Beverly J. Tepper

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.

Genetic taste sensitivity to 6-n-propylthiouracil influences food preference and reported intake in preschool children.

Adult tasters of 6-n-propylthiouracil (PROP) are more sensitive to bitter taste and fattiness in foods, and often show lower acceptance of foods that are high in these taste qualities. This study hypothesized that PROP taster children would show lower acceptance of these same foods. Sixty-seven preschool children were classified as PROP tasters (N = 43) or nontasters (N = 24) using a suprathreshold screening solution. Children rated acceptance of 10 bitter and/or fat-containing foods using a 5-pt. facial scale. Parents completed a food frequency questionnaire to estimate their childs intake. Taster children showed lower acceptance of raw broccoli and American cheese (p < or = 0 x 05). Taster-girls showed lower acceptance of full-fat milk than nontaster-girls (p < or = 0 x 05). This effect was not seen in boys. Nontasters reported more daily intake of discretionary fats than tasters (p < or = 0 x 05), an effect largely due to nontaster-girls, in whom reported intake was 2--3 more servings per day than taster-girls, and boys of both groups. These data suggest that PROP taste sensitivity plays a role in acceptance of certain bitter cruciferous vegetables and cheese by young children. In addition, taster group differences in acceptance of full-fat milk and intake of discretionary fats seen in girls, suggest that gender-specific environmental factors might interact with genetics to influence fat preferences.

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.

Fat replacers and the functionality of fat in foods

Abstract Developing no- and low-fat products is a high priority for the food industry. Given the variety of fat replacers available, how does a product developer decide which to use? Fat replacers can be divided into three classes on the basis of their composition: protein-based, carbohydrate-based and fat-based. Each has different functional properties that provide both advantages and limitations in specific applications. Presently there is no ‘silver bullet’ — no single fat replacer that contributes all of the desired sensory and functional qualities to all products. A systems approach, one that makes use of a combination of two or more wisely chosen fat replacers, coupled with formula and procedural changes appears to be the best current strategy.

A paper screening test to assess genetic taste sensitivity to 6-n-propylthiouracil

The purpose of this study was to develop a quantifiable method to fix 6-n-propylthiouracil (PROP) onto filter paper disks and to test the validity of the method relative to the three-solution test, previously developed in this laboratory. Filter paper disks were impregnated with 50 mmol/l PROP or 1.0 mol/l NaCl then dried. The concentration of PROP per disk was determined to be 0.280 mg+/-2.2% (CV) by ethanol extraction. Subjects were studied in two groups (n=62 per group). All subjects were initially classified by the three-solution test and then were independently classified by the paper disk test. In the paper disk test, group means for PROP (+/-95% confidence interval) were calculated and used to establish numerical cutoff scores for taster group classification. Cutoff scores for Group 1 were used to classify subjects in Group 2, verifying that the cutoffs were applicable to another subject group. The percentage of nontasters, medium tasters, and supertasters identified by paper disk was 27%, 42%, and 31%, respectively, which is consistent with expected frequencies in the population. For Group 1, the agreement between the two classification methods ranged from 86% to 94% across taster groups. For Group 2, the agreement ranged from 83% to 100%. The contingency coefficient (P) of the degree of association between the two classification methods was high (P=0.77 and P=0.74 for Groups 1 and 2, respectively; P< or =.001). These results demonstrate that the paper disk method is a reliable screening tool for assessing sensitivity to PROP that has numerous applications in basic and applied research.

Influence of genetic taste sensitivity to 6-n-propylthiouracil (PROP), dietary restraint and disinhibition on body mass index in middle-aged women

A previous study from our laboratory reported a small, inverse association between taste sensitivity to 6-n-propylthiouracil (PROP) and body mass index (BMI) among lean, young-adult males. Weaknesses in study design precluded making this same observation in females. To overcome these shortcomings, the present study investigated this relationship in older, heavier women characterized by dietary restraint and disinhibition. We tested the hypothesis that lower taste sensitivity to PROP would be associated with higher BMI but that high dietary restraint would mask this association. Thus, no relationship between taster status and BMI was expected in those with high dietary restraint. Eighty-six, middle-aged women (39.0+/-1.0 years) with a mean BMI of 27.4+/-0.8 participated. They were classified as PROP nontasters (n=23), medium tasters (n=32) or supertasters (n=31). Initial analyses revealed that disinhibition had a strong positive influence on BMI that was unrelated to PROP status (P< or =.001). After adjusting for disinhibition, a strong interaction between PROP status and restraint on BMI was noted. Among women with low dietary restraint, nontasters (P< or =.01) and medium tasters (P< or =.05) were heavier than supertasters by 6 and 4 adjusted BMI units, respectively. No differences in BMI were found across taster groups in women with high dietary restraint. These data confirm that the inverse association between PROP status and BMI reported earlier in men is also present in women and that this relationship becomes apparent when variables relevant to eating behavior in women are taken into consideration. These findings are discussed in the context of emerging theories relating genetic differences in taste to fat acceptance, fat intake and body weight.

6-n-Propylthiouracil: a genetic marker for taste, with implications for food preference and dietary habits.

6-n-Propylthiouracil (PROP) and phenythiocarbamide (PTC) are members of a class of compounds known as “thioureas.” These compounds carry the chemical group N-C=S, which is responsible for their characteristic bitter taste (for review, see Bartoshuk et al. 1994; Drewnowski and Rock 1995). As is true for many scientific discoveries, the bitterness of PROP and PTC were discovered by accident. In 1931, while Fox was synthesizing PTC in his laboratory, some of the white crystals became airborne. His colleagues perceived a bitter taste, but Fox tasted nothing.

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.

Common Variants in the CD36 Gene Are Associated With Oral Fat Perception, Fat Preferences, and Obesity in African Americans

Animal studies show that CD36, a fatty acid translocase, is involved in fat detection and preference, but these findings have not been reported in humans. The objective of this study was to determine whether human genetic variation in 5 common CD36 polymorphisms is associated with oral fat perception of Italian salad dressings, self‐reported acceptance of high‐fat foods and obesity in African‐American adults (n = 317). Ratings of perceived oiliness, fat content, and creaminess were assessed on a 170‐mm visual analogue scale (VAS) in response to salad dressings that were 5%, 35%, and 55% fat‐by‐weight content. Acceptance of added fats and oils and high‐fat foods was self‐reported and anthropometric measures were taken in the laboratory. DNA was isolated from saliva and genotyped at 5 CD36 polymorphisms. Three polymorphisms, rs1761667, rs3840546, and rs1527483 were associated with the outcomes. Participants with the A/A genotype at rs1761667 reported greater perceived creaminess, regardless of the fat concentration of the salad dressings (P < 0.01) and higher mean acceptance of added fats and oils (P = 0.02) compared to those with other genotypes at this site. Individuals who had C/T or T/T genotypes at rs1527483 also perceived greater fat content in the salad dressings, independent of fat concentration (P = 0.03). BMI and waist circumference were higher in participants who were homozygous for a deletion (D/D) at rs3840546, compared to I/D or D/D individuals (P < 0.001), but only 2 D/D individuals were tested, so this finding needs replication. This is the first study to demonstrate an association between common variants in CD36 and fat ingestive behaviors in humans.

Genetic Variation in Taste Sensitivity to 6‐n‐Propylthiouracil and Its Relationship to Taste Perception and Food Selection

The ability to taste bitter thiourea compounds and related chemicals is a well‐known human trait. The majority of individuals perceive these compounds, typified by the bitterness of 6‐n‐propylthiouracil (PROP) and phenylthiocarbamide (PTC), as moderately‐to‐extremely bitter. Approximately 30% of the population is taste blind to these substances. It has been hypothesized that PROP/PTC tasters are more sensitive to other bitter tastes, sweet taste, the pungency of chili peppers, the astringency of alcohol, and the texture of fats. Tasters may also show lower preferences for foods with these taste qualities than nontasters who show the opposite set of responses (i.e., lower taste sensitivities and higher preferences for these sensory qualities). This pathway is illustrated in the following model: