As I’m getting ready to start my third multi-day fast of my life I thought I’d do a much better job of documenting it on my blog. To start off I wanted to lay out my very amateur thoughts on fasting and how I have done it in the past. This is a very long post so use the table of contents to jump around to the parts you may find worth reading if you don’t want to read the whole thing.
Fasting, whether intermittent or prolonged (multi-day), is not a new thing in human history but it has achieved some new-found fad status in the 21st century. The intermittent fasting variety first came to my attention about 10-15 years ago when a body builder friend was using it to help with his shredding phase. The multi-day water (or nearly calorie free) variety as a fitness regiment is something that I started seeing several years ago as well. I’ve done my share of both over the last few years. As I am getting my fitness dialed in I’ve decided to follow the advice in The Longevity Diet by Valter Longo and start incorporating regular multi-day fasts into my annual routine as well. To kick this latest one off I’ve decided to write about my thoughts about fasting, why I do it, and how I do it (hopefully) safely. The usual disclaimer applies though. I am not a doctor, trainer, dietitian, nutritionist, or any other expert in any related field. I’m talking about my amateur and anecdotal experiences here and none of this should replace expert medical advice.
Fasting is literally just the process of abstaining from food and or drinking. It can be as simple as delaying eating your first meal of the day. “Breakfast” has been the word English has used for the first meal of the day, breaking the fast from the last time we ate from the night before, since the 13th century. People fast for many reasons. Catholics used to fast before their Sunday mass if they intended to take the Eucharist. Nowadays that’s just a one hour fast before mass. Muslims fast during sunlight hours during the month of Ramadan as part of a spiritual cleansing process. Some people fast for medical reasons, say before a blood test or a medical procedure. In recent years fasting as a means of losing weight has become very popular with the aforementioned intermittent fasting being one permutation. For many years people have been looking at extended calorie restrictions and fasting as a means of improving longevity.
Types of Fasting I’ve Tried
In this context I’m going to be referring to fasting is going to be abstaining from eating/drinking calories for a given period of time either for short or long term health reasons. These therefore fall into two categories: intermittent fasting and prolonged fasting. Both are exactly what they sound like by their names but there are some devils in the details.
Intermittent fasting is intentionally drastically reducing, usually to near zero, the amounts of calories you are consuming for an extended period of time less than a day. The most usual form of this is a time-restricted eating window per day. The idea is to have at least a 12 hour window of no caloric consumption. Technically a lot of that can be sleep. At which point most people for most of history were “intermittent fasting”, having not eaten after bed and eating breakfast about 12 hours later. Usually this takes the form of shorter eating windows and thus much larger fasting windows. Popular variations are 16 hours of fasting to 8 hours of eating (16:8) or (18:6). Both of these essentially make room for having a lunch and a dinner or a breakfast and a lunch. More aggressive versions of these can collapse that window down to just 1-2 hours, thus one meal. These are essentially 24 hour fasts as you are eating about the same time each day. Obviously the larger the window the harder it will be to adjust to it.
Beyond fasting in a single day there are prolonged fasts as well. In less-aggressive versions of these fasts there can be alternate day fasting. In this sort of routine it is more like alternate day dieting. Essentially one day you eat normally and the next day you eat drastically reduced calories (like 500-800 calories). In an actual alternate day fasting one eats normally on one day and then abstains from eating the next day, and so on.
Much longer versions of zero-calorie multi-day fasts are harder but potentially have additional benefits, that I’ll get into below. In these sorts of fasts one goes multiple days of not consuming major calorie sources. Most of the time these protocols call for 2-3 days, maybe a week. Some people have taken these sorts of fasts to the extreme of weeks or months. The world record for the longest someone went without consuming substantial calories was Angus Barbieri who went 382 days without eating.
During any of these fasting periods, whether it be the short intermittent fasting or multi-day fasting, the primary common metric is to minimize the amount of calories consumed. Some people take it to mean that literally nothing but water is to be consumed. Others take it to mean non-caloric beverages, such as coffee or seltzer water. The big thing is to not consume large amounts of fat, carbs, or proteins. That means that coffee or tea may be fine but that creamer or sugar would not. What about non-nutritive sweeteners? That all depends on the person. For longer term fasts sometimes broth is included, or electrolyte solutions, in order to avoid some medical risks highlighted below.
It all therefore can get a bit complicated. There are lots of wrong ways to do fasts but there is no one right way to do one. The design of the fast is heavily dependent on the person and the benefits that are being sought by performing a fast.
Theoretical Benefits of Fasting
One of the big reasons why fasting has become the rage recently, especially intermittent fasting, is because it can help with weight loss. There are several papers on the topic including this systematic review of papers on the topic . It definitely shows that intermittent fasting can achieve similar weight loss goals as calorie restricted eating. This is often, but not always, just a function that under controlled settings there is a net reduction in calories consumed. The benefit of fasting for keeping weight off long term is not as conclusive. There is discussion about how fasting “teaches the body” to be more insulin sensitive as it is not always in a state of high blood glucose from continual feeding. Similarly it is believed that additional fat loss may occur because for longer periods the body is having to tap into fat reserves as it needs more fuel between the longer feedings.
Weight isn’t the only biomarker that can be improved with fasting. Fasting has been proven to produce similar or greater improvement in biomarkers such as fasted blood glucose, HBA1C, and IGF-1 compared to weight loss from continuous calorie restriction, which this paper gets into comparing . Generally these sorts of biomarkers improve with weightloss which is why it was important to compare it to the effect of weight loss in general.
With longer term fasts, even a so-called “Fast Mimicking Diet”, there can be comparable improvements in biomarkers even when all other aspects of the diet remain the same, such as in this study . Along with reduction in biomarkers directly there is a lot of talk about “cellular autophagy” , which is the process of your body breaking down old/damaged cells when it is under metabolic stress induced by a fast. Essentially within 24-48 hours of fasting your body will begin this process. This hypothetically has the benefit of helping to clear out the weakest cells, which are often the ones with genetic degradation. This therefore has the possibility of helping to reduce your cancer risk, as detailed in this paper . The potential cancer prevention aspect is actually the reason why I’m interested in longer duration fasting in the first place.
Unrealistic Claimed Benefits of Fasting
Both kinds of fasting have the potential to help in all the ways mentioned above. That doesn’t stop the usual rush for claims that some health intervention has nearly magical outcomes. The first nonsensical claim is that all of the above claims are 100% proven. They are not. There is good evidence to suggest that both intermittent and prolonged fasting can help with all of those things in the short term. The question is how it affects the long term effects and how that has an overall effect on longevity. That’s often one of the first places things go off the rails with claims about fasting. Fasting may improve longevity. It may not. What fasting won’t do is guarantee that you will live to 100, or even beyond. The more ludicrous claim that fasting will “stop the aging process” or “make you younger” are even more unfounded.
Fasting as a band aid to “fix your health” when normally your lifestyle is the antithesis of that won’t work either. Many years ago I had an acquaintance that was pretty hard on their body most of the time. Heavy smoking, drinking, and even not so occasional drug use were a big part of their lifestyle. So too were regular suntanning to get super-tanned, including tanning beds in the winter, eating a very rich western diet etc. They worked hard and they partied harder. Each year they would do a one week detox vacation. This would be nothing but relaxing activities and a “juice cleanse” of things like concoctions made of beet, celery, and carrot juice with lots of antioxidant type herbals added to it. The idea was that doing that once a year would flush their systems clean and make up for their habits the rest of the year. It did not. If it was better than doing nothing then it would be short lived at best. One week of this sort juice cleanse or any other type of fasting isn’t going to magically negate a year of beating up your body.
Fasting will not magically cure any disease either. As shown above, it can potentially greatly improve health and biomarkers. It will not cure diabetes, especially Type 1 diabetes. It along with other things may help improve insulin sensitivity but in and of itself it has no magical properties to cure these things in one fell swoop. Many of these things are aliased into the same health and disease improvements that come from weight loss and eliminating unhealthy foods from the diet in general.
As much as I’m doing this specifically for potential anti-cancer benefits the fact is that it will not cure cancer. It has been studied as a means of making chemotherapy more effective in particular trials. The whole cellular autophagy thing may lead to reducing cancer risk. If you have cancer though doing a fast isn’t going to make the tumors magically disappear. The same goes for skin cancer or skin abnormalities. I’ve seen claims as ludicrous as during a prolonged fast all of their moles “fell off” and they now have perfect skin. No, just no.
I’ve seen some studies that talk about how fasting may have improved symptoms in people with Parkinson’s, Huntington’s, and Alzheimer’s disease. These are still at best preliminary. What no one studying it has claimed is that it cures these diseases. In all of these cases it may be that fasting can improve some conditions. Often this is because it is improving the biomarkers which are out of whack. Curing on the other hand is a not even wild speculation. It’s just pure BS.
Lastly, fasting will not “teach your body” to be able to go without food or water. Every once in awhile it seems some adherent to breatherism pops up on main stream media or alt-health media making these claims. The human body needs nourishment from food and it needs water. Once you go long enough without either you will die. Doing longer and longer prolonged fasting to “teach your body to exist solely on air and sunlight” is akin to jumping off incrementally taller platforms to “teach yourself to fly”. It isn’t going to happen. Sorry.
Side-effects and Dangers of Fasting
Fasting sounds pretty simple and there are some potential gains. That’s why I am doing it after all. However it is not without some potential risks. If you are a healthy generally well nourished person you can probably roll right into intermittent fasting pretty easily and without problem. Prolonged fasts are a bit trickier but not by much, for shorter duration versions anyway. There are still some risks associated with fasting of course.
First, if you do not fall into the category of someone that is healthy and well nourished then you should consult a doctor before attempting anything beyond a “skipping breakfast” level of fasting. If you haven’t been to the doctor in years that’s probably a good first step before beginning anything regardless to ensure you don’t have any conditions bubbling under the surface. It’s a good idea to get a physical and blood work done every year anyway. Assuming that all comes back good there can still be some dangers and precautions to worry about, especially as the fasting window gets larger.
For intermittent fasting level fasts the two biggest drivers of side effects are going to be lower blood glucose levels than what your body is used to and not being used to abstaining from eating for such longer periods of time. These will manifest in any several ways. The most prevalent symptoms from these drivers will be: fatigue, headache, and feeling light headed. Depending on how sensitive your digestive system is it may also lead to either constipation or diarrhea as your system adapts to the more irregular eating. As the fasting window gets larger it is also possible to experience a feeling of being unusually cold for a given ambient room temperature. And of course, with all of this would come the usual “hangry” symptoms we have experienced even without going through any fasting.
For prolonged fasting, especially as the number of days get longer, all of the above drivers and symptoms are in play but there is an additional one that needs to be factored in: electrolyte imbalance and dehydration. Those sound somewhat contradictory but we often don’t realize how much of our liquid consumption happens around meals and how much of it is in the food we are eating. It is therefore a good idea to keep track of how much water you are consuming for a few days before so you can get some idea of your baseline and try to maintain something at or just below that. At the same time if we are excreting salts over time it will be potentially necessary to replenish those. Electrolyte imbalances often manifest in the same sorts of symptoms, especially headaches, but will change relatively quickly if you consume some salt. There is more to electrolyte imbalance than just table salt but that is often where the earliest symptoms arise.
Coming out of a prolonged fast introduces its own challenges which are not there for intermittent fasting. Your system will have been used to having no food to process for several days. It will be in a starvation mode. It is therefore a good idea to ease into eating again. Usually this means to start eating more slowly. The first meal after a fast is often a cup of broth. Then one eats some smaller meals of foods that are easy to digest and that don’t irritate their system. If the first thing you do after ending a fast is head over to the local diner for an all you can eat breakfast bonanza you can be setting yourself for substantial discomfort. Your digestive system needs a little bit more time to get moving so you could be setting yourself up for nausea or diarrhea.
More severely however is the possibility of initiating refeeding syndrome . This is a very serious and potentially fatal condition that can develop within a day or so of introducing too much food too quickly to someone who has been chronically malnourished for long durations of time. It creates an electrolyte imbalances (again), that produce all of the types of above symptoms (headache, fatigue, nausea, diarrhea) but some that are far far worse. It can cause dangerously low blood pressure, seizures, coma, heart attack, etc. It is not something to be trifled with. The longer the fasting period is and the more malnourished you are going into the fast the higher the probability of this happening. This is the reason why one should be sure they are totally healthy with no metabolic problems or nutrient deficiencies before starting a prolonged fast. It is also why we do a transition diet for a day or two for prolonged fasts that are under a week and longer periods for longer fasting windows.
Along with the acute health problems mentioned above during the fast it is also possible to be introducing longer term problems via excessive fasting. As stated above, fasting will not teach your body to not need nourishment. Fasting can drastically cut down on the amount of food being consumed. This is great for chronic over-eaters who can use it to control their appetites. However it is possible to have too much of a good thing. If one is continually doing tight intermittent fasting windows without a well balanced diet, or closely spaced prolonged fasts, it is possible that they are not consuming enough of some nutrients. This is again why it is important to regularly get a physical and blood work. Using nutrition tracking software like Cronometer can be helpful in ensuring one is getting all their necessary nutrients over time with this as well.
How to Ease Into Fasting
I’m intentionally trying to scare readers a bit with my description of the side effects and dangers of fasting. There is too much “too good to be true” stuff I see about it. It has the potential to help one improve their health and longevity. That’s why I do it. But I want someone reading this to take this seriously, especially prolonged fasts. It is necessary to listen to your body and its reactions to these changes. A little discomfort and being hangry isn’t the end of the world. But because some of these things can lead to dangerous if not fatal consequences in the extreme case I don’t want people to be too cavalier about it either. I have done both intermittent and prolonged fasts but have eased my way into it. At the top level I started with longer intermittent fasting windows and then move on to prolonged fasting.
First and foremost, once again, don’t do anything until you’ve had an annual physical with blood work. You should know how healthy you actually are not just how healthy you think you are anyway. If results come back with any issues then one must proceed with greater caution. It is also worthwhile to discuss with your doctor what you are attempting to do with fasting. Be aware that standard medical advice is going to be that prolonged fasts should only be done in a medical supervised setting. It truly is the safest way to do that. The TrueNorth Clinic in California offers programs that can exceed a month of fasting while in a nice retreat style environment with intense medical supervision. That said, easing into the fasting has made it possible for me and others to do it safely at home.
Along with the above mentioned blood work one should also keep a food journal in a tool like Cronometer for a week or more leading up to attempting the fasting. This will tell you what your baseline nutrition consumption level is. You’ll be able to see how many calories you get, whether you are getting all your vitamins and minerals, and about how much water you are drinking. With that baseline we can then begin to get used to intermittent fasting and see how it impacts our overall nutrient consumption level. Now we can move on to trying fasting.
The first baby step is to cut out any post-dinner eating. After dinner you can continue to drink non-caloric beverages, but that’s it. That will add several hours to your natural fasting window from while you are sleeping. Next baby step is to skip a larger breakfast but add a mid-morning healthy snack. By doing this we are able to easily create a relatively large fasting window without cramping style too much. For example if one finishes dinner at 7 pm and has their mid-morning snack at 10 am then they now have a 13 hour fasting window and 9 hour eating window. Remember though that while beverages like coffee don’t break the fasting window, once you start adding all the creamer and sugar in it you have. So you have to be sure to cut that out as well.
The first big step will be to cut out eating altogether in the morning and making lunch your first meal. By doing this and continuing to cut out post-dinner eating one is creating a very natural 5-8 hour eating window with a corresponding 19 to 16 hour fasting window. These ratios of eating and fasting are in a pretty common range for people who practice intermittent fasting. If that is all one was going for then they are done. However if one wants to do prolonged fasting, or experiment with longer fasting windows, then we has a few more steps to go.
The next big step will be to start shrinking your eating window from the 5-8 hour window down to essentially eating once a day. You’ll do this by skipping lunch and having a small health snack in the afternoon and then jump to consuming just dinner in a two hour window. Once you’ve done this you can jump to trying skipping eating altogether for one day. In order to build up your mental reserves you may want to try this sort of progression with an alternate day fasting type protocol. That would be to eat normally, or with the standard 5-8 hour window one day, and then eat in the more restricted range the next day.
With these larger steps you will want to observe how your body is reacting to these longer intervals. Are you getting fatigue and light headed? Are you experiencing more serious symptoms? Did you get headaches or body aches? Do you feel like you should abstain from operating heavy machinery, like an automobile, in this state? It could be helpful to check vital signs like blood pressure or blood glucose levels if you are having more than mild symptoms. And of course if you have any prolonged concerns then consult your doctor. From here you can determine if prolonged fasting is going to be right for you. If it is and you still want to try to get some of the benefits perhaps doing a Prolorn Fast Mimicking Diet (FMD) could be a better solution for you.
My Own Fasting History
Early Explorations and Alternate Day Fasting
I’ve written several times on this blog about my experiences and thoughts on fasting . It was some time in 2015 that I first started getting very interested in the topic, as I wrote in “Feast then Fasting” . Ironically a lot of that was being goaded on not just from the literature talking about health benefits but from the reality TV Series Naked and Afraid . I was struggling with getting back on track back then but I decided to start doing alternate-day fasting for 3-4 days a week until I got my weight more in check. I highlighted some of my plans and struggles with kicking that off in this post . As I wrote in the above section, I recognized that I wanted to try a longer multi-day fast for cancer prevention benefits but that I knew I had to get more comfortable with even just alternate day fasting.
Within a couple weeks of doing it my body was more than adapted to the alternate day eating cycle, as documented here . At that point I was doing 32-34 hour fasting windows a few times a week. The “feeling buzzed” or “loopy” feeling I would get on the initial fasting days would no longer occur. The feeling famished all day cleared up pretty quickly as well. I didn’t keep that up long term but I learned through that that my body can more than handle longer term fasts. A year later I did this month long experiment of alternate day eating for weight loss showing how nutritionally complete it still was for weight loss. From time to time I’d do this sort of alternate day fasting. Each time after a short transition of feeling a bit buzzed/loopy on the first day my body would adapt. These were always for weight loss though. What I still had yet to conquer is my first multi-day fast. That didn’t come until September of 2020.
First 3 Day Fast
I’m not sure if people remember but 2020 was one hell of a year. I can’t recall why though, can you? In all seriousness though, because we lived in the “COVID is just a cold so no lock downs, social distancing, or masking” state of Florida, didn’t have to leave the house to earn income, had a good home setup, and it looked like effective vaccines would be available at some point in 2021, we essentially quarantined at home until we were vaccinated. I would do regular outdoors stuff like running, walking trails, etc. But we did no shopping, no restaurant eating, no in personal socializing. Going into 2020 my fitness regiment was pretty good but earlier in the pandemic I pretty much dropped all my fitness stuff. I had started getting things dialed back in by the mid-summer period and decided that doing my first multi-day fast for health reasons was in order.
I didn’t blog about any of it but I did write about it in my personal journal. It started after my after dinner snacks around 21:30 on Monday the 31st of August, a relatively gluttonous 2900 calorie day with a decent amount of junk food. It lasted until Friday the 4th of September with one ounce of peanuts at around 9:30 that morning. For each of the fast days all I consumed was decaf coffee, water, Coke Zero, and a couple cups of vegetable broth for dinner. The transition into it could have been a bit better but the transition out should have been a lot better. Yes I started off with just a handful of peanuts. By lunch I had a couple of Beyond Meat sausages. Not bad but not great. Dinner on the other hand was an even bigger gluttonous affair than the day before the fast. We were celebrating finally closing a deal ultimately a year in the making and after a lot of effort. We ate a 3300 calorie dinner of steak, macaroni and cheese, Red Lobster style biscuits, cheesecake, and washed it down with a couple glasses of champagne and a couple glasses of red wine. So much for worrying about refeeding syndrome! Overall the experience went off without a hitch a hitch though. During the fast I would get some of that loopy feeling from time to time like I got in my early days of trying alternate day fasting. I definitely had some fatigue but nothing that made me non-functional. I would get the usual feeling cold thing during the day as well, which happens to me during longer intermittent fasting intervals as well. The biggest difference was my obsession about food, especially while dreaming. The overly gluttonous transition out did not produce any ill effects at all. It didn’t jump start my fitness the way I hoped it would but it was an overall success.
First 4 Day Fast
My second multi-day fast was in March of 2022. I had a good 30 day health reset going since late-February. That was more than just diet. It was exercise, digital detox, zero alcohol, etc. I decided I needed another health driven fast to finish it up. It was another 3 day fast like in 2020. The transition in was a bit different though. Rather than eating a lot leading into it I had been dieting. The transition day into it was a healthy eating day but light on calories, at around 1030 calories, and having no more than 45 calories of unsweetened oat milk after a dinner. Thus it started around 19:00 rather than 21:30. The transition out day was a lot more reasonable too with starting off with an omelet breakfast around 11:00, a salad for dinner, and a bit of cheese and salami for an evening snack. That totaled just 1235 calories that day. For the fast days themselves I tried the same routine of coffee (both decaf and regular this time), seltzers, and calorie free sodas. On the first day I was going to try to not have broths this go around. I had the same problems with loopiness from time to time but by the second day I was getting headaches too. When a little salt helped clear that up I decided to add the broths back in. The rest was pretty status quo as far as fasts go for me. There was some lethargy, the feeling cold issue, and some of the loopiness. Ironically the loopiness seemed to be more something in the morning and afternoon each day not something that got progressively worse. There was the obsession with food as well. I do have a note that on my first transition day back I was feeling more loopy than I felt the last two days of the diet. Nothing at a severe level but it was an interesting difference. Was that because I was more depleted going into it, the fact it was an extra day, or just a coincidence? All good questions to explore as I keep trying fasts.
My Perceived and Hopeful Benefits of Fasting
So with all of that, what have I gotten out of these fasting experiments? With respect to the intermittent fasting and alternate day fasting, I really get a better handle on hunger. I am a person that loves food (cooking and eating) and is never full for very long. These shorter term fasting windows really helps cut down on me from eating reflexively and “just because”. It also seems to make my cut off for full a lot lower too. That means that in a sitting I just can’t shovel in as much food, although I can still be ready to eat again moments later. Often when I go back to it the first day or so I can feel a bit loopy, I’m guessing all of that is blood sugar level changes, but very quickly I work through that. It is literally the difference between the first day of going into intermittent fasting feeling like I need to eat by lunch time and a bit loopy if I don’t to being able to do full blown workouts and cardio in the morning and not eat lunch until the early afternoon. This invariably helps me cut down on excess calorie consumption, junk food consumption, and therefore help me get my weight in the proper range. The multi-day fasts have similar effects but more magnified. On the last fast I was even able to continue doing my multi-mile walks and calisthenics each morning, although at more leisurely paces.
So for the short term that leads to the one tangible benefit being weight loss and the associated improvements in biomarkers that go along with it. I imagine a lot of that is back to the associated weight loss that has happened around it. If that was all that these fasting periods did for me then that’d be enough for me to continue doing them, especially the intermittent fasting versions. But I have one big hopeful benefit out of all of this, especially the multi-day fasting: cancer prevention.
There are several pretty big killers in my family health history. One of the big ones is cancer. These have generally manifested in people’s 50s and 60s. That means that doing things that reduce the risk of cancer is a big deal for me. That includes things like getting skin checks regularly, not smoking, etc. Because of the potential benefits of fasting in reducing cancer risk, this too is something I want to add to the arsenal. It shouldn’t be just a band aid which means I do need to over the long term eat more dialed in and get my exercise much more dialed in (like I have been doing the past couple months). Will doing this mean I will definitely avoid cancer? Unfortunately, no. But every bit counts.
Both kinds of fasting have potentials to create positive health outcomes but are no miracle cures any more than anything else. It should be a tool to help get one into a healthier lifestyle and/or to maintain it. I’d love to say that my exploration of fasting has lead to me being in a permanent new mode of healthiness over the years. By evidence of my blog that isn’t the case. In times that I have tried to get things dialed in it has helped substantially in the short term. I’m hoping that if I can continue to hone my lifestyle to be sustainably healthy in the long term then both kinds of fasting will be just added margin to help me avoid cancer and other diseases that could premature cut short my health span and/or lifespan.