by Dave Asprey
When I began intermittent fasting, it was like turning on a light switch. Back then, there were no blogs about it and no books. I knew that the Atkins diet recommended a “fat fast” to get into ketosis, but it was cheese based and used artificial sweeteners, so I hacked it. I already knew that Bulletproof Coffee made me feel great, so I had it for breakfast to kick off ketosis. Just by skipping breakfast and making my morning coffee Bulletproof, I lost more weight and didn’t even want lunch. When I skipped breakfast and had no Bulletproof Coffee, on the other hand, I got distractingly hungry at 11:30 in the morning and didn’t function well at work. It’s such a simple behavioral change, one that everybody is capable of doing: just go sixteen hours without eating anything inflammatory at all. Almost like magic, the anti-inflammation systems in the body start to kick in right away. (Except that it’s not magic at all; this is exactly how your body has evolved to work if you will just let it.) You get a rest from inflammatory food toxins. At the same time, your body switches into ketosis and you get a metabolic reconditioning.
For you, going on a basic sixteen-hour fast may well be the first time you’ve ever experienced a taste of life without new inflammation. Like me, you will probably become aware that you have food addictions. These are not just emotional attachments; they are true biological addictions to certain molecules and foods. Make no mistake: these addictions will be hard to break. If you have a biological addiction, milk protein can be as hard to quit as nicotine. Your body will fight back when you try to quit. The Big Food industry will make sure you see ads for those foods everywhere and that they are easy to grab when you go into the supermarket or drugstore. As soon as you start fasting, though, you start to assert control over them.
Two of the most common biological addictions are to wheat (gluten) and dairy products. You may think you don’t have to worry about them because you’re not allergic to either one. Truth is, you probably have no idea what effect they’re having on you. How many times have you gone three days without eating wheat or dairy protein? (Butter contains a negligible amount of protein.) Both gluten and dairy products have known inflammatory effects. You’ll never learn the impact they have on your body until you break your addictions, which is a lot harder than it sounds.
The gluten proteins in bread and the casein proteins in milk and cheese often break down in the body into molecules known as gluteomorphin and casomorphin. Notice the “morphin” part of their names? These molecules are both morphine analogs that trigger the opioid receptors in your brain—your brain’s pleasure centers. In other words, the way your body processes the high of eating a grilled cheese sandwich is a lot like the way it does a shot of heroin. The two produce different levels of euphoria, obviously, but both deliver an addictive sensation of gratification. That’s why when you eat bread, you’re going to want bread the next day and the next day and the next day. That’s why it’s so easy to fill up on the breadbasket at the beginning of a meal in a restaurant. Your body craves that opiate sensation. Try fasting while thinking about crusty French bread.
If you’ve trained your body for years that every morning it will get its fix—buttered toast, maybe, or a muffin, or milk poured over cereal made of grain—you’re probably going to get a little bit twitchy when you start intermittent fasting and deprive the body of that fix. That’s fine. It’s a manageable craving.
When your body starts asking “Where’s my hit of gluten?” you can respond, “Hey buddy, I’m giving you the gift of sixteen hours to repair yourself. It’s time for spring cleaning. You’ve got nothing else to do, so you might as well turn all the energy you were using to combat the inflammation from the food I was giving you into more enzyme production. Let’s perform a systems upgrade.”
THE JOYOUS EXPERIMENT
Around the time I was learning about the tremendous impact of inflammation and had begun to experiment with fasting, I went on a spiritual retreat in a remote region of western Tibet. During the trip, I’d been fasting and eating almost nothing bad for me—not out of choice, so much, but because there was very little food available at all. Halfway along the sacred path around Mount Kailash, I was offered yak butter tea, which is given to travelers to help prevent altitude sickness (I was 18,000 feet above sea level). To my amazement, I felt great afterward. I later found out that blending butter into the tea can do powerful things for inflammation and energy production.
It turns out that taking a brief period away from food does not lead to a sense of “I’m going to die.” What I was actually thinking up there on Mount Kailash was “Wow, this is what it’s like to have limitless energy and feel great.” That’s one of the most surprising, immediate benefits of reducing your inflammation.
Activating the power of fasting is not that simple, however. If it were, everybody would be doing intermittent fasts already. If you do a prolonged fast, especially a “dry” fast with no water or other liquids, the elation passes. Even a short fast can be seriously unpleasant if you jump into it unprepared. It starts to seem as though your fears about fasting are coming true. Your superpowers are replaced with nagging voices of hunger, fatigue, and irritability. The question becomes “How can these things be managed?” and then “Can they be managed?”
The answer eluded me for quite some time. I couldn’t figure out how to re-create the surge of energy that ran through my body on Mount Kailash. I had watched how Tibetan people could subsist on little more than a few cups of yak butter tea each day, yet carry more than I could through freezing temperatures for twelve hours without more food. They weren’t strictly fasting, but it was close. I researched different styles of fasting and introduced a regular discipline of fasting into my life. I tried fasting for four days, twenty-four-hour fasting, fasting with and without coffee, tea, and butter. And on and on, until I discovered the biohacks that work to create more energy than I know what to do with.
Part one of the answer is Bulletproof Coffee, a concoction inspired by the yak butter tea I drank in Tibet. This is the difference between a Bulletproof Fast and a regular fast. It allows you to experience more of the inflammation-free euphoria and near-zero hunger, and it minimizes the energy dip most people encounter when going without food.
Part two is embracing that idea that fasting is not just one thing; there are many styles of fasting and many rhythms of intermittent fasting. All of them provide anti-inflammatory and other benefits. If your fast allows some flexibility, it’s a lot more likely to fit in with the rest of your life. In my case, I have kids, and I’m the CEO of a good-sized company. Planning a forty-eight-hour fast isn’t always easy. Sometimes it works best when the kids and my wife go skiing or do something else that I don’t. (I have screws in my knee; that’s a whole other story.) Or I’ll do the same thing sometimes on business trips. Afterward, I always feel better and get that feeling of rejuvenation. The difference is the lack of inflammation.
Part three is drawing on your social support network, especially when you first start doing intermittent fasting. You can easily find apps and online communities to help you out, but I really recommend that you find a buddy who wants to try fasting with you. Social bonding is yet another way to reduce inflammation, by the way. In 2020, a group of researchers at the University of Surrey and at Brunel University London found that social isolation is associated with increased inflammation in the body. Isolated people showed elevated levels of C-reactive protein, a protein produced in the liver, which normally floods tissues after an injury. It also elevates levels of fibrinogen, which promotes blood clotting. The research team also found that the link between social isolation and inflammation was stronger among men than women.6 You’ll read more about the gender differences in fasting in chapter 9.
Part four drives home the point I made earlier: don’t look at fasting as a burdensome chore to lose weight or to tend to your health. You will probably lose weight, and you definitely will be healthier—but neither of those things will happen if the fast makes you so miserable that you quit. That’s why fr
iends, flexibility, and a well-timed Bulletproof Coffee are so essential. They let you experience what it is to be freed from the demon of inflammation. You get to fast, you don’t have to.
If fasting brings pleasure instead of misery, you’ll keep doing it—not because you swore an oath you’d keep going, but because you’ll want to keep feeling good. And once you feel good more of the time, you’ll be more likely to make other changes that reduce inflammation and enhance your sense of well-being: making better food choices, exercising regularly, avoiding smoking, reducing or quitting alcohol consumption, and getting enough sleep. Taking short breaks from food is part of a broader program of steering yourself away from self-destructive tendencies.
Look at fasting, then, as a decision to be in charge of yourself and work toward being your best self. Fasting makes your body work better. It makes you tougher. It makes you more resilient. It prepares you mentally to take on everything in the world. We all say we want to live a long life, right? But what we all really want is an enduring high-quality life. Fasting is central to both parts: living long and living well.
For decades, many leading biologists promoted the idea that human longevity is largely controlled by our genes. If your parents and their parents and their parents before them all lived into their nineties, for instance, there was a good chance you would, too. Your family had “good genes,” whatever those might be. On the other hand, if your ancestors didn’t make it past their fifties, well, too bad for you. Several major research groups continue to sequence the genomes of centenarians, searching for quirks in their DNA that could account for their extreme longevity. Researchers working on the New England Centenarian Study have flagged more than a hundred genetic variants that preferentially show up among the oldest old.7
But mostly what such studies have revealed is that genes are just a single, somewhat ambiguous component in the mix of factors that determine health and longevity. Diet, lifestyle, and other daily choices are just as important—and not necessarily in the ways you might think. Mikhail Blagosklonny, a gerontologist at the Roswell Park Cancer Institute in Buffalo, New York, is a leading proponent of the once-controversial theory that certain types of weak stresses, including fasting, can extend life span by activating the body’s self-repair mechanisms. “Life span can be extended by either (a) slowing down aging [or] (b) by increasing aging tolerance,” he declared in one influential paper.8 In his view and the view of a growing number of his colleagues, increasing aging tolerance is exactly what weak stresses do.
Experiment after experiment has demonstrated that animals tend to live longer when underfed, whereas if they are given all the food they need to survive, they have demonstrably shorter life spans. In the laboratory setting, this underfeeding technique is known as caloric restriction. It’s an extreme version of the insidious “calories in, calories out,” or CICO, diets that have recently developed an unfortunate following. It typically involves giving the animals about 30 percent fewer calories than in their baseline diet. What the science doesn’t tell you is which calories to cut or how to cut them. Some antiaging obsessives have tried to apply the lab techniques to human diets, simply cutting calories across the board. It’s similar in approach to some of the old-fashioned calorie-counting diets, which told people that the way to lose weight and stay thin was to remain hungry—pretty much forever.
No wonder people almost never stayed on those diets for long. Just as CICO diets are the very definition of misery, so, too, are long-term caloric-restricted diets, especially if you ignore what food makes up the calories you’re eating. It might be worth it if it was the only way to live a lot longer, at least for some people. But for most of us, calorie restriction and the suffering that comes with it just aren’t tolerable over time. That’s why intermittent fasting is so exciting. When you do a smart intermittent fast, you’re probably going to end up eating less overall—not because you’re forcing yourself but because you’re just not as hungry as you used to be. In the early days after I developed the Bulletproof Diet, many people thought it worked just because people were eating less. Now we can show what’s actually happening; there are hormonal changes and inflammation changes associated with the fasting process and with the diet itself. But you often do end up reducing your calorie intake as well, and you get the knock-on benefits of that, too. You may end up cutting close to the number of calories that people on calorie-restricted diets do—you just do it with more energy and joy and better health as a bonus. It boils down to a simple formula: Eat good-quality food until you’re full. Stop for a while. Do it again. Enjoy a better quality of life.
And you probably will have more of that life. You know how your brain feels exhausted at the end of a long, busy day? Well, it genuinely is exhausted at the cellular level. The nonstop firing of your neurons creates waste products that have to be disposed of. A fast of at least twelve (ideally eighteen) hours gives your cells the signal that it’s time to clean house. Likewise, your mitochondria need regular periods of rest, repair, and regeneration. The textbook description that the mitochondria are the “powerhouses of the cells” is a cliché, but it’s true: these little capsule-shaped structures are found inside almost all of the cells in your body, and they generate most of the chemical energy in your body, storing it in a molecule called adenosine triphosphate, or ATP. The mitochondria are the prime movers behind your metabolism. You need well-fueled, plentiful mitochondria in order to stay energized, mentally focused, and happy.
Reduced function of the mitochondria is connected to the symptoms of aging we most dread, including fatigue, increased body fat, and declining cognitive ability. Researchers have found links between mitochondrial dysfunction and nearly every age-related disease, including Alzheimer’s and cardiovascular disease. Tying all of these strands together, a recent study led by medical researchers at Cambridge University showed that mitochondria act as tiny switches that toggle the inflammation response in the body.9 Healthy mitochondria do a better job regulating your inflammatory and anti-inflammatory systems. When they’re in good working order, all of your other biological systems do a better job of taking care of you, too.
The bottom line is that fasting reduces inflammation, promotes regeneration, and makes you feel younger and more energetic. Fasting makes you harder to kill. More important, it gives you more to live for.
TRUTH TIME: WHY YOU SHOULD FAST
It is truly remarkable how fasting can troubleshoot your biology, boost your energy, and cut your risk of disease. I want you to have all of these benefits. But I’m also a realist who has guided a lot of people into intermittent fasting and watched some of them fail to stick with it. The only way you’ll cut inflammation and tighten up your Krebs cycle is if you find a way to make fasting satisfying for you—not at a molecular level but at a personal level. It’s not about the science. It’s about you, and you’re more than science.
People almost always claim that they care about their health. But if someone hands you a bagel—or shows you a picture of a sexy person or shows you a way to make a ton of money—the concept of health will probably fly right out of your mind as those new motivations jump to the top of your priority list. Cravings are extremely effective at making us forget our goals and our priorities. Even if you are trying to take good care of yourself, it’s really hard to remain mindful of your health all of the time. Otherwise, tending to your health is probably around number seven on your “honey-do” list.
Instead of fighting against reality, let’s try some radical honesty: You are not going to fast just for your health. And you’re certainly not going to fast if it makes you miserable. You shouldn’t even try to make health your guiding motivation. That may sound strange, given the messages you hear all the time in books and articles and on TV shows. It’s a nonstop drumbeat: “You’ve got to do this exercise or eat this superfood or follow this complicated diet so that you can be healthier. You must, if you want to take care of yourself! If you don’t, that must mean you don’t care about you
rself!”
None of it is true. None of it lines up with the way the mind and body really work. Your desire for great health is not as biologically strong as your need for safety, satisfaction, connection with other people, or even power and success. No judgments here. I’m describing deep-seated human psychology that we all share: you, me, everyone you know.
Take the social aspects of food, for example. People like to go out to eat because they need to connect with other people. That’s a powerful motivation. Sure, you might master the self-control to remind yourself that you’re fasting for your health, and that reminder might enable you to maintain your fast during a social occasion—but damn, it’s hard to say no when someone passes you a plate of fried whatever. Giving in doesn’t make you weak or a bad person. Food is one key method through which human beings connect. Denying yourself human connection is a really bad use of your power of self-control.
That need to connect reminds me of the days when so many people decided that they would get healthy by running a marathon. Many of the newly enlisted runners were heavily overweight and not conditioned. Their outrageous scheme was to go from being total non-athletes, unable to do so much as jog around the block, to running the 26.2 miles of a full marathon. They convinced their friends to join them in order to experience camaraderie. Then they all started training. Amazingly, a lot of them managed to complete their goal and run an entire marathon—just not for the reason they thought. Mostly, they believed that they were running for their health. In reality, they were running to satisfy their deep desire for connection.
If you’ve ever made it to the finish line of an endurance event like that, you probably know that a sudden decision to run a marathon is really rough on you. Simply running the 26.2 miles doesn’t work very well as a health and wellness plan. Look at the bulk of the runners who are doing it. They may accomplish the challenge, but if you pay attention to the many body types in a pack of first-time marathoners, you’ll see a whole lot of metabolic issues that are not fixed by running a marathon.