Bitter taste and diet: The exploration of the associations between phenylthiocarbamide (TAS2R38) gene polymorphisms with dietary intake, diet-related phenotypes, and smoking behavior

In animals, bitter taste sensitivity serves as a primary defense against ingestion of toxic compounds in foods. For modern humans, the role of bitter taste perception for the avoidance of noxious food is less important. However, it is thought that individual differences to bitter taste sensitivity may influence health outcomes through its effect on dietary behaviors. In this regard, sensitivity to the bitter compounds phenylthiocarbamide (PTC) and propylthiouracil (PROP) has been used as a marker to investigate the role of bitter taste on perception and preferences of bitter foods. Three single nucleotide polymorphisms in taste receptor type 2 member 38 (TAS2R38 ) was shown to explain 55-85% of the variability of PTC sensitivity. In this thesis, we explored the association of TAS2R38 gene with measures of dietary intake, diet-related phenotypes, smoking and drinking behavior in the Singapore National Health Study and the Framingham Offspring Population.; In the Singapore population, non-tasters and medium tasters were more likely to have metabolic syndrome compared to tasters. In the Chinese, TAS2R38 haplotypes was associated with vegetable intake, metabolic syndrome, waist circumference, and smoking. Compared with the taster subjects, the non-tasters and medium tasters were less likely to consume the recommended servings of daily vegetables, to have higher waist circumference, more likely to have metabolic syndrome, and to smoke. In the Indians, medium tasters were more likely to have metabolic syndrome and non-tasters were consuming more vegetables compared with the tasters. In the Malay, no significant associations were observed with any of the parameters examined. These data provide supportive evidence that TAS2R38 has an influence on vegetable intake and may be a potential marker for personalize dietary recommendations to prevent the development of disease such as metabolic syndrome.; In the Framingham population there was a significant association with total vegetable intake where non-tasters and medium tasters were less likely to be in the higher quintiles of intake compared to tasters. Similar associations were observed for the non-cruciferous vegetables but not the cruciferous vegetables. For the non-cruciferous vegetables, non-tasters and medium tasters were less likely to be in the higher quintile of intake compared with the tasters. TAS2R38 haplotypes were associated with total cholesterol and LDL cholesterol where tasters had higher concentrations compared with medium tasters, and non-significantly with non-tasters. There were no significant associations with smoking and drinking behaviors. However among smokers, tasters smoked fewer cigarettes compared to non-tasters. These results are inconsistent with the current knowledge of PTC sensitivity with vegetable preferences.; The results from the two population studies show some associations between TAS2R38 haplotypes and measures of dietary intake, diet-related phenotype, and smoking habits. However, there are inconsistencies in the associations both within and between populations indicating that TAS2R38 is not a consistent marker for these phenotypes in these populations. Therefore this thesis refutes the hypothesis that PTC sensitivity has a major influence on health outcomes through its effect on dietary behaviors in humans.