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Katie: Hello, and welcome to “The Wellness Mama Podcast.” I’m Katie from and That’s wellness with an E on the end. It’s my line of good for you from the outside in personal care products like hair care and toothpaste. You can check those out at That’s wellness with an E on the end.

This episode is all about fasting. And this is a topic I get a lot of questions from you guys about, especially because I’ve mentioned that this has been a big part of my own health improvement over the last couple of years and something I do regularly. It’s also not something that I think is the same and beneficial for everyone in the same way. I think there’s a lot of nuance and some caveats that are important to understand. And in this episode, I’m here with Dave Asprey, and we go deep on this topic. If you don’t know Dave, he is the founder and chairman of Bulletproof. He’s also a three times “New York Times” bestselling author and he’s been called the father of biohacking. He has spent about $2 billion taking control of his own biology. And we talk about today how a lot of those were fun experiments for him but it does not have to be nearly that expensive or expensive at all to take control of your biology. And one of the ways to do that is through fasting.

So we go through the myths related to fasting, important things you need to know, how to actually control your hunger while fasting, the benefits of fasting both from a mental and physical perspective, different types of fast that you can do, and how to make sure that you aren’t hurting your body when you are fasting. Very in-depth episode, as it always is with Dave. And if you have any questions about fasting, they’re probably answered in this episode. So, let’s jump right in. Dave, welcome back to the podcast.

Dave: I’m so happy to be back, Katie.

Katie: Well, I’m excited to chat with you and I’m excited for our topic of conversation today, which is also the topic of your newest book and something I talk about a lot, which is the topic of fasting. So, to start broad, there’s literally dozens of directions I wanna go with this to answer listener questions. But first of all, what led you to write an entire book about the idea of fasting?

Dave: I have a little bit of I’m gonna call it author PTSD over the Bulletproof diet because I put together a whole bunch of stuff. There was intermittent fasting in the book. There was keto and how it needed to be cyclical. And it was a very early book. And I felt like I couldn’t zoom in enough on each of these. And the recipe for writing a fasting book is really easy. Here’s how to fast. Don’t eat for a while. Okay? And then oh, here’s a bunch of references from PubMed that say how good it is. And there are a lot of good books on the science of fasting, but there’s no book that talks about how to actually do it. And so I wanted to write a book that was different than fasting books that also accounted for the fact that fasting is, in one of its incarnations, a spiritual practice, and in other ones, it’s beneficial. And I really don’t want us to go down the path that I call the vegan trap, or the keto trap, or now the fasting trap, which is that if something’s good, therefore, you should do more of it. And, you know, the same thing happens, where if masks work in a doctor’s office, therefore everyone should wear one all the time, even when they’re sleeping. Well, there’s probably somewhere in the middle is the truth. And I feel like the truth around fasting is that you can fast too much. And I’ve seen for the last 10 years in Bulletproof people, this thing, oh, I feel good when intermittent fasting today, therefore, I’m gonna do it every day for the rest of my life. And then there’s predictable things that happen. So I really wanted that message. Don’t overdo it and think about the spiritual side of it and the psychology of, you know, why you might break a fast early, and how it’s probably not your fault.

Katie: Such important points. And I think you’re still right, I see that as well, that trend of if something is good, then more should be better. And that definitely isn’t the case, like you said with fasting. And I think that’s also the case important to pay attention to with supplements. And when it comes to eating, you know, more is not always better. We pay attention to that.

I also personally have a rule that I don’t do anything every single day except for basic things like sleep, even supplements. I cycle them. I do different types of fasting every day or some days don’t fast on purpose. With the goal that long-term, my thought is we wanna have metabolic flexibility. Like, I want my body to be able to handle anything and everything I throw at it, versus adapting to a very narrow range of things that I make it do every single day. And I’m guessing you come from somewhat the same approach when it comes to this, right?

Dave: I don’t know, Katie. I feel like we should just suppress all oxidative processes in our body every day by taking huge amounts of antioxidants. I mean, because what could go wrong there?

Katie: Another great example, that’s a perfect one.

Dave: No, I’m completely with you. And that was a big part of what’s in this. Like, it’s okay to not fast sometimes. It’s okay to eat carbs sometimes. In fact, probably more often than not. And it’s okay to say, “I’m not exercising today because I’m overtrained.” And it seems like with health influencers, and you’ve seen this, and your content is very clean, and well-thought-out, and science-based. But you see people who take out and they really don’t have a background, and they’ll kind of copy one of your posts. And they become like a cheerleader without breaks. And that’s not okay. Like, you have to teach people how to do it right.

Katie: Absolutely. Okay. So with that important caveat that more is not better and don’t do anything every single day, let’s talk about some of the different types of fasting and how someone might know what kind of fasting they should start with or where to kind of dip your toe in when it comes to fasting?

Dave: It depends on where you are metabolically. If you’re like I was in and you’re 100 pounds overweight, and you feel like you’re gonna die if you don’t eat a snack at 10:00 and you don’t have lunch at 11:50, you’re probably gonna start differently than someone who’s like, “You know what? I eat, you know, four or five times a day, but generally I’m in pretty good shape, and I don’t have a lot of extra fat.” I actually think people who wanna do intermittent fasting, but are really metabolically unfit, for the first month, if they’ve never done anything, they probably should have a breakfast as soon as they can when they wake up that has protein and fat and no carbs. And that’s actually how you start for a month.

But let’s assume that you’re not there, where I used to be, and you’re somewhere along the health curve. Then start with at least a 12-hour fast just to show yourself you can do it, and this is so easy. Have a bit of an early dinner and then you’re going to go to bed without a snack and you’re gonna wake up and you’re gonna wait 12 whole hours. That means you can go from 8:00 pm to 8:00 pm. And that’s just like a can you do it? You’re not gonna get huge benefits from fasting, but there’s some. And then if you’re comfortable with that, you go to a 14-hour fast, which means you can still have a late breakfast and you’ll be okay.

And from there, you can go into what’s the most common intermittent fast, the 16/8 fast, where you don’t eat for 16 hours, which means basically have lunch and dinner. And this is very doable for people, except it would have been impossible for me when I was heavy. And in Fast This Way, I’m presenting three fasting hacks with all the science to go behind them that give you energy, because it’s one thing if you’re like, “Okay, I don’t have kids at home, I don’t have a particularly stressful life right now,” which isn’t most people. “So I’m just really gonna focus on this and I’m willing to be a little bit of a zombie or a little bit hypogly-bitchy,” which is my favorite word ever to describe myself. At least back when I was heavy and didn’t know how to do this. And for those, you can make fasting absolutely painless and energizing. And the more you do it, the easier it is. And so, those fasting hacks are precious when you don’t wanna burn willpower you don’t even have.

Katie: That’s a great point. Okay. So I’d love to kind of break out the differences between these intermittent fasts and then, like, also called time-restricted eating in some of the literature and, like, longer water fast and kind of the pros and cons of each.

Dave: Well, I don’t recommend doing longer fasts until you’ve done some intermittent fasting. And I recommend, especially for women, especially when they’re getting started, don’t intermittent fast every day. You know, it’s okay to have some breakfast sometimes. And for a lot of women as they’re getting metabolically fit, you actually wanna go every other day. And the reason I’m calling out women specifically is there’s a chapter in the book that’s written for women in fasting, because as you know, Katie, a lot of literature is written about young men because they’re the most obvious guinea pigs in college, at least they were historically. Now, college has more women than men, and we’re seeing changes in medical literature because now we’re actually looking at women and men. So only about a third of the fasting literature that I reviewed was looking at women versus men. And so we’re a little bit short on data there.

But you start out and get yourself comfortable with at least several days a week. And then you might start out with doing what sounds really, you know, superhero, like, “I’m gonna do OMAD,” you know, one meal a day. What that just means is you skip breakfast and lunch, and then you have dinner and there you go, you went 24 hours. And you get some autophagy, some benefits, some keto benefits from that, and you feel clearer and much better. And then what I found worked really well is I said, “Okay, what if I just say, I’m gonna play a little bit of willpower here, I’m just gonna skip dinner?” If I didn’t really plan it that much. You kind of trick yourself into that. And then all of a sudden, if you go until the next morning, I just did a 36-hour fast and you feel even clear and even better.

There are people who will say, “You have to do a water fast because that’s what the mice did in the study.” I don’t think that’s particularly scientifically valid for the simple fact that mice don’t have espresso machines. And most of history when people fast, they drink tea. So you ought to have either coffee or tea. And there’s a really important reason for that. And it’s because the amount of caffeine in two small cups of coffee doubles ketone production. And if you have ketones present at very low levels, about 0.48 and 0.38 are the two magic numbers. This is lower than nutritional ketosis. That causes a shift in two different hormones. One is called CCK, cholecystokinin, which is the fullness hormone. So if you can get your ketones up a little bit, the food stops asking you to eat it when you’re fasting and it’s a lot less work.

One of the studies that I came across in Fast This Way says that about 15% or higher of the average person’s thoughts each day are about what’s their next meal. And if that voice shuts up, you have a lot more space in your brain to do other stuff. So if a little bit of caffeine does that and has other benefits, that’s pretty advisable even during a longer-term fast. Have a cup of coffee in the morning. You’ll probably fast better. You’ll have more energy and you’ll have more ketosis. And the polyphenols in it are good for your gut bacteria. You actually feed the bacteria that thin people have that way. And it starves the bacteria that fat people have. So you can shift your gut microbes by having polyphenols without any sugar and without any protein during a fast. And that’s still a fast by every definition. It’s just a better fast.

Katie: I’m so glad you brought that up, because that was one of the recurring questions that seems to come up with any discussion about fasting is what about noncaloric beverages, especially coffee? And I find that a lot of people seem to be able to fast much more easily if they can have coffee. So I love that you are basically making a case to clarify that not just is it okay to have coffee during the fasting window, but it can actually be beneficial. Just making sure I’m hearing that right.

Dave: You’re hearing it right. In fact, there’s a lot of self-flagellation that it gets associated with fasting, that may even verge into orthorexia. Like, I’m not really fasting unless I do this. The definition of fasting that really is throughout Fast This Way is that fasting just means to go without. And when you decide to eat healthy, you’re fasting from junk food. And when you go keto, you’re fasting from carbs. And if you go vegan in a mistaken attempt to improve your health or to improve the planet, then, well, you’re fasting from animal products. And if you decide you’re not gonna drink, you know, it’s abstinence.

And there’s so many types of just going without that you can build into your thought processes, where you can even do breathwork, where you’re going without oxygen for brief periods of time, cryotherapy, you’re going without heat. Anytime you teach the body to feel safe when you’re going without something, the body responds by becoming stronger and more resilient. And that’s why this perfectionism around fasting is actually harmful and wait until I tell you the other two hacks.

Katie: Well, you can’t leave that hanging. Let’s go there now.

Dave: All right, so the second hack is one that I am well-known for. I’m not trying to sell it. But if you put a little bit of grass-fed butter and a little bit of MCT oil in your coffee, different things happen. And a lot of people have fast experience being cold. And the Tibetans who make Yak butter tea were the inspiration for Bulletproof coffee. And this is a part of the world where there’s no air and there’s very little food. And for some strange reason, they always blend in a butter churn, before they had battery-powered, easy to use hand blenders. They blend their coffee, sorry, they blend their tea and their Yak butter. They never just eat the Yak butter and drink the tea. And it drove me nuts because even with Bulletproof coffee, I tried to eat a stick of butter and drink some coffee, and it doesn’t work.

I funded research at the University of Washington, just an open grant without an outcome in mind for Gerald Pollack, and said, “Can you look at water chemistry and what’s going on?” And he tested a whole bunch of different oils and water to see which one makes the biggest exclusion zone in water, which is what your body does. You drink normal water and then your body puts the water next to cell membranes, which are made of fat. And then it provides 1200 nanometer light, also known as body heat. And that combination builds a little layer of water that has different viscosity than normal water. And you must have that in order to make ATP, in order to burn sugar, in order to burn ketones, and in order to fold proteins. Everything that your body does requires the water to be transformed by heat. If you do it in a blender with a little bit of fat in your coffee, a couple of magic things happen. One, you’re less likely to be cold. And your body says, “Okay, I can immediately go into my metabolic processes without having to scrounge energy from somewhere.

And because the MCT is ketogenic, at least if you’re using the stuff I’ve recommended for 10 years, the C8 form, what you end up with is that also raises ketones. And the other hormone aside from CCK that really makes a difference is called ghrelin. And when your ketones go up, just a little bump that you get from putting that stuff in coffee during a fast, what you get is the clarity that happens on the third day of a fast but you get it the morning of the fast. And then you’ll see people say, “But that’s not fasting.” Yes, it is.

And the reason is that you don’t change insulin levels at all. And third parties have validated this. And you still do turn on autophagy. In fact, I interviewed Siim Land, who’s an expert in this, wrote the book “Metabolic Autophagy.” And we actually went through, you know, how the process works and why you still can have autophagy. The trick when you’re fasting is to skip protein and to skip carbs, and having moderate amounts of fat, which you want your body to burn anyway, just improves how you feel during a fast and makes it possible to fast with much less willpower. Those are big things. I’m not talking two tablespoons, which is more of a breakfast replacement. But even if you do that, you lose weight and you get many, many of the benefits of fasting but I recommend going a little bit lighter on the butter during a fast. And you’ll just find that all of the physical anxiety that you have during a fast, it just melts away. And you’re able to fast without effort. And that’s really valuable.

Katie: So you mentioned the term on autophagy, and I think a lot of listeners probably are familiar with that term but for anyone who isn’t, can you explain what autophagy is and how we can know if we’re getting the benefits of autophagy or not?

Dave: Sure. Autophagy is simply when the body looks around either at the cells or at the little subcellular things called mitochondria that make power and make hormones and do all sorts of other things in the body and it says, “Some of these are weak. Let me get rid of the weak ones and build new strong ones.” And this is why fasting is so powerful, because if you eat six times a day, the body, which is very efficient says, “Oh, there’s no need to have young mitochondria so you can have a young person’s energy” because there’s always energy present. I don’t need to be strong. And so, when you do this, the body says, “Oh, oh, I got no carbs, I don’t have enough energy, I need to do something about this.” And then it does. And that’s what autophagy is. And the two forms are autophagy of cells, and then mitophagy, which is when your mitochondria replace themselves. And you can do both of those when you’re only in fat-burning mode.

Katie: Cool. And you also mentioned ketones and ketone levels in the body. And I know that there’s been more and more talk of exogenous ketones lately. So for anybody who is not familiar with that, can you explain what exogenous ketones are and also give us your take on if you think they can be beneficial or not?

Dave: Sure. Ketones are simply fat-burning bodies that happen when your body is not burning carbs, and it says, “Oh, I’ve got to use fat as energy. Ketones have more energy in them than glucose does, which is what your body and your brain usually is. So, if you can start burning ketones, that’s great. And there are three kinds of exogenous ketones. The first kind and the kind that I am a fan of, and the kind that I popularized is MCT oil. And the most common and cheapest MCT oil doesn’t have this power but the shorter chain ones like CAMCT do. They’re shown in studies to raise ketones by about 4X. And what this is, is something the body takes it and transforms it into a ketone. And it has a triglyceride molecule that it strips off and it makes beta-hydroxybutyrate, which is the ketone body you’re looking for. Your body will make these naturally if you fast for about two days. Usually, they’re two uncomfortable days unless you’re using some of the fasting hacks.

And the two other forms of exogenous ketones that are out there are not ones that I recommend. The first type is called a ketone salt. And I actually formulated a ketone salt for Bulletproof as in, we had the packaging ready, we’re ready to go. And I pulled the product. I was the last person to interview Dr. Veatch, who studied ketosis for 40 years and actually mentored underneath Hans Krebs, the guy who invented the Krebs cycle, who cracked the code for how our mitochondria make energy in our bodies. And he said in the interview, which is still on Bulletproof radio, ketone salts are dangerous for mitochondria, they’re harmful over time. And I pulled the product as a result of that. And I don’t recommend ketone salts on a regular basis. It’s okay to use them if you have cancer. It’s okay on an occasional basis but to rely on those for ketones puts a heavy load on the kidneys. And because one of the most studied guys I’ve ever met about ketosis says straight up, “I have seen them cause mitochondrial harm in the lab,” I do not recommend or take ketone salts.

If you are going to take them against my advice, make sure you get something called racemic salts, which are closer to what the body does, you still have a large load of calcium, magnesium, or potassium or sodium that your kidneys done have to deal with. And I don’t think over time, those are a good strategy. If you wanna do a race on them, fine. You’re gonna take them every day, probably not.

What they also do is they tend to raise your blood ketone levels quite high. And we have this thing I call them the Keto Bros. If you ever have a carb again, you’re a bad person. My ketones are higher than yours. And this is the logical equivalent of people saying, “My blood glucose is higher than yours.” If you have high ketones in your body, it means your body is not able to burn the ketones present. People who are metabolically flexible actually use ketones in their blood, so the levels don’t get super high.

The second type of exogenous ketone that’s out there is called a Ketone Ester. And I first synthesized these about eight years ago for Bulletproof to see if we could turn them into a product. And at the time, they were $40,000 a kilo, which is a little bit expensive, and they taste like gasoline, which I still think they kind of do. The issue with those is that de-ester-fying a ketone in the liver places a heavy load on the liver. And, Katie, you know very well how important kidney and liver function is overtime for all sorts of detoxing and anti-aging.

And so my mindset has been pretty much, “Why do I need to spend more money to get my ketone levels higher when I can get them high enough with MCT oil, which creates bioidentical natural ketones without putting the load on the liver or the kidneys?” This is why I’m still an advocate of MCT oil, even though I’ve played very heavily in the labs and in product formulation with looking at esters or salt.

Katie: I’m really glad you brought up the point of just higher ketones for the sake of higher ketones, it’s not necessarily a good thing. And I think that’s a great point, especially like I track my ketone levels and my blood glucose whenever I’m doing fasting, especially extended fasting. So, for someone who’s willing to do that, and I recommend it, I’m a big fan, as I know you are, of as much data as possible and quantifying so you know. What are some good levels to aim for and when might we wanna pay attention if levels started getting beyond a certain point?

Dave: Well, I like to see my ketone levels above 0.5. And that’s where you get the basic metabolic benefits. And if you’re doing an extended fast, they’re gonna go up to 1 or 2. But I see people like, “Yeah, I took a whole bunch of exogenous ketones.” By the way, you can’t get that high with MCT oil, because it’ll give you the runs. But like, basically, “I have my levels at 5 or 6!” I don’t know that that’s a great place to be, unless maybe you’re doing an extended fast and you have a lot of fat to lose and the body’s just burning fat.

One of the things that I talk about in Fast This Way is that if you burn fat quickly, you will become a zombie. And I’ve seen this over and over. I’ve had a guy lose 75 pounds in 75 days on a ketogenic thing I created a while back called the Rapid Fat Loss Protocol. And the problem with this is you have heavy metals, you have pesticides, hormones, and other pollutants stored in your fat tissue. And if you melt a lot of fat, your liver and your kidneys will become overwhelmed and then they will give you huge brain fog and inflammation, and you’ll feel like a zombie.

So whenever anyone’s fasting, one of the supplements I recommend in the chapter on supplements that are good during fasting and supplements that are bad during fasting is activated charcoal, which has been a core Bulletproof thing for years. Activated charcoal sticks to lipopolysaccharides in the gut. So when your gut bacteria get stressed, they won’t make you stressed. And when you start dumping fat, you start dumping fat toxins, it’ll absorb those toxins so your liver and kidneys don’t have to and then you just excrete them through poop.

And that’s a really important thing to talk about when you’re talking about getting really high ketone levels during a fast. Also, as, you know, they got really high, you’re probably burning a lot of fat. And if you’re burning a lot of fat, you’re making a lot of toxins available in your body. So you’ve gotta balance that out.

Katie: Gotcha. Okay. I love that you also… I wanna circle back to supplements again in a minute. But you mentioned kidney and liver function. And I think this gets ignored a lot when people start talking about fasting or even when people just start taking more and more and more supplements, thinking more is better. Let’s talk a little bit about kidney and liver function and health, and how we can make sure that we’re being cognizant of that and protecting these extremely vital organs when we’re fasting.

Dave: Well, it’s harder to protect the kidneys. One of the things that I recommend during a fast is something called Calcium D-Glucarate, which is shown in studies to protect kidneys, as well as something called Calcium AEP. And both of these things will provide some level of protection there. And those are very fasting friendly. Then in terms of supporting the liver, you can take glutathione or you can take liver herbs, like milk thistle during a fast and it’s okay. You might not wanna take glutathione if you’re not dealing with a high toxin load and you don’t need it. It isn’t antioxidant. But generally, it’s very supportive of fasting and the detox pathways. So those are some of the very simple protective things that you can do and that I think are really worth doing during a fast. Otherwise, what ends up happening is the liver’s like I’m overwhelmed with toxins. I kind of don’t know what to do, and it does its very best. But here’s what toxins do, whether they’re from fat or from gut bacteria. They give you insane cravings. So then you’re in this situation where I’m trying to fast but the voice in my head screaming at me to eat. It gets worse and worse as your toxin level goes up because those toxins tell your liver, “Hey, you need some glucose. You can oxidize me and excrete me.” And the liver says, “I got no glucose. You didn’t eat any sugar. What am I gonna do?” And in order to liberate that it has this magic power. It’s called adrenaline and cortisol. And it’ll ask for those hormones and then you’re like, “Yeah, okay. I feel good right now. I’m a little bit jittery, but I’m okay.” And then you burn some muscle when you do that, but you get a little bit of glucose that the liver wants. And then the liver says, “I still don’t have enough, how about some more? And then you end up getting adrenal burnout. And this is why cycling your fasting, cycling your ketosis and not overfasting are so important.

Katie: So, how can someone know if they’re crossing that line into overfasting?

Dave: Well, if your sleep quality drops dramatically, you have an issue. Most people who start fasting or just start a healthier lifestyle, and I’ve seen this for 10 years with the Bulletproof diet, “Is it normal to need an hour less sleep?” And the answer is yes. People who sleep 6.5 hours a night are the ones who live the longest. It’s not because sleeping less is good for you. It’s that healthy people need less sleep. So if you find a reduction in the amount of sleep, you need to be rested, you’re doing it right. If instead, you wake up and, like, “Oh my God, I feel like I’m hungover and I didn’t even drink.” Or if you use an Oura Ring or similar sleep tracker, you find you’re waking up multiple times per night, that’s usually a sign that something is wrong and that you might wanna back off a little bit.

And if you’re doing a four-day fast, hey, your sleep might be a little bit weird, that’s fine. But if it’s happening regularly, and you’re fasting every morning, one of the easiest things to do is have some carbs at dinner. And if you sleep like a baby, that should tell you something, maybe you’re overdoing it. So, have some breakfast, but just don’t have carbs for breakfast for a morning or two and then go back in.

Katie: That’s great advice. Okay. So you’ve mentioned a few supplements. This is definitely it seems like a controversial area as well because there are the dogmatic sources that say you should consume nothing but water when you’re fasting, so no supplements. But then it seems like there’s actually some really solid data of certain supplements being helpful, both during fasting and also before and after fasting. I know that you are really big on delving into the research. So I’m curious what you do as far as supplements during fasting and also before and after.

Dave: One of my favorite supplements during fasting is proteolytic enzymes. And these are enzymes that eat protein. And I’m talking about things like serrapeptase, and natto kinase, and other protein digesters. When you take those and the body’s pancreas is like “Oh, I don’t have anything to do. I might as well take my enzyme production capability, and put it into making enzymes that catalyze biological reactions, like burning fat, like healing DNA, and healing mitochondrial DNA, and things like that.” So you’ll find that having extra protein degrading enzymes helps greatly during a fast with just getting more anti-aging benefits from it.

And I cannot find any scientific reason why this wouldn’t be a good idea other than if you’re, you know, a fasting or hair shirt self-flagellation faster, where you can only have water. But even those guys, if they have any ounce of research are at least gonna put salt in their water because as you fast, especially for longer periods of time, your electrolytes get out of balance, and that makes you not feel good. So, putting some sea salt or some Himalayan salt in your water is a minimum. But then what balances out sodium? Oh, potassium does. So maybe you take some potassium along with your sodium. Oh, and then what about magnesium? We’re all deficient anyway and the demand for magnesium just went up.

So if you have the basic things that your body needs to do what it’s trying to do while you fast, it’ll do well. And if instead you’re saying, “Oh, I’m gonna take, say, something like a D-ribose, which is a sugar that helps you make mitochondria, but it raises your insulin briefly, even though for a lot of people that lowers blood sugar, then maybe you don’t wanna take that one. And so the idea that, you know, you only have to have water is just not good science.

But also some supplements, there’s some I write about in the book, I call them the Barfy Four. Things that are very likely to give you extreme nausea on an empty stomach, you might not wanna take those. And so, there’s a list of about a dozen or so supplements in the book that are safe during fasting and some other ones that you absolutely don’t wanna take. And what you’ll find is if you do tolerate minerals on an empty stomach, having more minerals, things like zinc, and copper if you need it is a really good idea. Because those are used as a catalyst for your fasting.

Should you take a vitamin D pill? You might have, you know, 0.25 grams of fat or something in it, I think you should keep taking your vitamin D during a fast. It might not absorb as well as it would have when you had it with a fatty meal but you’ll still get some of it. And having your vitamin D levels drop during a fast doesn’t make a lot of sense to me.

Katie: That seems like an extremely balanced and important view I think to look at. And to your earlier point, if you’re getting most of the benefits of fasting from simply avoiding the protein and the carbs, most of the supplements you just mentioned are extremely like low to negligible calories to begin with and aren’t gonna be a significant source of protein or carbs. So they would still be achieving the desired metabolic effects while keeping you from having deficiencies in these other areas, which I’ve gotten much less dogmatic about that as well. So typically, even on my longer fasts now, I experiment with a lot of supplements as well.

And I wanna circle back to something you mentioned earlier. You used the word metabolically fit. And I think this is a really important point to focus on because to me, this should be the goal of health, in general, and especially of fasting. We shouldn’t just be fasting for the sake of, like you said, self-flagellation. It should be directed toward a goal. So, when we talk about metabolic flexibility and becoming metabolically fit, can you define what that actually means and how we can measure it?

Dave: What it means is that your cells have the ability to quickly turn on energy, whether it’s coming from glucose, from fat, or in some cases from amino acid oxidation. And most of the time, people are stuck where they can only get energy from sugar and their cells have forgotten how to get energy from fat, whether it’s stored fat or fat that you consume. And the amino acid pathways oftentimes are blocked because of other problems, like toxins or mineral imbalances, or lack of B vitamins and things like that. So a metabolically fit person can actually eat some sugar, and their blood sugar goes up, and then it goes right back down to healthy levels. And they’re actually okay. That doesn’t say that eating sugar and having a big glucose spike is a great idea. But you can because your body is able to consume all the things that our bodies are meant to consume and burn all of them.

Katie: That makes complete sense. And another area that you talk about and it’s even mentioned in the title of the book is healing inflammation, dealing with inflammation. This is definitely a common theme that I think we’re finding with any kind of chronic or metabolic disease. So walk us through how fasting helps the body deal with inflammation.

Dave: It’s interesting. We combine about 30lbs of air with whatever food we eat or we don’t eat. And we use that to make electrons. And if we do that efficiently and effectively, we have energy for our willpower and for breathing, and acting, and loving, and hating, and all the things that people do. And when we don’t have that going for us, we end up with inflammation because the food and air still went in, either they went to electrons that did something or they went into inflammation. And when you eat properly, your inflammation levels go down.

There’s just one problem though. Your cell membranes are made of tiny droplets of fat. And these tiny droplets of fat change based on what kinds of fat you eat. So a metabolically fit person is able to express cell receptors through their fat membranes effectively, things like insulin receptors. And someone who’s not metabolically fit probably has been eating too much Omega 6 oil for a long period of time and they haven’t been eating enough saturated fat, enough monounsaturated fat and enough Omega 3, not plant-based Omega 3s, but I’m talking about EPA and DHA like from fish oil.

And when you get that fat ratio right in your diet, it takes… And I’ve published this in 2012, actually, I found this old study, it takes about two years to replace half the fat in your body. And another two years after that, another 25% of it gets replaced with the good fats you’re eating. And this matches perfectly with what I’ve seen over a decade of people doing Bulletproof coffee, is that the first two years of it, if you were on a plant-based diet like I was, when I was a vegan and wrecked my health that way, you end up with this craving, like, “Oh my God, I need more of that grass-fed butter. Like, it’s life itself.” And after two years or so, like “You know what? I like butter. I make it a part of my diet. But just the focus of, like, this is life itself,” it goes down, and it just becomes a nutrient and delicious. And I think that’s because you’re fixing your cell membranes. And good cell membranes equals less reactive oxygen species in the body, which equals less inflammation.

And you must have oxidation in the body. That’s how you make energy. So you oxidize the food with air. And there are different byproducts of that that get made. And normally your cells handle all of that. The mitochondria have their own built-in antioxidant systems called SOD and actually several other ones as well. And having healthy amounts of oxidation from energy production that cause the cells to work better, that’s good. Having excessive because the cells are broken because of the kind of fats you ate or because you ate too much sugar, that’s bad, and that leads to extra inflammation throughout the body.

Katie: Okay. Another area I’m personally curious about and don’t have as much personal knowledge is the idea of how to manage exercise while fasting. I feel like this is also a somewhat controversial area. And some sources say you should not exercise while fasting because it’s gonna make you more catabolic and you’re gonna break down muscle, I’ve actually found I feel great doing certain types of exercise while fasting and I’ve hit some of my lifting PRs while fasting. I don’t know if that’s actually good for the body or not. So, give us your take on exercise while fasting and if it’s okay to do it, how we should navigate that?

Dave: I believe it’s best to exercise towards the end of a fast. If you’re doing a multi-day fast, gentle exercise. Going for a walk is fantastic. You are probably capable of hitting a PR simply because the amount of energy that was going into digestion is reallocated in the body. You literally have more energy available for your muscles and for your brain, and the body will, you know, let you use that energy. However, you’re likely to get much higher levels of cortisol if you exercise while fasted.

So the idea is exercise at the end of a fast. And there’s a really cool thing that’s been kind of a part of my work since I first wrote about it, I think in like 2012, and it’s called tripling down on mTOR. Now, we have to define mTOR. So mTOR is mammalian target of rapamycin. And this is what the body uses to build muscle and to create tissues. If it’s chronically elevated, you’re much more likely to get cancer. And if you don’t have enough of it because you don’t eat enough protein, you don’t exercise, etc., then you’re likely to get muscle wasting and be too skinny, and wear those vegan sized genes.

And what you wanna do though, is you wanna have spikes in mTOR so that you put on muscle after you exercise and they don’t have it low the rest of the time. And the way you raise mTOR is by pressing it down like a spring. And there’s three things we know that suppress mTOR. So we’ll come rebounding back really strongly. And my logic has been and this has been borne out by people just doing it, is that why don’t you do all three? So here’s three things that suppress mTOR that we know for sure from studies. Number one, coffee, which is way better than kale. And so drinking coffee suppresses mTOR. Number two is fasting. So, if you were to fast and exercise at the end of a fast, you’ve already suppressed it because now you’ve had coffee and fasting. And the third thing that suppresses mTOR is exercise itself. And it’s what happens after you exercise that causes that mTOR to come springing back.

So if you did all three of those, you have coffee in the morning, you’re fasted, and then you hit the gym, well, as soon as you’re done, your mTOR is going to come springing back up. And that’s when you eat and you eat a meaningful amount of protein, you have some fat, and probably some carbs too, especially if it’s been a meaningful fast. And that is gonna give you really substantial benefits. If you wanna stay in ketosis, you don’t have the carbs. If you wanna put on more muscle, you have the carbs. I don’t mean sugar. I’m talking you have some white rice, you have some sweet potato, etc., the safer carbs. And that gives you the most ROI on the exercise because you did all three of the things in the right order.

Katie: I’m so glad you brought up mTOR. And that’s really, really helpful advice. I think there are a lot of misinformation when it comes to mTOR and a lot of extreme viewpoints. And I fully agree with you. You can use it to your advantage, you just have to understand it a little bit. And then it can become an incredibly powerful tool. Also, I’m glad to hear you say that exercise is okay while fasting and it makes perfect sense why I feel the best exercising when fasting.

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I am curious just on a personal level, and I think a lot of listeners might be as well, what you do when it comes to fasting and what type of… Like, what is your normal routine and rotation of fasting look like? Because knowing you in person I have seen you continue to kind of just age backwards over about probably seven years that I’ve known you now. And I know that’s a topic of interest for a lot of people listening. So, I’m curious what you do and what you find works.

Dave: Thank you for mentioning the word rotation in there. Having a routine is relatively bad. And we talked about that a bit earlier. You’re doing the same thing every day. So, a big part of Fast This Way talks about how getting stuck in a rut isn’t good. And there’s this fasting trap, you know, that if I do it more, I’ll be better. And the same thing goes with exercise and with fasting. If you do it the same way every day, you get acclimated and you don’t get the same benefits. You might get overfasted, you might get overtrained.

So what I like to do is I like to wake up in the morning, and I look at a couple of things. How do I feel? And what did my Oura Ring readiness score look like? And the readiness score is based on something called heart rate variability. If I am biologically stressed because I don’t know why. There could be lots of reasons, toxin exposure, bad sleep for whatever reason. You know, maybe… Actually, I don’t really have lots of disagreements that keep me up at night, that hasn’t been a problem in a long time. But if there’s emotional stress, we’ll put it that way, then you wake up, you’re going, “Wow, my heart rate variability was crap last night, I’m probably gonna put, you know, 40 grams of collagen in my coffee in the morning and that’s breakfast, so I’ve had protein and I’ve had fat, right? Or maybe I’ll just have breakfast. And that’s an act of kindness towards myself.

And then other times when I’m at normal or high heart rate variability, it’s like, “Okay, I’m going to fast.” I don’t schedule lunch on my calendar until 2:00. So on a very typical day, I have an early dinner around 5:30 and then I don’t eat until 2:00 the next day. Sometimes it’s just black coffee. Sometimes it’s Bulletproof coffee. And sometimes I use the third fasting hack, which is going to really piss off some people, and fasting, the hair shirt fasters, but I’m fine to do that. And this is something that no one has talked about until I wrote this book in the context of fasting. And it is that you can have prebiotic fiber during your fast.

And there’s three reasons we fast. We fast for weight loss, we fast for anti-aging, and some people are fasting to allow their guts to heal from whatever is going on. And the prebiotic fiber can work in all three of those depending on what’s going on in your gut. You might not wanna take it if you’re doing certain kinds of healing of the gut like SIBO. And these prebiotic fibers are not digestible by you. They’re only digestible by your gut bacteria who take the fiber and turn it into propionic acid and butyric acid, which are both ketogenic. It also is shown in lots of studies that they suppress hunger and lots of studies that they make you live longer. And a lot of people don’t get enough soluble fiber. And this is not like Metamucil and the kind of sawdusty thing that they have. This is actually stuff that gets eaten by bacteria in the gut and it makes the good guys grow.

So, some mornings, I’m like, “Oh, this is great. I’m gonna have my coffee and I’ll put in 20 grams of soluble fiber.” And, of course, I’ve made a prebiotic for Bulletproof, etc., etc. But what’s happening there is I did that because I found that when I did longer-term fasting and longer-term keto, the number of species of gut bacteria in my gut was lower than it should be. And we know a diversity of gut bacteria is good for you. I quadrupled the number of species in my gut on lab tests by adding prebiotic fiber. And you still get the benefits of fasting. Your blood sugar didn’t go up, you didn’t have any protein, your probiolytic enzymes are still able to do the things. You’re still able to do autophagy, but you didn’t have to think about food.

So there’s your three fasting hacks, black coffee, coffee with butter and MCT, also known as Bulletproof and prebiotic fiber,. And those things take fasting from, “Oh my God, I think I can do it,” to “I’m not thinking about food, I’m thinking about my job, my kids, my life, and I got the benefits of fasting.” And I’m going to save the feeling, the pain for when I do a spiritual fast, which is a major part of Fast This Way that’s also missing from fasting books.

And what I did when I did my first four-day fast, I used to be really happy. And I was frankly, scared of being hungry. So way back in 2008, before I wrote my first post, as I was doing some of the experimental stuff that led up to the Bulletproof diet, I hired a Shaman to drop me off in the desert in a cave. I also realized from personal development stuff that I was actually afraid of being alone. It wasn’t like conscious fear. It’s an unconscious fear because that’s what fear is. And so I said, “All right, I’m gonna face these things down. Drop me off in the cave. There’ll be no food and no people for 10 miles in any direction. And pick me up in four days.” And I tell the story throughout the book. I honestly think this is my best book in terms of readability and actual info, but just the story, like, here’s what happened, when I went on, you know, a spiritual fast.

And what I’m doing for people who read the book or people who order the book is I’m taking them on a two-week fasting course where I teach them the book. And it’s like, “Okay, here’s how to get started. Here’s the fasting hacks. Here’s what to do. We’re gonna do it in the community, but the final couple of days is gonna be a 24 or 48-hour spiritual fast, where we do the personal development work and you actually look at your hunger and you say,” “Okay, what’s going on in there? Like, what my body’s telling me right now, is it true or is it not true?” And this is something that every spiritual group, every religious group has incorporated in their histories around the world. And if we strip that part of fasting out, I think we’re missing something fundamental to being human, where, you know, sometimes the point of fasting is awareness. Other times, it’s just to make your metabolism work.

And you don’t have to do the personal development stuff if it’s the middle of the day, and you have deadlines, and you have kids hanging off each arm because they’re stuck at home with you, that’s not the time to feel the pain of fasting. That’s the time just to get the benefits and feel the pain when you can use the pain to help you be a better, more aware human being. Those are both part of the fasting experience. I don’t wanna lose that second part.

Katie: Such an important point, I think, especially for parents, and I’m glad you brought that up and that distinction as well. I typically start the year with a 7 to 10 day fast. And that’s something I do for the spiritual benefits because I know that fast that long can be controversial from the health perspective. But for me, much of that is the inner benefits versus just the physical benefits. And I spend that time rereading books like Viktor Frankl’s “Man’s Search for Meaning” and “The Four Agreements,” and that’s kind of my time to spiritually align and get focused as much as it is to physically get the benefits of fasting.

A little bit more controversial, and we don’t have to go deep on this but I think I should at least ask this. I’ve gotten enough questions from people. What do you think about dry fasting? Because this is another thing that has become more popular in a lot of different online sources and one that is arguably much more dangerous. So I’d love to get your take on it.

Dave: Well, I will absolutely answer that. And first, we’ve known each other for about seven years, and you’re just a well put together person, psychologically. Like, you’re stable and nonreactive. And I appreciate that about you. And you’ve just explained why, which is really cool.

Katie: Oh, thank you. That means a tremendous amount coming from you. Thanks, Dave.

Dave: You’re welcome. Now, you also asked about dry fasting. I think there is merit to dry fasting. There’s lots of historical practices that involve that. And something neat happens. When you dry fast, your cells actually shrink because they get dehydrated. And that going without ethos, that’s woven into Fast This Way. Going without water for a day, like we can all go without water for three to five days and sometimes a little bit longer. It’s bad for you if you are full of toxins, if you haven’t been taking care of yourself, it’s probably not worth to start. And I don’t make that a big focus of the book for that reason.

And that said, I think doing up to 48 hours is going to be intense, but it’s probably gonna be beneficial because your cells will get replenished with fresh water when you do it right. It also creates a lot of stress in the cells, which is good because it’s short-term stress that creates a benefit, what we call hormetic or hormesis. And so, I think there’s validity to doing it. I haven’t gone more than 24 hours, then again, I only have one kidney and I don’t really need to increase the load I have on that.

Katie: Awesome. And lastly, I wanna make sure I respect your time. I know how busy you are. But I wanna make sure I mentioned that your book, I’ll have links in the show notes at And I believe you have an additional bonus that you’re offering people when they order the book that they can get directly from you. Can you talk about that a little bit?

Dave: Sure. Just go to, order your book wherever you like to order books, and then send me your receipt, and I will enroll you in a two-week program where I will teach the book to you. And I was a teacher at the University of California for five years. And I feel like with some of my other books, I spent, you know, 2,000 to 5,000 hours writing a book, and then I’ll say, “Well read the book, it’s all in there.” But a lot of us learn with other people and we learn by doing. So I’ve just decided that it’s my job when I write a book to teach it. And I’m doing it just as a gift for people who do me the honor of pre-ordering “Fast This Way,” and all the info for that is on

Katie: Awesome. I’ll make sure that link is in the show notes. You guys can watch out for that. And another question I love to ask at the very end of interviews is obviously other than your own, if there are any books or number of books that have really influenced your life, and if so what they are and why?

Dave: That’s a big question. I’ve interviewed almost 800 authors.

Katie: Wow. Incredible.

Dave: Thank you. I’m gonna go for Robert Greene. Robert Greene is the guy wrote “The 48 Laws of Power,” which changed my business life because I was, like, “Here’s why executives do the weird things they do. They’re actually following a playbook I don’t know.” And his most recent one, which is the Laws of…I think Consciousness or Self-Awareness. Jeez, I’m forgetting it. Robert Greene’s latest book, is his opus after many, many years of being a fantastic writer, and science writer, and student of psychology. And that book has almost everything you need to know to figure out what’s going on inside of you and to explain why others do what they do. And it is a book that I consider to be required reading. It’s a wonderful, wonderful book because he talks about things like ego and how to tell when you’re acting out of envy or when someone else is acting out of envy. And in his style, he always says, “These are the signs it’s happening and here’s the countermeasures, so that you don’t do it to yourself. And you don’t allow others to do things to you based on their own trauma and their own pain.” So if you wanna be in charge of yourself, I just consider his work, especially his latest book to be a non-negotiable reading.

Katie: I love it. I’ll make sure that’s linked in the show notes as well. Dave, I know how busy you are. And I’m really appreciative of you being here today and I really enjoyed your new book. Definitely recommend it to all of you guys listening. You know, fasting has been a big part of my journey, and I love how comprehensive your new book is, and how practical and actionable it is. And thank you for compiling that. And thank you for being here today.

Dave: Hey, Katie, keep doing what you’re doing, and just from one author to another, your blog is super legit. So, congratulations on keeping it real and having the science. I enjoy what you do.

Katie: Thanks so much. And thank you guys, as always for listening, for sharing your most valuable resource, your time with us today. We’re so grateful that you did, and I hope that you will join me again on the next episode of “The Wellness Mama Podcast.”

If you’re enjoying these interviews, would you please take two minutes to leave a rating or review on iTunes for me? Doing this helps more people to find the podcast, which means even more moms and families could benefit from the information. I really appreciate your time, and thanks as always for listening.