Gulp: Adventures on the Alimentary Canal

by Mary Roach

I’m not saying I don’t appreciate a nice meal. I’m saying that the human equipment—and the delightful, unusual people who study it—are at least as interesting as the photogenic arrangements we push through it. Yes, men and women eat meals. But they also ingest nutrients. They grind and sculpt them into a moistened bolus that is delivered, via a stadium wave of sequential contractions, into a self-kneading sack of hydrochloric acid and then dumped into a tubular leach field, where it is converted into the most powerful taboo in human history. Lunch is an opening act.

nose. It’s a big, lasting passive sniff.* This is why dogs stick their heads out the car window. It’s not for the feeling of the wind in their hair. When you have a nose like a dog has, or Sue Langstaff, you take in the sights by smell. Here is California’s Highway 29 between Napa and St. Helena, through Langstaff’s nose: cut grass, diesel from the Wine Train locomotive, sulfur being sprayed on grapes, garlic from

The nose is a fleshly gas chromatograph. As you chew food or hold wine in the warmth of your mouth, aromatic gases are set free. As you exhale, these “volatiles” waft up through the posterior

sniff the ale. I sip it, push it around my mouth, draw blanks. I can tell it’s intense and complex, but I don’t recognize any of the components of what I’m experiencing. Why can’t I do this? Why is it so hard to find words for flavors and smells? For one thing, smell, unlike our other senses, isn’t consciously processed. The input goes straight to the emotion and memory centers. Langstaff’s first

impression of a scent or flavor may be a flash of color, an image, a sense of warm or cool, rather than a word. Smoking jackets in a glass of Noel, Christmas trees in a hoppy, resinous India pale ale.

Verbal facility with smells and flavors doesn’t come naturally. As babies, we learn to talk by naming what we see. “Baby points to a lamp, mother says, ‘Yes, a lamp,’” says Johan Lundström, a biological psychologist with the Monell Chemical Senses Center in Philadelphia. “Baby smells an odor, mother says nothing.” All our lives, we communicate through visuals. No one, with a possible exception made for Sue Langstaff, would say, “Go left at the smell of simmering hotdogs.”

“In our society, it’s important to know

colors,” Langstaff says over a rising happy-hour din. We need to know the difference between a green light and a red light. It’s not so important to know the difference between bitter and sour, skunky and yeasty, tarry and burnt. “Who cares. They’re both terrible. Ew. But if you’re a brewer, it’s extremely important.” Brewers and vintners learn by exposure, gradually honing their focus and deepening their awareness. By sniffing and contrasting batches and ingredients, they learn to speak a language of flavor. “It’s like listening to an orchestra,” Langstaff ...

While not discounting genetic differences, Langstaff believes sensory analysis is mainly a matter of practice. Amateurs and novices can learn via kits, such as Le Nez du Vin, made up of many tiny bottles of reference molecules: isolated samples of the chemicals that make up the natural flavors. A quick word about chemicals and flavors. All flavors in nature are chemicals. That’s what food is. Organic, vine-ripened, processed and unprocessed, vegetable and animal, all of it chemicals. The characteristic aroma of fresh pineapple? Ethyl 3-(methylthio)propanoate, with a supporting cast of lactones, hydrocarbons, and

aldehydes. The delicate essence of just-sliced cucumber? 2E,6Z-Nonadienal. The telltale perfume of the ripe Bartlett pear? Alkyl (2E,4Z)-2,4-decadienoates.

Taste—as in personal preference, discernment—is subjective. It’s ephemeral, shaped by trends and fads. It’s one part mouth and nose, two parts ego. Even flavors that professional evaluators agree are “defects” can come to signify superior taste. Langstaff mentions a small brewery in northern California that has been taking its beers right up to the doorstep of defective, adding strains of bacteria known for their spoilage effects. Whether through exposure or a desire to ride the cutting edge, people can acquire a taste for pretty much anything. If they can come to like the smelly-foot stink of Limburger cheese or the corpsey reek of durian fruit, they can come to enjoy bacteria-soured beer. (One assumes there are limits, however. Leaving olive oil in contact with rotting sediment at the bottom of a tank can create flavors enumerated on Langstaff’s Defects Wheel for Olive Oil as follows: “baby diapers, manure, vomit, bad salami, sewer dregs, pig farm waste pond.”)

Unscrupulous vendors turn the situation to their advantage. In China, nouveau-riche status-seekers are spending small fortunes on counterfeit Bordeaux. A related scenario exists here vis-à-vis olive oil. “The United States is a dumping ground for bad olive oil,” Langstaff told me. It’s no secret among European manufacturers that Americans have no palate for olive oils. The Olive Center—a recent addition to the Robert Mondavi Institute for Wine and Food Science, on the campus of the University of California at Davis—aims to change that.

palatants most often take the form of a powder, liquid is better for tasting. To experience taste, the molecules of the tastant—the thing one is tasting—need to dissolve in liquid. Liquid flows into the microscopic canyons of the tongue’s papillae, coming into contact with the “buds” of taste receptor cells that cover them. That’s one reason to be grateful for saliva. Additionally, it explains the appeal of dunking one’s doughnuts.

“Catfish are basically swimming tongues,” says Rawson.

It seems odd to think of tasting without any perceptive experience, but you may be doing it right now. Humans have taste receptor cells in the gut, the voice box, the upper esophagus, but only the tongue’s receptors report to the brain. “Which is something to be thankful for,” says Danielle Reed, Rawson’s former colleague at Monell.

Otherwise you’d be tasting things like bile and pancreatic enzymes. (Intestinal taste receptors are thought to trigger hormonal responses to molecules, such as salt and sugar, and defensive reactions—vomiting, diarrhea—to

“It may be that that otherness is something specific to the cat,” says Rawson. Perhaps some element of the taste of meat that humans cannot perceive. The feline passion for pyrophosphates might explain the animal’s reputation as a picky eater. “We make [pet food] choices based on what we like,” says Reed, “and then when they don’t like it, we call them finicky.”

There is no way to know or imagine what the taste of pyrophosphate is like for cats. It’s like a cat trying to imagine the taste of sugar. Cats, unlike dogs and other omnivores, can’t taste sweetness. There’s no need, since the cat’s diet in

the wild contains almost nothin...

of carbohydrates (which include simple sugars). Either cats never had the gene for detecting sweet, or they lost it som...

Rodents, on the other hand, are slaves to sweetness. They have been known to die of malnutrition rather than step away from a sugar-water drip. In an obesity study from the 1970s, rats fed an all-you-can-eat “supermarket” diet that included marshmallows, milk chocolate, and chocolate-chip cookies gained 269 percent more weight than rats fed standard laboratory fare. There are strains of mice that will, over the cours...

The problem is that the average dog’s nose is about a thousand times more sensitive than the average human’s. A flavor that to you or me is reminiscent of grilling steak may be

overpowering and unappealing to a dog.

Gone are the colored pet-food pieces of the early 1990s. “Because when it comes back up, then you have green and red dye all over your carpet,” says Rawson. “That was a huge duh.”

I like chicken skin and pork rinds. Why the hesitation over muktuk? Because to a far greater extent than most of us realize, culture writes the menu. And culture doesn’t take kindly to substitutions.

Hoping to change this, the National Research Council (NRC) hired a team of anthropologists, led by the venerable Margaret Mead, to study

Another strategy was to target kids. “The human infant enters the world without information about what is edible and what is not,” wrote psychologist Paul Rozin, who studied disgust for many years at the University of Pennsylvania. Until kids are around two, you can get them to try pretty much anything, and Rozin did.

By the time children are ten years old, generally speaking, they’ve learned to eat like the people around them. Once food prejudices are set, it is no simple task to dissolve them. In a separate study, Rozin presented sixty-eight American college students with a grasshopper snack, this time a commercially prepared honey-covered variety sold in Japan. Only 12 percent were willing to try one.

To open people’s minds to a new food, you sometimes just have to get them to open their mouths. Research has shown that if people try something enough times, they’ll probably grow to like it. In a wartime survey conducted by a team of food-habits researchers, only 14 percent of the students at a women’s college said they liked evaporated milk. After serving it to the students sixteen times over the course of a month, the researchers asked again. Now 51 percent liked it. As Kurt Lewin put it, “People like what they eat, rather than eat what they like.”

So powerful are race- and status-based disgusts that explorers have starved to death rather than eat like the locals. British polar exploration suffered heavily for its mealtime snobbery. “The British believed that Eskimo food . . . was beneath a British sailor and certainly unthinkable for a British officer,” wrote Robert Feeney in Polar Journeys: The Role of Food and Nutrition in Early Exploration. Members of the 1860 Burke and Wills expedition to cross Australia fell prey to scurvy or starved in part because they refused to eat what the indigenous Australians ate. Bugong-moth abdomen and witchetty grub may sound revolting, but they have as much scurvy-battling vitamin C as the same size serving of cooked spinach, with the additional benefits of potassium, calcium, and zinc.

I would wager that if you look hard enough, you will find a welcoming mouth for any safe source of nourishment, no matter how unpleasant it may strike you. “If we consider the wide range of foods eaten by all human groups on earth, one must . . . question whether any edible material that provides nourishment with no ill effects can be considered inherently disgusting,”

writes the food scientist Anthony Blake. “If presented at a sufficiently early age with positive reinforcement from the childcarer, it would become an accepted part of the diet.” As an example, Blake mentions a Sudanese condiment made from fermented cow urine and used as a flavor enhancer “very much in the way soy sauce is used in other parts of the world.”

With organ meats, where the prep may include, say, “removal of membrane,” the last phase will be slow-going. Unlike filets and stewing meats, organs look like what they are: body parts. That’s another reason we resist them.

“Organs,” says Rozin, “remind us of what we have in common with animals.” In the same way a corpse spawns thoughts of mortality, tongues and tripe send an unwelcome message: you too are an organism, a chewing, digesting sack of guts.

To eat liver, knowing that you, too, have a liver, brushes up against the cannibalism taboo. The closer we are to a species, emotionally or phylogenetically, the more potent our horror at the prospe...

Pets and primates, wrote Mead, come under the category “unthinkable to eat.” The same cultures that eat monkey meat have tr...

A sled dog was more or less a piece of equipment. When I told Makabe Nartok that I had a cat, he asked, “What do you use it for?” In America, pets are family, never fare. That feeling held fast even during the years of World War II rationing, when horse or rabbit—delicacies right over the pond in France—might, you’d think, have seemed preferable to organs. In the 1943 opinion piece “Jackrabbit Should Be Used to Ease Meat Shortage,” Kansas City scientist B. Ashton Keith bemoans the “wasted meat resource” of jackrabbit carcasses that were being left for coyotes and crows after being killed by ranchers in “great drives that slaughter thousands.” (Most of these seemingly collected by Keith’s mother: “Some of the pleasantest recollections of my boyhood are of fried jackrabbit, baked jackrabbit, jackrabbit stew, and jackrabbit pie.”)

The children were wise to be wary. Compulsive hair-eaters wind up with trichobezoars—human hairballs. The biggest ones extend from stomach into intestine and look like otters or big hairy turds and require removal by stunned surgeons who run for their cameras and publish the pictures in medical journal articles about “Rapunzel syndrome.” Bonus points for reading this footnote on April 27, National Hairball Awareness Day.

Just as he believed in extracting the most nourishment possible from a mouthful of food, he sought to extract the maximum use from each sheet of stationery. Around 1913, he switched from double- to single-spacing and began typing on both sides of the page. Because the paper was thin to the point of transparency, Fletcher’s words bled

through, causing some of the missives, though typed, to be practically illegible. What I am getting at is that there is a point at which efficiency crosses over into lunacy, and the savings in money or resources cease to be worthwhile in light of the price paid in other ways. Horace Fletcher danced around that point his whole career. What amazes me is the degree to which he was taken seriously.

At one chew per second, the Fletcherizing of a single bite of shallot would take more than ten minutes. Supper conversation presented a challenge. “Horace Fletcher came for a quiet dinner, sufficiently chewed,” wrote the financier William Forbes in his journal from 1906. Woe befall the non-Fletcherizer forced to endure what historian Margaret Barnett called “the tense and awful silence which . . . accompanies their excruciating tortures of mastication.”

yourself tests of bowel transit time*—the time

“Nutritional science is dogged by the idea that if some is good, more is better,” he said, “and this has led to the belief that we should endeavor

to extract as much as possible of whichever fashionable component is in vogue. This is to ignore evolutionary biology and the imperative of survival.” He pretty much ran Horace Fletcher through the Model Gut.

The human digestive tract is like the Amtrak line from Seattle to Los Angeles: transit time is about thirty hours, and the scenery on the last leg is pretty monotonous.

More recently, the digestive action of a healthy adult male obliterated everything but 28 bones (out of 131) belonging to a segmented shrew swallowed without chewing. (Debunking Fletcher wasn’t the intent. The study served as a caution to archaeologists who draw conclusions about human and animal diets based on the skeletal remains of prey items.) The shrew, but not the person who ate it, was thanked in the acknowledgments, leading me to suspect that the paper’s lead author, Peter Stahl, had done the deed. He confirmed this, adding that it went down with the help of “a little bit of spaghetti sauce.”

When I’d composed myself sufficiently, I put in a call to Grime. The answer is yes. Higher-end detergents contain at least three digestive enzymes: amylase to break down starchy stains, protease for proteins, and lipase for greasy stains (not just edible fats but body oils like sebum).

Laundry detergent is essentially a digestive tract in a box. Ditto dishwashing detergent: protease and lipase eat the food your dinner guests didn’t.

you’re eating,” I asked Grime, “does it make sense to dab it with saliva? As a kind of natural laundry presoak?” “That’s an interesting thought.” Dr. Grime carries a Tide stain pen. He does not use his own spit. Art conservators do. “We make cotton swabs on bamboo sticks and moisten the swab in our mouths,” says Andrea Chevalier, senior paintings conservator with the Intermuseum Conservation Association. Saliva is especially helpful for fragile surfaces that solvents or water would dissolve.

In terms of pressure per single burst of activity, these are the strongest muscles we have.