The research, published in Chemical Senses, reported that the 25 human bitter receptors and their respective genes (known as taste receptors, type 2’s or TAS2Rs) have higher than expected levels of genetic variation, which may influence response to bitter compounds in the food supply.
Such genetic variation may affect dietary choices, such as whether we eat enough vegetables, drink alcoholic beverages or enjoy citrus fruits, suggested the researchers from Penn State's College of Agricultural Sciences.
“Just like some people are colour blind, some people are taste blind and simply can't taste bitter things that others can,” said John Hayes, assistant professor of food science at Penn State.
“This study moves us beyond the one-size-fits-all approach,” said Hayes. “It turns out that different bitter foods act through different receptors, and people can be high or low responders for one but not another. Thus, you may despise grapefruit but have no problem with black coffee.”
Bitter tastes are mediated by a family of 25 TAS2Rs. The receptors are identified by number, based on either their ability to taste certain bitter ligands or by the structure of the receptor itself.
“It seems each one is tuned to pick up a different group of chemicals,” explained Hayes.
The receptors are expressed on the tongue, where they act synergistically to sense bitter taste. However, the amount of individual variation in receptor expression, and how this may impact taste perception, remains unknown.
Previous studies have shown that variations in sensing bitter taste influence people's diet choices, and subsequently their health. For example, Hayes noted that research has shown people who are more sensitive to bitterness eat 25 per cent fewer vegetables, and as a result are at greater risk for colon cancer.
The new study tested for associations between TAS2R variants and sensations, liking, or intake of bitter beverages among healthy adults.
Hayes and his colleagues tested approximately 100 healthy adults. They tasted and carefully rated the bitterness of grapefruit juice, alcohol (Scotch whiskey) and espresso coffee and provided detailed diet histories and DNA samples.
The researchers confirmed that TAS2R polymorphisms “appear to influence the sensations, liking, or intake of common and nutritionally significant beverages.”
For example, the Penn State researchers observed that variations at a TAS2R19 single nucleotide polymorphism (SNP) were associated with increased bitterness and decreased liking of grapefruit juice.
“Bitter tastes are sensed through different pathways …this doesn't affect just bitterness. Since bitter and sweet are in opposition in the brain, if you experience more bitterness from a food, you also perceive less sweetness. This means not all foods taste the same to all people,” said Hayes.
The researchers explained that they hope to use bitter-taste research as a springboard to a better understanding of other aspects of food perception.
“Bitterness is only one example of genetic differences that may alter sensations from food and influence liking … Our team also is interested in differences in sweetness perceptions,” said Hayes.
“We also are focusing on the burning sensations you get from spicy foods,” he added.
While the study did not measure fussy eating, Hayes also contended that the results of the study may provide new insights into pickiness.
“Some people may not be acting whiny when they say they don't like certain foods - they actually experience those foods differently,” he said.
Source: Chemical Senses
Volume36, Issue3, Pages 311-31, doi: 10.1093/chemse/bjq132
“Allelic Variation in TAS2R Bitter Receptor Genes Associates with Variation in Sensations from and Ingestive Behaviors toward Common Bitter Beverages in Adults”
Authors: J.E. Hayes, M.R. Wallace, V.S. Knopik, D.M. Herbstman, L.M. Bartoshuk, V.B. Duffy