by Dave Asprey
For some people, especially those like me who have a hard time sleeping or going to bed on time, the impact of fasting is much more pronounced if you strictly follow the “no food after dark” rules. For people who suffer from moderate to severe sleep apnea, consuming calories close to bedtime can increase the number of sleep disturbances (caused by lack of oxygen to the brain due to throat closure) that happen during the night and can contribute to a lack of deep, restful sleep. On the other hand, going without dinner entirely is tough for beginning fasters.
Here’s a tip to help you fall asleep more quickly while not feeling hungry when you go to bed: when you sit down for dinner, indulge in some white rice and a little sweet potato. You may say it sounds as though I’m contradicting myself: I’m suggesting you eat carbs, and carbs are the enemy of ketosis. Think of this as fine tuning, keeping some flexibility in your fast. Don’t overindulge, but a little dose of carbs at dinner can be really helpful in reducing physical anxiety. Carbs produce serotonin, a neurotransmitter (brain-signaling chemical) known to help us fall asleep. By eating a dinner including a tiny bit of carbs three to four hours before bedtime, you set yourself up for a deeper, more restful night of sleep.
So long as it’s just a modest bite or two of carbs, you can eat it and stay in ketosis if you have MCT oil with it. You might even enjoy a small dessert containing a few grams of sugar or, ideally, a little bit of raw honey once or twice a week. This can take you out of ketosis for a little while, but you will go right back after a short fast. The reason I recommend raw honey is that it raises the level of glycogen in the liver. Liver glycogen preferentially feeds the brain. And as much as your muscles regenerate and recuperate during a good night’s sleep, it’s your brain that benefits the most from that period of rest. It needs a full energy supply to do its cleansing and regeneration. Good sleep, good eating, and good brain health all go hand in hand.
There is one important disclaimer: it’s entirely possible that you will get into a state where you wake up in the middle of the night while fasting, especially when you first start out. Don’t despair; you’re not doing anything wrong. You’re still on the path to better sleep and improved cognitive function. What you’re experiencing is the effect of cortisol, a hormone that acts like an alarm signal in the body. It’s sending a message that you should have a few carbs or skip a day or two of intermittent fasting.
People often talk about cortisol as if it’s the enemy. Health reporters typically describe it as the hormone that’s related to too much stress, coffee consumption, sitting, and negative emotion in our lives. Some people also connect high cortisol levels with adrenal fatigue, which is a real problem. (I can attest to that, because I’ve had it before; adrenal fatigue can cause lethargy, aches, disrupted sleep, and digestive problems.) But as with all the chemicals your body makes, cortisol has a damn good reason for being there. It turns out that having low cortisol is much worse than having high cortisol. If you don’t have enough cortisol, your body’s ability to make energy, as well as to control inflammation—and even to maintain the baseline blood pressure we need to think—is impaired. When your metabolism is trained to fast, your cells switch easily between burning glucose and burning ketones, you have more energy, and your cortisol levels will likely resolve to become like Goldilocks’s favorite chair: not too big, not too small, just right!
If fasting makes your body believe it’s running out of energy—particularly glucose—your body will pump out cortisol as a quick fix because cortisol immediately raises blood sugar, which is a mechanism meant to keep you alive. This is similar to the fight-or-flight response that fills you with energy if you feel that you’re in danger. The first thing the brain does is declare an emergency. It triggers a rapid secretion of cortisol and adrenaline to create blood sugar. Your whole body goes into a state of high alert. That’s why I call nighttime cortisol production a chemical alarm signal.
When you start fasting, this emergency process can kick in at a particularly inconvenient moment, around three o’clock in the morning. To the brain, this time coincides with a critical part of the sleep cycle when it needs access to a lot of energy so it can wash itself free of toxins. This process, called glymphatic circulation, is very important for consolidating memories and putting them into your long-term recall. As part of your middle-of-the-night brain wash, your neurons pump out their water, getting rid of the toxic proteins that built up during the day. The brain then replenishes itself with fresh, clean cerebral spinal fluid so you can wake up and feel good the next day.
This is a beautiful thing if the process unfolds the way it’s supposed to. But beginning fasters—or unending keto cultists—can get an unwelcome surprise if the fight-or-flight, where’s-my-energy response kicks in during the night. By releasing cortisol and adrenaline, the brain rapidly gets the energy it needs for glymphatic circulation. Your individual neurons are happy and clean. However, the whole you—the person reading this book—won’t be so happy. The 3:00 a.m. freak-out includes racing thoughts and an inability to go back to sleep. If this happens to you, try eating a little raw honey before bed. It’s an easy fix to keep you going until your body adapts to fasting. A little bit of sweetness will keep your brain content and will keep you content, too. If carbs don’t work for you, even a little MCT oil can help by increasing the level of circulating ketones, which provide alternate energy for your brain.
RESPECT THE RHYTHM OF LIFE
You’ve begun the process of taking control of your circadian rhythm, making it part of your program to own your biology. To keep going, you’ll want to know even more about how your internal clock works. The circadian rhythm is responsible for much more than regulating sleep and wakefulness; it also promotes a healthy metabolism and immune system, which helps explain why good sleep is associated with such a vast range of positive health effects.
Your circadian rhythms exert a delicate, complex influence on all of the 30 trillion cells in your body. Its impact goes even deeper than that. Each active cell contains hundreds to thousands of mitochondria that drive your metabolism by extracting the chemical energy from the food you eat. Ideally, every single mitochondrion in your body knows when it’s day and when it’s night. And just as ideally, all of them act in unison, responding to the chemical signals of the circadian rhythm and mediating the way it is expressed in your changing mood, energy levels, and activity levels over the course of the day.
But this delicate dance can fall apart in response to sensory signals that clash with the rhythm. The strongest signal of all is the one that tells the brain whether it’s day or night: light. Cells in your eyes continuously measure the color, strength, and angle of the light around you and shuttle that information to the suprachiasmatic nucleus, to other parts of the brain, and beyond. I’m not talking about the things you see. I’m talking about much more subtle observations, ones you don’t consciously recognize even though they affect you to the core. Your circadian rhythm is constantly adjusting and resetting in response to nature’s light cycles. When you surround yourself with artificial light—which hits you with unnatural colors at unnatural hours—your rhythm changes. Your mitochondria change. Your exquisitely evolved biochemical dance can stumble into metabolic dysfunction. And when that light tweaks the function of your mitochondria, your blood sugar level is impacted, too.
That’s why I deliberately create an optimal sleep environment. I wear glasses that filter out junk light at night, and I dim the lights before bedtime as much as possible or use sleep-friendly light bulbs (more on this in a minute). I cover my windows with blackout curtains and make my bedroom into my own personal cave. Even if you’re not ready to go quite that far, you should be mindful of your evening illumination. It’s critically important that you turn down your lights at night, especially during fasting. If you don’t, you will end up undoing a lot of your good work. Yes, you can go on a bright-light-at-night fast, too.
You should also reduce, if not cease altogether, looking at screens when it
gets close to bedtime. No TV. No laptops. No phones. One hour before going to sleep is a good goal to aim for. Electronic screens emit a blue-enhanced light that resembles the rays of the midday sun. Finely tuned optical receptors in your eye are tricked into thinking it’s still daytime. Those receptors trigger the secretion of hormones to keep you awake and suppress the levels of sleep-inducing melatonin. When you finally do fall asleep, the lingering effect of the blue-tinged screens means that your sleep won’t be as deep or restful.
Paul Gringas at King’s College London helped raised awareness of this issue back in 2015.9 Since then, many electronics companies have added a darker, redder “night mode” to their phones. In 2008, I had a custom pair of glasses made to block the types of light that ruin sleep, and since then I have continued research, filed patents, and started a company called TrueDark that makes special light bulbs and eyeglasses to reduce your exposure to daylight-simulating rays at night. (You can do everything in this book without using my glasses, but they work, so I’m sharing them with you here.) The truth is that if you dim your lights, use the glasses, and heavily dim your screens, it’s possible to use screens right up until bedtime. I do it a lot, then sleep like a baby, but you have to be militant about your light exposure.
Still, these hacks are no substitute for switching off entirely. That’s because restricting the amount of time you spend in front of the TV or staring at your devices is also a great first step toward a dopamine fast. I’ll tell you more about how to do that in chapter 10. The key idea here is to cut back not just on the bluish light but on the whole addictive pattern of looking at videos, texts, and social media all the time. This is another craving that you can master and one that will help you feel more alive.
What you really want to do is attend to all of the factors that affect your sleep hygiene so that you optimize the way that sleep and intermittent fasting support each other. It’s harder to fast when you get a bad night’s sleep. You can start working on your sleep even before you begin your first fast. If you’re like most people, the time you fall asleep and the time you wake up are determined more by habit and obligations than by what your body wants or what’s best for you. Work on developing a plan that allows for a consistent six and a half to eight hours of rest each night. Think about when you really want to go to bed and when you want to wake up. Then you can decide where to place your “sleep window”—the hours that you choose, for yourself, to be your period of restoration.
Two things that are going to tell your body that it is time to wake up and shut your sleep window: bright light (especially sunlight) and available calories. Experiment to determine if there are new times when you might want to begin and end your sleep. If those times don’t line up with what your body is doing now, you can hack them with fasting and light.
HOW TO DO A CIRCADIAN RESET FAST
Another way to tap into evolutionary patterns of sleep and fasting to your benefit is what I call the circadian reset fast. You use it for a short period to rapidly change your sleep/wake cycle to better fit the life you want, to fix jet lag, or to deal with shift work.
I’ve been tracking my sleep for fourteen years. As an author and as someone who likes to dive deep into research, I find that there’s an especially productive writing time that happens very late at night. It’s quiet. It’s a time when I can focus. And since nobody else in my home is awake then, it’s a great period of alone time. As much as I enjoy those late hours, they come at a cost. In the morning, I still have to take the kids to school at the usual hour. Staying up until 2:00 a.m. and then waking up five hours later over and over wears me down. It would wear anyone down. After a while, that kind of schedule makes you feel like garbage in the morning, and you wonder whether the exhilaration of the late-night creative burst is really worth it.
So of course, I decided to search for a biohack that would help me sleep normally when I’m done writing a book like this one. (It is 3:00 a.m. as I type this; it’s when I tap into my best writing mode.)
In order to hack sleep, you have to hack billion-year-old evolutionary mechanisms, ones that predate the origin of animals—even the origin of sleep itself. I’m talking about back when the most complex form of life on Earth was single-cell bacteria floating in the ocean. Peak nutrients were available at noon, when the sun was highest. The sun would come up, and those ancestral bacteria would float up from the cold depths of the ocean. They would reach the surface and get their first jolt of morning sunlight, which would be a reddish color—because, hey, that’s what sunrise looks like when you’re floating in a primordial ocean. And then they would start getting energy from the sun and begin feasting on whatever was in the water around them. That whole legacy still lives on inside of you. The daily cycle of light and nutrition is encoded into your cells, and it’s persisted for eons because it’s kept us in sync with our planet. By selectively going without—without food, artificial light, or electronic distractions—you can restore harmony with your ancient internal rhythm.
You’re going to combine the timing of food and sleep to trick your brain into moving your sleep window. Think about the stimuli that affect your body clock. The first is light, including its color, intensity and angle. The second is calories, or rather calories consumed. You can tweak this if you know how to fast. If you believe you’ll starve without three meals a day, your sleep window will remain frustratingly out of your control! There aren’t yet any ironclad studies to back up my theory, but I estimate that light controls about 70 percent of the strength of your circadian rhythm, food about 20 percent. And room temperature is probably the other 10 percent. These are the variables we’re going to work on hacking to reset our circadian rhythm. The formula I’ve come up with boils down to this:
Wake at the new time, with or without an alarm.
Turn on bright indoor lights (halogen are best), or go outside without sunglasses.
Drink coffee (with butter and C8 MCT oil) and have at least 30 to 50 grams of protein within thirty minutes of waking.
Eat lunch normally, including lots of fat and grass-fed protein.
Fast from 2:00 p.m. onward.
Dim the lights and/or put on TrueDark glasses two hours before bed.
Repeat for a week, and do not eat dinner at all—you are looking at a “reverse intermittent fasting” schedule where you eat all your calories in a morning eating window.
This formula works astoundingly well. I reliably went to sleep at about 2:00 to 4:00 a.m. for most of the last fourteen years. I just don’t get tired until then. Using the above techniques, I now get tired and go to sleep at 11:00 p.m. and wake without an alarm clock six and a half to seven hours later. I wish I’d known about these sleep hacks when I had a day job!
On the other side of the coin, if you happen to be the rare person who goes to bed at 9:00 p.m. and wakes at 4:00 a.m. and you want to reset your clock, you can use the same basic techniques to shift your bedtime later.
Eat dinner an hour after dark, including lots of protein and a few carbs.
Keep bright lights on for an hour (or maybe two) after the sun goes down.
Avoid caffeine at night.
Sleep in a very dark room.
Wake up as late as you can.
After you wake up, use low lighting and/or wear TrueDark glasses for one to two hours.
Do not drink coffee until two hours after you wake up.
Do not eat food of any type in the morning; butter and C8 MCT oil in your coffee are okay if you’re hungry.
Eat a late lunch at 2:00 p.m., including lots of fat and grass-fed protein.
Repeat for a week.
It is truly remarkable how combining fasting with light can recalibrate your body’s internal clock.
BRINGING ORDER TO DISORDERED SLEEP
So far, we’ve been discussing what you could call universal sleep problems: difficulty falling asleep, restless sleep, difficulty waking up, not enough sleep—the kinds of problems virtually all of us have. Adjusting your sleep wi
ndow and your eating window will improve all of these issues. But a huge number of people also suffer from more specific sleep disorders. Intermittent fasting and taking control of your sleep schedule can help here, too.
The best-known sleep disorder is snoring, or sleep apnea as more severe cases are called. Sleep surveys suggest that up to 7 percent of the population suffers from apnea.10 For snoring (formally defined as the sound air makes as it flows over relaxed tissues in your throat, forcing them to vibrate) the numbers are drastically higher.
If you stop eating several hours before bedtime so that your body can complete the first parts of the digestive process, it will help with your overall quality of sleep and should help tame mild to moderate snoring as well. The problem is that many of us lead hectic lives and can’t always follow ideal eating patterns.
Let’s say you’re with an important client in a distant city. Your business dinner runs late, so by the time you get back to your hotel and you’re ready to hit the hay, it’s been just an hour since you ate. You’re aware that this isn’t optimal and that your body is still busy turning that food into energy, keying up your metabolism at a time when your circadian rhythm wants to shut you down for the night. Still, you do your best. You don’t turn on the TV. You close the blackout drapes to banish outside light from your temporary castle. Maybe you use something like the SleepSpace app on your phone as a white-noise machine to create a neutral-sounding environment and duplicate your at-home sleep experience.
