Genetic Taste Factors

The term “taste genetics” refers to variations in basic taste responses that can be directly associated with variations in the human genome. While there is substantial variance across humans in response to all the basic tastes (sweet, salty, bitter, sour, and umami or savory taste), the genetic ability to taste bitter compounds like phenylthiocarbamide (PTC) and 6-n-propythiouracil (PROP), which share a thioruea chemical moiety (N-C=S), is the most widely studied. Genetic variations in the ability to taste these compounds were discovered in 1931 by a chemist named A. L. Fox. When some of the PTC he was synthesizing dispersed into the air, his colleague detected a strong bitter sensation while Fox detected nothing. In response to this accidental discovery, Fox collaborated with his colleague, A. F. Blakeslee, to test this finding on larger groups of related and unrelated individuals. They concluded that about 65 to 70 percent of participants find PTC crystals to taste extremely bitter (“tasters”), while between 30 to 35 percent detect no taste from the crystals (“nontasters”).

It is now known that there are large variations in the breakdown of tasters and nontasters, depending on geographic location. In general, northern Europe has a higher percentage of nontasters (about 30 percent), while some parts of sub-Saharan Africa [Page 326]have the lowest (less than 2 percent). From an evolutionary standpoint, the ability to taste bitter compounds is advantageous in that it helps individuals avoid the consumption of potentially toxic plants. The fact that the inability to taste the bitterness in PROP and PTC has remained as high as 30 percent in some populations is of particular interest, particularly because it does not appear to have obvious genetic advantages. Presently (2007), numerous internet publications and news media reports have publicized the phenomenon of tasters and nontasters, and health researchers continue to be intrigued as to why this variation in taste remains in the human population.

Inherited variations in response to PTC and PROP are associated with food preferences, diet, and possibly risk for chronic diseases such as obesity and cancer. The first studies to report this relationship did so in the 1960s, from the laboratory of Roland Fischer. Instead of using PTC, Fischer began using PROP, a related compound that has less of a sulfuric odor than PTC. Currently, most studies use PROP, although a few laboratories still use PTC because it has a more direct relationship to the genetic sequence that confers this trait. Fischer used questionnaires to determine that in general, PROP tasters have more food dislikes than nontasters. He also noted that tasters tended to be more “slender” and hypothesized that this was attributable to their having more food dislikes than nontasters.

From the time of these early discoveries, many advances have been made in the field of taste genetics. It is now evident that the ability to taste PTC and/or PROP is associated with the perception a variety of other basic tastes. For example, PTC/PROP tasters also perceive greater bitterness from caffeine and sweetness from the taste of sucrose. These general differences in taste perception between tasters and nontasters may be a result of differences in the number of taste buds (papillae) between the two groups. Tasters have more taste papillae, the anatomical structures that hold the taste cells that are responsible for detecting basic tastes. Because of this anatomical difference, tasters perceive greater taste sensations from many basic tastes compared to nontasters. Moreover, these differences in basic taste perception are also likely to affect food preferences between the two groups. Studies have noted that tasters tend to dislike foods that are bitter or hot, like green leafy vegetables and hot peppers. On the other hand, nontasters have demonstrated higher preferences for some high-fat foods. It is important to note that despite genetic differences, food preferences are complicated behaviors, influenced by a broad array of biological and environmental factors. Thus, influences due to PTC/PROP sensitivity are often masked by other more salient factors.

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