Sex Sleep Eat Drink Dream (12 page)

As you pursue the tasks of the afternoon, are you sitting quietly at your desk, pretty much a static lump? Or are you nervously tapping your foot? Pacing the halls? Popping up every few minutes to stretch or find that missing page from your manuscript or get another drink of water? Your fidget factor could be an indicator of your tendency to gain weight.

Just by living, by keeping your heart beating, blood circulating, kidneys, lungs, body cells working, you burn up 50 to 70 percent of the calories you consume, says Eric Ravussin of the Pennington Biomedical Research Center in Baton Rouge, Louisiana. This, your so-called resting metabolic rate, or RMR, is the pace at which the body burns calories while at rest to produce energy to keep its basic functions going. Some 20 percent of daily energy expenditure goes to the brain, about 10 percent to the heart and kidneys, another 20 percent to the liver, and up to 10 percent to digestion.

I recently had my RMR tested at a local health clinic with a portable calorimeter, a relatively new instrument designed to help people with weight problems figure out how many calories they burn daily. "Trying to lose weight without knowing your RMR," the literature told me, "is like balancing your checkbook without knowing how much money you're spending."

The physical therapist at the clinic asked me to breathe into a mouthpiece while the machine measured how much oxygen I inhaled and exhaled. People with a high metabolic rate use up more oxygen because they oxidize (or burn) more calories every hour. I had hoped for a high score, because I thought that people with a high metabolic rate are generally protected from gaining weight.

My rate, however, was a disappointing 1,180 calories a day, quite a bit lower than average. It turns out that metabolic rate is partly determined by body size and composition. Big people usually have a higher rate than smaller people; the more mass you have to move around, the higher your RMR. The physical therapist told me she had seen the full range, from 700 a day in a petite woman in her late seventies to 3,500 a day in a six-foot-five man who weighed more than 400 pounds. On average, a 175-pound man in his thirties burns about 25 calories for every kilogram (2.2 pounds) of weight, which comes out to about 2,000 calories a day. For women, it's typically around 1,400 a day, unless they're pregnant or nursing, which requires an extra 300 to 800. One important factor is the amount of lean muscle mass in your body. Weightlifters burn as much as 15 percent more calories all day long, even in their sleep.

However, the formulas are not so simple. "Though RMR seems to be fixed for a given person," says Ravussin, "there can be large differences even between people of the same sex, weight, and body composition." Why? Scientists are just beginning to unravel the mystery.

A small portion of your calories are burned off daily through thermogenesis, the generation of body heat induced either by exposure to cold or by excess food intake. These days, cold exposure is not much of a factor. "Because humans have evolved behavioral strategies (clothing) to maintain body temperature in cold environments," Ravussin says, "cold-induced thermogenesis accounts for only a small portion of daily energy expenditure."

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. Scientists at Harvard have shown that DIT is under the control of the sympathetic nervous system, which increases activity in the heart, pancreas, liver, kidneys, and other tissues and organs in response to overindulgence. 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. Variations in this gene may be part of the reason why certain people who pig out never put on an ounce, while others who eat the same amount get plump from the glut.

There may be another thermogenetic explanation for the light/ heavy divide. In one two-month study, scientists at the Mayo Clinic in Minnesota kept at a constant level the food intake and physical activity of a group of subjects, then overfed them by one thousand calories a day. Using state-of-the-art equipment to determine where those extra calories were going, the team found that, on average, a third accrued as fat, a third went to RMR, and a third were burned off by so-called nonexercise activity thermogenesis, or
NEAT.
This includes all the fidgeting, shifting position, standing, walking, drumming of fingers or toes—in short, all the unplanned physical activity one does in the course of a day.

Overeating didn't stimulate the same amount of
NEAT
in everyone. Some people fidgeted more in response to the gorging and managed to maintain nearly stable weight; others, who fidgeted less, gained up to nine pounds. This natural fidgetiness of an individual, say the researchers, is probably controlled by genetically determined levels of brain chemicals and can account for a big wedge of calorie consumption, from 15 to 50 percent. That can mean the difference between gaining an extra pound from that surplus pie or burning off these excess calories as you go through the motions of your day.

In 2005, the Mayo Clinic team set out to pinpoint the individual differences in energy expenditure. With precise sensors, the researchers measured the posture and body positions of twenty self-proclaimed couch potatoes during a ten-day period. Half of the subjects were lean, half mildly obese. All wore underwear with embedded sensors to monitor movement every half-second. With the help of this covert window into the subjects' energetics, the scientists discovered that the lean people moved around for two and a half hours more each day than did the overweight people. The difference in activity levels amounted to an expenditure or savings of as much as 350 calories a day.

"When people decide to increase energy expenditure for weight control, they usually include only structured exercise in their calculations," says Eric Ravussin. But the observed difference in
NEAT
between obese and lean individuals suggests that obesity might be prevented by spending less time in the chair and taking more trips to the water cooler. The researchers do not recommend that we quit our health clubs and exercise programs, just that we note the comparable health benefits of
NEAT
activities and perhaps step them up. In other words, to get your middle little, don't sit the day away, but rather stand when you have the chance, and by all means squirm, fiddle, twitch, and jiggle.

Afternoon

The afternoon knows what the
morning never suspected.

SWEDISH PROVERB

6. THE DOLDRUMS

I
T'S MIDAFTERNOON,
when the day, the light, the heat are at their peak—but you, suddenly, are not. For an hour or so after lunch, you were humming along, working on your report, writing that difficult letter, with a fresh mind and full acuity. Now, seeping through your back and shoulders, stealing up your neck to dim your brain, here it is: a slow tide of sleepiness. Your eyelids droop and your blinking intensifies; your face grows slack except for the jaw-stretch of one uncontrollable yawn after another. You give up on the demanding task at hand and slog through the minutes, filling them with whatever mundane tasks may have accumulated during the morning.

It's the doldrums, "where nothing ever happens and nothing ever changes," says Norton Juster in
The Phantom Tollbooth,
"where it is unlawful, illegal, and unethical to think, think of thinking, surmise, presume, reason, meditate, or speculate."

For most of us, the doldrums lie somewhere between 2 and 4
P.M.,
a dip in the day when the fog of fatigue drifts in to cloud thinking and numb limbs, when we grow inattentive and forgetful and may perform as poorly in matters of manual dexterity, mental arithmetic, reaction time, and cognitive reasoning as if we had quaffed several bottles of beer.

If we lived in Brazil or Panama, we might go home for a siesta (a word derived from the Latin for sixth hour, or the middle of the day). But we have no such civilized tradition, so we struggle through our stupor.

Is this dip—often called the post-lunch or postprandial decline (from the Latin
prandium,
or late breakfast)—inevitable? Or is there some way to avoid the sleepy slide?

This and other questions of weariness, fatigue, rest, and rhythms were the focus of a group of scientists who met not long ago for an annual meeting of the Society for Sleep and Biological Rhythms on Amelia Island in northern Florida. Off the coast, a big storm was brewing; white waves roiled in from a stormy sea, and a warm, gale-force wind thrashed the palm trees and whipped the beach into stinging eddies of flying sand. People gathered their beach umbrellas and blankets and made a run for shelter as a dark mass of ominous clouds moved in from the east.

Inside the well-insulated auditorium of the conference center, however, things were calm and comfortable: the seats deeply cushioned, the air conditioner humming softly, the lights low in anticipation of lecture slides. Soon to speak was Mary Carskadon of Brown University, known for, among other things, devising a system of measuring alertness by testing sleep latency—that is, how long it takes to fall asleep—now the gold standard of assessing daytime sleepiness. Her talk that day promised news on alertness and the sleep-wake cycle at different stages of life.

Despite my eager anticipation of her words, conditions were conspiring against clearheaded attention. On the 7-point Stanford Sleepiness Scale, I must have logged in between a 5 ("foggy; losing interest in remaining awake") and a 6 ("sleepy, woozy, fighting sleep; prefer to lie down"). My mind wandered feebly in the lexicon of lethargy: languor, lassitude, loginess, sluggishness, apathy, stupor, torpor, weariness, drowsiness, sleepiness, and a word I just learned: pandiculation, the act of stretching and yawning.

I was not alone. The man next to me had his eyes closed, head bobbing gently in time with his breathing. Periodically, the sudden blow of chin on chest would awaken him, and he would straighten up momentarily, but then his head dropped again. The woman to my left stifled a yawn; I tried to suppress mine, too—twice—but finally gave in to that satisfying deep inhalation, average duration about six seconds, although it tends to be slightly longer for men.

According to neuroscientists, a yawn can occur alone or in association with stretching and/or penile erection (which may help to explain its duration in men). Its function is still largely a mystery. People once thought it served a role in respiration: Triggered by low oxygen or high carbon dioxide levels in the blood, a yawn was the body's way of trying to take in more oxygen or rid itself of extra carbon dioxide. But when Robert Provine, a psychologist at the University of Maryland, tested this theory by comparing the effect of breathing various gas mixtures on yawning, he found that air rich in oxygen or high in carbon dioxide had no significant effect. Even people breathing pure oxygen feel the urge. Now yawning is thought to be akin to stretching, a way of increasing blood pressure and heart rate and flexing muscles and joints during transitional periods between wakefulness and sleep.

It's also considered a social signal. "Yawns may be a primitive form of nonverbal communication to indicate one's thoughts or mental condition," says Steven Platek of the University of Liverpool. This may suggest why they're contagious. As Dr. Seuss said, it often takes just one yawn to start other yawns off.

Humans begin to yawn in utero, about eleven weeks after conception, but the act becomes contagious only in the first year of life—and only in about half the population. To probe the nature of contagious yawning, Platek and his colleagues conducted a series of experiments to see what might make certain people susceptible.

The team tested sixty-five college students for personality traits that revealed their level of self-awareness and empathy, and then showed them short videos of people yawning, while observing them through a one-way mirror. Just over 40 percent of the subjects yawned in response to the video. There was a tight correlation between a high score on the self-awareness/empathy test and the susceptibility to contagious yawning. The scientists hypothesize that people who yawn contagiously are both more self-aware and more skilled at reading the thoughts of others by observing their faces. A follow-up fMRI study showed that viewing someone yawn evokes activity in parts of the brain involved in these skills. "Yawning may be more of a reflection of our nature as social beings than of our sleep cycles," says Platek.

So here's a new gauge of character and the potential for friendship: Yawn and see who yawns back.

What's going on in the body during this hiatus? By midafternoon, are we just tired, tuckered out from our half day of exertion? According to Carskadon, young children don't experience the midday trough, even after plenty of physical activity, but kids in mid- to late puberty do. During adolescence, the dip becomes entrenched in our days and is present nearly every afternoon of life thereafter. In the elderly, the window of weariness broadens to include the period between 11:30
A.M.
to 5:30
P.M.

Fatigue does accrue over the day, depending on your level of activity during the morning (and, of course, on how much sleep you got the night before). Once, when I was in high school, I played Helen Keller's mother in a series of afternoon performances of
The Miracle Worker.
I remember peeking out from behind the curtain before one show and spotting my own mother in the third row of the auditorium. She sat up, head erect, looking straight at me, it seemed, but her eyes were closed. When I got home later that afternoon, she had left me a note: "I don't know how you play that role day after day."