in: Health, Health & Fitness, Podcast

• Last updated: January 17, 2023

Podcast #862: Heal the Body With Extended Fasting

In the last several years, intermittent fasting — only eating for a short window each day — has gotten a lot of attention, particularly for the way it can facilitate weight loss. But as my guest will explain, going longer than a few hours or even a full day without eating also has some striking, potentially even life-changing benefits too, and may be able to heal a variety of health issues. 

Steve Hendricks is the author of The Oldest Cure in the World: Adventures in the Art and Science of FastingHe spends the first part of this conversation offering a thumbnail sketch of the history of extended fasting as a medical treatment. From there, we get into what emerging modern science is showing as to how prolonged fasts lasting days or even weeks can prevent and even cure a variety of diseases, from type 2 diabetes to rheumatoid arthritis. We then talk about fasting‘s effect on cancer, and how it may address mental health issues by offering a metabolic reset. If you’re an intermittent faster, you’ll be interested to hear why it is you should ideally schedule your eating window for earlier rather than later in the day. We end our conversation with how to get started with extended fasting.

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Brett McKay: Brett McKay here and welcome to another edition of the Art of Manliness podcast. In the last several years, intermittent fasting, only eating for a short window each day, has gotten a lot of attention, particularly for the way it can facilitate weight loss. But as my guest will explain, going longer than a few hours or even a full day without eating also has some striking, potentially life-changing benefits too and may be able to heal a variety of health issues. Steve Hendricks is the author of The Oldest Cure in the World: Adventures in the Art and Science of Fasting. He spends the first part of this conversation offering a thumbnail sketch of the history of extended fasting as a medical treatment. From there, we get into what emerging modern science is showing as to how prolonged fast lasting days or even weeks can prevent and even cure a variety of diseases, from type 2 diabetes to rheumatoid arthritis.

We then talk about fasting’s effect on cancer and how it may address mental health issues by offering a metabolic reset. If you’re an intermittent faster, you’ll be interested to hear why it is you should ideally schedule your eating window for earlier rather than later in the day. We end our conversation with how to get started with the extended fasting. After the show’s over, check out our show notes at

Alright, Steve Hendricks, welcome to the show.

Steve Hendricks: It’s so very good to be with you, Brett.

Brett McKay: So, you published a book called The Oldest Cure in the World: Adventures in the Art and Science of Fasting. In this book, you take a deep dive into the history and into the science of using fasting as a medical treatment. I’m curious, what was going on in your life where you wanted to take this deep dive?

Steve Hendricks: Yeah. I first got interested in fasting about 20 years ago, partly for the same reason a lot of people get into it, I needed to lose weight, but partly because there was some very intriguing research that showed that fasting made animals live longer, nearly twice as long in some cases, and they live those long lives with a lot less disease as well. And the research suggested that we might just be able to live longer and with less disease too if we fasted. So, I experimented with fasting, and I wrote a bit about this, and about 10 years ago, I was approached by a couple of publishers to write a book about the history and science of fasting. I said, no. Frankly, I thought that the history would bore me to death, but mostly, I just didn’t think the science was far enough along to make a compelling book about fasting as a medical treatment.

What changed was that over the last decade, the science of fasting has just blossomed in the most beautiful way. I also started looking more deeply into the history of fasting, and it turned out to just utterly fascinate me. And I had also, in this time, fasted quite a bit myself, and I’m certain that fasting helped me recover my own health, which had taken a real nose dive in my 40s. I’m 52 now. So, a couple of years ago, I finally thought I had enough between the science, the history, and my own experiences to make what I hope turned out to be a compelling book.

Brett McKay: Well, let’s dig into a bit of the history of fasting as medical treatment. You started off talking about, human beings have probably been fasting since human beings were human beings, but it was probably unintentional, right? Cavemen, maybe, went days, weeks without food, because they didn’t get a hunt or there was a famine. But, in the historical record, when do we see humans fasting? Like, “I’m intentionally fasting. I’m intentionally abstaining from food,” when does that start happening?

Steve Hendricks: Yeah. Unfortunately, we don’t have much evidence from archaeology, which is really good at showing what people did, what they ate, for example, but not so good at showing what they didn’t do, like, not eating. So the first strong evidence of intentional fasting shows up shortly after the first writings emerged in various parts of Asia, Africa, Europe. Those first writing fragments dates about 5000-6000 years ago, and once we get fragments long enough to have sentences, fasting shows up pretty quickly. And does so all over the place, in almost all cultures and religions. Now, it was almost always religious fasting, not fasting for health, although most ancient people wouldn’t have made that distinction, because they didn’t view the body and spirit as separate. But it’s pretty safe to say that this fasting, which was quite intentional, was for the spirit and not for health. And it dates, as I say, to the earliest human writing records that we have.

Brett McKay: Okay. So fasting started off as a spiritual practice. When did we start seeing fasting, not just as a spiritual practice, but also as a medical treatment?

Steve Hendricks: It really began with the ancient Greeks, specifically the Hippocratic writers 2400 years ago. There’s a body of about 60 texts associated with Hippocrates who probably wrote very few, if any of them. They’re the work of his disciples and family, but whoever wrote them, they’re remarkable, because they’re the first to say, disease isn’t caused by supernatural phenomena. It’s not caused by evil spirits and so on. Diseases have natural causes that we can try to understand and can sometimes treat. Unfortunately, there was a taboo on dissecting human body, so the Hippocratics couldn’t look under the hood and figure out how things worked, they just had no idea. So they concocted all kinds of nut ball theories about disease and how to cure it. A few of the Hippocratic writers briefly mentioned fasting, but they just didn’t know how to use it. So there’s a text called Aphorisms, for example, in which the writer said that spasms and hiccups could be cured either by fasting or by not fasting, specifically overeating. And the reader is sitting there wondering, “Well, which the hell is it? Do I stuff myself, or do I fast?”

Even so, one or two of the Hippocratic writers were onto something. There’s a writer of a text on acute illnesses, things like fevers, colds, who suggested that fasting for a few days to treat those illnesses would be useful, and who also suggested periodic fasts as a kind of reset for the body. But unfortunately, his good advice was mixed up with all the chaos and craziness of early medicine. And fasting, though it got its birth with the ancient Greeks, was never used rigorously or scientifically or frankly usefully by the Greeks.

Brett McKay: When did fasting really started picking up steam as a medical treatment? Was it after the Renaissance? When did that start happening?

Steve Hendricks: Yeah, you’re right, right after the Renaissance. It really wasn’t till the birth of a more scientific outlook with the Age of Reason, so let’s say 16th, 17th centuries that finally sort of threw out all the quackery that was medicine throughout, pretty much all of recorded history to that point. But the progress was really slow, so it wasn’t really until the early 19th century that you start getting pretty impressive accounts in the US and Europe from doctors who began to notice that when there was, say, an outbreak of typhus or yellow fever, their patients who refused to eat often did better, usually did better than their patients who ate. They also observed that patients who fasted did better than patients who took their rudimentary medicines and their other crud treatments of the day which were things like bleeding and purging people to give them diarrhea and giving them emetics to make them vomit and things like that.

These early doctors who turned to fasting at this time, were really onto something that could have been deeply helpful to patients, because medicine in that era was still almost entirely quackery. Unfortunately, what happened is, most other doctors called these fasting doctors quacks, they just could not accept that conventional medicine was as it in fact was, doing more harm than good, and it was too counter-intuitive for them to understand that by not treating the body at all, that by taking away food, the body could heal itself better than the doctors could with their so-called medicines. So, conventional doctors kept fasting well off to the margins, which unfortunately is a theme that has continued for the last couple hundred years.

Brett McKay: And it makes sense why. You imagine the doctor is thinking, “Well, I’m here to treat the person, fasting is like, I just… I’m not doing anything. It’s like, why do you even need me?” And so, I can see why, “Well, we’re not gonna do that because that requires me not to use my services.”

Steve Hendricks: It makes total sense, both from a very sort of practical economic view and personal view of what you’re talking about the doctors. The doctor has come there to do the healing. So the doctor wants to give a medicine and the patient frankly wants to receive a medicine and be cured, but there’s also this bigger thing going on where fasting is quite understandably deeply counter-intuitive. Everyone knows that food makes you healthy. You eat food, you feel better, you grow up, you grow big and strong. Everyone knows that when you don’t eat, you feel like crap, you feel weak, and to think that this could actually help you, that there are repair mechanisms going on when we stop eating, that’s just a very foreign concept to people, and it’s very understandable why.

Brett McKay: So in the 19th century, you had some doctors experimenting with fasting as a medical treatment, but what was happening too in the culture, there was just people, regular folks, who were just kind of doing individual experiments on themselves to help them get better. And then, fasting also became sorta like now, it was kind of like a fad, people were seeing each other doing fasting, and, “I wanna see if I can up this guy.” And there’s this guy you start the book off, Henry S. Tanner. Tell us about this guy and what influence did he have on bringing fasting to the wider culture?

Steve Hendricks: Yeah, he is the father of modern fasting for sure. Henry Tanner was what was called an eclectic doctor, which would be something like a naturopath today, and he had experimented on himself with fasting for a few days and also with his patients. In 1877, when he was living in Minneapolis, he fell ill with what was probably a stomach flu. He said he had a rheumatic heart, which is kind of a heart inflammation and something like a nervous breakdown, probably because his wife had just ditched him and his medical practice was tanking. So Tanner decides he’s going to fast until he either cures himself or kills himself. And by one account, he didn’t care what the outcome was. At the time, men of science thought you couldn’t go longer than eight to 10 days without food. But as Tanner approached that supposedly fatal 10th day, he actually found his ailments dropping away one by one, and eventually, he felt so good that he, for example, resumed his daily walks, we’re talking like, 15 or 20 mile walks.

He ends up fasting 41 days, word gets out about his fast and he’s widely ridiculed and called a liar. No one can believe that this has happened. So a few years later, when an opportunity arose in 1880 to fast on a public stage in New York City, he took the chance to redeem his reputation, and this fast in New York got enormous public attention, partly because he got involved with a very personal duel of words with a famous New York doctor, a former Surgeon General of the United States who said all this fasting stuff was nonsense. And at first the press and public took that famous doctor’s side and ridiculed Tanner too, but eventually, all the big newspapers sent these tag teams of reporters to watch him 24 hours a day and report on him. They’re on the stage of this lecture hall, where he fasted and slept and lived in full view of the public who were just captivated, especially after Tanner passed the supposedly fatal 10th day and was still alive.

He was a huge sensation, bigger than the presidential race that year, it was reported on, not just in every newspaper in the United States, but in great many newspapers in Europe, Africa and Asia. He eventually fasted for 40 days. The trouble was, unlike in his Minneapolis fast, he didn’t have any illnesses to cure in New York, so while he had proved that you could fast for a long time without harm and that was important, he hadn’t proved that fasting could cure anything. Still, the publicity that he got was so substantial that it kicked off the modern interest in fasting, which eventually led people, including scientists, to give fasting a much closer look, and we are still benefiting from that work at showmanship of Henry Tanner today.

Brett McKay: Yeah. And you also talk about another guy that popularized fasting in America, a guy named Bernarr Macfadden. We did a podcast about him a while back ago, that’s episode number 624, if you want to check it. This guy is crazy. He’s just a crazy guy, but he was like the first fitness influencer. He had this slogan that I love, it’s like, “Weakness is a crime, don’t be a criminal.” [chuckle] But he was really big into fasting and he helped popularize it. And then, throughout the 20th century, fasting was still kind of on the outskirts of traditional medicine. You said now with the research that we have about fasting, people are starting to take it more serious. Doctors are starting to take it more serious. Let’s talk about what some of this research is showing about the benefits of fasting as a medical treatment. So for starters, what does a fast look like to get these benefits? So it sounds like some of the things you’ve been talking about, this is not just a one-day fast, this is like, multiple day fast. Correct?

Steve Hendricks: Yeah. Basically speaking, there are two kinds of fasting, there’s daily fasting, which a lot of people call intermittent fasting, which is just narrowing your eating window each day, and that has shown very impressive results for preventing diseases we don’t yet have. But then, what we’ve mostly been talking about is prolonged fasting, which is fasting for multiple days, even weeks, and that has been shown not just to prevent disease, but in many cases to reverse diseases that we already have. And we’re talking about some of our leading killers, like, cardiovascular disease or type 2 diabetes or other conditions that are becoming epidemic, like, irritable bowel syndrome, or non-alcoholic fatty liver disease. So yes, research into such fasts for such conditions has been growing and a few doctors are starting to recommend it.

Brett McKay: And these are water fasts, so they’re just… You’re drinking water, but you’re just not eating. Correct?

Steve Hendricks: For the most part, yes.

Brett McKay: Yeah.

Steve Hendricks: Fasting doctors in the US fast their patients on water only. In Europe, most fasting doctors use a different form of fasting, it’s called a modified fast, and people take about 250 calories a day, mostly in vegetable broths. That’s not too many calories that it will bump you out of fasting metabolism, but it is enough calories that it gives you some energy, you’re able to do some things like hiking and you can have fewer side effects, like, headaches, nausea, which some people get on a water-only fast if it goes long enough.

Brett McKay: How long are some of these fasts? So, Henry Tanner went 41 days, he bested Jesus. What’s the longest fast that we know about?

Steve Hendricks: Yeah. So you can fast as long as you have the fat stores to live on. So, the longest fast on record was a fast of 382 days by a Scotsman in the 1960s who weighed 456 pounds at the start of his fast. He wanted to get down to 180 pounds, and after more than a year of fasting, he did so.

Brett McKay: So what goes on in the body that allows for an extended fast like that? And sometimes you can not only survive it, but you can thrive, like, this Henry Tanner, but other people talk about 10 days in their fast, they’re feeling great, they can go on hikes. So what is going on physiologically in our body in a prolonged fast that allows for that?

Steve Hendricks: Yeah, we survive by living off of our fat, just technically, actually off a breakdown product of our fat that a lot of people are familiar with now called ketone bodies. The body’s preferred fuel is glucose, that’s the sugar from the carbohydrates in our meals. But when we go without food for long enough, the body will shift its metabolism so that it can run on ketones, and in some respects, the body may even actually run more efficiently on ketones. As it does so, the body turns on when it gets into this fasting metabolism of ketosis, it also turns on a bunch of repairs, and these are partly responsible for what allows us to thrive while fasting. See, our bodies are these marvelous self-healing machines, they’re constantly making repairs all the time in our cells to spare us from disease. But they usually make these repairs only at a very low rate, because they’re so busy most of the time doing all the other things that make up our lives.

And one of the biggest tasks is digesting our food each day, processing the nutrients from that food and putting the nutrients to work and cells all over our bodies. But when we give our bodies a break from that immense labor, evolution has endowed ourselves with these beautiful mechanisms that take advantage of the rest to ramp up cellular repairs. These are repairs like, patching up more damaged or mis-copied DNA, which, if not fixed, could cause disease and increasing the recycling of cellular parts that have gotten worn out and could also cause disease, if not fixed, or increasing the antioxidants in our bodies that wipe out the free radicals that can damage ourselves. When these repairs go on during a prolonged fast, we see immediate very healthy changes, high blood pressure drops and starts to normalize, people who are insensitive to insulin grow more sensitive to it.

The repairs that I’m talking about do happen on the daily fasts with the narrowed eating window each day, but they really happen with prolonged fasts of a week or multiple weeks.

Brett McKay: Now this sounds… I mean, again, people… Hear this, this sounds counter-intuitive, you can go a year without eating and you’re okay, because I think a lot of people might have heard this about this experiment, you talk about it in the book, it’s the Minnesota Starvation experiment, which happened during World War II. The military just basically wanted to see what would happen if we don’t give a lot of food to our soldiers out in the battlefield. And so, they took conscientious objectors and did this experiment on them and didn’t feed them. And these guys didn’t do very well. So, why was it like, these guys in the Minnesota Starvation experiment, why did they fare so poorly, but that Scotsman guy who went a year without eating, he’s okay? What’s the difference between the two?

Steve Hendricks: Yeah, great question. The problem is that eating half rations, which is what these guys were on. For six months, they were eating 50% of their normal amount of calories each day. Eating half-rations is very different metabolically from fasting. So, for a start, there’s the fact that when you’re fasting and living on your own fat, the ketones that are the breakdown product that you’re actually using for fuel from the fat, suppress hunger. They actually suppress your hunger hormones. What drove these Minnesota starvation experiment people just half crazy… I mean, one of them resorted to taking an axe to chop off some of his fingers in order to get out of the experiment and then was so confused, he couldn’t explain why he thought this was the best way of getting out of the program. But they were just driven half mad by hunger.

So when you fast, the irony is, eating zero calories as opposed to eating 50% of your calories results in zero hunger, so it’s a much easier thing to maintain, but there’s more than that. If you’re eating as the men were, in the Minnesota experiment, even if it’s just half rations, your body doesn’t go into the repair mode that it goes into when fasting. Your body still has enough work to do processing those half-rations that it doesn’t have time to make all of these repairs, so you don’t get fixes to your DNA, you don’t get a decrease in high blood pressure, an increase in insulin sensitivity or a decrease in body-wide inflammation the way fasters do. So, you might say that half rations is all pain and little gain, whereas fasting is something like the opposite.

Brett McKay: So you mentioned some of the conditions that can be treated by fasting, I would like to go into more detail about this. Let’s talk about metabolic conditions like type 2 diabetes. This is increasing significantly in the west and in other countries that are starting a western-type of diet, so what happens in an extended fast that can help treat things like type 2 diabetes and things like that?

Steve Hendricks: Yeah, so scientists are still figuring out the mechanisms. We know that fasting clinics report reversing as many as 80% of their type 2 diabetes cases with prolonged water-only fasts, and a very large proportion of cases of other metabolic diseases like, non-alcoholic fatty liver disease, which hurts us by smothering the liver and fat and is becoming epidemic. What we know so far is that when we fast, our bodies have this knack for burning a lot of the most harmful fat first, the fat that seems to do us the most harm seems to be the visceral fat, the belly fat, which is behind diseases like fatty liver. During a fast, we burn off way more visceral fat than we do the other less harmful fat. Scientists also think that fasting does a great job of getting rid of the fat inside of our muscle cells and inside of our liver cells, and this is the kind of fat that causes type 2 diabetes. We often think of diabetes as a sugar disease and in a way it is, but the research is clear that the inability to tolerate sugar is much more of a symptom of diabetes and not the cause.

The cause is the fat inside our cells that makes the cell’s insulin receptors malfunction. So when insulin comes knocking at the cellular door and says, Hey, let the sugar in, that’s insulin’s job to move sugar out of our arteries and into the cells, the cells can’t hear insulin knocking at the door. So the sugar stays in our arteries where it dings them up, causes them to harden, which leads to strokes, heart attacks, dementia, a bunch of other awful stuff. But once you get rid of the extra fat in the cells, as it happens on a fast, the cells become much more sensitive to insulin, which is then able to move the sugar from our arteries into the cells. There are undoubtedly other mechanisms at play, but one of the frustrations of fasting is, as beautiful as the sciences that has blossomed in the last decade or two, we just don’t know anywhere near as much about it as we would hope to. Many, many, many mechanisms remain to be discovered, and that includes for diseases like type 2 diabetes.

Brett McKay: So one thing that doctors have noticed with anyone who does a prolonged fast is that their blood pressure drops. What’s going on that allows blood pressure to drop during a fast?

Steve Hendricks: Yeah, so we have excellent studies going back 20 years that show fasting, in just about every case it’s ever been looked at, lowers high blood pressure. One of the fascinating things is, if your blood pressure is normal, it doesn’t lower it, so it appears to only be treating disease. I mean, it’ll lower your blood pressure a little, but not to a completely unhealthy level or anything. It’s not like you keep fasting and your blood pressure just drops out the bottom and you die or anything. I don’t think scientists really know why fasting has this effect. What they do know is that the greatest drop in hypertension ever reported in the peer-reviewed scientific literature came not from pills, came not from a conventional procedure, but from fasting for 10 days at a Fasting Clinic. And in that study, the average drop in high blood pressure was 37 over 13 points, which is like double or triple what most blood pressure pills can achieve. And the best news is, the sickest patients, those with the worst stage 3 hypertension got a drop in their systolic pressure, which is the top number in a blood pressure reading of 60 points. 60. That is just off the charts.

Conventional medicine can’t touch it. Unfortunately, we don’t have much more data than that, but that’s still enough to go on, even if you don’t know the mechanisms behind it, right? You have getting the cure, [chuckle] one would think would be great because most medical organizations will tell you they don’t have a cure for high blood pressure. And yet, despite this research having been in the scientific literature for two decades and with follow-up studies and so on, confirming these results, most doctors who are dealing with hypertensive patients know nothing about it and do not suggest that their patients look into it, which is quite a pity.

Brett McKay: Another contributing factor to cardiovascular diseases like lipids, So cholesterol, triglycerides, what does fasting to do that stuff?

Steve Hendricks: It does fantastic things for them. Again, both daily fasting and prolonged fasting. You find studies where people are having their triglycerides and cholesterol drop 10, 20, 30, sometimes even 40 or 50 points. Sometimes when you do a prolonged fast, your triglycerides in particular, I think it is, certainly some of your lipids will rise, which originally led some doctors to be concerned. The rise appears to be temporary. It rises because you are mobilizing all your fat, your lipids, you’re stored cholesterol and so on, that gets into your blood. And after a few weeks after the fast, it goes away and you end up quite usually with lower lipid readings than you had before.

Brett McKay: We’re gonna take a quick break for a word from our sponsors.

And now back to the show. So there’s a lot of people out there that have autoimmune diseases, like lupus, rheumatoid arthritis, and this is a debilitating condition where basically, your body is attacking itself. Your body’s immune system is attacking your body. And the treatment for this is sort of you can manage symptoms often, but then there’s research that shows that fasting, prolonged fasting can help with even autoimmune disease. Can you walk us through some of the research and patient stories on that?

Steve Hendricks: Yeah, you’re right. The autoimmune diseases like rheumatoid arthritis, as you mentioned, ulcerative colitis, lupus, psoriasis, these diseases where the body is attacking itself, the body seemed to calm down and the attacks lessen and sometimes it can go away completely when people do prolonged fasts. The best studied of these conditions is RA, rheumatoid arthritis. There were a few pilot trials back in the 1980s that found, when people with RA fasted their neutrophils calmed down. Now, neutrophils are normally good things, they’re white blood cells that kill harmful bacteria, but in RA, they turn on the body, they attack the linings of the joints, which lead to these really nasty inflamed, often deformed, very painful joints.

So finding this mechanism and finding benefit from fasting, there was a more rigorous randomized control trial that was set up. Randomized controlled trials are the gold standard of clinical research, very good trial. In that trial, a bunch of people with RA fasted for a week, and then they ate a plant-based diet for a year. Now, the background for this is that we don’t have a cure for RA. We’ve got drugs with pretty terrible side effects that can slightly slow the progression of the disease, but nothing that can reverse it. In this fasting trial though, both during the fast and then afterward on the plant diet, the volunteers showed remarkable improvements, they had less inflammation, less pain, less morning stiffness, better ability to grip things and on and on. The control group who didn’t fast, didn’t improve at all, in fact, they got worse.

Now, this study was so convincing that in 1990, its results were published in The Lancet, which is one of the world’s most prestigious medical journals. Now again, remember, we’ve got no conventional treatment that can reverse this disease, and here the researchers had shown that fasting reversed it. But the medical establishments simply couldn’t accept it, they just roundly rejected it, forgot all about it, if they ever paid attention to it at all. To me, that’s the real quackery, even though they were calling fasting quackery, the more scientific approach would have been for the rheumatologists to heed the science presented in this very good trial and advise their RA patients who’ve got nothing else to go to a Fasting Clinic.

Brett McKay: So another area you explore how fasting can be used as a treatment is cancer. And you start off the book with the story about a woman who got diagnosed with cancer, and then she decides to go to this Fasting Clinic in Northern California. And when I first started reading this story, I’m like, Oh my gosh, this sounds like Steve McQueen when he had cancer, trying all these treatments that ended up probably speeding up his death. But this woman, cancer started going into remission, when she started extended fast. So tell us about that experience and what the research is showing about fasting and cancer.

Steve Hendricks: Yeah, so this woman had follicular lymphoma, which is a cancer that attacks the lymphatic system. And your note of caution is right, and I’ll get to why we should be cautious in a moment, but in her particular case, she went and fasted for… I believe it ended up being about three weeks at this Fasting Clinic, and her tumors disappeared. She had some very good scans and so on that were done before she went to fast and after she went to fast, that could verify that these tumors went away. Now, follicular lymphoma is a weird cancer, it’s very slow developing, it can come and go, there are often spontaneous remissions where the cancer looks like it’s gone away, and a year later, two years later, comes back. Well, years passed, her cancer never came back. So the doctors and researchers at this clinic wrote up her case for a very important medical journal called the British Medical Journal Case Reports, and it was published.

When her cancer still didn’t come back years later, they published another study showing that it hadn’t come back. It’s now been eight years and I talked with her a few months ago, she is still cancer-free. Now, so we think that that fasting can in fact entirely eliminate follicular lymphoma, at least in some patients. There are also very credible anecdotal reports, these aren’t published in the peer-reviewed literature, but they’re credible, and they suggest that fasting can slow or even reverse other cancers. But here’s the catch, temporarily, alright? The problem is that cancer is crafty. It almost always finds a way around the hurdles that fasting throws up. So, most people, if they’ve got cancer and they go to fast and they may get some good results for a little while, but they’re probably gonna end up dead if that’s all that they’re relying on.

We have no evidence that fasting can reverse the great majority of cancers in humans, though it’s possible, we will find some more because we do have evidence that it can reverse certain cancers in lab animals. But it’s really hit and miss, like, fasting can completely retard, eliminate one form of leukemia in mice, but not another form of leukemia in mice and scientists don’t really know why. What they’re excited about and where they think fasting’s real promise seems to lie for cancer is in using it as an adjunct to conventional treatments, like chemotherapy. Because scientists have found that prolonged fasting does indeed weaken some cancers, and it does this by starving them of their preferred fuel, which is glucose, which obviously is gone during a fast, fasting also tamps down on the growth factors that cancer hijacks to divide and spread. And fasting also ramps up the body’s immune cells that attack cancer, so that’s all really good news.

Now, at the same time, when a cancer patient fasts for just a few days, their healthy cells go into a protect and repair mode. They kinda hunker down and they lick their wounds, so when cancer patients fast and then get chemo or radiation, their healthy cells do a better job at repelling the devastating effects of those treatments, so their cells either aren’t as badly hurt or do a better job at quickly fixing whatever damage it is that they suffer from those treatments. The result, and this is the headline here for chemo and radiation patients, is that they have far less nausea when they fast a few days around their treatment, they have far less vomiting, less diarrhea, fewer headaches, less fatigue.

That is just huge. But the final piece of it, which may be even better, scientists are still trying to figure this piece out, is that during the fast, the patients’ cancer cells, unlike the healthy cells which were hunkering down, the cancer cells pay no attention to the fast, and they continue with their single minded mission to grow at all costs. They just keep gobbling up any and all inputs, including the chemo. Because the fast has already weakened the cancer, the chemo may kill more of the cancer cells. And since the healthy cells are better protected, and the cancer cells are more vulnerable, doctors should be able to give higher doses of chemo to kill even more cancer without killing the patient, and that at least is what happens in mice. And we have trials underway now to see if the same will hold true in humans.

Brett McKay: So again, this is a prolonged fast. I think the way you described it, when chemo patients do try to combine fasting with the chemotherapy, they might do like a 36-hour fast before their chemo treatment, and then like, another 24 hours after the treatment, correct?

Steve Hendricks: Pretty close. They tend to be 48 to 72-hour fasts before the treatment, and then 24 hours after the treatment. And there’s a very prominent researcher at the University of Southern California named Walter Longo, who has come up with a fasting-mimicking diet for people who are scared of fasting or don’t wanna fast, that gives you a few calories, it’s 200 or 300 calories a day, very specially calibrated, so that if you wanna have a little bit of food to see you through that you can do that. So it’s fasting or fasting mimicking diets for a few days before and one day after.

Brett McKay: And is the research ramping up on this with fasting and cancer?

Steve Hendricks: Yeah, it’s huge. Now, the catch is, so Longo, who I think is a fantastic researcher, he’s really just done some of the most amazing work, when he was trying to put his trials together, he found that oncologists and patients were extremely reluctant to fast. I mean, you can understand this. People who… Many of them, most of them probably have no experience with fasting, and they’re saddled with cancer, which is horrible, and then they’re told they’re doing chemotherapy, which is all the worst, and then you ask them to fast on top of it, they just completely freaked out. And so, he had a very hard time convincing oncologists and patients to go along, which is why I think wisely he came up with the fasting mimicking diet. The catch is this, you can make a lot more money off a fasting mimicking diet, a product that you can sell for a couple of hundred bucks for four days or so, then you can off just telling people not to eat.

So, almost all the research into fasting and cancer treatment is going into actually fasting, mimicking diets and cancer treatment, because the company that’s behind the diet wants to do that research. Fasting Clinics don’t have a lot of extra money, they’re not doing this kind of research, even though they are doing a little bit of research. So there’s a shortage, I think, of actual research into actual fasting for cancer, and knock wood, that will be remedied some day.

Brett McKay: So you mentioned that fasting has been shown or a prolonged fast has been shown to help us live longer. What’s going on there?

Steve Hendricks: Yeah, so when we fast, the biomarkers for longevity move in the right direction, often in a big way. Some of these biomarkers are ones that we’ve talked about, like, lower blood pressure, greater insulin sensitivity and so on. But some of the markers are quite specific to longevity. There’s a gene called CERT1 that’s sometimes called the longevity gene, because of several things that it does, like, making more antioxidants or protecting our telomeres, which are the protective tips that keep the ends of our DNA from unraveling, like the plastic tips on the ends of our shoe laces. In one study, when volunteers ate for just four days in a daily fasting pattern, in this case, they were eating for six hours a day in the morning and early afternoon, and then fasting for the other 18 hours, the activity of CERT1 increased by 10%, which is an astonishing gain for just four days of changing not a thing about what they ate, only when they ate.

Even bigger was an increase in the recycling of worn out cellular parts that process, which some of your listeners probably know is called autophagy, which protects us from disease. One marker for autophagy in this four-day study increased by 22%, that is just simply astounding. Again, not a single change to their diet, only a change in when they ate the same foods that they would have eaten otherwise. So, scientists believe that increases in these kinds of markers will eventually translate into longer life. They will result in less disease and they shouldn’t result in more longevity, though, of course, it would take 120 years of study for us to verify that. So, it’s partly speculation, but it’s really well-grounded speculation.

Brett McKay: So we’ve been talking about extended fasting’s effect on our physiology, it could be autoimmune diseases, diabetes, cancers. What does the research say about extended fasting and mental health?

Steve Hendricks: Yeah, this is another area where we need far more research, but what we do know is extremely intriguing. The best work on this was done clinically by a Russian psychiatrist named Yuri Nikolaev. Between about 1948 and 1990, Nikolaev decided that the barbaric treatments of the day, things like electroshocks, were more harmful to mental patients than helpful. And he had grown up fasting now and then, so he decided to give this a try on his patients at the large mental hospital in Moscow where he worked. And the results were spectacular. We’re talking hard core schizophrenics, institutionalized people who were very severely deranged, who seemed to be beyond all help, often recovered with fasts of about three weeks. Nikolaev ended up fasting about 10,000 patients, and many of them, I think the majority, became completely normal and resumed healthy, happy lives. And he maintained their remissions by having them eat a vegetarian diet and doing periodic maintenance fasts of a few days here and there.

Now, he didn’t have the research to say why fasting helped them. And even today, we don’t have a ton more, but we do know a few things. For example, one of the ketones that’s burned for fuel and fasting, it’s called BHP, beta-hydroxybutyrate. This ketone increases something called brain-derived neurotrophic factor, BDNF. BNDF is important for our brains, because it grows new neurons, it maintains existing neurons and it forms new synapses between neurons. So when we fast, we get all these benefits in our brain. Fasting also increases the amount of feel-good hormones we have circulating, like endorphins, and what might be called feel-good neurotransmitters like, serotonin and endocannabinoids, which is like, your body’s own cannabis. So, we have a few details, they’re all very encouraging, but we are a very long way from understanding all of this.

Brett McKay: And you provide stories, these are all… Again, we gotta be clear, these are anecdotal stories from doctors who were treating patients with mental health problems. I think there was one, there was a woman who was just severely depressed and she didn’t wanna eat and the doctor was like, “Okay, well, just don’t force her to eat, just give her water,” and she basically started this unintended extended fast, and I think a week or two weeks into it, she started feeling better and she was fine after that.

Steve Hendricks: You’re right. And these are just anecdotes, it’s a good thing to remember, these are not randomized controlled trials. However, when the weight of the anecdotes piles up over 150 years of fasting doctors recording what they’ve seen, and patient after patient, for instance, in mental institutions who refuse to eat, get better, it should, to the scientifically-minded researcher or doctor, peak their interest in, “Well, I don’t know, this is really strange, but why don’t we put it to the test and try a trial and see what happens?” Unfortunately, it is so counter-intuitive that, that sort of scientific part of the doctors’ and scientists’ brain just goes out the window, they can’t even see the evidence before their eyes. But it is important to note, as you say, these are anecdotes, there could be something else going on there, but it seems awfully likely to be the case that it is the fasting that is bringing about these changes.

Brett McKay: Well, in the section on fasting, it reminded me of a recent podcast we did with Dr. Chris Palmer, he is a Harvard psychiatrist. Just came out with a new book, where he lays out his theory that all mental illness, whether it’s depression, anxiety, schizophrenia, addictions, the underlying cause is a metabolism issue. And so, it made me think that fasting helps improve our metabolism, ’cause it just basically allows our metabolism to reset, so maybe that’s what’s going on with fasting and mental illness, it’s just helping our metabolism improve.

Steve Hendricks: Yeah, Palmer’s theory is certainly provocative and interesting. It’s certainly possible. I mean, our psychology is so complicated. Your metabolism can be great, but if, I don’t know, you live in a war zone or something, you may well be depressed. [chuckle] I have found… One of the problems that I’ve had for most of my adult life was clinical depression, and I had been on anti-depressants for a quarter of a century. And I thought, “Well, gosh, wouldn’t it be interesting if I tried going off my anti-depressants?” Now, for the previous 25 years, any time I had done that, I would last about three or four months and I would completely crash. It was just grim times. This time, however, when I tried it, I didn’t crash. It’s been almost four years now that I’ve been off anti-depressants, the longest that I have ever been off any depressants before, and I do think it has a great deal to do with exactly what you’re saying, some metabolic reset that we don’t yet understand that happened in my fast, and then that I maintained, and this is another important part, by changing my diet to a far healthier diet.

Because you have to ask yourself, “Well, look, if the condition gets better when we take the food away, is it possible that there’s something in the food itself that might be causing this illness?” And researchers like Christopher Palmer, who you mentioned, are on the forefront of trying to look at what these nutritional contaminants, for lack of a better word, are, is that throws off our nutrition and throws our metabolism and contributes to, for some of us, our mental illness.

Brett McKay: You also mentioned that when we eat, when we do eat, can have a big impact on our health. Talk more about the research there, how the time we eat can either be detrimental or help us?

Steve Hendricks: Yeah, this is really new and really exciting research just in the last decade, some of it just in the last couple of years. And to summarize it, scientists have found two very important things. The first is that our bodies make more repairs during our overnight fasts, right? We all fast overnight, it’s just a question of how long. Well, our bodies make more repairs during those fasts when we fast for at least 12 hours each night, which of course then means limiting our eating to no more than 12 hours a day. These repairs increased dramatically if we limit our eating even further, cutting our eating window down to eight or even six hours a day. That’s why you see so many people these days following, say, a 16/8 eating pattern, where they’re eating for eight hours a day and fasting the other 16. I mean, actually most of them are probably doing it to lose weight, but a bunch of them are doing it because they’re aware that it steps up our repairs.

The second big recent finding, and this one almost nobody knows about, is that our eating window is far healthier if we put it in the morning and early afternoon. See, most people who practice daily fasting do, as I did when I first started it, they skip breakfast. They wanna eat dinner, so they start eating around 11:00 AM or noon and they knock off after dinner, maybe around 7 o’clock, that’s the way I did it for a couple of years. But it turns out that our circadian rhythms have hard-wired us to process food most efficiently in the morning and early afternoon, and we get worse and worse at it as the day goes on. By night time, we’re frankly pretty terrible at processing nutrients. So when we eat later in the day or at night, nutrients linger in places where they shouldn’t and our overnight repairs become interrupted. And there seems to be just nothing we can do to change this circadian rhythm that governs all of these processes.

So from these two findings, researchers think that the healthiest eating window, the one that will maximize our literally vital overnight repairs that our bodies make each night, is a window that starts about an hour or two after we wake up and continues for about six hours. So, for many people, that would be something like a eating window from 8:00 AM to 2:00 PM. Now, I know that that sounds crazy, and believe me, I hated hearing this news, because I just loved eating late, I nearly always skipped or skimped on breakfast, and I did not wanna try this, but I wanted to follow the science. And so, I experimented, and as I described in the book, I actually found it was a surprisingly easy change to make, as if my body had kinda been waiting for me to be eating in sync with its circadian rhythms for half a century.

And hooray, I finally got around to it and had more energy and many other benefits. But I will say this, of course, most people want to eat dinner, most people with their work schedules will need to eat dinner. And for these folks, scientists think there may be a compromise. Scientists say that you can probably get a lot of the same health benefits of eating in an early window if you just take the great majority of your food each day in that early window. So, doing most of your eating before mid-afternoon and then trying to keep your dinner early and light. So it turns out that the adage coined in the last century to “eat breakfast like a king, lunch like a prince, and dinner like a pauper,” was actually good advice.

Brett McKay: So, people who are listening to the show about this extended prolonged fast and think, “Oh, I might wanna try that,” is this something you need to do under medical supervision?

Steve Hendricks: Yeah. So, fasting doctors have mixed opinions on how long people can safely fast without medical supervision, and we don’t have great research to say, so we’re really reliant on the fasting doctors’ clinical experience. Some of them say, “If you’re in good health, you’ve got no diagnosed conditions, you don’t suspect any illnesses, you’re on no medications or supplements, you can safely fast on your own for up to a week.” Other fasting doctors say, “Well, there are some people out there with very rare disorders, people for example, who can’t process the by-products of the fat that they’ll burn during a fast, and these people could end up in a coma or even die.” Now, they’re really few and far between, but they do exist, so some doctors think that no one should fast on their own for more than about a day. Now, where all doctors agree is, they say that if you do have a medical condition, you’re taking some meds or something like that, you should never fast without medical supervision.

And I think they’re wise to say that, because lots of things can happen to people who are in great health when they fast. Even if you’re healthy, none of the doctors recommends fasting on your own for more than a week, because even healthy people can run into trouble on a fast and an experienced fasting doctor should be examining you physically each day, checking your pulse and things like that, testing your blood and urine periodically and doing other things that will help the doctor spot trouble signs that may come up. Those are all the caveats. So that said, if you are in fact healthy, you’re not on meds, you can just stop eating and see how it goes, but there are a couple of things you need to be aware of, and I’ll just try to very briefly mention them. The first is that you have to drink lots of water to stay hydrated, like, half a gallon or more a day. And the second is, you need to be aware that the greatest danger of prolonged fasting isn’t what people usually think it is, it’s not usually damage to your heart or your liver or something, it’s fainting, because when you fast, as we discussed, your blood pressure will drop.

That usually starts about a day or two into the fast, and if you stand up too quickly, your blood may not stand up with you and get to your head quickly enough and you can faint. A very simple remedy, fasting doctors advise that you just pump your legs before you stand up to get the blood flowing, that you stand up in stages, but you just be ready [chuckle] on a moment’s notice to sit right back down if you feel light-headed. You do that, most people, almost everyone, is safe on a week-long fast, who are healthy.

Brett McKay: Should you do this on a vacation or like a week, long week… Let’s say, you wanna do a three-day fast, would it be good the first time you do it on an extended three-day weekend?

Steve Hendricks: Yeah. So it’s highly variable. That’s the way I would do it. I would try doing it at a time where I can rest and I don’t have to work. Some people, when they fast, they get more energy. Writers, artists, composers talk about creating their, whatever it is they’re creating, in just are flurry during their fasts. If you have that kind of response to a fast, heck, you may just do it during the work week. However, a lot of people feel extremely tired, exhausted, just the whole sort of catalogue of being worn out, for those people, I think you’ll wanna do it on a weekend. Part of the answer is, it depends on why you’re trying to fast. If you’re trying to fast just ’cause you’re interested in seeing how it goes, or you want to get some of these repair and maintenance benefits, but you don’t have an illness or something, you may not need rest as badly as someone who’s actually trying to cure an illness.

So, if that’s you, fasting doctors recommend resting the body in order to give your body… If you’re not moving around, your body has fewer functions to attend to, the theory is it can attend to those repairs more. So you know, it depends on why you want to do that fast.

Brett McKay: What does your fasting protocol look like right now?

Steve Hendricks: So, I do a daily fast every day, and just my normal eating pattern where I eat from most days, about eight in the morning till oh, 2:00, 3:00 in the afternoon, and I’m flexible about it. If we’re having friends over for dinner or something, I’ll eat at the normal dinner time. And then, I do a prolonged fast about every six months of approximately a week on my own at home. And every so often, I don’t wanna fast for more than a week on my own, because I don’t think it’s especially safe. And so, every so often I wanna go to a fasting clinic and maybe try fasting for a couple of weeks, but that would be about every, say two, three years. See, as I mentioned, my health was terrible in my 40s, and I do credit fasting and my dietary change with helping me get my health back, but it’s only been two, three, at most four years, that I’ve really started to feel healthy.

And I feel that the fasting, or at least I should say, I hope that the fasting and I think the research supports this hypothesis at least, will help me maintain these gains. I sort of still see myself as a recovering sick person and not a fully healthy person. If I were in perfect health, I would probably only do a prolonged fast once a year for about a week, call it good, and then just do my daily fasting.

Brett McKay: Well, Steve, this has been a great conversation. Where can people go to learn more about the book and your work?

Steve Hendricks: Thanks. My website is probably the best place. And that’s just my name, The book is a narrative about fasting, it’s not how to, though you can get a lot of help to information out of it, but to help people who want even more how to than is in the book. On my website, there is a frequently asked questions page and people have I think found that pretty helpful. There are, gosh, I don’t know, 10,000 words of answers to the most common questions I get about how to fast mostly. So those would be the places to start.

Brett McKay: Alright. Well, Steve Hendricks, thanks for your time. It has been a pleasure.

Steve Hendricks: It’s been great, Brett. Thank you so much.

Brett McKay: My guest, it was Steve Hendricks, he’s the author of the book, The Oldest Cure in the World, it’s available on and book stores everywhere. You can find more information about his work at his website, Also check out our show notes at where you can find links to resources, where you delve deeper into this topic.

Well, that wraps up another edition of The AOM Podcast. Make sure to check out our website at And while you’re there, sign up for our newsletter,, get the daily update or the weekly digest, and it’s completely free. And if you haven’t done so already, I’d appreciate if you take one minute to give us a review on Apple Podcasts or Spotify. It helps out a lot. And if you’ve done that already, thank you. Please consider sharing the show with a friend or family member who you think would get something out of it. As always, thank you for the continued support. And until next time, this is Brett McKay reminding you to not only listen to the AOM podcast, but put what you’ve heard into action.

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