Why I Had My Sense of Flavor Genotyped

W.W. Norton & Company, April 2017 As soon as I decided to write a book on the science of flavor, I knew I wanted to have myself genotyped. Every one of us, I learned through my preliminary research for Flavor: The Science of Our Most Neglected Sense, probably has a unique set of genes for taste and odor receptors. So each person lives in their own flavor world. I wanted to know what my genes said about my own world. Sure enough, there was a lesson there—but not the one I expected. Our senses of smell and taste detect chemicals in the environment as they bind to receptors on the olfactory epithelium in the nose or on taste buds studding the mouth. From these two inputs, plus a few others, the brain assembles the compound perception we call flavor. Taste is pretty simple: basically, one receptor type each for sweet, sour, salty, and the savory taste called umami, and a family of maybe 20 or more bitter receptors, each of which is sensitive to different chemicals. Smell, on the other hand, relies on more than 400 different odor receptor types, the largest gene family in the human genome. Variation in any of these genes—and, probably, many other genes that affect the pathways involved in taste or smell—should affect how we perceive the flavors of what we eat and drink. Hence the genotyping. One April morning a few years ago, I drooled into a vial and sent that DNA sample off to the Monell Chemical Senses Center in Philadelphia, home to what is likely the world’s biggest research group dedicated to the basic science of flavor. A few months later, I visited Monell to take a panel of perceptual tests and compare the results to my genetic profile. I had already learned that I’m a so-called supertaster from another researcher, who had offered that conclusion after counting the taste-bud-bearing fungiform papillae on my tongue. “Supertaster” is an often-misused term for someone who is acutely sensitive to bitter tastes, and probably other ones as well. Despite the “super,” it’s generally not something to be proud of—because their taste sensations are so intense, supertasters often confine themselves to narrow, bland diets. But not me. I love all sorts of intense, bitter foods: black coffee, highly hopped beers, bitter green vegetables like broccoli rabe and collard greens. My genotype yielded equally puzzling results. My version of the sweet-receptor gene is less responsive than normal, which should make me prefer sweeter food and drinks to get the same flavor bang. And sure enough, on the perceptual tests I’d rated a 12 percent sugar solution as highly pleasant, while many people find it far too sweet. But that doesn’t match my eating habits: I’m generally indifferent to dessert, and I detest sweetened coffee or tea. The picture wasn’t any clearer for the few odor-receptor genes I was tested for. Most of the time, my ratings of the pleasantness and intensity of odors like earthy 2-ethylfenchol or sweaty isovaleric acid aligned poorly with the predictions based on my genes for the relevant odor receptors. So why don’t my genes match my culinary preferences? The reason, probably, is that nurture matters at least as much as nature in molding anyone’s flavor destiny. Like many people, I’ve learned to like my coffee unsweetened, and that main courses are more interesting than desserts. We’re also good at learning to link flavors to consequences. We associate coffee’s bitterness with the wake-up jolt of caffeine it delivers, so what was once a warning—bitterness—becomes a beacon. And we pair the taste of beer or gin and tonic with the pleasure we get from an evening out with friends. With associations like that, it’s no wonder so many of us love what are, objectively speaking, such nasty, bitter flavors. Bob Holmes is a correspondent for New Scientist. Read an excerpt of Flavor: The Science of Our Most Neglected Sense.