by Dave Asprey
The site was sacred, she warned me in stern tones, and had been used ceremonially for ten thousand years. It is called First Woman based on the mythology of the Yavapai tribe of Arizona. They believe that they are all descended from a woman named Kamalapukwia, whose offspring emerged from that cave in the Yavapai equivalent of the Adam and Eve myth. The cave also earned its name because its opening is shaped like a giant vagina. The resemblance was hard to miss as we were driving up. (Note: This is not a cave for tourism. I am being intentionally vague about some details to protect its rightful use by those with permission to be there. You will not find it online.)
It was my second time getting settled in a cave for my vision quest but the first time that it felt real. It was October, when the Sonoran Desert is still hot during the daytime but chilly at night. I was glad for my sleeping bag. The weather reminded me of autumn days when I was growing up in New Mexico, where you knew you would either sweat or freeze. On the first day, when I ventured out of First Woman cave and into the livid sun, I took off my shirt, knowing that no one would see the stretch marks I was still ashamed of—scars from my hard-won battle with obesity.
Two days into my vision quest and two days into my very first long fast, I hiked a mile carrying a backpack. For newbies like me, the second day of a fast is when you feel the most hunger. I was getting that. The second day is also a time when exhilaration can kick in. I was getting that, too. Thank you, catecholamines!
I was becoming attuned to all of the physical detail around me. It felt as though my eyes could focus on every speck of dust inside the cave, though at the same time I could feel that the air was full of dirt particles that were far too fine to see. I explored the cave as far in as it went, pondering where among the endless uneven surfaces I should set up camp. It was a dry sandstone cave about thirty feet deep and twelve feet wide, with a roof low enough that I could touch it in most spots. The history all around me was palpable. How many tens of thousands of fires had built up the thick soot on the roof of the cave? Who had been here, and had their thoughts been anything like mine? Eventually my mind settled and I made my little camp on a nice, flat ledge halfway into the cave—a piece of the roof that had probably fallen down thousands of years before. I laid out my water and sleeping bag and ventured out to gather some sticks to make a fire.
After that, there was nothing else to do except wonder if a scorpion, rattlesnake, or some large predator would visit. I was alone—truly alone—in a cave, cut off from human support and sustenance. The dancing shadows from my fire had a hallucinogenic quality, and I was already in a hungry, meditative state. I thought about all the other people who must have looked at similar shadows flickering on the same wall in a cave that’s been used for ceremonies for ten thousand years. From there my mind wandered all over the place, including into the forbidding corners of fear and loneliness.
It felt like an impossible task in the utter darkness of that lonely cave, but I tried to get some rest. I was trying to listen to the rhythms of my body and trying to feel liberated from food and companionship. My imagination kept conjuring up visions of a very large snake slithering up to eat me. Eventually, though, sleep won out and my consciousness slipped away.
SLEEP CLEAN; GET CLEAN WHILE YOU SLEEP
Getting a good night’s sleep is one of the most powerful ways you can enhance the impact of your fast. From a simple bookkeeping point of view, the connection between the two is obvious: while you’re sleeping you aren’t eating, so sleeping makes it a hell of a lot easier to get through the hours of a 16:8 fast. The connection goes way beyond that, though. Sleeping, like fasting, influences cellular and biochemical processes throughout the body. Combine intermittent fasting with healthy sleep patterns (what researchers call “good sleep hygiene”), and the results are synergistic.
You can easily understand how vital sleep is, even if you know nothing about what it does for you. On average we spend a full one-third of our lives unconscious, immobilized, and unresponsive to sights and sounds. That’s fine for modern people snoozing away in our cozy bedrooms, but think what all of those sleeping hours meant for our ancestors: they spent one-third of their time utterly defenseless against attack. Sleep seems like a terrible survival strategy, something that would have quickly been weeded out by evolution, yet every person does it. Every animal alive sleeps, and as near as scientists can tell,1 that’s the way things have been since animals first appeared on Earth more than 500 million years ago, during the Ediacaran period.2 Evolution is ruthlessly efficient. If sleep is ubiquitous, that means it must be essential to life—more important, even, than being able to run away from a predator that wants to eat you. We have to treat it with respect.
Have you ever gone a full day or more without sleep and felt as though you were going to drop dead? Death by sleep deprivation is a real thing. In a famous 1989 study,3 researchers at the University of Chicago actually observed it happen to a group of lab rats. (It would be completely unethical to run the equivalent experiment on humans, but there’s every reason to think that the danger is equally real for us.) Humans will die from lack of sleep long before they die from lack of food, yet most people would instinctively choose to be tired instead of hungry.
Conversely, you know how sharp and focused you feel after a particularly restful sleep? It seems as though every day there’s another study backing up that feeling and scientifically documenting the benefits of a good night’s sleep. The nightly hours of inactivity provide an opportunity to regenerate, both mentally and physically. This is the time when your subconscious mind solves problems and your muscles rest and grow stronger through increased protein production. During sleep, inflammation in the brain is flushed away by the recently discovered glymphatic system,4 in which glial cells open up little garbage chutes to remove cellular waste from the cerebrospinal fluid. The cleansing action of the glymphatic system appears to reduce the risk of Alzheimer’s disease and other brain disorders; it may slow overall aging of the brain as well. Sleeping six and a half to eight hours each night appears to reduce the risk of heart attack by staving off high blood pressure. There’s also evidence that getting a good night’s sleep reduces your risk of developing cancer via multiple mechanisms, including higher melatonin levels, reduced inflammation, and cellular repair as protein-digesting enzymes get to work while you slumber.
Yet 35 percent of Americans report that they regularly get fewer than seven hours of sleep a night, according to statistics collected by the Centers for Disease Control and Prevention (CDC).5 There’s a good chance that you’re one of them, and there’s a 100 percent chance that the CDC didn’t ask whether people get good sleep even if they sleep more than seven hours. So before we even get into the potent connections between sleep and fasting, consider the importance of sleep itself:
Sleep reduces stress.
Sleep reduces inflammation.
Sleep speeds healing.
Sleep enhances cognitive function and memory, making you sharp and alert.
Sleep enhances your sex drive.
And yes, sleep helps you lose weight.
Unless you’re sleeping in a jungle where a predator might attack you at any moment under the cover of darkness, there’s no downside to getting a good night’s sleep. Fasting can help you do just that.
Strictly speaking, the period of time you spend sleeping is time spent fasting. That’s how the meal of breakfast gets its name: literally “break-fast.” If you choose to skip breakfast and go a few more hours without sleeping, you have now begun intermittent fasting. Keep fasting just a few hours past the time when you wake up, and your body significantly reduces the secretion of insulin while it increases secretion of human growth hormone, or HGH. This is important, because HGH aids in cellular repair, encourages fat burning, and assists in the development of lean muscle mass.
To maximize the benefits of this process, you should wait at least six hours after rising before you eat your first meal. Your sleep cycle also helps set the time when y
ou should finish eating for the day. If you eat late in the evening, particularly close to bedtime, your body will still be actively engaged in the digestion process when you lie down for the night. All that food in your gut is a signal to your circadian timing system that it must be near daytime still, because humans aren’t nocturnal! Devoting all of that metabolic energy to digestion can make it more difficult for you to fall asleep. Your blood glucose and insulin levels also stay elevated for a longer time after an evening meal than when you eat during the day, which can lead to an elevated risk of glucose intolerance, type 2 diabetes, and high blood pressure. For the past several years, I’ve used continuous blood glucose monitoring designed for diabetics, and I’ve consistently noticed that a late dinner causes me to have higher blood sugar levels the next day, even during an intermittent fast. Skip the late dinners!
After you fall asleep, those elevated blood sugar and insulin levels can also cause you to awaken frequently, because your body is still engaged in digestion. You might not notice these times of wakefulness during the night, while you’re in that half-asleep/half-awake fog. What you will notice is that you don’t feel properly sharp and focused when you wake up for real in the morning. A simple way to find out about your sleep quality is to buy one of the many good commercial sleep-tracking devices. At the time of publication, the best device is the Oura ring, which is used by professional athletes such as NBA players to track their sleep, and the best phone-only sleep tracker is the SleepSpace app. They will pinpoint how many times you wake up during the night. The results might make you think twice about late-night snacking. Good sleep hygiene and good fasting habits go hand in hand.
Ideally, you should always leave at least three hours between your meal and the time you go to sleep. Ruth Patterson and Dorothy Sears, health researchers at the University of California San Diego, recently conducted a thorough review of the literature on the link between eating and sleeping.6 They concluded that each three-hour increase in the gap between the last meal and bedtime significantly reduces the odds of elevated blood sugar levels and elevated levels of C-reactive protein, an indicator of inflammation. Other studies show that working the night shift triggers many of the same negative biological responses as eating right before sleep and that fasting can offset those issues.
Again, good sleep hygiene and good fasting habits go hand in hand. As for why they do—well, that’s a whole fascinating story in itself.
YOUR INNER CLOCK
Our bodies are guided by an internal clock known as the circadian rhythm. It dictates when we fall asleep and how we wake up. It also directs when cells should activate different energy-producing chemical pathways, such as burning fats instead of sugars while we’re asleep. Eating too close to bedtime brings on metabolic dysfunction because it conflicts with your natural circadian rhythm. The culprit isn’t just the food you’re eating, then, but your body itself—specifically, a tiny region of the brain called the suprachiasmatic nucleus, located just behind the eyes. The suprachiasmatic nucleus is the master timekeeper, sending out chemical signals that instruct us when to sleep and when to awaken.
Broadly speaking, the circadian rhythm evolved to synchronize the sleep-wake cycle with the rising and setting of the sun. The existence of biological rhythms as an internal clock, and not just a response to day and night, was first noted in 640 BCE by the Greek poet Archilochus of Paros, who wrote that we need to “recognize which rhythms govern man.” (Archilochus is also the author of the insightful aphorism “The fox knows many things, the hedgehog one big thing.” There’s great value in being a hedgehog who pays attention to foundational truths, rather than a fox who gets distracted by many little details.)
From there it took an astonishingly long time to learn more about the clock inside us. The French astronomer Jean-Jacques d’Ortous de Mairan deduced the existence of a regular biological rhythm in plants in 1729, more than two millennia after Archilochus. The discovery of equivalent rhythms in animals didn’t happen until early in the twentieth century. Progress was so slow that the biologists Jeffrey C. Hall, Michael Rosbash, and Michael W. Young won a Nobel Prize in Physiology or Medicine “for their discoveries of molecular mechanisms controlling the circadian rhythm”—in 2017!7
We now know that the circadian clock regulates a wide variety of metabolic processes so that they recur every day at the optimal time for the functioning and survival of the organism. Daylight helps reset this rhythm, but it keeps on ticking inside us even if we don’t see sunrise and sunset. Unfortunately, the modern lifestyle doesn’t always align with that ticking, in much the same way that today’s scheduled eating patterns run counter to the way our species evolved. Our master clock is easily influenced by outside stimuli, including social events, screen time, and that late-night snack you popped into your mouth ten minutes before going to bed.
Sleep researchers sometimes call these stimuli zeitgebers, which is not as rude as it sounds; it means “time givers” in German. Zeitgebers can prompt your liver, muscle, and fatty tissue to be active at times when they should be shutting down for the night. The brain, meanwhile, can get confused when this occurs, attempting to prepare the body for bed based on time of day and your normal sleep pattern, even as specific organs and tissues are kicking into a high state of action. The resulting disruption of the circadian rhythm triggers inflammation and altered immune responses; those changes, in turn, can further mess with the rhythm, leading to a vicious cycle.
One potential result, according to a 2017 study out of the University of Sydney in Australia, is a cascade of inflammatory-related respiratory diseases, including chronic obstructive pulmonary disease, allergic rhinitis, and asthma.8 Or, more succinctly, “trouble.”
But even as your binge watching and Instagram swiping and ill-timed snacking are insulting your body with zeitgebers, placing a time restriction on when you eat can switch the body into a more consistent sleep routine. Establishing a routine makes it easier to fall asleep and allows you to wake up naturally without the jarring shriek of an alarm. And as with the natural mood enhancement provided by the body’s release of endorphins during a fast, you don’t have to stick any medications into your body. You don’t need sleeping pills or other pharmacological assistance to fall into a deep natural sleep. You merely need to get your circadian rhythms into working order.
I know. That word, merely, may seem to downplay the challenge. How are you going to go without your Netflix and social media and all of your comfort food? Remember, going without does not mean going without everything. Remember, too, that I have a whole set of biohacks to share with you, ways that emphasize your sense of control and steer you away from suffering. You can have your cake and eat it, too, if you know how your body works and when to eat it!
SNOOZE YOUR WAY INTO AN EASY FAST
Intermittent fasting is a biohack that will help you with sleeping. Restful sleeping is a biohack that will help you with fasting. How cool is that?
It’s common for people on their second night of fasting (or longer) to need less sleep. In fact, people typically find they need an hour less sleep each night during a multiday fast, while they’re intermittent fasting, or even while they’re just eating less inflammatory food. Alertness and the production of neurochemicals that stimulate wakefulness in the brain increase during daytime periods of fasting, but the levels of those chemicals tend to decrease at night, which supports deep sleep. The way a healthy sleep curve works is that during the first half of the night, you get your deep sleep. During the second half, you get your rapid eye movement, or REM, sleep, when you do your intense dreaming. If you wake up an hour earlier during your fast, you’re going to get less REM; if you go to bed an hour later, you’re going to get less deep sleep. Either way, you are going to wake up feeling more refreshed than before you started fasting.
Think of fasting as a gift. That hour not spent sleeping is a bonus time in your day to read, write, meditate, enjoy your friends and family, and generally just be good to yourself. A
n hour a day for a year works out to fifteen full twenty-four-hour days saved, or about six weeks of working eight hours a day. Is eating a late dinner really worth throwing that gift of time away?
Establishing an eating window will do a lot to help you reap these benefits. That’s easier than it sounds, because society already runs on regular mealtimes. That gives you a ready structure to start with. Now make it your own. My personal eating window is between noon and 6:00 p.m. in winter, when it gets dark early, and from 2:00 to as late as 8:00 p.m. in summer. Earlier is better. Nothing after dark is ideal. Or you might say, “I’m going to eat only between 10:00 a.m. and 2:00 p.m.” if a schedule like that works for your life. The key is to pick a schedule that makes sense to you and that you can sustain comfortably. You may find that late business dinners get in the way. In those situations, I usually eat my real dinner on time, then go to the business dinner and pick at a salad to make other people feel better about their late dinner.
Having a window doesn’t mean you should eat anything you want during those six or eight hours of consumption. This isn’t a dirty keto diet or the Coke and Doritos diet—not even the plant-based Coke and Doritos diet. You’ll be much happier if you eat simple, healthy meals. But even if you do follow the Coke and Doritos diet, eating them in moderation and not putting any food into your mouth three hours before bedtime will still result in weight loss and better sleep.
The most workable intermittent fasting schedule for all but the most extreme is to skip breakfast, then eat lunch and dinner. It seems extravagant to call such a straightforward guideline a “biohack,” but that’s really what it is. Create an eating rhythm that supports your sleep rhythm and the circadian rhythm that underpins all of it. Don’t consume your nightly meal too late. The breakfast-skipping approach to fasting is very pragmatic. The strongest possible circadian-supporting schedule is to plan your eating window in the morning—breakfast and lunch, then no dinner—but few people can stick to it because it’s not worth the social awkwardness that comes from skipping dinners.
