Food: The Science of Scrumptious

Do we eat to live, or live, in part, to dig into that second helping of banana cream pie? Since the 1930s, nutritionists have believed in "the wisdom of the body," the idea that we are programmed to eat precisely what we need to keep our bodies supplied with the right balance of nutrients and energy. By that rationale, hungers for specific foods are just behavioral consequences of metabolic requirements. You crave steak because you need protein, scarf up sardines for the salt, and pig out on potatoes because they are energy-dense. It's simple: We like food because it keeps us alive.

But this straightforward idea just doesn't account for our eating habits. The foods we love tend to be either nutritionally bankrupt (Twinkies, French fries, Coke) or downright dangerous (bacon, cheesecake, scotch). Popeye notwithstanding, we generally loathe vitamin and energy powerhouses like spinach and liver.

The idea that eating is merely life support also doesn't explain our gastronomic trajectory. We begin life as newborns who drink only milk, become babies who happily gum any substance from beer to bugs, then grow into 4-year-olds who throw tantrums when faced with anything more complex than PB&J. As we reach adulthood, we just get stranger, loving foods any rational kid would find repulsive: the nasal cannonball of wasabi, a ripe raunchy slab of blue cheese.

In short, we're all weird about food. An anthropological analysis found that more than a third of us reject slippery food like oysters and okra. Twenty percent of us don't like our foods to touch on the plate. The next time you wander a grocery-store aisle packed with jars of pickled jalapeños and boxes of instant scalloped potatoes, consider this: One-fifth of us eat from a palate of just 10 or fewer foods.

The rich blend of instincts and habits that shape our eating patterns has baffled biologists. Although, new knowledge of the neurological highways that connect gut and brain, combined with psychophysical studies probing the perception of flavor, has shed light on the gourmand within. The study of "hedonics"—the pleasure of eating—has determined that we are hardwired to prefer sweet and avoid bitter and that the love of fat seems to be an acquired taste. The flavors we sample while we're still in the womb stay with us into infancy and perhaps well beyond. And, as anyone who has heard the call of a cream puff at 3 a.m. will not be surprised to hear, eating beloved foods stimulates some of the same neural pathways as addictive drugs like cocaine. Other research suggests that our stomachs may literally be thinking for us: A separate sensory system located in the gut sends subliminal messages to the brain about what's good to eat and what's not.

In this age of dietary obsessions and national guilt about fat, the joy of eating and the quirks of the palate are seldom discussed, a dirty little epicurean secret. But understanding what we like to eat, fascinating in its own right, may also help solve one of the biggest health problems of our time: why we eat so much.

If eating is our first love, sugar is its handmaiden. Humans are born loving sweetness: On its very first day of life, a newborn prefers sweetened drinks to bland ones. Sugar's siren call can even block out pain—pediatricians have shown that newborns who have injections or blood drawn don't mind the needle as much when also given a sugar-coated pacifier to suck.

Soon after birth, babies begin to reject intensely sour or bitter flavors. During the first few months, they also learn to appreciate fatty foods and recognize salty tastes. "Their taste world is organized into liking sweet, learning to like fat, and rejecting—spitting out—bitter taste," says Adam Drewnowski, director of the Center for Public Health Nutrition at the University of Washington in Seattle. ("Tastes" are detected directly by the tongue—salty, sweet, sour, bitter and umami, a Japanese word for the taste Westerners recognize in foods like Parmesan cheese. "Flavors" are the complex mix of tastes and odors we sense when we eat.)

Babies and children seem to have a taste world all their own. The fondness for face-puckering sourness is a good example. The Sour Patch candy makers may have figured this out a long time ago, but Monell Chemical Senses Center biopsychologist Julie Mennella confirmed it: In the first formal study of the appeal of tart, she found that kids between ages 5 and 9 actually enjoyed the flavor of concentrated citric acid.

Bitterness, by contrast, is a pleasure of wizened adulthood. During youth—and during pregnancy, as any mother could tell you—we can't stand bitter flavors. That's probably because bitterness is often a sign of toxicity, and it's especially important to avoid toxic compounds during these sensitive periods of growth and development. The mouth has a hair-trigger for bitter: While the human tongue has only a few varieties of taste receptors specialized for sugar, it has an elaborate bitter alarm system that includes at least five dozen different types of sensors, says Drewnowski. After all, a creature that misses a sweet meal will probably live to eat another, but one single poisonous snack could spell the end.

As we age, we develop a taste for foods with hints of bitter, especially if they are sweet or fatty, like buttered Brussels sprouts or dark chocolate. That may make physiological sense, Drewnowski hypothesizes. Acrid-tasting foods like broccoli and kale are loaded with cancer-fighting antioxidants. The bitterness is no accident. The anticarcinogenic compounds that taste astringent to us are actually toxins too—poisonous to the insects that chew on the plants. Human efforts to cultivate milder versions of bitter vegetables may be breeding the nutritional value right out of them, Drewnowski observes: "The amount of bitterness in the food supply is a fraction of what it used to be."

Our palates all have the same five types of detectors, the same aversion to bitter and mania for sweet. So why are our individual preferences so different? Mennella, for one, thinks our proclivities are shaped at a very early age. Her experiments show that we probably get our first taste of the world through the amniotic fluid that shelters us and that this prenatal experience carries over into the first year of life. If pregnant women drank carrot juice daily during late pregnancy, Mennella found, their babies at 6 months seemed to like carrot-flavored cereal much more than other 6-month-olds. She and her colleagues at Monell have also shown that nursing babies seem to detect flavors like garlic, ethanol (from alcoholic drinks) and vanilla in their mothers' milk. A baby who has never tasted garlic will suckle longer the first time his or her mother eats it, presumably gathering extra information about this peculiar new flavor. "[Mother's milk] is one of the first ways babies learn," she says.

Breast-fed babies whose mothers eat a wide range of foods are more likely to embrace new foods later on, her research has shown, and infants fed on harsh-tasting formulas remain more tolerant of bitter and sour at age 4 or 5. Mennella thinks this may be a hint as to how individual flavor preferences begin developing. "Our olfactory memories are oldest, most resistant to change," she says. "I think that underlies why certain foods are very much preferred—they are associated with things that occur early in life."

Cravings—intense and specific longings for one particular food—probably also have more do to with culture and childhood than with a biological urge for missing nutrients. In cross-cultural studies spanning three continents, psychologists Scott Parker of the American University in Washington, D.C., Debra Zellner of New Jersey's Montclair State University, American University student Niveen Kamel and Ana Garriga-Trillo of the Spanish national university UNED demolished the dictum that women universally crave chocolate. While women in Egypt, Spain and the United States do tend to crave sweeter foods than men do, the hankering for chocolate varied. Men and women in Spain were equally likely to crave chocolate. Egyptian women, by contrast, couldn't care less about cocoa—only 6 percent named chocolate as their most favored food. Mostly, they craved savory treats like meat-stuffed eggplant or a typical Egyptian broth-based soup.

Attitudes toward eating in general are strongly cultural, and the legendary food psychologist Paul Rozin of the University of Pennsylvania has shown that Americans have a particularly bad attitude toward food. While the French relish their meals and gobble down cheese, sausage and other high-fat delicacies, Americans are consumed with worry and anxiety, fearing fried eggs as death-in-a-skillet and obsessing over fat-free treats. Compared to the Japanese, the French and the Belgians, Rozin found, Americans worry most about food but are least likely to call themselves "healthy eaters." He hypothesizes that losing touch with the hardwired pleasure of eating may itself be bad for our health. In the United States, "one of the most pleasant of human activities has become drenched in worry," he argues.

Family and culture don't account for all our individual variability, though. "The correlation between parents' and their children's food preferences only goes so far," says Rozin. Pickiness, for example, seems to be highly idiosyncratic. In the first comprehensive survey of food pickiness among adults, anthropologist Jane Kauer interviewed nearly 500 adult Americans about their attitudes toward foods, food variety and eating habits. Kauer, who conducted the research as a doctoral student with Rozin, found that mild pickiness is quite widespread—about one-third of her volunteers described themselves as "unusually picky eaters."

It may not be surprising to learn that 60 percent of us like to leave our plates clean or that close to half of us eat just about the same thing for breakfast nearly every day. But stranger habits are also common. Many people refuse to drink while they eat. Others won't eat food that is lumpy or has a filling, like raviolis or egg rolls. Nearly 20 percent of us are repelled by raw tomatoes (something about the gooeyness inside the firmness), and about the same fraction of us simply don't like trying new foods.

In the course of her survey, Kauer found a few extremely picky people. (One woman she interviewed, for example, ate little more than canned brains, undercooked French fries and fried eggs. Kauer thinks this intensely fastidious eating is probably related to obsessive-compulsive behavior.) Questioning the pickiest third further, Kauer identified a master list of foods that are almost universally accepted: fried chicken, French fries, chocolate chip cookies, and above all else, Kraft macaroni and cheese. ("People seem to respond to the orange color," she says. "Maybe it's a signal that it's really fake and therefore really safe.") Obviously, these are all classic comfort foods, but more important for the picky person, they are unlikely to have weird or surprising ingredients. "We all know what's in fried chicken, for example, even if we get it from some place we've never been before," she says.

Most of us roll our eyes in irritation at a dining companion who insists on garlic-free pasta or shreds a brownie to pick out the nuts. We should be more tolerant, Kauer says. Food habits are a deep part of identity, closer to religion than to biology. The omnivore who devours durian fruit and fried locusts is just as proud of his neophilia as the choosy eater is of his selectivity. "We don't talk about it, but all of us have very strong feelings about what we eat and don't eat," she says.

Kauer theorizes that fastidious eaters have lost touch with the social context of food. As part of her survey, Kauer asked people to imagine three different scenarios in which they might choose to eat a food they hated: if they'd had nothing to eat for 12 hours, if they'd gone without anything at all for three days, or if poor hosts offered the food and it would be insulting to refuse it. That last scenario—in which rejecting the food would be a social embarrassment rather than a physical hardship—was the most powerful motivator for everyone except the pickiest eaters, who still refused it.

The psychology of pleasure and of food choice has been largely overlooked in the massive scientific effort to combat obesity and other food-related health problems. But as Rozin suggests, what we think about food could turn out to be as important as what we put in our mouths. It's a pleasure principle most of us could learn to live with: Eat up—it's good for you.