First Bite: How We Learn to Eat Page 5

  Ninety years after Davis’s experiment, the view that likes are predominantly innate—or genetic—looks shaky. When trying to get to the bottom of where tastes come from, scientists have often turned to twins. If identical twins share more food likes than nonidentical twins, the chances are that there is a genetic cause. Twin studies suggest that many aspects of eating are indeed somewhat heritable. Body composition—measured as body mass index, or BMI—appears to be highly heritable in both boys and girls. So is dietary “restraint,” or the mysterious urge to resist eating the thing you want to eat. But studies that look at likes and dislikes are much less conclusive. Several twin studies have suggested that identical twins are more likely to enjoy the same protein foods than nonidentical twins, but when it came to snacks, dairy, and starchy foods, their likes were only marginally more similar than those of the nonidentical twins. Overall, the evidence for tastes being heritable is very modest, accounting for only around 20 percent—at most—of the variation in foods eaten.

  Genes are only ever part of the explanation for what we choose to eat. As one senior doctor working with obese children put it to me, you could be cursed with all the genes that make a person susceptible to heart disease and obesity and still grow up healthy, by establishing balanced food habits. “All of it is reversible,” he said. Parents and children resemble each other no more in the foods they like than couples do, suggesting that nurture—whom you eat with—is more powerful than nature in determining food habits. Whatever our innate dispositions, our experience with food can override them. Maybe the reason you share your parent’s hatred of celery is that you have seen them recoil from it at the dinner table. Researchers found that when they gave three groups of preschool children different varieties of tofu—one group had plain tofu, one ate it with sugar, and one with salt—they quickly came to prefer whichever one they had been exposed to, regardless of their genes. It turns out that, so far from being born with genetically predetermined tastes, our responses to food are remarkably open to influence, and remain so throughout our lives.

  If you want to know what foods a person does and does not like, the single most important question you can ask is not “What are your genes?” but rather “Where are you from?” Had he lived in a part of the world where cornflakes are hard to come by, the cornflake boy would have had to find another way to annoy his parents. To a large extent, children eat—and therefore like—what’s in front of them, particularly in conditions of scarcity. “If you want your children to be less fussy about what they eat,” a friend who had fallen on hard times during the recession advised me, “I can recommend poverty.” It’s not really an option to be picky about the staple food of rice if you live in rural China.

  Genes do make a difference—to the foods we like, the way we taste them, and even how much we enjoy eating—but they turn out to be much less significant than the environment in which we learn to eat those foods. Contrary to our deepest beliefs about ourselves and our children, our likes and dislikes—the important ones, anyway, such as whether we eat enough vegetables or how much variety and balance we have in our diets—are much more about nurture than nature. Apart from changing the infants’ food environment, there was another, bigger trick to Davis’s experiment that she did not mention, perhaps because it is so obvious. She radically changed the children’s social experience when eating, removing all extraneous social influence. In place of the hubbub of the family dinner table, the babies had only expressionless nurses who “might not comment” in any way on their choices. The thought of being served in this silent, impassive way is creepy, particularly for the oldest children, who must have been as old as five by the time they left the orphanage. They ate without anyone caring what they ate, without any siblings fighting them for the last slice of pineapple, without any surrounding ideas about cuisine.

  Davis was mistaken if she thought this was the way to discover the true nature of children’s appetites. Though the nutritional outcomes were excellent, it was a not-quite-human way to eat, and one that no child in a real situation will ever replicate. We cannot arrive at the truth about appetite by removing all social influences. Appetite is a profoundly social impulse. To a large extent, our likes and dislikes are a response to the environment we eat in. From our first toothless tastes, we are picking up cues about which foods are desirable, and which are disgusting, which, sadly, are so often the very ones the grown-ups most want us to eat.

  The public discussion of eating habits is focused on temptation and the idea of resisting desirable foods. But if we look at eating through the eyes of a child, we see that disgust may be even more powerful than desire in forming our tastes. Our urge to avoid eating something that makes us feel sick is often at the root of disordered eating, as we swerve away from whole categories of foods that we imagine would make us feel queasy. The most common reason for disgust is nausea: anything eaten just before a bout of stomach bug may be hated for life. Psychologist Paul Rozin, the world’s leading expert on disgust, has argued that a central feature of disgust is “contagion: when a disgusting food touches otherwise acceptable foods, it renders them permanently inedible.” And yet most of the foods that we happen to find disgusting are not toxins but perfectly edible and wholesome foods. Brussels sprouts, for example.

  If there is one food associated with personal dislikes in the Anglo-Saxon world, it is the Brussels sprout. Many people assume they have no choice in this matter—they just can’t stand them. Are they right? In an article singing the praises of Brussels sprouts, the great chef Yotam Ottolenghi noted that there was a “genetic explanation for why people either love or loathe” these little green brassicas. Ottolenghi argued that being a sprout hater was likely a consequence of having a certain gene—TAS2R38—which “makes a protein that reacts with a chemical called PTC to create the sensation of bitterness.” Could this really be true? Is there a molecular basis to our hatred—or otherwise—of green vegetables?

  Some people definitely taste certain flavors more acutely than others. To take one of the stranger examples, up to 30 percent of the population cannot physically pick up on androstenone, one of the key aromas that make truffles such a luxury. If you served them a plate of sumptuous pappardelle with truffle shavings, they would have no idea why it was meant to cause such joy. A different minority has a heightened sensitivity to coriander leaf, making it taste soapy and gross, rather than herbal and fresh. And as Ottolenghi says, we vary hugely in our response to bitter tastes. All babies find bitterness somewhat horrible, which is probably a survival mechanism, given that in the wild, toxic substances tend to be bitter. The bitter response of a newborn includes arched lips, a protruding tongue, an expression of anger, and spitting: all pretty vivid signs that babies do not consider bitterness to be yummy. Over time, however, it is possible to learn to love bitter substances: witness the fact that the world’s two most popular beverages are coffee and beer.

  Some learn to love bitterness; some tolerate it because they enjoy the buzz they get from a bottle of IPA or a cup of strong French press coffee; and some hardly taste it at all. Psychologist Linda Bartoshuk of Yale University was the first to use the term “supertaster” in the mid-1990s to refer to individuals with a heightened response to certain tastes, predominantly bitter ones (the phenomenon was first observed in the 1930s). Bartoshuk and colleagues found that there were significant genetic differences in the way we perceive bitterness. PROP (6-n-propylthiouracil) and PTC (phenylthioucarbamide) are chemical substances that either taste incredibly bitter or slightly bitter or of nothing at all, depending on whether you have the gene to taste them. Around half of us are medium tasters, a quarter are nontasters, and another quarter are supertasters. Women are more likely to be supertasters than men. Bartoshuk has shown that PROP supertasters have more taste buds on their tongues than nontasters. There’s a very simple way to self-diagnose whether you are a supertaster. Swab your tongue with a little blue food dye and place a hole-punch reinforcer ring on
your tongue. Count how many pink bumps you can see inside the ring—these are the fungiform papillae, each containing three to five taste buds. If you have fewer than fifteen, you are a nontaster. If you have fifteen to thirty-five, you are a medium taster. If you can count more than thirty-five inside the ring, you are a supertaster.

  Psychologists got excited about the concept of PROP tasting, because it seemed to hold out—at last—the genetic key to likes and dislikes. Could bitter sensitivity be the secret to why some people eat unhealthy diets with few or no vegetables? Is it because they lack a gene for sprouts? The world of flavor must be a very different place to PROP supertasters and nontasters, and it would appear obvious that this would translate into food habits. When seventy-one women and thirty-nine men were asked to taste asparagus, kale, and Brussels sprouts, the PROP supertasters did indeed find the vegetables to be more bitter and less sweet.

  The surprising thing, however, is that, from a mass of research into PROP tasting, very little does point to genes determining food choices, either in children or adults. Over time, your PROP status is not a particularly strong predictor of what your likes and dislikes will be. If anything, PROP nontasters—the ones who can’t taste bitterness in the sprouts at all—are slightly more at risk of an unhealthy diet and weight than the PROP supertasters.

  There’s clear evidence that PROP supertasters are more sensitive to certain flavors than medium tasters: the burn of chili, the warmth of cinnamon, the acrid glow of coffee, the rasp of alcohol, the aftertaste of sweeteners and grapefruit—all of these are perceived more strongly, often unpleasantly so. What is not so predictable is how this affects preferences. Given that supertasters perceive alcoholic drinks as more bitter, you’d expect them to drink less of them—indeed, being a nontaster has been identified in some studies (though not others) as a risk factor for alcoholism: if whiskey tasted like water, how easily it might go down. But a study of young adults found that being a PROP taster did not predict how much beer was drunk. After decades of enjoying countless glasses of wine from all the great terroirs in the world, the leading wine writer Jancis Robinson found out that she was a supertaster, something which in theory should make wine taste odiously acrid to her. That’s not how it turned out. As she put it, “if I enjoy wine less than the rest of you, you are very lucky wine drinkers indeed.”

  When it comes to childhood, the key question is whether being a PROP taster sets you up for a lifetime of disliking the leafy green vegetables every nutritionist wants us to eat more of. Greens—especially those in the cabbage family—contain bitter-tasting glucosinolate compounds. One study suggested that PROP-tasting children were more likely to dislike raw broccoli, but not cooked broccoli. Another study found that when offered black olives, cucumber, and raw broccoli, PROP-nontaster children ate a larger quantity than tasters did. But when studies have looked at actual preferences rather than what children are prepared to eat in front of researchers, the signs are that PROP tasting in no way dooms you to dislike bitter vegetables. When 525 Irish children (aged seven to thirteen) were asked to record their intake and liking of cabbage, cauliflower, Brussels sprouts, and broccoli over a three-day period, there were few significant differences between tasters and nontasters. The supertasters did show a marginally lower liking for Brussels sprouts, and nontasters liked cauliflower the most. But when their consumption of bitter vegetables overall was totaled up and averaged out, there were no differences in intake for PROP tasters and nontasters. In this study, being a PROP taster mattered less than the simple fact of whether these Irish children were boys or girls: girls tended to like bitter vegetables more, or at least to be polite enough to pretend that they did.

  A 2013 survey of college students pointed to a similar conclusion. The supertasters and the nontasters showed no marked difference in likes and dislikes for a list of foods including Brussels sprouts, broccoli, cabbage, spinach, crushed red pepper, jalapeno peppers, red wine, beer, salad dressing, and mayonnaise. The only substances that emerged as having significant negative connotations for PROP tasters were dark chocolate, coffee, and chili: the dark, pungent end of the bitter flavor spectrum. The team of researchers concluded that environment mattered more than genes in determining preference. In America, they noted, many people “know they are not going to like spinach, tofu, liver or ‘healthy food’ and learn that fast food burgers, soda pop and sweet breakfast cereals are delicious . . . before they ever take a bite.”

  Some of the most telling research to date on PROP tasters looked at how genes interacted with the food environment of children. The study confirmed that household income and access to good food were more critical in forming tastes than being a supertaster. Over the five years from 2005 to 2010, researchers studied 120 New York children aged four to six. Their PROP status was measured, and each child was deemed to be living in either a “healthy food environment” or an “unhealthy food environment,” as judged by the slightly crude method of dividing the number of healthy food sellers by the number of unhealthy food sellers within a half-mile radius of where the child lived. In a healthy food environment, likes and dislikes followed the pattern that Ottolenghi—and common sense—would suggest. In this experiment, unlike the Irish one mentioned above, the PROP nontaster children, who couldn’t detect bitterness, did indeed show a higher acceptance of vegetables—with fewer dislikes—than taster children in the same healthy environment. The interesting—and troubling—thing was what happened to the children in the unhealthy food environment. Here, the likes and dislikes of tasters and nontasters were not very different. The big difference was in the BMI of the children. In the unhealthy environment, the nontaster children had higher BMIs than any of the other groups studied. Their average BMI score was over 1.6, which counts as obese.

  What matters most for determining whether your tastes will be healthy ones is not whether you have a sprout-hating gene, but how your genetic predispositions interact with your food environment. Once environment is taken into account, being a nontaster poses bigger health risks in our current state of plenty and junk than being a supertaster. Several studies have now found that nontasters—adults as well as children—are the ones who tend to have higher BMIs. The theory is that nontasters—since they do not experience certain flavors with the same intensity—are more responsive to the influences around them, for good or ill. They learn their likes more easily than supertasters. In a healthy food environment, they will easily acquire healthy tastes. When offered vegetables, they are less likely than supertasters to dismiss them as too bitter. But if they learn to love the wrong foods, the nontasters can find themselves—like those New York children—obese by the age of six.

  So, no, you can’t blame your dislike of sprouts simply on having a faulty gene. If everyone’s first nibble of sprouts was of Ottolenghi’s own sprouts with caramelized garlic and lemon peel, charred in a hot pan until sweetly blackened at the edges, maybe they would be the most popular of all the vegetables. Perhaps your parents were sprout-haters and—without meaning to—turned you against them. Or perhaps they forced them on you too vehemently. I know someone—a PROP supertaster, as it happens—who says she can never enjoy Brussels sprouts—though she has no quarrel with broccoli—because of memories of Christmas Day, when she was compelled by her parents to cut each hated sprout into quarters, and swallow them unchewed, like bitter pills. Maybe you never actually tasted sprouts because you “knew” you wouldn’t like them, because in our society the child who loves sprouts is considered a little odd. When the food writer Michele Humes arrived in the United States from Hong Kong, it took her a while to get her head around the concept that “children weren’t supposed to like vegetables.”

  Likes and dislikes cannot be reduced to molecules and genes. This is bad news for the more sensationalist health pages, which thrive off headlines like “Revealed: The Obesity Gene.” For the rest of us, it is—potentially—excellent information. It means that our food habits are not final and fixed, but
adaptable and open, if only we will give ourselves half a chance. We did not come into the world disliking bitter greens; we were taught to dislike them by our environment. Taste may be identity, but it is not destiny. The hope—and admittedly, it’s a slim one at present for the children whose dislikes are vegetables and whose likes are all junk—is that while we are stuck with our genes, the environment is something that can change.

  The main way we learn to like foods is simply by trying them. The term “mere exposure” was coined by Robert Zajonc in 1968. Zajonc’s thesis was that affection is triggered by familiarity; and that disliking, conversely, is fear of the novel. Some of Zajonc’s early experiments involved showing subjects complex shapes for very short periods of time. When the subjects were later asked to choose their favorite shapes from a lineup, there was a marked preference for the shapes they had already encountered. Zajonc has suggested that there are similar forces at work when we favor Brie over Camembert. These cravings are a function of prior experience. One or other cheese may trigger a recognition in us that we cannot necessarily put into words. Zajonc later observed this phenomenon of “mere exposure” at work across cultures and species.

  It’s a truism that we know what we like and we like what we know. If you ask young children which foods they most detest, they tend to be the ones they have never actually tasted, often vegetables. To an adult, this sounds crazy: you can’t know if you hate something until you have tasted it. “Go on—you might like it!” I find myself urging, ineffectually, at the dinner table. But to a child, there is nothing paradoxical in saying: “I don’t like it—I never tried it!” The foods that ranked highly on the “never tried” list of a group of 70 American eight-year-olds included avocado (49/70 had never tried it), beets (48), prunes (43), collard greens (49), rye bread (43), lima beans (39), radishes (38), and fried liver (55).