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.
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