Last night, I ate too much, drank too much beer, and fell asleep too early. So I woke up at about three in the morning, feeling overheated, awake, and generally uncomfortable. I grabbed a nice tall glass of water, and pulled out this book to re-read this passage: "So-called diet-induced thermogenesis, or DIT, is the body's way of converting surplus calories directly into heat – in essence, wasting energy – and it varies a great deal from person to person. … Usually our cells burn only as much energy as they need to. But when we eat too much, the brain may sense the surfeit and activate DIT to burn off some of the excess calories as heat. One of the genes responsible for this neat feat makes a protein that acts as a kind of switch to rev up the amount of energy a cell burns in response to overeating."
I also found this passage: "Alcohol affects the thalamus, a region of the brain integral to sleep-wake rhythms and to the spindle waves that occur during stage 2 sleep. So sensitive is the thalamus, researchers say, that just a drink or two will make for lighter sleep in the middle of the night, or even full wakefulness."
Cool, no?
And so, that's why I liked this book. It's an attempt to offer brief details on the current state of knowledge in about a million different aspects of bodily functions – linking our behaviors and experiences with hormones and chemicals, bacteria and genes in the body. (And you still get the sense that we're still living in the dark ages. We still don't really know why we yawn. There's nothing in this book about hiccups, itching, or crying.) Ackerman is a writer by trade with a natural inclination toward scientific research that makes it an easy read.
The information is loosely organized by time of day, which makes sense given her emphasis on research studying circadian rhythms. At different times during the day, our bodies have different temperatures, varying levels of calorie production, varying levels of alertness, and so forth. Obviously a lot of what's interesting about the body is more constant (and therefore doesn't fall so neatly into her temporal structure), but a lot of the best material is about these cycles.
To wit: "Requiring older adolescents to attend school and attempt to take part in intellectually meaningful endeavors in the early morning may be biologically inappropriate." Young adults are clearly bothered by distraction in the morning, but later in the afternoon it is as if the distraction were invisible to them; meanwhile, the data for older adults show the opposite pattern. Also, levels of testosterone are significantly lower in the late evening and higher in the morning, cresting at about 8 a.m., while semen quality, ironically, peaks in the afternoon. One thing I never would have thought about is that giving cancer drugs at carefully selected times of day can maximize their therapeutic effects and minimize their toxic side effects.
Particularly interesting is the idea that in turning on lamps and lights after the sun has set, we unintentionally reset our "circadian pacemakers." We're not designed for jetlag or artificial light. Worst of all is taking on a job with a swing shift, which will really screw you up (high blood pressure, high rates of heart attacks and prostate cancer).
The book also, not surprisingly, acts as a self-help book too. A consequence of understanding bodily functions is understanding what not to do to your body. (For example, don't eat and drink too much before going to bed.)
There's a lot about stress remedies, and how meditation or music, humor and companionship can help a person. "More than a hundred studies have found that aerobic activity reduces feelings of anxiety. People who work out daily feel the biggest benefit, but just fifteen minutes of activity two or three times a week can lift spirits for two to four hours after exercise."
And she really has a lot of nice things to say about napping. "The latest siesta studies suggest that just fifteen to twenty minutes' rest sometime between 1 p.m. and 2:30 p.m. can relieve fatigue, boost cognitive performance, and recharge your mental batteries. Longer naps of, say, forty-five minutes to an hour may require some recovery time – about twenty minutes or so – while the grogginess of sleep inertia wears off." Hooray!
I plan on keeping this book on my shelf for the simple reason that it has an index and I suspect I'll be looking up various passages again.
Here's a sampling of a few tidbits I deemed worthy of underlining:
"You may have been a sterile, singular being in the womb, but once you entered the birth canal and then the world of nipples and hands and bed sheets, you picked up an ark of microbial handmaidens. Soon the little buggers were everywhere, like words filling a page, in folds of skin, in orifices of nose and ears, and especially in the warm, cozy tunnels of your digestive tract, from mouth to anus."
Saliva is "a fluid made of 99 percent water and 1 percent magic – magic in the form of sodium ions, enzymes, and a host of other organic substances, among them bacteria-fighting mucins, without which our teeth would decay."
"When scientists recently analyzed a single gene that codes for a red-sensing protein in 236 people around the globe, they found 85 variants. … This variation likely gives us each a unique view of hues."
"More women than men have a heightened reaction to bitter taste, though the sensitivity seems to vary over a woman's lifetime, rising at puberty and peaking during early pregnancy. After menopause, the sensitivity tails off, possibly because there's no longer a need to protect a developing child."
"The body seems to respond to a loss of a few hours' sleep in the same way it responds to a deficit of about one thousand calories – by cueing its systems to slow metabolism, deposit more fat, and step up appetite, particularly for high-calorie foods."
"Contributing to the blood flow that initiates and sustains an erection is nitric oxide, the same gas formed during a lighting storm and so essential to the heavy breathing that accompanies exertion. In the penis, nitric oxide acts as a potent muscle relaxant on the smooth muscles that surround the blood vessel walls, allowing the vessels to dilate."
"A diet with little roughage will produce about four ounces of excrement a day; one rich in fruits, vegetables and grains, about thirteen. A diet of meat makes for the strongest smell; of milk, the mildest."
"Researchers estimated the transit time of meals from food to feces to be fifty-five hours for men and seventy-two hours for women."
I don't know about you, but I needed to know this stuff.