What Happens If You Don’t Eat for 72 Hours? | Fasting Guide | Dr. Josh Axe

So I am constantly getting questions about this. And by the way, this is also something that I started practicing after first reading the Bible. And it's a health practice that might be one of the most powerful things you could ever do to heal your body. It's also free, requires no equipment, and your body is literally designed for it. It's fasting.

And today I'm going to talk about what happens in your body in the first 24, 48, and 72 hours of fasting. I'll walk you through how you should approach a 3-day fast and While it sounds really simple, there is absolutely a wrong way to fast, especially coming in and out of a fast and what you're eating, what to take during it.

I'll also walk you through maybe the one of the most important things, who should not fast, which is actually a pretty large group of people, and the fasting benefits that even the early church fathers knew about. Welcome to the Dr. Josh Axe Show. The average American eats for 15 to 17 hours each and every day.

That means insulin, the hormone, stays consistently elevated, so your body's fat-burning engine never gets switched on, which is why a 3-day or 72-hour fast can be so beneficial. And so your body has 2 powerful systems. It has the quick burn system, which burns sugar, which is glucose for energy, and the secondary system where your body burns fat. And/or ketones for energy as well.

And most people today only ever use system 1. And so what I want to do is walk you through what happens when you start to fast and how to do it properly. Well, here's what starts to happen in the first 24 hours. Number 1, insulin drops. Insulin is your storage hormone. When insulin is high, you store body fat. When insulin drops, Your body gets permission to release fat.

Insulin drops roughly 35% within the first 24 hours of fasting. This allows the body to begin to mobilize your stored body fat, especially the visceral fat around your organs, which is why fasting has been associated with decreasing numerous medical conditions. Now, most people think you start burning fat when you exercise.

You actually start burning fat When insulin drops, that's the signal in your body to start to burn fat. Here's the second thing that starts to happen in your body the first 24 hours when you're fasting. Your body starts to use up its glycogen stores. Now, think of glycogen as your body's pantry.

When you eat carbs like bread or fruit or rice or even vegetables, your body breaks those down into glucose. And whatever your body doesn't immediately use for energy, it stores in your liver and in your muscles. Okay, so after that first 24 hours is where it gets really uncomfortable and people want to quit, by the way. Listen, if you've ever fasted, you know exactly what I'm talking about.

The first 24 hours is absolutely the hardest. This is when your energy dips, you start to get irritable, sometimes you develop, even some people, headaches. This isn't just hunger, this is your body switching engines. Your body's going from sugar-burning mode to fat-burning mode, and there's major hormonal switches also being turned on in your body.

I can remember some of the fasts I've done over the years. One time I did a 21-day fast, and I remember getting the mild headache, but I remember again, that first 24 hours for me, it was these hunger spikes up and down and up and down. And so those symptoms are very, very common.

And the other thing I was blown away by, I remember looking, I weighed myself after the first 24 hours and I lost around 3 pounds that first 24 hours. In fact, consequently, most people lose about 3 to 5 pounds in the first 24 hours of fasting. But I want to say this, don't get too excited.

Something most people don't know is that glycogen is stored with water, and you've got about 3 to 4 grams of water for every gram of glycogen. And most weight loss that you're losing in the first 24 hours, it's actually water weight. Hunger is largely driven by this hormone called ghrelin, and ghrelin does not rise randomly. It rises at your normal meal times. So your, your body's smart.

Your body says, okay, I usually get hungry around this time. And that's when your body starts, your stomach starts to growl. You start to get those cravings around your normal mealtimes, but it starts to go away after that. So most people experience this around, you know, 8 or 9:00 AM, around noon to 1:00, and then around 6:00 PM.

And that's when ghrelin spikes at those exact mealtimes because your body's expecting it. And here's another thing to know about hunger signals. If you know, you know what, I've eaten enough already, but you still feel hungry, if you wait approximately 20 minutes. Most of those signals will pass on their own because ghrelin levels will fall off even without eating.

So even if you're not fasting and you're sitting there after a meal and you're like, I'm still hungry, but you need to lose weight, you're trying to heal, you know that you need to eat less food, follow the 20-minute rule. Wait 20 minutes and then see how your body feels.

Now, the 4th thing that starts to happen within 24 hours of fasting Is your hormones start to change significantly, especially growth hormone. Now, growth hormone is your body's repair hormone. It supports growth and regeneration and even healing. And growth hormone increases approximately 2 to 5 times from baseline during a 24-hour fasting window. One study found a 14 times increase.

In women.

Now, why do we care about growth hormone? Most people assume that fasting destroys muscle. Now, your body will lose some muscle, but your body will also lose a lot of body fat. But your body releases a surge of growth hormone specifically to protect muscle and in addition, help heal and regenerate.

Your body will actually start to flood your body with something called stem cells, which are what go to different areas of your body if you have an injury and actually heal and repair your organs and tissues. So one of the greatest things you could ever do to heal a damaged area of your body is fast on a regular basis. So here's what happens by the end of day 1.

Insulin is down, glycogen is gone, growth hormone is up, and your body has switched fuel systems. Now it has to decide what to do with all that stored body fat. So when most people walk into day 2, because they had these big hunger spikes on day 1 and maybe started to have certain symptoms, I think they— most people expect to just Hit a wall.

Here's the biggest thing most people say, though, on the second day of fasting. They experience a very high level of mental clarity. Now, here's why. It's because ketones take over after 36 hours of fasting.

Ketones can provide 60 to 70% of the brain's energy needs, and ketones produce fewer oxidative byproducts than glucose, meaning less inflammation throughout your entire body, including the area of your brain. And your body has now shifted to fat as its primary source of fuel, and it converts fat, your own body fat, into ketones or ketone bodies, specifically beta-hydroxybutyrate.

And your brain loves this for fuel. Many people fasting on day 2 report clearer thinking, better focus, and even more stable energy. And I think when most people think about ketones, they think about a ketogenic diet, and that's where you're cutting all carbohydrates and focusing primarily on fat as your main source of fuel.

And there's no doubt that the ketogenic diet does allow your body to switch from sugar burner to, to fat burner and get more in that ketosis state. But fasting has the same benefits and likely even greater healing benefits for your entire body. The biggest myth about inflammation and chronic symptoms is that they're all separate issues.

In reality, your symptoms behave more like a chain of falling dominoes. When one goes down, it triggers several more, and before you know it, everything feels off.

I'm currently offering a simple at-home blood test that actually tests for the right things— targeted biomarkers that reveal the very first dominoes impacting your hormones, your inflammation, your thyroid, and your Plus a full hour with one of my senior health advisors to review your results and show you exactly how the Health Institute can help you stop the chain reaction so you can finally heal.

If you want to check it out and grab one before they're gone, just go to mybloodwork.com now. Now let's step into the next thing that occurs on that second day in that 48-hour period when you fast. And this science actually won a Nobel Prize in 2016. A Japanese biologist discovered the mechanisms of autophagy. Autophagy means self-eating.

Your cells begin to consume and recycle their own damaged parts. Think of this like cleaning out a garage that's been cluttered for years. Okay? You've got old proteins, dysfunctional mitochondria, cellular debris. Basically, imagine a city with a bunch of garbage in it.

And now your body can go through, remove the garbage, recycle some of the usable materials, and put them back into usable things and allow your body to heal and rebuild itself anew. You know, this is one of the primary reasons why fasting is associated with longevity, is it's not just about restricting calories. It allows your body sometimes for the first time in a long time to finally clean up.

Uh, all of the garbage that's in there. Think about this, like your body spends so much energy in digesting and detoxifying and doing so many things. So your liver and your digestive system and your cells, they're working hard all the time, just dealing with the food you eat, dealing with toxins, all these different things.

When you stop eating, now your body has all of this energy to expend doing something else. It's saying, you know what? Oh wow, I have a free day today. I've been meaning to— have you ever had this happen where it's like you've been doing stuff for a long period of time, right?

You had work, you had kids, stuff, you have, you had all kinds of things on your plate, and then finally you have a day off. And now those things you needed to get done around the house, you know, those things that have been stacking up for the past year, you're now able to get to them. That's what fasting does.

Now your body doesn't have to use all of this energy doing all of this work of digestion and detoxification and other things. And now it can just get rid of the bad and prepare to heal. Now, there are 2 signals that sort of, uh, amplify this pathway. Okay.

Uh, and, and so your body is, oh, by the way, one of the most important parts of healing that people don't talk about enough is cellular communication. Your body's always sending signals in terms of hormonal signals and enzymatic signals and things. Your, your body's constantly communicating. At the cellular level?

Well, there are 2 signals in particular that start to happen when you fast, and one is related to something called mTOR, and the other one is related to something called AMPK. And mTOR is the signal that tells your body to grow and regenerate. It's tied to being anabolic. Have you ever heard of anabolic steroids? Think about somebody, you know, a male taking steroids. There's muscle growth.

There's all of this growth happening. In the body. Now, that can be good for some people, but here's when you don't want that. You don't want that when you have a really severe infection, like a, or a cancer, right? You don't want growth of cancer. You want it to starve. And so mTOR will start to drop when you fast. And again, mTOR is the build signal.

When food is abundant, mTOR stays active and cells grow. When mTOR starts to drop, now your body can start to cleanse and repair. The other one is AMPK. And by the way, by the way, these are probably the 2 most prominent markers that are talked about in longevity medicine. The other thing, so mTOR drops, AMPK starts to go up, and this is your body's repair signal.

When food is scarce, when you don't have food and your body runs out of glycogen, AMPK activates. And the AMPK pathway is your body's cellular repair pathway. So when this starts to go up, your body says, okay, it's, it's time to start taking this house. And here's the best analogy to think of. Think about a construction crew. When you have a house that has damage, right?

Let's say you've had termite infestation or water damage. The first thing you need to do is go and remove that damaged material. That is step number one. You can't go and put new drywall on or brick up on, uh, you know, this damage because it'll actually start to rot and start to impact even the good material. That's what happens.

So this process of fasting is when your body, this construction crew, comes in and says, okay, it's, it's demolition time. We're going to come in and we're going to start to get rid of all of the toxins, the bugs, the viruses, the termites, the cancer cells, everything our body doesn't need. We are going to get rid of it.

So this is your body's cleanup crew that has to take action before your builders come in and start to rebuild your body. Now, there's another process related to this that's often talked about in longevity medicine related to fasting, and it's called senescent cell cleanup. Okay? So what happens is all of us have cells and they tend to divide and replicate about 50 times per cell. Okay?

So your body's continually replicating, creating new cells, and you need to do that to live a long time, to be healthy. That's normal. But a lot of times when we get to that 50th time, or your cells replicate a lot over time, Some of those cells start to not work so well. Now, here's another major issue. These senescent cells, in fact, they're called zombie cells, uh, in scientific literature.

And they call them zombie cells because these cells actually start to leak toxins that then cause inflammation everywhere throughout the body. So one of the greatest things you can do for anti-aging and reversing the clock and promoting longevity is clear these senescent cells.

Out of the body, but I want to share with you something that I think is the most overlooked part of the conversation when it comes to fasting. Around 100 AD, so 100 years, just 100 years after Christ, one of the earliest Christian documents outside the Bible—it's called the Didache—which actually means the teaching encouraged believers to fast two times a week.

And for the first several centuries, fasting twice a week. On Wednesdays and Fridays was considered a foundational spiritual discipline in Christianity. In fact, in some churches they said, this is really not optional. This is part of, like, communion. This is part of what every Christian does in honoring Christ.

And in the 4th century, St. John of Chrysostom called fasting the foundation of prayer and the mother of health. In fact, there have been many priests over the years when somebody was sick would recommend fasting for healing. And the amazing thing here is, is the Bible is always so far ahead of its time.

Those early believers were doing something modern researchers are now validating— twice weekly fasting, which mirrors much of the intermittent fasting research of today. And we also know Hippocrates, who's known as the father of modern medicine, wrote in 400 BC, instead of medicine, Fast for a day. And I can tell you personally, fasting goes so far beyond the physical benefits.

There are numerous physical benefits for the right people, but for me, I can share this. The biggest thing that hit me with fasting was how dependent I was on food. And also, I just, just, it was a humbling experience. I think that's what I would say. I would say, you know what, I really, I need food. But even more than that, I need Christ.

I think there's also this, you know, the way that Christ talks about himself as the bread of life, right? Like, you got to sustain yourself. It's the way you sustain yourself physically is with food. Christ, that's the way you sustain yourself spiritually. And if you go a single day without, it's very hard and difficult.

I can tell you, anytime I've woke up in the morning and I've been in a rush and I just kind of went out, you know, I started my day without Connecting with God, it was a harder day. I'm less kind, I'm less virtuous, I'm less impactful.

Um, all of those things versus if I am eating my daily bread, connecting with Jesus, reading the Bible, doing those things, there is a sustenance and an empowerment that happens in doing that.

Now I wanna dive into Day 3, something astonishing starts to happen in that once you get into a 3rd day of fasting, and most people report that hunger has faded, energy is stable, and inside the body, something even more remarkable starts to happen. Your body starts to go into a deeper level of ketosis. So these ketones signal society directly. So, so, so your hunger.

Actually starts to really go down. This first— the first day's the hardest. The second day, you're still going to have some hunger, but the third day, that really starts to drop. Now, here's another big thing. Your inflammation markers drop dramatically. Your body gets into a highly anti-inflammatory state.

People will start to say, my joints, my chronic pain, this thing I've dealt with for years starts to feel better. There was a study published and it found that when you're doing a 2 or 3-day fast, Your body shifted something called hematopoietic stem cells. These are the stem cells that form blood cells. Those stem cells started to self-renew.

And so not only did you have those stem cells, it created more within your blood. And these are the cells that heal your body and regenerate your body. And this is especially important for issues like autoimmune disease, or if you have chronic damage in your body. Now, the other thing that started to happen was Clearing old immune cells and stimulating the production, production of new ones.

So your immune system was strengthened and bolstered as well. Growth factor in your body, particularly one called IGF-1, which, which this growth factor is associated with aging. It dropped by up to 60% within just 2 to 3 days of fasting. In order for that hormone to drop, it typically takes months. Of restricting calories. However, if you do fasting, you fast-track it into just 2 to 3 days.

This hormone that's associated with, in certain population with cancer, is now dropped by 60%. Now, I want to be clear, fasting is not a cure for all diseases. However, it can be part of a protocol in healing and curing many diseases. There is an abundance of evidence in the scientific literature. By the way, I just scratched on the surface. We went through some studies.

But there are thousands and thousands of studies proving that fasting has tremendous benefits at reducing inflammation, boosting your immune system, fighting cancer, reversing chronic health issues, getting rid of brain fog. I mean, there are many, many benefits. Hey guys, I'm here with my good friend, Dr. Dave Jockers. In fact, we've been friends for more than 20 years. He runs the podcast.

The Dr. Dave Jockers Functional Nutrition Podcast. Dr. Dave, tell us a little bit about what your podcast is about.

Yeah, absolutely. We, we dive deep on functional nutrition, really how to personalize your nutrition plan for better energy, mental clarity, better hormone balance. And we talk a lot about cellular health, mitochondrial function, cell membrane. We do a deep dive on every major nutrition topic and natural health topic. So everything you need right there at your fingertips.

Dr. Jockers Functional Nutrition Podcast.

I wanna encourage you, run out and listen to the Dr. Jocko Show. Again, I'm a big fan of it. I think you will be as well. Now, here's one of the most important things to discuss with fasting, and this is what most people don't talk about.

And I want to say, I think I have a unique perspective on this as a physician and working with thousands of patients with chronic health conditions, everything from autoimmune disease to cancer to, uh, ADHD to heart disease. And there are many people that can greatly benefit from fasting. But there's also a fairly large segment of people that need to build their body up before we break it down.

There are numerous people that need to be more anabolic and not catabolic, and there's a lot of people who need to get more catabolic and clear and get rid of the bad stuff and then go and focus on building first. So let me walk you through the best candidates who will benefit the most from fasting. The first is those people dealing with insulin resistance and metabolic syndrome.

This is people with type 2 diabetes. With prediabetes, any type of insulin issue, those people will benefit greatly, especially if you're overweight and storing a lot of body fat. You will benefit greatly from fasting. Another one is fatty liver disease. Fasting reduces liver fat more rapidly than almost any other dietary intervention.

And then those with major chronic inflammation, fasting drops inflammatory cytokines within 48 hours dramatically. And then those people dealing with brain fog, if you've got major neurological symptoms, ketones reduce that neural inflammation. And then also, here's another big one.

If you just feel like you are absolutely stuck, you're stuck metabolically, you're stuck mentally, physically, or here's a big one. If you feel like you're stuck in a place spiritually, this may be the ultimate reset for you. Now, I want to share that I had a friend of mine and his daughter was going in for surgery to remove a tumor. She had cancer.

And we got together and I fasted, he fasted, another Christian brother of ours fasted together. We spent the day praying together for his daughter, and God worked a miracle in saving her life when doctors thought she couldn't survive. And so I experienced that. I've prayed for, for business outcomes. I felt like I was stuck in a place, um, professionally Saw an outcome there.

So I've prayed for people being sick, in business, for spiritual breakthroughs, and fasting is the ultimate tool for breakthrough in that way. You know, it's interesting, there are passages in the Bible where Jesus says this kind does not come out without prayer and fasting. So fasting, even Jesus used and recommended for breakthrough.

Now, when I had questions come in about fasting, I think I probably had the most questions come in about who should not fast. And I want to say this, for most people who come into my practice at the Health Institute or locally at the Longevity Clinic, most of those people, I actually don't recommend fasting at first, or at least for 3 to 4 months.

I take care of a lot of men and women, but even more women who are struggling with major hormone disruption, very high cortisol, Thyroid issues, mitochondrial dysfunction. And the, a lot of those issues are related to poor cellular energy. The mitochondrial energy is low and the body truly just does not have enough energy to heal.

If you fast, the primary benefit of fasting is not gonna be boosting cellular energy. In fact, in some cases, it's going to lower it by a small degree. And so if you've got this mitochondrial dysfunction, Going under more of a natural stress of fasting is, is really what— it's not what's best for those people.

With those patients, I really focus on healing their hormones in a completely different way. And whether you're going to fast or not, you'd want to follow a protocol like that for complete healing, though fasting can be part of the protocol. Now, I want to give you some hope here.

If you are already stressed out, you're burnt out, you're worn out, and you want to experience true cellular healing, Here's the thing: you can get there without fasting. Listen, I love fasting; it's beneficial for so many people. Just just so you know, for myself, I have a very high metabolism. I'm already very lean, low body fat, and so I need to be careful not to overfast.

I have you know a couple of my best friends I'm thinking of; they fast more. I do it when I really feel for myself more so when I need a spiritual breakthrough because my diet is already mostly fruits, vegetables, and salmon. I mean, that's that's the predominant part of my diet, and so I'm really not in that excess. Category.

But this is also really where personalized nutrition and personalized medicine come into play. For some of you, you could do a really long fast and benefit greatly. For others, it might be a short fast, like the early church, where you're taking a day a week and, and not eating one meal or two meals in order to honor God and spend more time with him and to experience a spiritual breakthrough.

And for some of you, now's not the time. We need to build your body. You need a specific health plan To deal with your nutrient depletion, to deal with chronic inflammation, to deal with your chronic condition, and to help your body finally heal.

And if you want to learn more about exactly how you can rebuild and fully heal your body and get something personalized for you, you know, this is why I created the Health Institute. This is my virtual practice.

And if you're interested in also getting blood work done to know if you are deficient or not, you could go to mybloodwork.com and simply, you know, get an at-home blood work kit done and see Hey, do you have enough vitamin D? Do you have enough vitamin B12? What is your CRP, your inflammation levels?

And this will kind of allow you to know if you're a good candidate for fasting or not and exactly what you need to do to move forward to fully heal your health and body. I just want to mention here, we have limited spots for consultations this month, and we just had a price drop. So if you've been waiting to grab your blood work consultation, go get it now.

But I wanted to mention that because Because my goal in doing this show is to help you fully heal and give you all of the resources you need to fully heal and live your best life and have a long, healthy life and honoring God with your body. I have a few last things to hit on here with fasting I think are really important.

You know, one question a lot of times I get is, is there a difference between men fasting and women fasting in terms of how their body responds physiologically? And my answer is, Yes, absolutely. Women are much more hormonally sensitive to caloric restriction than men. Okay? Men tend to be able to fast and do with it much better and longer than most women.

And the reason is, is like, listen, men's hormones are like this. It's the same. It's a straight line across. It is very stable. Women have Greater daily cycles, greater monthly cycle, greater life cycles in their hormones changing and fluctuating and what happens there. If you're a woman, let me just say this.

Women should avoid extended fasting, especially during the late luteal phase, which is the week before their period. Okay? When a woman is going into her period, that is not a good time to fast and weaken the body. Okay? Putting the body at a Deficit.

Also, if a woman's cycles are irregular, if you are in the state of fertility challenges, typically with infertility, when I create a protocol for women in practice, I really focus on stabilizing their blood sugar with very specific types of protein and fiber and fat and really specific nutrients. Okay? The body is typically more deficient infertility than it is an excess for almost all women.

And also, if you're a woman and you have really high chronic stress and you know your cortisol is likely off and thyroid hormones, that's definitely not a state you want to do fasting in. And what fasting should do is support your hormones, not disrupt them.

Now, if you are feeling spiritually called to do a type of fast, okay, and you still are in one of those categories, then I just wouldn't recommend a full 3-day fast. I would do A morning fast one day a week or a morning lunch fast, and then eat dinner still that night. And that's the type of fast that your body could most likely tolerate and still benefit from.

Now, if you're going to do a 3-day fast, here's how to do it the most safely and the most effectively. One, make sure to get lots of electrolytes. Your body needs sodium and potassium and magnesium, and deficiency is why most people feel terrible and start to get things like headaches. So it's not just the fast, it's the mineral loss.

So you can add a little bit of electrolyte powder Here's the second thing. Drink way more water. Okay? Minimum of 2 to 3 liters of water per day. Take at least your body weight in half and drink that in ounces of water that day. Number 3, move. You do not want to do heavy working out.

You don't want to do heavy lifting or any high-intensity cardio, but you do want to do some light walking in order to move. Next, you want to prioritize sleep. Get to bed early and allow your body to sleep in a little bit. This is going to support hormones like growth hormone getting exactly where it should be. To promote longevity and cellular healing in your body.

The next is, if you're going to drink, drink mostly water. But if you want something else, do plain tea. And if you have to, a little coffee is acceptable. Okay? Now, don't add creamer in there. I'm talking about black coffee or an Americano. Those things are fine. But you also don't want to do too much excess caffeine, especially for women, because that can spike cortisol.

So you're best off doing just water or water and herbal tea. It could be a little bit of green tea or jasmine or chamomile, something like that. That's perfectly acceptable and fine. A little bit of coffee, but not in excess. And then when you are breaking your fast, you want to consume something that's very easy to digest, something like bone broth or soup, right?

A very simple, you know, chicken, rice, and vegetable soup, eggs, fish, small amounts of protein, well-cooked vegetables. Those are the easiest foods to digest and consume during a fast. Now, I want to close with something I think is more important than any protocol. Fasting is not deprivation. It's not a punishment. It is— it's not a trend either.

It's one of the oldest healing practices in human history. It's practiced by nearly every major spiritual tradition. It's prescribed by the earliest physicians. It was built into the weekly rhythm of the early church, and it's now being validated by Nobel Prize-winning cellular biology. Your body has a built-in repair system, a built-in fat-burning engine, a built-in cellular cleanup process.

You were born with all of these systems. The only question is, are you ever giving them a chance to activate? If you've been stuck feeling foggy, inflamed, metabolically slow, a strategic fast might be exactly what your body's been waiting for. I want to say thanks so much for tuning in here to the Dr. Josh Axe Show. If this episode gave you something valuable, Share it with someone who needs it.

Also subscribe so you never miss what's coming next. And I can't wait to see you on the next episode.