Factors Influencing the Phenotypic Characterization of the Oral Marker, PROP.

In the last several decades, the genetic ability to taste the bitter compound, 6-n-propyltiouracil (PROP) has attracted considerable attention as a model for understanding individual differences in taste perception, and as an oral marker for food preferences and eating behavior that ultimately impacts nutritional status and health. However, some studies do not support this role. This review describes common factors that can influence the characterization of this phenotype including: (1) changes in taste sensitivity with increasing age; (2) gender differences in taste perception; and (3) effects of smoking and obesity. We suggest that attention to these factors during PROP screening could strengthen the associations between this phenotype and a variety of health outcomes ranging from variation in body composition to oral health and cancer risk.

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

BACKGROUND: Exposure to a variety of energy-dense foods promotes increased energy intake and adiposity. Taste blindness to the bitterness of 6-n-propylthiouracil (PROP) has been associated with increased adiposity in women and might be linked to an increased energy intake and greater selection of dietary fat. OBJECTIVE: We investigated whether PROP nontaster (NT) women would consume more fat and energy in a buffet setting than medium taster (MT) or supertaster (ST) women. DESIGN: Seventy-five non-diet-restrained, lean, young women [mean ± SEM BMI (in kg/m²): 21.5 ± 0.6; age: 26.1 ± 1.3 y) ate lunch and dinner in the laboratory for 3 consecutive days under the following 2 conditions: ad libitum control meals (CONTs) or high-variety buffet meals (BUFFs). A standard breakfast was consumed each day of the study (4 - d washout between conditions). RESULTS: NTs and MTs consumed more energy and fat (as the percentage of energy) from BUFFs than did STs (P < 0.01), which contributed to higher daily energy intakes in these 2 groups of women during BUFFs (2149 ± 49 kcal/d for NTs and 2209 ± 48 kcal/d for MTs compared with 1933 ± 50 kcal/d for STs; P < 0.01). Together, NTs and MTs consumed an extra 246 kcal/d during BUFFs than during CONTs. In addition, compared with STs, NTs and MTs consumed more added fats and sweets (servings/d; P < 0.003) and more energy from snacks (P < 0.01) across all study days. CONCLUSIONS: NT and MT women consume more daily energy than do ST women when eating in a buffet setting, which is a common type of dietary exposure. This increase in energy intake over time could contribute to a positive energy balance and increased adiposity previously reported in these women.

Greater energy intake from a buffet meal in lean, young women is associated with the 6-n-propylthiouracil (PROP) non-taster phenotype.

Taste blindness to 6-n-propylthiouracil (PROP) is a common phenotype that has been associated with increased adiposity in women, and might be linked to increased selection of dietary fats. Since exposure to a variety of high-fat/energy-dense foods is known to promote excess energy intake, we investigated if PROP non-taster women would consume more fat and/or energy in a buffet setting than super-taster women. Subjects were non-diet restrained, lean, young women; 14 were non-tasters and 18 were super-tasters. Subjects ate lunch in the laboratory on four separate days. On one day they consumed an ad libitum, fixed-item lunch (control). On the other three days they consumed different buffet lunches (pizza/tacos/sub sandwiches with salad bar and choice of beverage and dessert). Energy intake from the control lunch did not differ between groups. When intake was averaged across the buffet lunches, non-taster women consumed 357+64 kcal more energy than during the control lunch (88% more), whereas super-taster women consumed 198+71 kcal more energy than during the control lunch (38% more). Neither fat intake nor selection of high-fat foods differed between groups. These data suggest that non-taster women consume more energy from a buffet meal than super-taster women, but not more fat. Increased responsiveness to a variety of energy-dense foods could be one mechanism contributing to increased energy intake and greater adiposity in non-taster women.

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: PROP Sensitivity --> Food Perception -->Preference --> Selection. Robust associations between PROP status and taste perceptions have been well documented. However, subsequent links to food preferences and diet selection have been more difficult to demonstrate. This is not surprising given the complexity of human ingestive behavior that is influenced by numerous factors including health attitudes, personality traits, and cultural norms. Our laboratory has been using PROP screening to investigate individual differences in the selection of bitter foods, especially bitter tasting vegetables and fruits that may have long-term health implications. This chapter will discuss new and recent findings addressing the following issues: 1) whether PROP-related differences in perception of bitter compounds predict the perception and liking of bitter foods; 2) the role of bitter taste modifiers; and 3) the influence of personal characteristics such as food attitudes and cultural background on PROP-related food preferences.

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.