by Bob Holmes
As we’ve seen, a few of our flavor preferences are clearly innate. Even newborn babies like sweet tastes—and they have to, otherwise they might not latch on to the mother’s breast and feed. And those same babies naturally reject bitter tastes, which are often an indication that something is toxic. Once past those few simple cues, though, our flavor preferences are wide open. Each of us has to decide which potential foods we will eat and which ones we will shun. A panda doesn’t have to learn this—it eats only bamboo. A lynx eats rabbits. An anteater eats ants. But people are different: as omnivores, we have to learn the flavors that mark the foods we eat.
That learning starts before birth, as flavor molecules from foods eaten by a pregnant mother pass into the amniotic fluid and are ingested by the developing fetus. In essence, the fetus samples what the mother eats—and, later on, recognizes and likes those flavors. Nursing infants get the same chance to sample mom’s diet through breast milk. The best demonstration of this early learning comes from Julie Mennella at Monell. Mennella asked one group of pregnant women to drink a glass of carrot juice at least four days a week during the last trimester of their pregnancy. Another group drank the carrot juice not during pregnancy but while nursing their infants, while a third group never drank carrot juice. Later, after the infants had begun to try solid food, Mennella watched as they got their first taste of carrot-flavored baby food. Most babies make scrunchy faces when they taste something new, but the babies who tasted carrots in utero or while nursing made fewer expressions of distaste than babies whose mothers had avoided carrot juice during pregnancy. The carroty babies’ mothers also thought they enjoyed the carrot-flavored cereal more. In short, the babies who’d experienced carrot through their mother were more comfortable with the flavor when they first encountered it directly.
And it’s not just carrots. Over and over again, researchers have shown that babies who are exposed to flavors ranging from anise to garlic through the mother’s diet prefer those foods when they first encounter them directly. In short, we learn to like what our mothers eat. “It’s a really beautiful system,” says Mennella. “For the baby to learn to like a food, the mother has to eat it. You can’t pretend to eat it, because the flavors don’t get in.”
Those early, learned preferences can linger for many years. In Germany, for example, almost all infant formula used to be flavored with vanilla. Many years after the practice had stopped, researchers took advantage of this natural experiment by comparing taste preferences of children who were infants just before the change—and who therefore almost certainly drank vanilla-laced formula—with those born just a few years later who drank vanilla-free formula. Sure enough, the children who had tasted vanilla as infants liked it better, years later, than those who hadn’t.
The odd bit of vanilla flavoring notwithstanding, formula-fed infants don’t get the same exposure to the flavors of foods their mother eats. Instead, they get exactly the same set of flavors with every bottle, unless the parents switch brands now and then. A formula-fed infant, then, arrives at weaning with little or no experience of the flavors he or she will soon experience firsthand. That’s especially true of infants who feed on cow milk formula or soy-based formula, which tend to be sweet and bland. In contrast, formulas made of hydrolyzed protein have bitter and sour flavor notes, so that infants who drink them get some familiarity with those “difficult” tastes. That familiarity helps those babies—like their breast-fed neighbors—be more accepting of vegetable flavors when they eat their first solid food, Mennella finds.
There seems to be a window of opportunity during the first few months of life when babies will accept almost anything they’re given—even hydrolyzed protein formula, which most adults find nasty tasting. But even after weaning, toddlers and older children gradually learn to accept new foods if they try them often enough. Toddlers and young children tend to be wary of new flavors and will often reject a new food the first few times they sample it. After eight or ten tries, though, most kids will begin to accept it in their diet—although they’ll often continue making skeptical faces well after that. (Parents should ignore the faces and pay attention to what their child actually eats, Mennella says.) Simple variety seems to matter, too, so children who have the opportunity to sample many different foods are more likely to accept new flavors. And they learn by watching what their parents and older siblings eat.
The lesson for parents is very clear: Eat what you’d like your children to eat. “Children learn through repeated exposure, variety, and modelling. I don’t know what more I can say,” says Mennella. “It’s just the basic tenets of learning—and learning as a family. Foods identify what that family is. Eat the healthy foods that you enjoy and like. Offer them to your kids in a positive context. Kids will learn.”
Perhaps the most vivid demonstration that it’s easier to learn to like something if you grew up with it comes from the high Arctic. The Chukchi and Yupik people of the Bering Strait region traditionally lived on a diet of fish and walrus, and many favorite dishes involve burying meat, blood, and fat to ferment for months and become what the locals call “tastily rotten.” To someone who hasn’t grown up with the practice, such foods can be hard to take, even with all the open-minded goodwill in the world. Here’s how one anthropologist, eager to try indigenous foods, described her first encounter with aged walrus meat:
What a shock! The smell of the thoroughly aged meat permeated my senses. My only thought was that as a guest I should not be rude. I must finish this piece of meat. I chewed and chewed and chewed. . . . Finally [one of the hosts] said quietly, still smiling, “You know, Carol, you are turning green!”
Even among the Chukchi and Yupik themselves, their fondness for these foods depends on their childhood experiences. Elders raised on traditional diets generally love them and still go out of their way to eat them. However, a generation of children raised during the 1960s–1980s, when the Soviet government actively discouraged traditional foods, often struggle to eat these foods. Their aversion was so strong that many still refused to eat them even when they had little choice, after outside food became very scarce after the collapse of the Soviet Union. And anthropologists report that many young people today are happy to honor and spend time with their grandparents—but only if they can leave before dinnertime. Even those who now eat these tastily rotten foods sometimes do so wearing latex gloves to avoid the lingering aroma.
A few preferences, in contrast, don’t seem to be open to learning. Newborn babies suckle more and make happy faces when they have something sweet in their mouth. And there’s not much that parents can do to change that preference. Gary Beauchamp—the same flavor researcher I gargled with in the Monell boardroom—tried to get people used to eating less sugar. Decades earlier, Beauchamp had found that putting people on a reduced-salt diet for a few weeks shifted their tastes so that they preferred the less salty food over what they used to eat, which they now regarded as too salty. But when Beauchamp tried to do the same experiment for sweetness, he found that people didn’t respond the same way. After three months on a low-sugar diet, his test subjects preferred exactly the same sweetness of vanilla pudding or raspberry drink as people who ate their usual diet. To Beauchamp’s knowledge, no one else has tried a similar study, and he cautions against concluding too much from a single experiment. However, if he’s right—and if children respond the same way as adults—then parents might be able to relax a bit about sugar. “Every person on the face of the Earth, almost, believes that if you feed kids lots of sugar, they’re going to like it more. There’s no evidence of that,” he says. Nor does a sugar-free diet keep kids from craving sweetness. (Beauchamp recalls one child he tested whose parents were fanatical about avoiding processed sugar and other sweets. The kid told him that at school, he got his sweet fix by pulling used chewing gum off of chairs and chewing that.) Sweet is sweet, and it always tastes good—and there’s nothing parents can do about that.
In most societies today, the most pressing question a
bout food is how we can nudge people to eat less of it. As everyone knows, Americans have been gaining weight for decades, and more than two-thirds of American adults now weigh enough to be classified as overweight or obese. Europeans and even Chinese and Indians are now starting to join them. Worldwide, 39 percent of adults are overweight or obese, and overnutrition now kills more people each year than undernutrition.
Since this book is about flavor, we’re going to look at just one tiny piece of the puzzle: how the flavor of our food helps determine what we choose to eat and—more critically for weight control—how much of it we pack away. Even that little piece of the diet pie gets tricky. The first complication arises because we generally stop wanting something once we’ve had enough. The clearest illustration of this is the phenomenon of sensory-specific satiety that we touched on in the last chapter. The more you experience the flavors of a single food item during a meal, the less your brain’s reward system responds to the sensory input, no matter how many calories it packs. Even if you really like something, you enjoy it less with each bite.
This is a big reason why high-end chefs gravitate toward tasting menus that feature a long progression of tiny dishes. At Chicago’s Alinea restaurant, for example—generally rated among the world’s best—you can expect a meal of more than a dozen tiny courses, each consisting of just a few bites. The chef, Grant Achatz, learned much of his craft at the renowned French Laundry in California’s Napa Valley, another restaurant famous for serving a long succession of “small plates.” Here’s how Achatz’s mentor there, chef Thomas Keller, described why he does that:
Most chefs try to satisfy a customer’s hunger in a short time with one or two dishes. They begin with something great. The initial bite is fabulous. The second bite is great. But by the third bite—with many more to come—the flavors begin to deaden, and the diner loses interest.
The same principle applies to any meal. If your holiday meal consisted of nothing but mashed potatoes, you’d almost certainly eat a lot less than you do when you’ve also got turkey, stuffing, green beans, and brussels sprouts on your plate. Sensory-specific satiety kicks in within fifteen to twenty minutes after you start eating a food, so it may help turn off your appetite for what’s on your plate even before other satiety signals like stomach fullness kick in. (The effect wears off within an hour or so, so other satiety mechanisms must be more important in determining when we start thinking about eating again.)
Some people have suggested that more highly flavored foods might be better at inducing sensory-specific satiety. If so, people might be able to lose weight by maximizing the flavor per bite. For example, Edmund Rolls—who discovered sensory-specific satiety—notes that in most cultures, the staple foods, the ones that people eat the most of, tend to be relatively bland starches like rice, potatoes, or bread; the more highly flavored meats and vegetables usually take a smaller share of the plate. On the other hand, there’s only a little evidence to date to back the notion that maximizing flavor could keep us thinner.
Perhaps the clearest support comes from a recent Dutch study where researchers used plastic tubes threaded up the back of volunteers’ throats to deliver either a strong or a weak tomato soup aroma. Either way, the volunteers drank the same bland, flavorless soup, but they perceived it as either a richly flavored or mildly flavored tomato soup, depending on the intensity of the piped-in aroma. Sure enough, they ate about 9 percent less of the more highly flavored soup, as long as the more intense aromas were present more than fleetingly.
If sipping soup with a hose up your nose sounds unpleasant, just be thankful you didn’t end up in the experiment that some other young Dutch men volunteered for a few years ago. Researchers wanted to sort out whether we stop eating because our stomachs are full or because we’ve had enough flavor. To answer that question, they needed to separate chewing and flavor release from swallowing and filling the stomach. The way they did it wasn’t pretty.
If you’d been part of that experiment, you would have come in to the lab sometime after eating a normal breakfast, and a technician would have threaded a skinny stomach tube, thin enough to poke into the headphone jack on your phone, up your nostril, down the back of your throat, and into your stomach. After an hour of sitting around and filling out paperwork, you’d have been given a half pound of cake. You’d have been told to chew the cake normally, but then, just when you were about to swallow it, spit it out into a cup instead. Take another bite, chew and spit, over and over, for either one or eight minutes. When you were done, a technician—presumably the one who drew the short straw—collected the contents of the cup, dried them, and weighed them to make sure you hadn’t swallowed any cake on the sly. While you chewed, the stomach tube flavorlessly deposited into your stomach ninety-nine calories’ worth of the same cake, pureed in a blender with either a small amount of water (one hundred milliliters, which is around three ounces) or a larger, more belly-filling amount (eight hundred milliliters, around three cups). A half hour after all the spitting and pumping (and after the stomach tube was snaked out of your nose again), you would have been given a sandwich lunch and instructed to eat your fill.
Sounds miserable, all this chewing and spitting and slithering of tubes. And apparently, the study participants thought so, too. Of the forty-three young men who signed up for the job, eight walked away once they found out what was involved, even though they would have been paid for their time. Five were sent packing for failure to spit out all their cake, and four washed out for other reasons, leaving just twenty-six to finish the experiment.
After all that, it turned out that when it comes to satiating us, flavor in the mouth matters at least as much as fullness in the stomach. On the days when the volunteers spent eight minutes chewing and spitting out their cake, they later ate 10–14 percent less of their sandwiches than when they chewed and spat for just one minute or not at all. In contrast, their sandwich consumption barely went down at all on days when they had more fluid pumped into their stomachs.
In another, slightly less unpleasant experiment, the same researchers pumped tomato soup into people’s mouths, either as big squirts separated by twelve-second pauses, or a series of small squirts separated by three-second pauses. Either way, the eaters got the same amount of soup per minute, but they got less flavor from the big gulp, because they spent less time with soup in their mouths. Sure enough, when people got the little doses—hence the more flavor exposure—they ate less soup before deciding they were full.
All of this would seem to suggest that advocates of thorough chewing may have a point: The more you chew, the more you’re exposed to food flavors, and therefore the quicker satiety may set in. In one study, people felt fuller after eating pasta with a small spoon, dutifully chewing each mouthful twenty or thirty times, than when they used a large spoon and ate as quickly as they comfortably could. (Unfortunately, the science isn’t quite clear-cut yet—though the long chewers felt fuller, they didn’t actually eat any less of the pasta despite feeling more sated.) Even if you buy into the notion that chewing more means swallowing less, you don’t have to take this to fanatic extremes—as advocated, most notoriously, by Horace Fletcher early in the twentieth century, who sparked a brief fad for “Fletcherizing,” or chewing every mouthful hundreds of times. Instead, you may be able to achieve the same end without obsessing over chews by playing with texture. Foods that are thicker, chewier, or crunchier force eaters to take smaller bites and chew longer, which slows the eating rate and ups mouth time.
More to the point, liquids such as soft drinks, juices, and beer go down much more quickly than chew-and-swallow food—as much as ten times faster, according to some studies. We get less exposure to their flavor in the mouth, which may explain why we tend to overconsume liquid calories: They don’t trigger our internal calorie meter as strongly as calories from solid foods do. And in fact, people find identical amounts of soup more filling if they eat it from a spoon, slowly, than if they drink it from a mug more quickly.
&
nbsp; Of course, another way to experience more flavor from your food is simply to eat more flavorful food. No one knows whether tastier meals will make you feel full more quickly, though many of the experts I spoke to said they wouldn’t be surprised if that was the case. And a few experiments hint at the possibility. People take smaller bites of more highly flavored vanilla custard, for example, and they ate less of a saltier tomato soup than of a less salty one that they rated equally desirable.
It’s tempting to think that the immense variety of foods available today might contribute to overeating, because when sensory-specific satiety kicks in we can just switch to a different food. When obesity first appeared on the social issues radar, back in the 1970s, a lot of people worried that the root cause was our modern “cafeteria” diet, in which we’re constantly exposed to a huge variety of potential foods. With so much to choose from, people worried, we’d hop from one food to the next and end up eating too much. It rapidly became clear that variety, per se, was not the culprit. In the early 1980s, researchers at Monell bought commercial flavors in a dozen rat-friendly flavors. (In case you ever want to charm a rat, the flavors were peanut, bread, beef, chocolate, nacho cheese, cheese paste, chicken, cheddar cheese, bacon, salami, vanilla, and liver.) Then they fed the rats standard rat chow spiked either with the same one flavor over and over again, or else a constantly changing smorgasbord of varied flavors. If variety causes overconsumption, the latter rats should have blown up like happy little blimps.