Mary Roach, author of the new book Gulp: Adventures on the Alimentary Canal, shares her discoveries about the digestive system (taste is just the beginning).
By Mary Roach
She peeked into human cadavers for Stiff, then tackled the science of sex in Bonk. Now, in Gulp, writer Mary Roach ventures inside our bodies to find out what goes on as -- and after -- we eat. Sound icky? Not to Roach, whose research took her from Northern California (where she learned how to taste-test olive oil) to the Netherlands (where she visited a lab that studies how we chew). "The poor alimentary canal gets no respect," Roach says, "but it does some pretty fascinating stuff." A few of her favorite findings:
Your nose has more to do with eating than you might think.
"You could actually throw away your tongue and still 'taste' a lot of what you eat, because smell accounts for as much as 80 to 90 percent of how we perceive food. In fact, we have two sets of nostrils -- the ones we see and a second, internal, set at the opening in the back of the mouth that leads up to the nasal passage. As you chew, some of the airborne molecules that are wafting around in your mouth go through this internal nose, and your brain processes the odors of what you're consuming. If you want to experience more complex, fabulous flavors, take a tip from wine connoisseurs: Hold the food in your mouth for a few extra seconds and breathe out through your nose so that all the aromas have to travel through your inner nostrils."
Your ears play a big role, too.
"You can change how appealing a food is by simply manipulating the sound it makes when you chew. This is particularly true with crunchy and crispy foods. In one study, researchers put headphones on a group of people and altered the pitch and loudness of the crunch they heard as they bit down on potato chips. If the crunch was muted, the testers judged the same chips to be staler than they were. There's likely an evolutionary reason for this: As a species, we probably acquired a dislike for mushy foods because they were likely to make us ill (due to rotting) and decreased our odds of survival. This developed into a preference for crunchy foods, which signaled freshness. Now scientists have isolated the optimum decibel range, which is thought to be produced by about 100 tiny cell bursts, that creates the most desirable sound between our teeth."
Thinking about eating won't make your mouth water.
"A Harvard researcher named Alexander Creighton Kerr brought a group of hungry people into a lab, fried up bacon and eggs in front of them, and found that they didn't salivate more after he began cooking -- though one man said he could feel his mouth watering. But as Kerr explained, the anticipation and sight of food simply makes people more aware of the saliva already present in their mouths. The most potent way to produce more saliva is to put something in your mouth and start chewing."
A little gas might be a good thing.
"Hydrogen sulfide -- the chemical compound largely responsible for giving our gas its unpleasant odor -- is at the forefront of biomedicine right now and may actually be beneficial to our health. We know that over-the-counter medicines like aspirin fight inflammation everywhere in the body but the digestive tract, where they can cause ulcers, and now lab studies are finding that when aspirin works in conjunction with hydrogen sulfide, the two combine to have a tumor-fighting effect. So while hydrogen sulfide is one of the least favorite by-products of digestion, it could turn out to help save our lives."
Got a small stain? Dab it with spit.
"Some of the best stain fighters are right in our bodies, because the enzymes that break down foods during digestion can break down those same foods on our clothes. If you drop a starchy food on your blouse, for instance, you might try rubbing saliva on it -- saliva contains amylase, an enzyme that digests starch. If it's a fatty, greasy stain, saliva won't be as effective, because the enzyme that digests fats is produced mostly in the pancreas. That's why laundry detergent works so well: It uses these enzymes on a larger scale, like a digestive tract in a box. The same goes for dishwashing liquids: They 'eat' the food your dinner guests didn't."
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