Accounting for taste

Beauty is in the mouth of the eater

By Mary Roach

August 20, 2007

Dinnertime, on the road from New Hampshire to New York, my big brother Rip and me. Old Clam Box, Next Exit, says the billboard. “I hate clams,” says my brother. “Look, there’s a Burger King.”

Rip orders a Whopper, his way. “No tomatoes, no pickles, no onions. Hold the mayo and mustard. Easy on the ketchup.”

I don’t know this guy. I want to crawl under the condiment bar. “Why don’t you order a regular burger and give the poor woman a break?”

“I don’t like their regular hamburgers,” says Rip. “The buns have funny little seeds. Besides, special orders don’t upset them.”

They upset me. Back in the car, I continue my tirade. “What’s wrong with you? You don’t like anything!” From Bellows Falls to Brattleboro, I reel off the most delectable foods I can think of, while Rip sits in the driver’s seat making yucky faces.

You say tomato, she says yuck.

“Mushrooms? Asparagus? Veal parmigiana?”

“Nope.”

“Dates? Salmon? Lamb?”

“Blechh.”

“Bing cherries, for God’s sake.”

“Maraschino. Maybe. If it’s in an old-fashioned.”

“You’re weird.”

“No, you’re weird.” It’s his turn now. “You eat stinky cheese and raw quail eggs. I saw you eat dry cat food in third grade. You’re a scavenger, an indiscriminate glutton.”

And so it goes. He says potato, and I say polenta. I say tomato, he says disgusting. Somewhere around the Vermont border, we called the whole thing off. But I was determined to get to the bottom of this. How was it possible for two people raised by the same parents, under the same roof, down the hall from the same refrigerator, to prefer such radically different foods? Is there really no accounting for taste?

My quest begins at the Monell Chemical Senses Center, a private research lab on the outskirts of the University of Pennsylvania campus. (You can’t miss it — it’s the one with the 12-foot brass sculpture of a human nose and mouth out front.) I talk to Gary Beauchamp, the assistant director. Beauchamp can’t tell me why my brother and I ended up with such different appetites, but he assures me we didn’t start out that way.

All human beings, even my brother Rip, are born with the same basic taste preferences. We like sweet things, and we don’t like anything bitter or sour. Since infants can’t be relied upon to fill out questionnaires, researchers can gauge their preferences with something called the gusto-facial reflex. In one study, sweet substances elicited sucking and little smiles. Sour tastes produced “lip pursing and wrinkling of the nose,” and bitter prompted “opening of the mouth with the upper lip elevated and protrusion of the tongue” — the classic yucky face.

Those reactions make evolutionary sense: Toxic plants are often bitter or sour, Beauchamp says, while sweeter vegetables tend to be more nutritious and less likely to be poisonous than bitter vegetables. Mothers’ milk is sweet. So are ripe fruits — all good sources of vitamins, minerals, and calories.

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But wait a minute: If it’s calories and nutrients our bodies are after, wouldn’t it be more logical for us to prefer the taste of fats and vitamins? “Vitamin needs get piggybacked onto sweet fruits and vegetables,” says Beauchamp. As for fats: “The chemical structure of a fat is much more complicated than that of a simple molecule like sugar,” he says. Human taste receptors — the little red dots clustered into “buds” on the sides and tip of your tongue — are built to recognize sweet, salty, bitter, sour, and perhaps one or two other compounds. “Designing receptors to fit the various fat molecules would be more difficult.”

Okay, I’m satisfied. But how do these molecular goings-on translate into love and loathing? “Different types of taste receptors project to different areas of the brain,” says psychologist Linda Bartoshuk of the Yale University School of Medicine. “It’s as though the brain is looking at this massive wiring diagram and saying, ‘Aha, that spot lit up, so that’s a sweet taste.’” But why, I persist, does an ordinary, unassuming tollhouse cookie register as unmitigated bliss when it hits the tongue? Bartoshuk sighs. “What makes humans experience sweet the way they do is a philosophical question.” I sigh.

Elliott Blass, a psychologist at Johns Hopkins University, has another idea: When the tongue’s sweet taste receptors relay their message to the brain, he believes, it triggers a release of endorphins, the body’s own opiates. Blass says sucrose affects infant rats much like morphine does: It makes them stop crying. (Yes, even rats cry. But you need ultrasonic equipment to hear them.) It’s a phenomenon known to mothers and nannies the world over: A teaspoon of sugar water will often quiet a howling infant. It also fits with another commonly observed phenomenon — the intense sugar cravings of heroin addicts.

Does that mean that people become addicted to sugar the way they become addicted to narcotics? Nobody knows. If sugar really were physically addictive, it would take higher and higher concentrations of sweet substances for the taste to remain a source of pleasure. Which doesn’t seem to happen, or nouvelle desserts like lemon mousse wouldn’t stand a chance against Twinkies.