Flavor is a combination of taste (sensory input from the surface of the tongue) and smell, but mostly it’s the latter. Humans perceive five tastes—sweet, bitter, salty, sour, and umami (brothy)—and an almost infinite number of smells. Eighty to ninety percent of the sensory experience of eating is olfaction.
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.
Cats, unlike dogs and other omnivores, can’t taste sweetness. There’s no need, since the cat’s diet in the wild contains almost nothing in the way of carbohydrates (which include simple sugars). Either cats never had the gene for detecting sweet, or they lost it somewhere down the evolutionary road.
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.
Human saliva contains histatins, which speed wound closure independent of their antibacterial action. Dutch researchers watched it happen in the lab. They cultured skin cells, scratched them with a tiny sterile tip, soaked them in the saliva of six different people, and clocked how quickly the wounds healed, as compared to controls. Other components of saliva render viruses—including HIV, the virus that causes AIDS—noninfective in most cases. (Colds and flus aren’t spread by drinking from a sick person’s glass. They’re spread by touching it. One person’s finger leaves virus particles on the glass; the next person’s picks them up and transfers them to the respiratory tract via an eye-rub or nose-pick.)
But it is not the jaw’s power to destroy that fascinates van der Bilt; it is its nuanced ability to protect. Think of a peanut between two molars, about to be crushed. At the precise millisecond the nut succumbs, the jaw muscles sense the yielding and reflexively let up. Without that reflex, the molars would continue to hurtle recklessly toward one another, now with no intact nut between. To keep your he-man jaw muscles from smashing your precious teeth, the only set you have, the body evolved an automated braking system faster and more sophisticated than anything on a Lexus. The jaw is ever vigilant. It knows its own strength. The faster and more recklessly you close your mouth, the less force the muscles are willing to apply—without your giving it a conscious thought.
You can witness the protective cutout reflex by hooking up a person’s jaw muscles to an electromyograph. The instant something hard gives way, the readout of electrical activity goes briefly flat. “The silent period, they call it,” van der Bilt says. It seems like a term kindergarten teachers might use, or people at a Quaker meeting. All these years, I’ve had it backward. Teeth and jaws are impressive not for their strength but for their sensitivity. Chew on this: Human teeth can detect a grain of sand or grit ten microns in diameter. A micron is 1/25,000 of an inch. If you shrank a Coke can until it was the diameter of a human hair, the letter O in the product name would be about ten microns across. “If there’s some earth in your salad, for instance, you notice immediately. It warns you for the wrong things.”
Here’s how badly people want to chew. Recall that dysphagia may knock out the reflex that repositions the larynx (voice box) to allow food into the esophagus. Jennifer Long told me these patients have on occasion asked to have their voice box surgically removed so they can swallow again. In other words, they would rather be mute than tube-fed.
Crispness and crunch appeal to us because they signal freshness. Old, rotting, mushy produce can make you ill. At the very least, it has lost much of its nutritional vim. So it makes sense that humans evolved a preference for crisp and crunchy foods.
To a certain extent we eat with our ears. The sound made by biting off a piece of carrot—more so than its taste or smell—communicates freshness. René told me about an experiment in which subjects ate potato chips while a researcher digitally altered the sounds of their chewing. If they muted the crunch or masked the higher frequencies, people no longer sensed the crispness. “They rated the chips as old even though the texture had not changed.”
Van Vliet is nodding. “People eat physics. You eat physical properties with a little bit of taste and aroma. And if the physics is not good, then you don’t eat it.”
Crispness and crunch are the body’s shorthand for “healthy.” The snack-food empires have cashed in on this fact, producing crisp, crunchable foods that appeal to us but fail to deliver in terms of health and survival.
The preference in California prisons for rectal smuggling is a little surprising given the preponderance of Latinos and African Americans—two populations that are, taken as a whole, somewhat less comfortable with homosexuality. Prison, I’m guessing, is a place where extenuating circumstances erode the stigma that otherwise attaches to extracurricular uses of the rectum.
Rodriguez speaks freely about the situation in Avenal. Rather than antagonize gay inmates, he says, gang leaders tend to employ them. “We call them ‘vaults.’ If they’re reliable, the homies will approach them—‘Hey, check it out, you want to make some money?’”
Any discussion of the sexuality of the digestive tract must inevitably touch on the anus. Anal tissue is among the most densely innervated on the human body. It has to be. It requires a lot of information to do its job. The anus has to be able to tell what’s knocking at its door: Is it solid, liquid, or gas? And then selectively release either all of it or one part of it. The consequences of a misread are dire. As Mike Jones put it, “You don’t want to choose poorly.” People who understand anatomy are often cowed by the feats of the lowly anus. “Think of it,” said Robert Rosenbluth, a physician whose acquaintance I made at the start of this book. “No engineer could design something as multifunctional and fine-tuned as an anus. To call someone an asshole is really bragging him up.”
The point I had been making is that nerve-rich tissue, regardless of its day-to-day function, tends to be an erogenous zone.
Presley was given laxatives and enemas on an almost daily basis. “I carried around three or four boxes of Fleets,” Nichopoulos says, referring to the enema brand and recalling his days on tour with Presley. Getting the timing right was, he says, “a difficult balancing act.” Presley sometimes did two shows a day, and Nichopoulos had to schedule the administration such that the treatments didn’t kick in while the singer was on stage. This was the low point of Presley’s career: the bulky jumpsuit and isosceles sideburns era. His colon had expanded so dramatically that it crowded his diaphragm and had begun to compromise his breathing and singing. Beneath the polyester and girth, it was hard to see the man who had performed on the stage of the Ed Sullivan Theater, his moves so loose and frankly sexual that the producers had ordered him filmed from the waist up. Now there was a different reason to do so. “Sometimes right in the middle of the performance, he’d think, ‘I’m passing a little gas,’ and it wouldn’t be gas,” Nichopoulos says quietly. “And he’d have to get off stage and change clothes.”
People who saw the Graceland master bathroom would remark on its extravagance—a TV set! Telephones! A cushioned seat!—but the décor was in equal part a reflection of how much time was spent there. “He would be thirty minutes, an hour, in there at a time,” Nichopoulos says. “He had a lot of books in there.” Constipation ran Presley’s life. Even his famous motto TCB—“Taking Care of Business”—sounds like a reference to bathroom matters. (The TCB oath touched on self-respect, respect for fellow men, body conditioning, mental conditioning, meditation, and, according to a group tell-all by Elvis’s entourage, “freedom from constipation.”)
I predict that one way or another, within a decade, everyone will know someone who’s benefited from a dose of someone else’s body products. I recently received an e-mail from a doctor in Texas, telling me the story of Lloyd Storr, a Lubbock physician who treated chronic ear infections via homemade “earwax transfusions”: drops of donor earwax boiled up in glycerin. Earwax maintains an acid environment that discourages bacterial overgrowth and possibly contains some antibacterial chemicals. Whatever it does, some people’s works better than others’. Khoruts has been encouraging a friend of his, a periodontist, to try bacterial transplantation* as a treatment for gum disease.
If things go as they should, the bacteria hysteria so lucratively nurtured by the likes of Purell and Lysol will begin to subside. Thanks to the courageous blender-wielding pioneers of bacterial transplantation, fussiness and unfounded fear will be buffered by rational thinking and perhaps even a modicum of gratitude.
The great irony is that in the beginning, the gut was all there was. “We’re basically a highly evolved earthworm surrounding the intestinal tract,” Khoruts commented as we drove away from his clinic the last day I was there. Eventually, the food processor had to have a brain attached to help it look for food, and limbs to reach that food. That increased its size, so it needed a circulatory system to distribute the fuel that powered the limbs. And so on. Even now, the digestive tract has its own immune system and its own primitive brain, the so-called enteric nervous system. I recalled what Ton van Vliet had said at one point in our conversation: “People are surprised to learn: They are a big pipe with a little bit around it.”
You are what you eat, but more than that, you are how you eat. Be thankful you’re not a sea anemone, disgorging lunch through the same hole that dinner goes in. Be glad you’re not a grazer or a cud chewer, spending your life stoking the furnace. Be thankful for digestive juices and enzymes, for villi, for fire and cooking, all the miracles that have made us what we are. Khoruts gave the example of the gorilla, a fellow ape held back by the energy demands of a less streamlined gut. Like the cow, the gorilla lives by fermenting vast quantities of crude vegetation. “He’s processing leaves all day. Just sitting and chewing, and cooking inside. There’s no room for great thoughts.”
Those who know the human gut intimately see beauty, not only in its sophistication but in its inner landscapes and architecture. In a 1998 issue of the New England Journal of Medicine, two Spanish physicians published a pair of photographs: “the haustrations of the transverse colon” side by side with the arches of an upper-floor arcade in Gaudi’s La Pedrera. Inspired, wanting to see my own internal Gaudi, I had my first colonoscopy without drugs.*
There is an unnameable feeling I’ve had maybe ten times in my life. It is a mix of wonder, privilege, humility. An awe that borders on fear. I’ve felt it in a field of snow on the outskirts of Fairbanks, Alaska, with the northern lights whipping overhead so seemingly close I dropped to my knees. I am walloped by it on dark nights in the mountains, looking up at the sparkling smear of our galaxy. Laying eyes on my own ileocecal valve, peering into my appendix from within, bearing witness to the magnificent complexity of the human body, I felt, let’s be honest, mild to moderate cramping. But you understand what I’m getting at here. Most of us pass our lives never once laying eyes on our organs, the most precious and amazing things we own. Until something goes wrong, we barely give them thought. This seems strange to me. How is it that we find Christina Aguilera more interesting than the inside of our own bodies? It is, of course, possible that I seem strange. You may be thinking, Wow, that Mary Roach has her head up her ass. To which I say: Only briefly, and with the utmost respect.
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