Mary Roach goes there in her new book, Gulp: Adventures on the Alimentary Canal.
Ever wonder why your stomach doesn't digest itself? Can constipation actually kill you? Why is crunchy food so appealing to us? Roach answers all these and more.
Here are 17 bizarre facts about food and your body that can be found in her new book! Enjoy!
1. Humans smell through two pairs of nostrils. When you exhale while chewing, food aromas waft up to the olfactory epithelium, at the top of the nasal cavity, through a set of “internal nares” in the back of the mouth. This is called retronasal olfaction, as opposed to orthonasal olfaction, the more familiar kind of smelling done through the nose.
2. A vigorous sniff has a mean duration of 1.6 seconds and a volume of two cups. Without sniffing, you miss as much as 90 percent of the smells going on around you. Only 10 percent of the air inhaled while breathing normally makes it up to the olfactory epithelium. Researchers used to study smell via the alarming-sounding “blast olfactometry”—controlled, measured artificial sniffs.
3. Taste is more than a sensual pleasure. People whose taste receptors have been destroyed by radiation or disease have been known to die of starvation. “Because everything tastes like cardboard,” one researcher said. “Your brain tells you, ‘This isn’t food,’ and it won’t let you swallow.”
4. Some food preferences develop extremely early. Traces of the flavors of the foods mothers eat are perceptible in breast milk and amniotic fluid. Babies whose mothers ate garlic, say, or broccoli, while pregnant are more likely to accept and enjoy these foods as children.
5. Why do babies drool? For starters, because they have no teeth to hold their saliva in. Also, without teeth to help break foods down, saliva is responsible for more of the work. Baby saliva—so cute!—contains extra lipase, an enzyme that breaks down fats. (Breast milk is high-fat.)
6. The stain-fighting enzymes in laundry detergent are the same food dissolvers our bodies use: amylase (a saliva enzyme) for breaking down starches, lipase for fats, and proteinase for protein. Laundry soap is a digestive tract in a box.
7. Contrary to what most people think, the smell of cooking food—according to two separate studies—does not make the mouth water. A researcher in the 1960s measured salivary flow rates in a group of hungry subjects who watched him fry up bacon and eggs in the lab. No change. His explanation was that thinking about eating turns your focus to your mouth and you suddenly become aware of your saliva.
8. There’s a reason animals lick their wounds and humans have a tradition of kissing their children’s boo-boos. Saliva contains potent antibacterial substances as well as nerve- and skin-growth factor. Wounds that take weeks to heal on skin will heal within a week inside the mouth.
9. The technical term for the face people unconsciously make when they eat something rancid (mouth open, tongue extended, nose wrinkled): the disgust face.
10. Teeth and jaws are best known for their powers of destruction, but they are remarkably sensitive. Studies have shown that humans can feel, with their molars, a piece of grit as small as 10 microns in diameter. Your jaw muscles automatically adjust their force as you chew, sensing when, say, a peanut gives way and instantly letting up to keep you from smashing and breaking your molars.
11. When you blush, the lining of your stomach blushes too.
12. Flow speed of a high-viscosity food bolus traveling down the esophagus: .22 mph, about the same as a tortoise.
13. Why doesn’t the stomach digest itself? It does. Thus it has evolved to be very efficient at regenerating its own tissues. You have a brand-new stomach lining every few days.
14. The typical cadaver stomach holds about a gallon before it ruptures. The stomachs of live humans rarely rupture, because the body has built-in emergency stomach-emptying reflexes. The Transient Lower Esophageal Sphincter Relaxation, or TLESR, or burp, relieves pressure by letting out gas. If that doesn’t suffice, the body calls in the heavy artillery: regurgitation.
15. Flatulence peaks twice a day: five hours after lunch and five hours after dinner.
16. Spacesuits have activated charcoal filters, lest astronauts’ flatus be circulated across their faces three times a minute for the remainder of the spacewalk.
17. The flatus of women has higher concentrations of hydrogen sulfide and has been deemed by professional odor judges to have significantly worse odor than men’s. However, the playing field is leveled somewhat by men’s greater, on average, volume per passage.