by Dave Asprey
When your body burns fat, the carbon and hydrogen in the fat molecules combine with oxygen, which forms carbon dioxide and water. You breathe out the carbon dioxide, and your body makes use of the water, so you’re actually hydrating your body as you go, the same way a camel stores water in its fatty humps. If you’re competing in a long race and you’ve practiced fasting while training—but not necessarily during the race—your body will be better able to metabolize the energy you get from ketones.
Research backs up the effectiveness of this fat-first, fasting-enhanced exercise method. What you’re doing is tapping into more of those chemical pathways that were shaped by millions of years of evolution. Enhancement of endurance through intermittent fasting was documented in a major study led by Krisztina Marosi when she was at the National Institute on Aging in Baltimore. “Evolutionary considerations suggest that the body has been optimized to perform at a high level in the food-deprived state when fatty acids and their ketone metabolites are a major fuel source for muscle cells,” she and her colleagues concluded.2
Your challenge, then, is to become so resilient and flexible that you can start out with a full load of ketones and switch over to burning sugar. Intermittent fasting is the tool that will enable you to do that. The human body is built to burn sugar, or, if there’s no sugar around, it will grumble for a little while, then start burning ketones from fat. In nature, ketones and glucose are never present at the same time. You can, however, trick your body into having both present at the same time using the wonders of supplementation!
Ketone supplements enable you to achieve ketosis without following a strict keto diet—that is, one completely devoid of carbohydrates. This works really well when you’re metabolically flexible because your cells can use both fuel sources at the same time. One method is to put cold Bulletproof Coffee into your exercise water bottle but make it with very little if any butter. The MCT oil in Bulletproof Coffee raises ketones because it converts directly into the ketone known as beta hydroxybutyrate, or BHB, and it does so even in the presence of carbohydrates.
It’s worth noting that there are companies that sell a product, ketone salts, that some athletes now put into their water bottles. They consist of BHB molecules that are bound to a mineral. I believe that taking ketone salts regularly is not a good idea. In the last interview he gave before he passed away, Richard “Bud” Veech, the world’s most experienced ketone researcher, who studied ketosis for more than four decades, told me that ketone salts cause mitochondrial harm. Are they safe for short-term use, as during a race? Almost certainly. Do you want to take them regularly? Probably not. It’s why I don’t sell them. I’m similarly dubious about commercial supplements that contain ketone esters. In this case, the BHB molecule is bound to butanediol, an alcohol molecule that chemists use to make polyurethane. That doesn’t mean ketone esters are bad for you—except that your body has to do some work to use them.
Ketone esters create a heavier load on the liver, and ketone salts take a load on the kidneys. I don’t consider either one advisable for daily use. MCT oil is a perfectly natural source of ketones that is 100 percent biologically compatible. That’s why it’s a key part of the recipe for Bulletproof Coffee. If you need a bit of rocket fuel that doesn’t have a metabolic cost and you use it carefully and occasionally, those alternatives could be acceptable. But I believe that MCT oil is a better and safer way to do it.
Ketone supplements work well for elite types of endurance events, but for overall strength and well-being what you really want to do is become highly resilient. You want to build up your innate strength so that you’re equally powerful when you’re on the basketball court or when you’re in home isolation stressing about a pandemic.
Intermittent fasting sets you up for developing that kind of resilience. You go all night without eating. You wake up, drink whatever beverage you need for whatever type of fast you’re doing: water, tea, black coffee, Bulletproof Coffee, whatever. Then, just before you’re about to break your fast several hours later, you do your workout. You don’t go for a long run. You could go to your strength trainer, work out with resistance bands at home, hop on your Peloton, whatever. You’re not a masochist, after all. What you want to do is just a short fifteen- to twenty-minute, intense series of sprinting and resting exercises. This is known as high-intensity interval training, or HIIT.
The sprint-style workouts of HIIT have been around for decades, but it’s only recently that science has shown the amazing fitness benefits they deliver. HIIT is the most simple, primal, and time-effective workout imaginable. A typical session goes like this: Sprint for fifteen to thirty seconds. Walk until fully recovered. Repeat. Do that for twenty minutes, if you can. Or up the game with seven to ten repeats of twenty seconds sprinting followed by just ten seconds of rest, which is a variation of HIIT known as Tabata.
When you run (or bike) at an all-out sprint, your body produces lactic acid, a by-product of burning glucose without enough oxygen present as it goes into oxygen debt. When your body produces lactic acid, it also produces copious amounts of adrenaline. This adrenaline directly corresponds with fat burning. In addition, a primal part of your being will panic as your muscles are depleted of glycogen. Your pancreas will release insulin into your bloodstream in an attempt to keep your body from starving. In time, this adjustment will enable you to metabolize fats and sugars far more efficiently. Although the workout is very brief compared with standard endurance workouts, the high intensity of HIIT (it’s right there in the name!) means your body will continue to burn calories in the hours after the session is complete.
The research behind this is compelling. During HIIT, a component of fitness known as VO2 (the volume of oxygen in the blood) is elevated and the release of certain enzymes is increased. VO2 level increases during short-duration HIIT intervals are equal to those during a standard endurance workout of running and biking. In other words, you’re getting a hormonal workout at the same time. A team of biologists at the Australian National University determined that HIIT boosts testosterone levels by 38 percent. In their study, blood levels of human growth hormone shot up by 2,000 percent!3
For you endurance junkies out there, it’s worth noting that if you’re training for a long competition, HIIT intervals are no substitute for a long run or bike ride, although for basic cardio fitness, there is research from the University of Colorado showing that two twenty-second high-intensity sprints on a bike produced exercise results superior to those of a forty-five-minute endurance exercise session on the same bike.4 For endurance athletes, research has shown that elevating VO2 is not as important as raising what is known as the anaerobic threshold, which is that personal red line where the body goes into oxygen debt. Either way, HIIT is an amazing way to increase your fitness without a major time commitment.
A short, intense workout unleashes the marvelous process of mitochondrial biogenesis. During biogenesis, the body increases production of ATP, the energy storage molecule in the mitochondria. This happens during endurance athletics, fasting—and, in this case, fasting with the addition of a HIIT interval. You know what it’s like when the battery in your phone starts getting weak after you’ve had it for a few years? An analogous process happens to the energy storage pathways in your cells. Mitochondrial biogenesis rebuilds the molecular machinery that pulls the energy out of the ATP molecules. You are literally increasing the amount of available energy in your body.
HIIT is all about alternating fast and slow movement. Sprint as though a tiger is chasing you, then walk gently for a couple minutes at a pace much more slowly than you normally would, or for maximum results lie on your back and pant. Then sprint like hell again for twenty seconds: you can almost feel the tiger’s breath on your back. Then walk very slowly for a couple minutes, and do it all again. Once you get used to the HIIT pattern, play around with your mental imagery to keep it interesting. Find your own make-believe pursuer. It never hurts to activate the amygdala’s primal fight-or-flight response to make
you sprint as though your life really depends on it.
If you do this routine near the end of a fast, even once a week, you’ll be amazed at the results you get.
THE BATTLE OF CHANGE VERSUS CONSISTENCY
The body resists change because it takes energy. Left to its own devices, that means the voice in your head that says you’ll starve if you don’t eat cake will also tell you to just lie on the couch to save energy. The thing that scares your body the most is rapid change, because it could indicate a life-threatening situation. That intense reaction means you can use rapid change to grab your body’s attention and cause your body to respond rapidly. In fact, the more rapid the change in inputs to your body, the more your body will respond. Therein lies a central paradox of human health: the body craves consistency (because it minimizes energy expenditure), but it also hates consistency (because it makes you weak). Exercise is a way to force your body to confront change, so that you can be strong.
HIIT works because your body has to go from 0 to 100 percent back to 0 percent in a short period of time. It’s actually harder to do that than to go from 0 to 75 percent and stay there for a while. Fasting works because you go from eating normally to eating nothing and then eating normally again. It’s more dramatic and harder than eating just 70 percent of the calories you need, but it drives far more positive biological change.
The same thing is true of weight lifting. Let’s say my arm weighs ten pounds and I decide to go to the gym to add another five pounds of weight to it. That’s not much of a change. I’m flopping around some puny five-pound dumbbells, trying to get bigger biceps, but nothing is happening. I burn a little energy, sure, but it isn’t as though my muscle cells are really stressed by those measly five pounds of additional weight. It’s time to switch to something far heavier. My new dumbbells weigh twenty-five pounds instead of five pounds, so I can exhaust the muscles in less time. As you’d expect, I see more gains in less time.
Thanks to this newly observed principle, which I call slope-of-the-curve biological response, you can consciously change the inputs to your system to be more dramatic, which saves you time and makes your body respond in ways it never would if you introduced changes gradually.
Another example of how you can create abrupt bodily change is a new method of strength training known as blood flow restriction, or BFR. You place inflatable cuffs, like blood pressure cuffs, around your upper arms and upper legs. Then you pump them up as you would a blood pressure cuff. They shouldn’t be particularly uncomfortable, and they certainly should not cut off blood flow completely. (At that point, the BFR band becomes what is known as a tourniquet, and if you leave it on all day you’ll end up losing a limb. You’ll lose weight, but it’s not the best way.)
After adjusting the BFR band properly with a hand pump, you exercise with almost no weight. You could even use those five-pound dumbbells. The crucial thing is that you’ve created a local hypoxic (oxygen-starved) state that switches your muscle cells into emergency mode. With BFR, you get the results of lifting heavy weights without having to put your ligaments and tendons under stress. You also cultivate a better cellular response. You’re putting your cells into a state in which they’re really panicking. The lack of blood flow and the resulting oxygen deficit activate all of their stress responses and their energy emergency mechanisms. Just as with HIIT training, the way to get the most out of BFR is to work out for a short period of time.
If you stack these things—fasting plus HIIT or fasting plus BFR—you ratchet up the intensity. The HIIT and BFR protocols work fine under normal dietary conditions, but they are even more effective during a fasted state. That trains your body to get its energy from fat and increases your metabolic flexibility. The more you exercise while fasting, the more you train your body to make a seamless transition between carbs/sugars and fat. If you do a HIIT or BFR workout at the end of your fast, though, keep in mind that it will not be your most vigorous workout. It will not be your fastest workout, either. But because it takes place while your body is already depleted of glucose, you will see great gains.
RUNNING HOT AND COLD
Here’s one more way to get outsize effects from fasting plus slope-of-the-curve biology: hot-cold therapy. This one could hardly be simpler: you wake up in the morning and take a cold shower or do some other form of sudden cold therapy. Your body is startled by the temperature change and responds by unleashing all of the biochemical tricks it has to deal with a sudden challenge.
This is a condition known as hormesis, in which the body thrives by adapting to adversity. The idea is that you hit the body with a modest challenge or stress and the body actually overcompensates, getting stronger in the process. Medical researchers have found that cold therapy appears to have a number of impressive benefits, including pain relief, faster recovery from injury, better mood, a boosted immune system, and weight loss.5 A regular ritual of cold-water immersion (whether through ice baths, cold showers, or plunges into a cold lake) has also been linked to a reduced risk of cancer and dementia, probably by strengthening the lymphatic system and circulation.
Note that you don’t gradually cool the water to make it comfortable. You take your nice warm shower, and at the end, direct cold water at your forehead and chest, where your cold receptors are. Yes, it will suck—for exactly three days. After that, the sudden cold will drive the level of cardiolipin in your mitochondrial membrane up, enabling your body to generate heat more quickly. It will also burn more calories all day long.
After the cold therapy, if you feel ready for another shock, try hopping into a sauna, or at least switching the shower to hot again. The switch to heat is going to increase your blood pressure, increase your heart rate, make you sweat, make you detox, and raise your level of heat shock proteins, your inflammation-mediating molecules. Heat shock proteins are produced in response to stress and, despite the name, can also be secreted by the body when it is exposed to cold temperatures and many other forms of sensory assault. They’re also not just a single type of protein but rather a whole family of protein molecules that protect against muscle wasting, making them a vital ally in antiaging.
The sauna will also raise your blood level of the molecule hypoxia-inducible factor 1-alpha, or HIF1A, which coordinates the biochemical response to an acute lack of oxygen. There are several other ways you can trigger HIF1A, including restricting blood flow, doing breathing exercises, or just holding your breath. By priming the HIF1A pathway in your body, that trip into the sauna has already prepared you for the oxygen-limited intensity of BFR training, a high-intensity interval sprint, or HIIT-style twenty-second sprints spread out over a five- or ten-minute period.
There is strong epidemiological evidence that sauna therapy is effective in halting cardiovascular disease and dementia.6 Cardiologist Jari Laukkanen from the University of Jyväskylä in Finland (a country where saunas are practically a way of life) and his colleagues conducted a twenty-year study of middle-aged men who used a sauna regularly and found that the men who sat in the sauna for twenty minutes at least four times a week decreased their risk of sudden cardiac death and experienced a 40 percent reduction in all-cause mortality during the period of the study. The sauna fanatics also had a markedly lower risk of developing Alzheimer’s disease.7
I should note that I first heard about infrared saunas in around 1998, before they were all the rage they are today. Back then, I was still seriously overweight and unhealthy; I had constant back pain and was inflamed all the time. In other words, I was desperate. I’d heard that a sauna could help with my symptoms, so I bought one of the early infrared sauna models available to consumers. You can learn from the long list of mistakes I made. I put the sauna in a corner of my living room, where it didn’t really have a strong enough electrical circuit; as a result, I had a hard time getting it hot enough, and when it finally reached a useful temperature inside, it shut off. The safety measures that shut off a sauna after an hour are there for a reason: if you were to pass out in a sauna and i
t stayed on, you could easily die in what would become a slow cooker.
Fortunately, saunas have progressed a lot since then. The newer infrared saunas heat up much faster and work much better. They toast you with a mix of far-infrared radiation, which penetrates and heats you on the inside, and near-infrared radiation, which warms mostly the surface of the skin. This combination may be especially effective for boosting your production of heat shock proteins. By the way, laptop computers and cell phones are a lot more heat resistant than they used to be, so if you absolutely must, you can be on your phone in the sauna these days. (Full confession: I do regular Instagram Live events from inside my sauna. When my phone overheats, I run ice water over it until it comes back on. Thank goodness most phones are waterproof now.)
I’d prefer that you treat the sauna as a meditative place, but the really important thing is to find a system that works for you. If you have a busy life and the only way to make time for the sauna is by multitasking—then fine, go on your phone. I find that being in the sauna for thirty minutes isn’t harming my day by taking away from my productivity, which it once did. Or maybe you want to take your devices into the sauna as part of your relaxation technique. Want to listen to audiobooks or podcasts? Do it! Do whatever makes your program of fasting, exercise, and body shocking fit your lifestyle.
My recommendation is that you master intermittent fasting first. Exercise on top of fasting. Try adding cold showers. Then experiment with an infrared sauna at a spa or at a friend’s house if you are lucky enough to have a friend with a sauna. That will tell you if you really want to make the considerable investment of dollars, time, and space to have a sauna of your own. All I can tell you is that I bought one of the new, improved infrared saunas, and I have no regrets.