Gulp: Adventures on the Alimentary Canal

by Mary Roach

What sets a professional nose apart from an everyday nose is not so much its sensitivity to the many aromas in a food or drink, but the ability to tease them apart and identify them.

Humans are better equipped for sight than for smell. We process visual input ten times faster than olfactory. Visual and cognitive cues handily trump olfactory ones,

The extent to which Americans project their own food qualms and biases onto their pets has lately veered off into the absurd. Some of AFB’s clients have begun marketing 100 percent vegetarian kibble for cats. The cat is what’s called a true carnivore; its natural diet contains no plants.

researcher who has been experimenting with using potent flavors—which, as we know from the last chapter, are mainly smells—to make up for absent tastes. Taste and smell are intertwined in ways we don’t consciously appreciate. Food technologists sometimes exploit the synergy between the two. By adding strawberry or vanilla—aromas we associate with sweetness—it’s possible to fool people into thinking a food is sweeter than it really is. Though sneaky, this is not necessarily bad, because it means the product can contain less added sugar.

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.

Breast milk and amniotic fluid carry the flavors of the mother’s foods, and studies consistently show that babies grow up to be more accepting of flavors they’ve sampled while in the womb and while breastfeeding.

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.

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 prospect of tucking in, the more butchery feels like murder. Pets and primates, wrote Mead, come under the category “unthinkable to eat.” The same cultures that eat monkey meat have traditionally drawn the line at apes.

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.

(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.)*

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.

A healthy adult has a new stomach lining every three days. (More clever stomach tricks: key components of gastric acid are secreted separately, lest they ravage the cells that manufacture them.)

people with capacious stomachs are no more likely to be obese. A study in the journal Obesity Surgery reported no significant differences in the size of the stomachs of morbidly obese people as compared with non-obese control subjects. It is hormones and metabolism, calories consumed and calories burned, that determine one’s weight, not holding capacity.

The flammability of methane and hydrogen is part of the reason for the seeming overkill of protracted bowel-cleansing that precedes a colonoscopy. When gastroenterologists find a polyp during a screening, they will usually remove it while they’re in there, using a snare with an electrocoagulating option to staunch the bleeding.

“Dairy sugar often travels with dairy fat, and big fat loads are hard on the gut,” says gastroenterologist Mike Jones. “People who claim lactose intolerance tend to also voice a belief that they’re gluten-intolerant. Usually with no evidence of either.”

The newest research suggests that slower transit time—that is, longer exposure to your nasty stuff, may in fact be of benefit. Hydrogen sulfide appears to prevent inflammation and its sometime consequences, ulcerative colitis and cancer. In rodent studies, anyway, the gas has a significant anti-inflammatory effect on the walls of the digestive tract: the opposite of what aspirin does in there. Aspirin and ibuprofen combat inflammation everywhere but the stomach and bowel; there they create inflammation.

The first reference I came upon, a passing mention in an art journal, suggested that the holy-water clyster was a routine weapon in the exorcist’s arsenal.

A 1991 study found that over a three-year period, 25 percent of the deaths from pulmonary embolism at one Colorado hospital were “defecation-associated.”

The bacteria species in your colon today are more or less the same ones you had when you were six months old. About 80 percent of a person’s gut microflora transmit from his or her mother during birth.

I asked Khoruts what exactly is in the “probiotic” products seen in stores now. “Marketing,” he replied. Microbiologist Gregor Reid, director of the Canadian Research & Development Centre for Probiotics, seconds the sentiment. With one exception, the bacteria (if they even exist) in probiotics are aerobic; culturing, processing, and shipping bacteria in an oxygen-free environment is complicated and costly. Ninety-five percent of these products, Reid told me, “have never been tested in a human and should not be called probiotic.”