Bitter is better

How bitterness established the genetics of taste and supertasters came to rule taste research

Bitter is better
How we perceive taste is based on our genetics, as well as our culture [Image Credit: iStockPhoto]
By | Posted January 18, 2013
Posted in: Life Science
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In 1931, a DuPont chemist named Arthur Fox was pouring phenylthiocarbamide, a whitish powder, into a bottle when he accidentally let some of it get airborne. Another chemist in the room, C.R. Noller, complained loudly about a bitterness in the air, which gave Fox pause, since he didn’t taste anything. Puzzled, he did what any curious scientist would do: take a lick.

The substance was still tasteless, Fox declared. Noller, not to be outdone, did the same and found it even more bitter than before. This moment of curiosity led to an experiment in which Fox, as he recounted in the Proceedings of the National Academy of Sciences, observed that “men, women, elderly persons, children… Chinese, Germans and Italians were all shown to have in their ranks both tasters and non-tasters.”

Fox’s experiment launched the study of taste, and also gave geneticists a way to test dominant and recessive traits in humans. Taste turned out to be a useful tool to study inheritance, and by the time the genetic basis for tasting phenylthiocarbamide had been established, it was considered robust enough to be used as a paternity test. Tasting bitter flavors has since been linked to a group of genes that produces bitter-sensitive receptors in taste buds. A single receptor gene controls the ability to taste both phenylthiocarbamide and propylthiouracil, or, PROP – a similar chemical used more often in taste research because it is less toxic.

But toxicity may be the key to why humans evolved to perceive bitter tastes. Chemicals like PROP can cause thyroid problems and toxic alkaloids found in poisonous plants often taste bitter, so the sense to avoid ingesting plants that produce these toxins might confer an evolutionary advantage. In humans, there are generally two versions of this receptor gene, one that confers the ability to taste bitter and one that doesn’t.

The Supertaster Era

Though scientists have studied taste for decades, recently their focus has turned to a special group within the bitter tasting population: “supertasters.” Psychologist Linda Bartoshuk of the University of Florida coined the term in 1991, referring to any individual who experiences intense taste sensations. Sugar can be sweeter; hot peppers, spicier; salt, saltier; and anything bitter, excessively so.

There appears to be a genetic component behind the trait, since supertasters almost always find PROP to be extremely bitter and usually carry two copies of the PROP tasting gene, rather than one or none. Compared to the normal taster or non-taster, their tongues often have more fungiform papillae, which are structures that hold taste buds. The combination of PROP tasting genes, how strongly they are expressed, and the number of fungiform papillae seem to be able to account for the continuum of bitter tasters seen in humans: from non-tasters to the most extreme supertasters. Also, trait inheritance and genetic variance seem to explain why roughly 25 percent of people are supertasters and why certain groups have more supertasters than others. Though genetics can help determine how people taste, what foods people actually like is also determined by culture and experience.

Much of today’s taste research looks at how the physical world of chemicals and receptors relates to perception in the brain – in essence, how genes influence experience and even behavior. How you taste largely determines what you like to eat, and what you eat is an important factor in health. Supertasters can be a bit of an enigma, as their notoriously picky eating habits are often both healthy and unhealthy. An added burn from alcohol often discourages them from heavy drinking and the bitter taste of tobacco keeps them from smoking. Though they tend to avoid fatty and salty foods, they also commonly dislike many vegetables, especially kale and brussels sprouts, finding them to be excessively bitter. These preferences have observable consequences – a lower risk for diseases associated with smoking and drinking, but a higher risk of colon cancer.

The Misunderstood Supertaster

Though supertasters have extraordinary taste perception, it’s no super power. Bartoshuk says she somewhat regrets her choice of wording, because it is simply another way to experience the world.

Some even find it to be a curse, rather than a blessing. While volunteering at an exhibit on food and taste at the American Museum of Natural History in New York City, Susan Koestler found out she perceived PROP to be extremely bitter. Her sense of taste can cause her problems when she hosts dinner parties. “So many of the spices I really don’t like, but my friends do,” she says.

The supertaster’s burden may be partly explained by an observation Bartoshuk and her colleagues made. On average, when supertasters are asked how much pleasure they get from their favorite foods and displeasure they get from their least favorite foods, they are significantly more likely to rate at the extremes. Their pleasure world is simply different.

Despite many commonalities, Bartoshuk stresses that, as with any human experience, there is no universal supertaster. “The primary determinant for liking or disliking food is experience,” she says, “you can’t discount experience in developing taste.”

Posted in: Life Science

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