Mary Roach’s Gulp  is a trip through the gooier side of human anatomy

By Matthew R. Francis

Mary Roach is one of the more fearless writers out there. Not in the physical sense — she doesn’t put herself into particularly dangerous situations, like certain reporters or travel writers — but intellectually. I don’t know if she’s incapable of embarrassment, but certainly she’s able to submerge that as she asks companies about using their blenders to process human feces, tries to identify subjects of obscure scientific papers through cold-calling, and having sex with her husband inside an MRI machine. She’s traveled to India to interview researchers investigating reincarnation and gotten the scoop on pooping in microgravity. (I also reviewed one of her previous books, Packing for Mars.)

Her latest book, Gulp, is full of such stories, all in the name of studying the human digestive tract, human eating habits, and a few subsidiary matters. Think of it as a liberal-arts approach to science writing: history, food science, and fart jokes all serve their purpose in the narrative. (If you don’t think fart jokes are part of the liberal-arts, you obviously didn’t attend the same college I did.) The driving force is Roach’s obsessive curiosity, coupled with (yes) her fearlessness in asking any question of anyone.

I don’t think whisper is a good substitute for burp [in degassing Tupperware], but it makes a lovely, poetic euphemism for the silent rectal passage. Forsooth, Horatio, even her whispers beguile me. –from Gulp

Those are great attributes for a science writer, but also for a scientist…or anyone. Consider this question a 6-year-old might ask: Why doesn’t the stomach digest itself? After all, the human stomach contains hydrochloric acid, which is uses to break down some pretty tough substances for digestion. The answer, as Roach points out, is that it does: The acid dissolves the lining of the stomach over the course of a few days, but new cells replace the destroyed ones. When a person dies, no new cells are born, leaving the acid to work undeterred…with predictably gross results.

However, Gulp isn’t a gross-out book, though I don’t advise you read the chapter on coprophagia (poop-eating) during lunch, as I did. In fact, the story Roach tells could help us see that our squicky feelings about digestion and its by-products are largely cultural. Digestion is an essential part of human life, and even such things as the smell of flatulence are indicative of normal bodily function. (In brief: the main chemicals in a fart are odorless—methane and hydrogen gas—but the tiny amount of sulfur that provides the perfume is a sign your gut bacteria are doing their job.)

Though the subtitle of the book reads Adventures on the Alimentary Canal, the side trips are often as illustrative as the main journey. Roach discusses why the nose is the most important organ for taste, a story for which she makes the huge sacrifice of drinking beer; she explains why humans are a really poor model for what our pets should eat; she uses the example of the mythical deadly Komodo dragon drool to explore the function of bacteria in human mouths. To bring these stories to us, she interviews a prison inmate (to understand how to smuggle contraband via the digestive tract) and Elvis Presley’s doctor (to investigate whether the King died of constipation). Even the biblical story of Jonah and the “whale” shows up, to examine whether humans or other animals could survive being swallowed alive.

FATLOSE stands for “Fecal Administration To LOSE weight,” an example of PLEASE—Pretty Lame Excuse for an Acronym, Scientists and Experimenters. –from Gulp

As with her other books, Roach lingers in a few pages on the fringes of science. One such story: a wacky proposal to reduce food consumption by chewing each bite a ridiculous number of times—counterproductive, in part because if you linger too long over a meal, your body becomes hungry again before you finish. Similarly, though the colon is responsible for absorbing some nutrients from food, you can’t survive by eating through your rectum; understanding why that’s the case helps illuminate (so to speak) the role of the lower digestive tract.

Mary Roach is among the funniest science writers in the business, without sacrificing real scientific content. I am intensely jealous of the way she made me laugh out loud at several points. It’s a rare talent to make (for example) fecal transplants amusing; the technique, once you get over initial squeamishness, is a medically powerful way to repopulate digestive bacteria for many people with serious illness. For someone to be both informative and funny seems downright unfair.

If you read Gulp—and I hope you do—let it be an inspiration to be curious and fearless.