. Historically, study of this variation revolved around genetically mediated bitterness of phenylthiocarbamide or propylthiouracil, but now it encompasses additional phenotypes (e.g. fungiform papillae number, bitterness of quinine) and emerging receptor genotypes. Aging and exposure to pathogens interact with genetics to further influence oral sensation. Orosensory variation is associated with differences in preference for high-fat foods, sweets, vegetables, and alcoholic beverages. Emerging data suggest this variation influences intake of these foods/beverages and thus diet-related chronic diseases (cardiovascular diseases, certain cancers, obesity).

SUMMARY

Oral sensation varies with genetics and gene-environment interactions. As this variation explains some of the differences in what we like/dislike to eat, attempts to reduce disease risk through diet should consider food/beverage preference to promote health and food enjoyment.

Food cravings, ethnicity and other factors related to eating out

OBJECTIVE

Our objective was to study factors related to eating patterns, specifically whether certain food cravings were associated with frequency of meals eaten away from home.

METHODS

Data were collected from 277 patients from a family medicine residency office in Arizona. The survey questionnaire included information about the respondents' demographics, socioeconomic status, food cravings, as well as, number of meals eaten away from home. The food craving inventory included foods in four categories identified by factor analysis: fast foods, carbohydrates, sweets and snacks. Data on food cravings were factor analyzed and scale scores were derived.

RESULTS

Being a Hispanic adult, working outside the home, and cravings for individual food items were related to eating more meals away from home. If the mother was working outside the home, the youngest child ate an average of two additional meals away from home each week. In general respondent's cravings for some specific food items were also related to higher numbers of meals their child ate away from home. Cravings for both fast food and snacks were positively correlated with adult eating out. None of the respondents' scale scores were related to child's eating away from home. Adults with Arizona Health Care Cost Containment System insurance (AHCCCS--a form of Medicaid) and older adults were less likely to eat away from home compared to patients with other types of insurance.

CONCLUSIONS

Socioeconomic status, ethnicity, and food cravings are related to adult and child patterns of eating meals away from home.

Revisiting sugar-fat mixtures: sweetness and creaminess vary with phenotypic markers of oral sensation

Genetic variation in oral sensation presumably influences ingestive behaviors through sensations arising from foods and beverages. Here, we investigated the influence of taste phenotype [6-n-propylthiouracil (PROP) bitterness, fungiform papillae (FP) density] on sweet and creamy sensations from sugar/fat mixtures. Seventy-nine subjects (43 males) reported the sweetness and creaminess of water or milk (skim, whole, heavy cream) varying in sucrose (0-20% w/v) on the general Labeled Magnitude Scale. Sweetness grew with sucrose concentration and when shifting from water to milk mixtures--the growth was greatest for those tasting PROP as most bitter. At higher sucrose levels, increasing fat blunted the PROP-sweet relationship, whereas at lower levels, the relationship was effectively eliminated. Perceived sweetness of the mixture exceeded that predicted from the sum of components at low sucrose concentrations (especially for those tasting PROP most bitter) but fell below predicted at high concentrations, irrespective of fat level. Creaminess increased greatly with fat level and somewhat with sucrose. Those tasting PROP most bitter perceived greater creaminess in the heavy cream across all sucrose levels. Perceived creaminess was somewhat lower than predicted, irrespective of PROP bitterness. The FP density generally showed similar effects as PROP on sweetness and creaminess, (but to a lesser degree) and revealed potential taste-somatosensory interactions in weakly sweet stimuli. These data support that taste phenotype affects the nature of enhancement or suppression of sweetness and creaminess in liquid fat/sugar mixtures. Taste phenotype effects on sweetness and creaminess likely involve differential taste, retronasal olfactory, and somatosensory contributions to these perceptual experiences.

Increased negative emotional responses in PROP supertasters

Based on animal data it has been suggested that an increased sensitivity to bitter tastes is linked with increased emotional reactivity. The present study examined for the first time in humans whether the intensity of experimentally induced negative emotional responses is related to sensitivity to the bitter tasting compound PROP (6-n-propylthiouracil). Normal-weight participants (61 men, 57 women) with a mean age of 24 years were classified into PROP non-tasters (n=54), medium tasters (n=25), or supertasters (n=39), and were shown two film clips to induce negative emotional response patterns: one pattern predominated by anger and tension, and another predominated by sadness and depressed mood. A third film clip was emotionally neutral. Before and after film clip viewing, self-rated emotional responses were obtained. PROP supertasters showed more intense responses than non-tasters or medium tasters after the anger-inducing film clip (increased anger, tension, sadness and fear as well as decreased mood and joy). Significant correlations were found between emotional responses and a continuos measure of PROP sensitivity. Group differences and correlations could not be attributed to personality measures, trait affectivity, or gender. For emotional responses after the sadness-inducing film clip, no differences between taster groups could be detected. PROP sensitivity appears to be related to arousability of emotions, in particular those emotions that are associated with an increased readiness to respond actively to stimuli from the environment, e.g. anger, disgust and fear.

Psychophysics of sweet and fat perception in obesity: problems, solutions and new perspectives

Psychophysical comparisons seem to show that obese individuals experience normal sweet and fat sensations, they like sweetness the same or less, but like fat more than the non-obese do. These psychophysical comparisons have been made using scales (visual analogue or category) that assume intensity labels (e.g. extremely) which denote the same absolute perceived intensity to all. In reality, the perceived intensities denoted by labels vary because they depend on experiences with the substances to be judged. This variation makes comparisons invalid. Valid comparisons can be made by asking the subjects to rate their sensory/hedonic experiences in contexts that are not related to the specific experiences of interest. Using this methodology, we present the evidence that the sensory and hedonic properties of sweet and fat vary with body mass index. The obese live in different orosensory and orohedonic worlds than do the non-obese; the obese experience reduced sweetness, which probably intensifies fat sensations, and the obese like both sweet and fat more than the non-obese do. Genetic variation as well as taste pathology contribute to these results. These psychophysical advances will impact experimental as well as clinical studies of obesity and other eating disorders.

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.