Mental approach and state related to long term water fasting

I'm on day 4 of a 5 day water fast now, four full days without eating, counting that I started on Sunday evening and it's Thursday evening now.  For some people that's not that long a duration; they can extend it into multiple weeks.  5 or 7 days is pretty common for significant length water fasts though.

I'll get into what I consider to be a water fast, but I'll start with the point here.  Fasting requires an interesting mental approach, and it's interesting how your mental state plays out over 5 days, or more or less time.  Maybe it's what one would expect; it would depend on what you would expect.

Back to the definition of water fasting; there are a few, but the way I'm using it I will drink tea or herb tea, or diet soda, but nothing with any calorie content.  Of course some people limit it to water; that is implied in the term I'm using for it.  Some people drink coffee, but I drink mine with milk and sugar, and don't want to try to switch over on a very empty stomach.  

I don't drink a lot of diet soda when fasting, but I might have one or two.  I drank one so far; that will be it.  A local Thai producer, Singh, makes a nice diet lemon or orange soda that's a pleasant break from tasting nothing but tea for days.  I usually only drink herb tea a couple of times, but not because I see it as a negative input.  Related to tea I've found that I can only drink shou pu'er, some hei cha, and aged white tea, because those are easy on your stomach.  Shou is best.  Not because I like that type, because it's definitely not a favorite, but it works best.

Not to go too far into the how-to scope here, or probably at all into why to fast, but for the most part the only other thing I ingest is sodium, potassium, and magnesium electrolytes, or salts.  I use the chloride compound version of all of those, because they are readily accessible and the cheapest.  I don't eat much for vitamins; I did just take a multi-vitamin, but hadn't up until then.  The magnesium I take as a tablet (gel coated capsule, I guess that was), and the other two I mix into water and drink.  What dosage to take is pretty complicated; I'll skip that here.  I will say that it takes forever to get a decent input range sorted out, and it probably varies by person, and by what that person is experiencing.

Mental state

Someone on Reddit mentioned that the added mental tension or stress from not eating is part of the reason you benefit from it, which I found very interesting.  Their idea was that if you feel a constant tension for several days, and could resolve it completely just by eating, but don't, then the rest of your life feels that much less tense or stressful, because you conditioned to experience temporary but sustained stress.  I can't say for sure if that works, but maybe, or probably.

I really wanted to pass on more subjective experience description here, not theory on how it plays out, to say what it's like.  It changes as you gain exposure to fasting, so the first three times it's very different than after a number of fasts.  

This might be about 12 for me; I'm not keeping track (maybe just over a dozen, thinking it through more, or it could be 15, since I fasted a lot that first year).  I try to fast for 5 days 4 times a year, but this year I've only done it once earlier this year, so far, about seven months ago.  I spent about six months with my kids, in Honolulu and then in Bangkok, the two places where we live, and I limit activities like that while I'm around them.  It's nice eating with them, and cooking for them, so I just skip the practice, until later.  I'm living with Keoni now but not my daughter; he just graduated high school, so he's back in Bangkok, not returning to Honolulu for now.

a full sized child, kitten, and tea; these are important parts of my life now

In the beginning it's very stressful, and you experience more severe hunger and energy level disruption.  You think about food a lot more, and it causes more stress.  After a half dozen fasts you don't think about food very often, but an emptiness persists, and some degree of stress.

That's already pretty much the short version.  Somehow it seemed deeper than that, more complicated.  The form of the stress is unique.  People into fasting claim that you experience an unusual mental clarity, and I agree with that.  I can get way more work done if I'm on days 3, 4, or 5 of a fast than normal.  But I'm a little edgy too, prone to being short with people, so it comes at a cost.

I guess in general the starting points seem more important, and valid.  Why fast?  If it's just to experience stress then there would be lots of ways to add that to your life.  There is a list of conventionally accepted benefits, but those are impossible to verify, both by personal experience and through research.  They center around autophagy, a body process that clears out damaged cell material to use as resources, which is triggered by exercise, but all the more so by fasting.  All of this is conventional understanding; it's not easy to verify.  Supposedly it reduces risk of cancer and diabetes, and who knows what else.

There's not much that personal experience completely supports.  I feel a little mentally clearer since taking up fasting.  I seem to experience more energy when I run.  That would relate to metabolic flexibility, another benefit, related to your body adapting to use fat energy better.  I'm in ketosis right now; fat or muscle tissue is all the energy there is to keep my metabolism going.  Reserve glycogen seems to run out on day three, but again that's just another guess.

One very odd positive result occurred, that I can't fully connect:  around when I started fasting the grey hair I had then mostly returned to being colored again.  It seems a stretch, doesn't it?  And could even relate to improving general health, making limited changes to diet and exercise, or getting a bit more sleep.  There's no way to track the cause and effect.

So I may be fasting for nothing; the supposed benefits may not be real.  For plenty of others it's easy to accept what random web sources contribute, but for me it's not.  There's research on autophagy, but not so much on fasting effects.  It would be all but impossible to separate cause and effect in studies too.

Taking up another tangent, people might wonder if there aren't clear signs that the stress on your body is negative.  Wouldn't someone get sick more often, while not eating?  Kind of.  I get a minor sore throat sometimes, and sometimes taking some vitamin C clears that up, and at least once I've quit a fast because that seems to be a sign to.  In general not though.  

You feel stress, and hunger, and get a bit grumpy.  Energy level can vary some, but not at all like the crazy shifts for the first two to three fasts.  It would be better to start gradually, to minimize all of that, but of course I didn't.  I tried to fast for 5 days the first time, and figured out that not supplementing electrolytes wouldn't work.  I experienced common side effects, like problems sleeping, muscle cramping, and even perceived irregular heartbeat.  

Of course I quit that first fast when all of that came up.  I think that's an important part of it; striking a balance between being really committed to the fast and also being ok with giving it up if you feel sick, or if stress level goes too high.  I've been busy at work before and stopped a fast early; you have to keep track of how much stress still makes sense.

Now I can sleep fairly well, not so different than normally.  That is a bit odd, that not eating for days doesn't affect my sleep, at all.

Of course it makes you wonder if you aren't as sharp mentally, and might make some sort of mistake, driving, in work duties, or whatever else.  I minimize work impact by fasting on Wednesdays, normally, so the end of the fast is on the weekend.  I just said that the first half is worse, earlier on, but the first day is fine, and really only the second relates to more hunger.  Day three energy level varies, which isn't ideal, but starting a fast on Saturday would cause that on a Monday, which also wouldn't be great.  This week I'm fasting Monday to Friday, because my son stays with me, so I want to eat when he does on the weekend.

Update after the fast; how it went

It's Friday evening now, when I was scheduled to end the fast.  I'll often pull the plug two hours early, related to the time I took the last bite five days ago, going from dinner to dinner over those days.  It often works out that I ended eating at 7:30 or 8 to start, and it makes no sense to wait until 8 to eat to really fulfill that 120 hours (5x24).  Plenty of people approach it that way though, which is fine.

Today I ate at lunch; it might have only been 112, so hardly over 4 1/2 days.  Work has been really intense this week, involving a lot of productivity, meetings, and need to think a lot, and I wanted to be a little sharper for Friday afternoon.  I already knew that within the first hour or two after eating your body is kind of focused on digestion, with blood sugar from that only becoming available as it gets processed, so you don't snap right back to normal.  But it sort of worked; I could do work that last half of the day without counting down to when I would eat.

This fast seemed a little harsher than usual.  Taking 7 months off seemed to leave me less acclimated.  Or so I'm guessing; the busy work-week probably didn't help.  I was in a car accident the day before I started the fast, which was minor, so not a concern, but the stress level from that didn't make for a great start, going into it less relaxed.

I walked a lot less than I usually do.  Often I'll see a fast as a great time to get lots of steps in, because any energy used comes out of fat, and I'm not mainly doing it to lose weight, but I could use to lose a few pounds.  I'm up close to 80 kg or 180 pounds now, maybe a bit under both, and at 1.7 m / 5' 7" that's not so heavy, but it's more than I weighed in my 40s and earlier 50s.  I run, and less body weight is better, less stress on everything.

I'm not running now, for the last two weeks, because my right foot isn't ok, experiencing what seems to be an early start on bone spurs.  I've been running on it for three months anyway, just cutting back, but for pretty much every running injury I get that pattern plays out, that I cut distance and intensity back, and then only heal when I take a break for a few weeks, or a month.  So I'm not walking that much now either, but some.

What lessons did I learn?  Even after dozens of days of fasting, maybe 60 to 80?, the experience can still vary.  It's great if you can experience very little stress, and some unproductive time.  Ordinary life is harder during fasting.  I think it helps a lot with my mental clarity the rest of the time, and general health, so it's probably still a positive trade off, across lots of dimensions of my life.

What 5 days of fasting feels like

 

Not long ago I wrote about fasting basics and some more detailed approach, here, but it occurs to me that there's another dimension that's harder to describe.  Fasting is a unique experience.  It's hard to just describe what hunger is like, once you acclimate, and the form changes.

Of course this has nothing to do with the theme of why to fast, and not all that much with how to do it, but it does overlap with that.  That earlier post was on the latter, and it's hard to pin down what research says, and not as reliable to convey hearsay or first person accounts of benefits.  I think I'm mentally clearer as a result of the practice, for example, but who knows how to place that.  Maybe I'm not, at all.  Maybe ramping up exercise or improving diet caused that, and there is no connection.  Or maybe I lose my mental faculties and don't know it.

So let's run through some parts of what it's like to fast instead, which will cover before and after acclimation.  I'm only having the latter experience now, because I've fasted for at least two months so far, in total.  

I try to fast 4 times a year, at 5 days each, and I'm on day 5 just now, not so many hours away from wrapping it up, at 4 days and maybe 19 hours.  I "call it" early because I fast from one dinner time to the one 5 days later, so for me it works better to "only" fast for 4 days and 22 hours or so, and if it works out to 20 or 21 that's fine too.  Otherwise I'd have to eat that first meal not so long before sleeping, which wouldn't be ideal.  I usually end up drinking milk after dinner the day before a fast, the last food to clear.

Reading back through those last ideas one might think that 5 days of fasting should really be 5 days and 6 nights, so really 5 1/2 days as clock time goes.  Maybe I will try breaking a fast the next morning instead at some point.  The mental pressure of fasting for "only" 5 days is already a bit to get through, though.

Fasting experience themes

Hunger:  the main factor, maybe.  Early on, for the first 2 or 3 trials, your body is shocked by the experience, and hunger is intense.  Physical cravings are coupled with what people call "food noise," repeating thoughts of eating.  Your body releases plenty of ghrelin, a hunger related hormone, so you keep producing digestive fluids, and experience stomach gas and discomfort.  Or at least that's my guess for why it feels like that.

After 4 or 5 fasts the experience completely changes, and that high degree of hunger largely drops out.  But you're still hungry.  It just takes on a feeling of emptiness, that runs in the background, so that if you smell food you really want it, but so that you can go a few hours without thinking about having not eaten.

One might naturally consider what they could drink to lessen the hunger experience (eating doesn't apply; pretty much no one ever eats paper or some other calorie deficient input).  It's normal for people to drink coffee, tea, or herb tea, and some drink diet sodas.  

I've had one diet soda in the past 5 days, a diet Strawberry Cream Pepsi.  It doesn't seem to change much, but I don't drink much of that.  I've had tea every day, and herb tea 3 of the days.  This time I started in on some pandan leaf and roselle tea I bought not so long ago, along with lemongrass tea, that I didn't get to.  All of those are common types in Thailand.  I don't use stevia to sweeten any of it, but I could.  

Related to the tea I usually drink shou pu'er or aged white tea, because they're easy on your stomach, but I also had some hei cha (Fu zhuan) and relatively oxidized sheng pu'er.  It would be nice to drink coffee but I'm not acclimated to drinking my coffee black, and that my hurt your stomach.  

I think it helps most to drink a tisane that you tend to drink a lot of, perhaps mostly because it boosts hydration input.  I can drink three 16 ounce mugs of chrysanthemum, and that adds well over a quart / liter to my daily fluid intake.  It's best to try to drink 3 liters of water a day, if you can, but that's a lot to get down.  You need to supplement quite a bit of salts (sodium, potassium, and magnesium; there's more on that in the earlier post), and I'm always struggling to get the intake amount right, and to work through salt water tasting awful, even in a diluted form.

Special hunger triggers:  I need to go to grocery store every time I fast because I let my food supply run out, and need to re-up it, usually on the last day.  Sometimes chance will have me visiting a market or restaurant with others I happen to be with.  In one sense it's not so bad, but in another it is.  Sometimes I'll cook for other people, and that is a different level of exposure.  Your digestive system can seem to turn back on, even when you just smell food.  

At worst that will lead you back to the earlier phase of stomach growling, that you tend to only experience early in fasting trials.  I just went grocery shopping on day 4, taking my mother-in-law to a store, and it was a little like that.  But even that level of exposure you acclimate to.  Cooking not so much.

Stress:  this is the other part of the experience of hunger.  It feels like an extra underlying stress, to me not completely unlike what extreme jet lag feels like.  If your normal stress baseline isn't bad it's no problem, but when other stressors enter in it can be too intense.  It's not hard to be productive when you fast, and that deserves it's own section, the extra mental clarity.  Even walking a lot or light exercise is fine.  But getting it all to balance requires a bit of extra attention.  

For me if other stressors add up too much I'll stop the fast.  The last example that comes to mind is too harsh to cite here, but even if work gets unusually busy it might throw it all off.

Other side effects (dizziness, low energy level, sleepiness):  this probably varies a lot by person, so what any one has to say wouldn't apply broadly.  But I'll include it.  In those first 3 or 4 fasts these negative factors were a lot more to deal with, especially the first two.  That's why I recommend people try period eating first (20-22 hour fasts), then 24, and build up.  I might feel a little dizzy a couple times a day.  Getting electrolyte balance (intake) dialed in offsets a lot of it, but your body seems to also need to adjust to a new range of experience.  If you fasted every other month you might stay well-adjusted to it, but if you let 3 or 4 months go between fasts you might end up adjusting again.

I don't really feel low energy level now, which is strange.  I've been walking 10,000 steps a day for all of the 5 days.  Typically I don't try to do much with losing weight, fasting for other reasons, but since I've climbed to 81 kg (178 pounds), up from 74 kg (163) I'd like to get that to drop again.  My blood pressure has been running high, and it might help.  I've been swimming a lot over the past year, and keep on adding a little extra muscle, so it's not that much fat gain, but it's some.

Lots of other potential side effects could be concerning.  If my electrolyte balance runs low I'll feel mild cramping, mostly in my calves, and that's not good.  That leads back into a longer and off-topic discussion about how hard it is to dial in an optimum electrolyte intake (sodium, potassium, and magnesium).  It should be easy, figuring out how much you need by trial and error, mixing up a diluted batch of that with water, then drinking that over the day (and taking magnesium by pill / tablet, because you need much less).  It's not so simple.  Some of that is probably user error, that I make it harder than it needs to be.  I'm back to just drinking some salt mix a few times a day, mixing it up without measuring it out per day, not using that more standard approach (standard within "fasting circles").  

This Reddit group is what I experience of that online discussion; it all requires some interpretation, and some extreme views come up, but that's normal for social media.  Note that the high end of their fasting wiki recommended electrolyte intake range is an awful lot of salt (or had been; per this following citation it's the opposite now); I have no idea how that could work out.

I take that back; in the past that wiki recommended a high end range of at least 3 grams each of sodium and potassium, and now it's a fraction of that.  There was a "snake juice" recipe for that daily mix for people to drink, and they've deleted that.  Lots of people had complained the high end was way too high, or maybe even the relative average, and maybe moderation staff changed on the page, and the guidance opinions they wanted to share with them.

This is the second version of that advice in two days; I cited it from yesterday (Feb. 15) and it was completely different.  Just keep in mind it's a rough guideline, not a final answer.  Individual requirements and tolerance for dosages would vary.  

One part that was interesting, in past versions of advice there in the r/fasting Electrolytes 101 wiki page, was that you can use either sodium chloride or baking soda, (sodium bicarbonate), and that food grade epsom salts can be used for magnesium input.  There is endless discussion there on what is the best magnesium compound form to supplement.  Maybe glycinate is recommended most, but I use magnesium oxide, because it's cheaper.  The concern is laxative effect.  Magnesium that is absorbed too quickly will cause that, so the compound form matters.  That's what laxatives often are (like milk of magnesia).

mental clarity, positive side effects:  mental clarity is about it for positive changes in the short term.  Even that comes and goes.  There are flashes where I can really get a lot done, and see complicated themes much clearer than I normally would.  My subconscious mind is also in on it; my dreams have picked up a really novel clarity and complexity over the last 3 nights (the first night I had eating hours prior).  

In one dream I dreamt I had accidentally broken the fast by eating, then woke up to realize it was a dream, but woke up in another dream where I experienced that.  I had an interesting exchange about child rearing practices with a fictional character in one last night.  I suppose the waking clarity is more meaningful and impactful.

I think the clarity extends to be a main positive effect from the fasting.  Maybe I'm also experiencing some aging effects less, but this is where it gets hazy.  My hair has returned to mostly colored since taking it up; I've lost the few grey hairs I had, except for very few around my temples, less than 10.  It's strange seeing a hair that's two colors, that had been grey and returned to brown, but I've experienced that.  I'm 57; I really should have greying hair now.  I don't care much about the aesthetic side, since I'm married, and it just doesn't matter, but it's an interesting change.

a visa renewal selfie from last month; you can see some grey hair

More on the vague side, I think that I have more energy when I run now, from greater "metabolic flexibility," or ability to use fat as an energy source.  Who knows; it would be easy to imagine that.  Or training experience tends to change in those kinds of ways over time. 

I think for many a main positive effect is a reduction of "food noise," and an ability to manage diet better.  My diet was pretty good to start out with, and I never snack that much, but I've used the fasts as resets, to make minor positive adjustment.  I keep going back to eating ice cream, and some chocolate, but the overall balance shifts.  It's much harder in the US than in Thailand; when Ben and Jerry's is on sale what can you do?  

I eat more fruit and vegetables than just about anyone now, and prefer that basis for my diet.  I eat some meat, to keep up protein intake, to adjust for exercising a good bit, but I eat nuts as a snack, a good bit of eggs and dairy, and use soy or pea protein shakes as a supplement.  

All that is a bit beside the point; the idea is that it's easier to improve your diet and change habits after a reset, of sorts.  For me I can only make minor changes each time, and if I try to shift too much after a fast it won't work.

risk:  I don't think much about this, but it's worth considering.  What could go wrong?  If your electrolytes get too far out of balance then lots of things could, up to and including having a heart attack.  It's important to get that dialed in as fast as possible, and probably gradually acclimating to fasting makes sense, even though it's more common for people to get the idea to try 3 to 7 days from an online video, and just go for it.  

The problem I do experience with dizziness could be much worse.  In the past 5 days I've stood up and felt light dizziness two or three times, which is pretty moderate.  It's something to keep an eye on.

The main risk is that if you ingest a lot of electrolytes at one time then you will experience diarrhea, even if you haven't eaten in days.  It's that "don't trust a fart" theme.  Then that carries over to "re-feeding;" if you eat low quality food to re-start eating you'll experience that for a couple of days.  

I've only tested that once though, and that was my experience.  I usually eat a burger and fries for a first meal, which sounds pretty low quality, but if you use good ground beef or pork (we don't eat beef much in Thailand), good bread, fresh potatoes or sweet potatoes for the fries, and some vegetables (tomato and spinach, usually), then it's not low quality food.  Of course most people who fast use an even more sensible approach, and eat different things in stages.  

Later editing note:  I ate a burger and fries again, yesterday, and my body digested it in 4 hours or so.  Maybe because I was still hungry and ate some yogurt, a little chocolate, and a bowl of cereal some hours later?  Or maybe looking forward to ending the fast too much prompted more rapid digestion.  What works would always vary by individual anyway.  The riskier "refeeding" cases relate to much longer fasts, well over a week in duration.  Then just winging it wouldn't be safe.

talking about fasting:  this is a bonus tangent; that pretty much already covers fasting experience.  In fasting circles people usually recommend keeping fasting experience a secret, especially during fasts.  Some people react negatively, of course.  In one online story an HR department told the person to start eating, not to fast.  People can be judgmental.  I don't talk much about it, but I don't avoid it either.  If people have problems with accepting someone else not eating, or a life practice they see as absurd, and probably harmful, then that's on them.

You can never really fully explain it.  People can only experiment with fasting and make of it what they do, for themselves, and that would vary by person.  It wouldn't be for everyone.  For some the negative side effects would be a complete deal-breaker.  For others acclimation, that I've been describing, might never seem to happen, even though it's my guess that within 4 or 5 trials most people would see negative aspects reduce.  And then a more primary point, for many there just wouldn't be any point to it, if they're not trying to lose weight, and see the health benefits as possible but not a given, and perhaps unlikely to occur.

I first tried out fasting, as an adult, because I met a guy who claimed he did it for spiritual reasons.  That's not entirely right; in an earlier life phase we would do multi-day juice fasts as some sort of cleanse / detox.  It made more sense in that life context.  I fasted for the very first time at the age of 10 or 11, passing 24 hours, but not fasting to my goal, 36 hours, or one complete day and night after waking.  I don't remember why I did that.  

Then I "fasted" a lot cutting weight as a wrestler in high school; I would go as long without eating as I needed to in order to make a competition weight.  Our team was really strong, and I didn't have the experience to be above average (I wrestled for 2 years), so I had to slot in at varsity wherever I could beat the other guys competing.  Good times!

So not eating for weight loss could work, and those other reasons may or may not be appealing.

Fasting basics, and a bit more on background and approach

this picture has food in it, but relaxing in nature with tea could be helpful while fasting

I mentioned that fasting may have improved my health in relation to aging aspects in a Reddit thread, and in a second comment covered basics on how to fast.  It all works as a great summary of the topic.  

Let's start with the first part, what seemed to improve as a result of fasting practice:

I'm really also pursuing health instead of avoiding aspects related to aging, or longevity related "biohacking." But I tried out fasting awhile back (maybe 2 1/2 years ago), and it seemed to make a difference. Now I try to fast for 5 days at a time 4 times per year.

It's hard pushing that to the next level for description, listing out likely benefits. I think I'm a little mentally clearer, and my energy level seems more stable, especially when running. That second part is a reference to metabolic flexibility; people are said to be able to use fat energy better when they routinely experience ketosis.

It's possible that it is offsetting other aging effects, but not in a way I can clearly link and justify. The few grey hairs I had mostly returned to being colored. That could've been for some other reason though; I exercised more around the same time, adjusted diet, and added a bit of supplementation to help with exercise recovery. My health checkup blood markers have all improved somewhat, but I'd expect exercise to be related to that.

Then someone asked about the details, in the form of these questions:

Curious about your fasting. Water only? For how long? How do you transition back to food?

My answer ran a bit long, since it seemed I could cover a few other basics, beyond those three questions:

Past 3 days you really need to supplement electrolytes, but that's it, sodium, potassium, and magnesium. People who fast often tend to drink things with no calories, and I drink tea or herb teas / tisanes, and sometimes a diet soda, but not often. I've never heard of anyone trying to eat something solid with no calories; that's not typical fasting. People avoid eating a single calorie, even though eating 10 to 20 might not re-trigger digestion response.

I try to fast 4 times a year for 5 days at a time. There's no clear reason for why 5 days at once or 20 days per year would be optimum; people sort out what they think will work on their own. Autophagy, a recycling process for inactive cells or damaged cellular material, is said to peak at or after 48 hours, but autophagy routinely happens to some extent, and that kind of hearsay input is only so reliable.

Transitioning back to food is a lot more difficult when you fast for 2 or 3 weeks, instead of 5 to 7 days. You can still get it wrong fasting for 5 days, but that has only happened to me once. I would normally eat a burger and fries to resume eating, but a natural version of it, using quality meat (pork; I live in Thailand and we don't eat much beef here), decent bread, home-made fries, often from sweet potatoes, and vegetables, spinach and tomato.

I once quit early for some reason and ate McDonald's food instead, thinking it would also work, but it didn't, and it took a couple of days to get past severe diarrhea. Beyond that, not eating fast food or junk, which is kind of common sense, people advise to avoid sugar. Probably moderating fiber right away would be as well, although you can eat a normal amount of it.

One benefit of fasting that may not be so intuitive is that it changes your relationship with food. The habitual eating, or "food noise," drops out. Not on the first couple of fasts, but eventually it does. You can reset to a better diet. You can only make so much change at one time, or it won't stick, but over the course of a few fasts you could completely reset what you eat and your related eating habits, and it wouldn't seem nearly as difficult as making extreme changes while still eating.

One potential negative, depending on how people see it, is that I think my metabolism might have slowed slightly, that I eat a little less and maintain the same body weight. I've gained weight in the last 2 1/2 years, but I've been exercising a lot, and I think it's mostly muscle weight. People discuss a risk of losing muscle mass during fasts but I'm certain that I don't. 5 days isn't that long a time period, and my body would have access to protein in my digestive system the first day.

To make it easier people recommend switching to a very low carbohydrate diet for a couple of days prior to the fast. Not necessarily to enter ketosis, but that is the general idea. An extreme version of that would be to not eat any carbs at all for 4 to 5 days, and you might enter ketosis then. If you are already using only fat and protein for energy, and mostly fat, it should be easier to switch to using body fat, in theory.

Later on you really do seem to take on greater "metabolic flexibility," an ability to use different energy sources, or at least it seems to me that I never feel any energy issues when I run, which I attribute to this. I'll run for 12 km for routine outings (3 times every 8 or 9 days) and energy level is never an issue, even though I'm 57, and everything works a little less effectively at this age.

And that's most of it.  I could add a little about what tea I tend to drink, given this is a tea blog, but that doesn't run long, because most types seem not to work well.  I can drink shou / shu pu'er, and sometimes go with aged white tea.  I would guess that some forms of hei cha would also be fine, and I've had positive results experimenting with that, but it would depend on the type.  Harsher Liu Bao wouldn't work at all, and milder Fu zhuan would probably be fine.

I think herb teas / tisanes are even more flexible, that few of those would upset your stomach.  I experience great results from drinking those, but I think it might be mostly because I'll brew a couple of rounds of a large mug of one, and drinking an extra liter of water is probably helpful.  You really should drink at least 3 liters a day while fasting, more than it feels natural to drink, and a full gallon (around 4 liters) is more the optimum people recommend.  Your body is said to use a lot of water by processing energy through ketosis.  

Again all of this is hearsay, which can only be confirmed so effectively through experimentation.  But I can notice that if I don't drink a lot of water I suffer negative effects, and that it takes a lot of electrolyte input to seem to balance that factor.  It's on the order of 1 to 2 grams per day of both sodium and potassium; an awful lot.  You don't need that much magnesium; maybe 400 mg.  All of this isn't dosing recommendations, and I suspect what works best for people would vary by a lot of factors, like body size, local climate (if they're sweating), rate of metabolism, energy use, and so on.  

Some people probably become very inactive while fasting, even though it works well for me to walk a good bit while not eating.  It's relaxing, and it takes my mind off not eating.  My thinking is that light activity helps over the first couple of days to switch over to full ketosis, so I'm not going through that adjustment period for three days, which seems to be the normal time-frame.  I've experimented with running while fasting, and that's fine, I can, but I suspect recovery is impacted, taking in no protein for days.  So I've never really pushed it, never running too far.  Maybe only 2+ miles / 4 km to test it out?

From there other factors seem vague.  People might try to do more meditation, to lean into a more spiritual side of the experience, or at least to offset anxiety that might come from the mild underlying stress of not eating.  I first fasted based on someone telling me that they fast for spiritual purposes, to replicate what yogis and Jesus experienced.  Maybe there's something to all of that.  It's a profound feeling experience.  I can't do it justice by description, and it takes a few fasting trials for the early stress to settle out, and for hunger experience to subside, so that you get on to experiencing different dimensions of it.

Then people might discuss how to deal with that stress and the "intrusive thoughts" part better, food noise.  All of that just varies by person, and largely drops out with more exposure, again after a few fasts.  Hunger experience really is extreme and novel the first 2 or 3 times.  I don't mean the psychological expectation either; your body is unfamiliar with the process, and doesn't know to drop the hunger trigger in the same way.  Put another way, in physiological terms, you seem to produce a lot more ghrelin in those early trials, and your digestion response doesn't slow down at all, instead increasing, but later on it's the opposite, and you don't think of food much, or hear your stomach growl, and experience gas, and so on. 

I guess one last part I didn't cover is that I recommend people start with no more than 24 hours duration.  Of course I didn't; I tried to start with 5 days, and then failed after three, when I noticed that you experience severe symptoms from not supplementing electrolytes, like trouble sleeping, muscle cramps, and what seem to be heart palpitations, an irregular heartbeat.  But it would probably be so much easier to do a couple of 24 hour fasts, then a couple of 48 hour versions, then 3 days, then 4, and so on.  I've never made it much past 5; a different form of acclimation seems to apply to go beyond that.  I'm sure with a few trials it would be fine, but for me 5 days covers what I'm pursuing, hopefully triggering an autophagy / health maintenance response.

Two more tangents

I could probably keep considering extra tangents at length.  I've participated in discussions of fasting practice and experience in a Reddit sub for a few years now (where there is a good electrolytes wiki reference), r/fasting, so parts keep coming up.  I'll stop at two last points, the first related to the input of artificial sweeteners.  Are those ok?  

People are in two different camps related to that.  One group thinks that those could potentially trigger an insulin release, which would be a bad thing, and that at a minimum their purpose in fasting is to avoid chemical inputs.  As an example, some people think taking a multivitamin makes a lot of sense, since you are skipping ingesting all nutrition, and others see it as a sort of cleanse function to keep intake of everything to an absolute minimum.  

No one really knows if there is a negative effect from drinking a diet soda, or sweetening tea with stevia or aspartame.  I mean related to fasting, but I guess there is also a broader concern about these things.  I've drank nearly a dozen artificially sweetened drinks over the last 2 1/2 years while fasting and notice no negative effects.  That's not much of a sample size, and the opposite of a well-controlled review process.

The other subject is perhaps the trickiest part of fasting, getting electrolytes sorted out (beyond not eating when you are hungry).  This problem comes in a few parts:  

-how much sodium, potassium and magnesium do you need?

-does it matter which compounds provide those, and which are optimum?

-what is the best intake form (eg. in a drink solution, should that be flavored, what can you take in a pill form, or what won't work in that form)?

-how frequently should you ingest it, or put another way, what dose can you tolerate at one time?

1.  (amount of electrolytes):  The wiki reference in the r/fasting sub provides input on this, but the high end of the suggested range there is awfully high (many grams of both sodium and potassium).  People need to experiment and sort out what works for them.  I've already mentioned a general range, about 1 to 2 grams each of sodium and potassium, and about 400 mg of magnesium per day.  That's not advice, not even offered as a starting point, just mention of the general range.  It's a lot.

Later editing note:  they updated that page (here), and deleted that whole section recommending both an input range for electrolytes and how to mix a batch of "snake juice" to drink over the day.  What they have replaced it with doesn't give much of a recommendation:

That citation is about diet (eating food), not really tied to fasting (it mentions food twice).  That citation is from editing yesterday (Feb. 15, 2026) and today the advice is different again:

It keeps improving.  I would take any advice with a grain of salt, so in a sense it doesn't matter that the page has shown three different forms of input, perhaps over as many months.

One thing to keep in mind is that you are trying to ingest a certain dosage of sodium (for example), not necessarily sodium chloride.  The chloride part may work out to be essential, for all I know, but it's necessary to keep straight that calculating input of sodium, and the others, requires some way to account for the other part of the salt compound, what that contributes to weight (dose).  

2. (which compounds to take):  for sodium it's down to sodium chloride (table salt) and sodium bicarbonate (baking soda).  I don't like the taste of baking soda in a salt solution, so I only use table salt.  For potassium the main form you run across is potassium chloride, so that's what I use, but it's not the only form.  You can buy it as a table salt replacement in grocery stores; I've bought it in Wal-Mart in the US and Tops in Thailand.  It costs almost nothing, and works well as a supplement to balance out your electrolyte input when you aren't fasting.

Then magnesium is where things get complicated.  I use magnesium oxide, because it's the cheapest, but people recommend different versions, or recommend avoiding different versions.  Over and over people say one compound has a strong laxative effect and another is relatively optimum, it just might not match which they prefer.  It would work to look up discussions in that group (sub) to use as input, maybe as a sort of voting process, going with what people tend to say the most.  Using a search function in any social media group is an extreme step, but it would work.

3.  (best intake form):  you can just take magnesium as a pill; that dose is so low that it wouldn't be a problem.  It might be nice if you could take it in the morning and then a couple of hours before bed, because it's said to support sleep.  

The other two, sodium and potassium, are harder.  The standard approach is to make up a solution of quite a bit of water and those salts and drink that throughout the day.  It seems to work well for me to treat that as a meal, to drink some at breakfast, lunch, and dinner time, and some in the evening.  Too much at one time causes a strong laxative effect, but breaking it into four parts offsets that.

People tend to not mention other tricks or approaches very much.  Since you don't eat anything there's no way to couple it with food, and it would make limited sense to drink a very salty version of coffee or tea.  I've mixed it with tisanes before, and that's promising, but it's too much extra work.  If you use a base flavor tisane and dried citrus rind, and a little sweetener (stevia, some chemical form, whatever) it is a bit like gatorade.  You need to keep drinking a lot of water to help process it, and support energy use from fat through ketosis.  Experimenting with what works for you seems critical.

4.  (maximum electrolyte dose at one time):  Again you'd need to experiment to sort this out.  I'm sure that ingesting a gram each of sodium and potassium at one time would go badly, for almost anyone, so you need to break it up into at least 3 different intakes, and 4 might work better, or others might prefer a half dozen.  

You might think a laxative effect wouldn't be possible, after 3 or 4 days without eating, but you would be wrong.  Apparently your body continues to release a limited amount of digestive fluid, which may drop with acclimation, so you can experience multiple very odd, liquid bowel movements over a 5 day period.  Ingesting a lot of salt / electrolyte at one time triggers that.  Not just magnesium either; the other two can have that effect.

In general my stomach feels better than one would expect; I have few problems or issues.  If I were to drink green tea or black coffee maybe that wouldn't be true.  I've had no problems with any tisanes, so it doesn't work to recommend which work best.

Conclusions

All of this went a little light on the benefits part, but I think that would vary by person, and my input would seem like claims that I really can't support.  Did it offset aging effects?  It seems so, but who knows.  Do I experience more metabolic flexibility, more energy while running due to more efficient fat use?  The same.  And mental clarity is the same; maybe that improved, but it's hard to identify, and impossible to be clear on causes.

I also skipped over lots of negative effects that occur in those first few trials.  Beyond being desperately hungry I experienced energy level fluctuations, sleepiness, dizziness, trouble focusing, and boredom.  I would go with my wife to a market or restaurant and that really heightened the desire to eat.  By the 4th or 5th fast all of that was moderate, and by the 10th or 12th I wouldn't be reminded that I was even fasting many times in a day.

There are periods of mental clarity and productivity that happen, after some exposure, that are also hard to describe.  At times I can get 6 hours worth of creative work done in an hour.  It's hard to focus or channel that; it happens when it happens.  It's possible to stay busier than normal, over the entire fast, but past a certain stress level it all seems to crash.  It adds some underlying stress, so you have to be careful.  You don't need to moderate the demands on your time and productivity, but you can't push it too far either.

Experiences with offsetting aging effects

This theme came up from discussion in a Reddit aging related sub-group, here.  The title for that post was "experiences with reversing aging," which this title version probably corrects a bit.  You can really offset some of the effects, maybe even reversing what is regarded as an irreversible outcome in some cases, but in general it's about positively affecting general health, not turning back the clock.  

To me it's not about aesthetics, but it could be for others.  It also doesn't tie so closely to health markers, from doing bloodwork (general health assessment), but I did just check those results within the last couple of months, and they look ok.  I missed the last two company health checks or I could've assessed changes.  I've started fasting practices and have escalated running volume over the last 2 1/2 years; those recent markers should be better than earlier ones.

Let's start with that post; it also includes limited intro, so a lot of that would be overdoing it:

It's not really one of my things, as it is with Bryan Johnson and those other typically sketchy aging research guys, but I've had limited experience with seeing the effects of aging reverse. My hair was greying some years ago, and it has almost entirely returned to the original color. To be more specific my son counted 13 grey hairs about two years ago, and there are just a few at my lower temple now.

To back up a little I'm 56. In some other ways, partly related to appearance, I haven't aged as fast as I might, with my skin holding up decently, not using reading glasses, still exercising, etc. I can't know direct causes but I'll speculate about that here.

I took up periodic fasting just over 2 years ago, now fasting 5 days at a time, 4 times a year, but it was more that first year, nearly a month in total. I've been running a lot for 3 or 4 years, but I've levelled off at being able to run 10 km three times a week; I can't seem to recover from more than that. I don't know if it makes a difference but I've been eating a little goji berry most days for a number of years (said to help maintain eye health). I've improved my diet quite a bit based on resetting it related to fasting, and have been keeping up with sleep for years. A long cycle of meditation practice may have helped with memory issues.

I have kids, and had them late, so most of that didn't apply in my 40s. I was definitely out of shape over that decade, not exercising much, but I stayed active. I suspect that being a little underweight during my 20s and 30s, related to being a vegetarian then, may have been an earlier cause for slower aging.

I wouldn't necessarily recommend that people try to suspend aging, but maintaining exceptional health seems reasonable.

Feb. 2025; looking a bit middle-aged, ok for 56

The "typically sketchy" part, about aging researchers, relates to them often seeming to package a product as much as search for answers for the benefit of society.  It's as well to not get side-tracked on that critique; parts of the research must hold up to further review, and will benefit many people.

Commentary

That group focus on a narrow range helped shaped what I tried to communicate there, on aging as affecting appearance and some narrow ranges of health.  Without that group-location framing I'd tend to focus more on discussion of just improving health, in general.  I'm also in a biohacking group on Reddit, which I might comment in but never post to, which would be more concerned with supplements, especially experimental versions.  Some people there see fasting as a functional form of biohacking.

Since I don't know the cause and effect sequences of making a few lifestyle input changes it's all vague enough.  I think fasting made a lot of difference, but any positive changes could have related mainly to better diet and getting more exercise.  I'll run through some potential positive changes in more detail here.

Life and location change as a possible input:  three years ago my family moved our kids to Honolulu, Hawaii to go to school here instead of Bangkok, intending to relocate my work, which never worked out.  I've been back and forth since, spending most of my time still in Bangkok, and working remotely part of the time.  

It may be that living a more active life in Hawaii changes things, even though I've only been spending 3 months a year here, while they spend 9.  I swam a lot this spring (in March through the end of May); an input like that couldn't hurt.  "A lot" is relative; I was swimming about 500 meters about 3 days a week, in the open ocean, out to a flag and back in a swim lane.  My son trains for competitive swimming and his daily practices cover a lot more distance, every day versus my weekly total.

out for an early run around Diamondhead

I swim out to that flag, and see turtles there (tourist for scale)

Diamondhead from my daughter's former school

Genetic factors:  one input I see as relating to appearing younger is kind of a random thing:  I have oily skin.  If I don't shower twice a day I end up looking a bit greasy, while living in a warm or hot climate.  That may be relatively equivalent to people using a lot of moisturizer in a cooler and dryer place (which I don't use).  My sister also looks quite young, also in her 50s, and good genetics for aging gradually probably go well beyond that.

these guys are holding up well

Food preferences probably have a lot of effect, along with eating what might be considered a good diet.  The luck of the draw might factor in, related to the former.  Thai food is typically based on natural, whole foods, not involving that much processing, even though use of frying and addition of some sugar does come up. 

I drink an awful lot of tea; it's odd that I didn't mention that in passing in that post.  I've considered before that beyond some polyphenols potentially supporting health, or offsetting aging effects, just ingesting extra minerals every day might make a difference.  Tea plants collect and store minerals, in addition to some contaminants, so I may be keeping topped up on a range of minerals.  Who knows about effects beyond that; maybe it is unusually healthy.

I started drinking coffee again within the last 6 months.  I can't imagine that's having a lot of effect either way, especially since I never drink more than one large cup a day (maybe 10 to 12 ounces), but it's an example of how other inputs keep shifting.  I last meditated regularly nearly two years ago; that's another example of ongoing changes.

Supplements, including anti-aging supplements:  I mostly take a multivitamin, magnesium, and D when I'm not getting that much sun.  I was also taking fish oil for awhile, and replace some salt intake with a potassium chloride based salt product; that's about it.

I also eat some goji berries most days, which is said to contain zeaxanthin, one of two compounds that promote eye health (along with lutein).  My wife said that it would help with eye health and hair loss, but who knows about traditional Thai medical claims.  It seemed like a bit of extra vitamin A couldn't hurt; those are supposedly a good source of that.

There are a broad range of other supplement or drug compounds being developed and tested now, but I don't really investigate those much, never mind taking any.  I'm more ok with aging normally than being a test subject, even though I am concerned enough about health to put effort into all of it.

Recommendations, and justification for them

Exercise:  there's no need to justify endorsing exercise, right?  I can add that running just a little early in my practice, starting nearly 7 years ago, seemed to make a lot of difference, but my cardio conditioning only improved once I ramped up volume.  I run 20 miles / 30 km a week when I'm more active, and maybe two thirds of that when I'm inconsistent, with some extra multiple week periods "off" in the past year or so.  I was more consistent and diligent before moving back and forth to Hawaii made that difficult.  It's not about making the time, or jet-lag disruption, but instead valuing the time with my kids in a different way after we re-unite.

If I run consistently for about 6 weeks my conditioning will change a good bit right around that time, but if I run consistently for only a month it won't.  I'm not implying that your health would change a lot, if you could lean into it all for 2 to 3 months.  Maybe that's true, and probably race conditioning works like that, but I don't know what supports general health well enough, versus what will "drop time" on training paces.

Fasting:  I suspect that fasting makes a lot of difference, but I'm not completely sold on hearsay related to autophagy, the process of your body recycling mis-folded proteins or whatever other damaged material.  Supposedly this always occurs in your body, and helps offset varying long term health issues, but vigorous exercise triggers more of it, or fasting for around 48 hours or longer does.  But if you try to look up research papers linking that this does occur, and that it relates to specific health-related outcomes, it's not easy making the connections.  

Again this isn't a claim either way.  I suspect that I am slightly mentally clearer related to periodic extended fasting, but who knows.  You could observe what you expect to, to some extent.  I also feel like I have more energy when running, that maybe greater "metabolic flexibility" helps with that, training my body to also use fat as an energy source.  I don't mind at all when meals run late, or skipping one is fine; I'm a lot less constrained by habitual eating now.

Diet changes:  my diet was never bad enough for me to see change effects in the same way someone moving off a truly bad diet could.  I took up being a vegetarian over 30 years ago, and tried to eat a healthy, balanced diet based on essentially no actual meat input for that next 17 years.  I was the "lacto-ovo" type; I still ate dairy and eggs, thinking that it would help me avoid deficiencies.  Then I think the deficiencies did enter in, around 13 years ago now, and my immune system stopped working normally.  I had been fine for that first decade, living in the US, watching my diet and eating supplements to help, but after I moved to Thailand I ate meat-based dishes without the meat, and it wasn't the same.  More idle speculation, probably, but that was my take.

So I'm describing improving an already pretty decent diet over the last few years, already based on input of plenty of fruits and vegetables, and whole grains, along with good quality meats input.  I've not eaten much for junk food, processed snacks, and fast food for a long time, with the exception of eating a good bit of ice cream.  Moving back to the US did add some challenges, since it's easy to appreciate different kinds of snack foods, that weren't options back in Thailand.  Those tubs of chocolate chip cookie dough are nice; I may have noticed the input of eating that on my body weight and cholesterol score.

Summary perspective:  the implied claim here, in all of this, is that I feel like I'm really 30 or 40, and not 56, and I guess that sort of holds up.  My exercise recovery is a lot slower; it's all that I can do to recover from around 30 km of running a week (20 miles), which to me doesn't seem like that much.  I switched to 12 km runs here in Honolulu, with hill sections (running around Diamondhead), and I could keep that up indefinitely on an 8-day, 3 run cycle, but not quite 3 times a week.  With more conditioning I could've got there; I was trying to ramp up and maintain that within a 2 month or so cycle.  But it's hard to make changes to training volume or intensity at this age, and I've experienced very minor injuries before that highlight that those can only occur gradually.

I guess that I feel fine.  I keep busy and active, walking a lot, doing many other things, and never feel like it's too much.  I don't notice much for aches and pains, or digestive system changes, or whatever else.  I really did feel less clear in my early 40s, when I was still adjusting to a busy office-life experience, but adding running seems to have resolved some of that.

I wouldn't consider TRT / HRT because all of that seems fine to me.  I don't see anything wrong with others making that choice, but I don't experience any of the other symptoms it's supposed to correct for (low energy, mood issues, problems with exercise, body composition, or sexual function, etc.).

Recommendations:  I should close this by recommending truly low-hanging fruit, what I think would make the most difference the fastest.  It's diet change.  For people accustomed to drinking soda just dropping that out would make a lot of difference.  Drinking water should be fine, or tea or coffee as a healthy input, or tisanes, herb teas.  Maybe drinking enough water alone would make a difference, versus falling short daily, or just getting enough sleep.

Changing diet could relate to making small, periodic changes, like swapping out fast food for cooking healthy natural food versions, or chips for nuts, or maybe replacing processed deserts with fruit.  Fasting makes this easy, because it's easy to see each break and renewed eating cycle as a reset.  But there must be other ways to push the same effect, like making a few small changes at the start of every month.  I "only" fast about 20 days a year, so not a high proportion, and I've gained weight over the past two years, so using fasting to lose weight would require a more specific focus on that.

Listening to your body is important.  The amount of sleep that's enough would vary by person.  Poor diet inputs or unusually helpful inputs also would vary by person in relation to positive or negative impact.  Related to exercise more would be better up to a point, but at middle age injury is an early warning sign that you're progressing too fast, and that's no good.

Being open to life changes may make a difference.  Of course it would help if those are positive.  I went through a period of meditating a lot, the second I've experienced in my life, and that seemed to help.  Getting a new pet can change things in a positive way (although losing one can also be really rough).  Life connections and activities seem to make a lot of difference.

Having kids late seemed to help.  I've been playing in kids' play areas for years (14 or 15), going to water parks, ice skating (a lot; the kids took lessons), biking and hiking with them, and so on.  That decade off exercise involved a lot of activity.  Some of it is just mental, not seeing yourself as sedentary and inactive, but it seems important for that to connect to physical activity.  I don't think it needs to be all that strenuous; hanging out laundry or doing gardening could be enough, to maintain flexibility through varied movement.

my other babies; I miss them terribly, while I'm away for this month

Beyond all of this I think accepting long-term transitions like aging is helpful.  You can focus on health, and change that, and some "symptoms" might diminish.  But in general life is about change, and walking a changing path, so feeling negatively about that context could be unhelpful.  Leaning into whatever activity works for you could tie in with feeling positive about your capacity, and enjoying different activities.  We--as a family, essentially--took up pickleball this year; it's nice when those can involve some limited exercise.

more on this here, especially relevant to people in Honolulu

good experience of meaning can't hurt

Fasting introduction; how to water fast for multiple days

 

shou / shu pu'er is best for fasting, very mild on your stomach

This topic came up in online discussion recently, one that I've written quite a bit about here.  Earlier posts were never really designed as a short introduction and how-to, so to supplement that other discussion I'll write that out here.  To be clear I might have only fasted for a total of 60 days or so, so I'm definitely no expert, really only getting started myself.  

Before getting into that I think a couple of preliminary factors apply:

1.  Why fast?

That discussion was about potential anti-aging benefits, and I guess that is one reason.  I've almost entirely reversed my experience of greying hair, probably from this input, over the course of the first year, or maybe less.  Of course I didn't take up fasting for that reason.  It is claimed to reduce risk of severe illnesses, especially cancer and diabetes, and it was partly about that.  But who knows about that, really.

It's also supposed to improve energy level, especially metabolic flexibility, use of internal fat for metabolism.  And to improve mental clarity, which I guess could've happened, but it's hard to track.  And it's hard to separate causes; I've been exercising more than ever and eating a better diet since I started fasting, about 2 1/2 years ago.  

Of course people also fast for weight loss, but that often may not work as well as expected.  I think my metabolism may have slowed slightly, related to fasting practices, and I've gained a few pounds in that 2 1/2 years.  It could just be muscle mass gain; I am exercising quite a bit, running 20 miles per week most weeks, swimming more than ever, and dabbling in pickleball most recently.

a picture from my running route this week; it's nice here, in Honolulu

2.  Are there risks?

There are risks related to almost everything, including fasting.  In general it's accepted as very safe to fast, by fasting practitioners, but it's probably not safe to fast for 3 days or longer without supplementing electrolytes (sodium, potassium, and magnesium).  Low levels of those will cause low energy level, headaches, muscle cramps, brain fog, dizziness, and problems sleeping.  

How much to supplement, and in what form, is quite complicated.  You can't take pills to supplement salts (what those are), because the volume is too high, and any type of tablet form could become stuck to the lining of your stomach and cause a problem.  Magnesium might be the exception to that; you only need to supplement about 400 mg a day of that, versus 1 to 2 grams of the other two (with that requirement varying by different factors).

I definitely wouldn't recommend ramping up fasting practices quickly; it would be better to give your body time to adjust to the new experiences.  Some degree of hunger experience is normal, of course, and also disrupted energy level and mental focus.  After 2 or 3 trials of an extended fast all of that subsides quite a bit, and your mental clarity actually improves, energy level is quite consistent, even high.  Later hunger experience takes on a completely different form, much reduced in intensity.

This isn't a comprehensive listing of risks.  Specific pre-existing conditions could connect with more serious risks.  In case of any concerns consulting a doctor would be best.

General approach

There's not so much to it; you supplement electrolytes, drink plenty of water, and don't eat.  Most people will consume coffee, tea, or tisanes (herb teas), and some will drink diet sodas, while others won't.  Anything containing next to no calories won't break a fast.  Something like adding lemon slices to water might constitute a grey area; there is some calorie input in that, so most people who fast wouldn't do this, but it probably wouldn't change much.  Discussion of bone broth as an input comes up; if that contains any calories, as it generally would, that would break the fast.  I won't take vitamin C tablets that contain 10 calories, typically, but I suppose in a special case I might make an exception, if my throat felt a little sore, for example.

The concern isn't necessarily the idea of pure fasting, instead that ingesting any calories could trigger hunger response and digestive system activity, even when that's as limited as a cough drop.  It's as well to err on the lower side.  Some people would continue taking multi-vitamins, and other supplements, and some see it as a good time to take a break from those, as something along the line of a "detox," a concept typically not utilized by most in discussion of fasting, per my experience.

To begin fasting one might do well to employ a staged approach, trying out limited period eating first (within a 4 hour window, for example), then 24 hour fasts, on to two days, and so on.  There is no need to try 3 to 4 days on an early attempt.  I did, but I'm communicating this to help others learn from my mistakes.  Experience of hunger over the first 48 hours is severe, and it doesn't decrease much over the next 2 or 3 days.  Your body can adjust to use body fat as an effective energy source, which is very readily available, there just for that purpose, but you need to condition yourself to do so.

How to supplement electrolytes

This is a lot more complicated than it probably first seems.  A first inclination is to buy a pre-mixed, flavored, pre-measured packet, like LMNT products.  That could work.  Even using this approach someone should consult a decent reference about daily requirements in relation to fasting, because the included levels may not be optimized for that.  

This Reddit fasting sub wiki could be helpful.  I think that recommendation range is a bit high, extending up to 6 grams a day of sodium and 4.7 grams of potassium.  My guess is that few people could tolerate anywhere near those amounts.  Everyone would need to experiment to see what works best for them anyway, probably starting much lower in the range.  Their magnesium recommendation of 300-400 mg per day seems about right, and that may be somewhat universally applicable.  The low end of the range they recommend, on the order of a gram a day for both sodium and potassium, might work for a starting point.  Note that this would be the weight of the sodium and potassium in the related compounds, not the amount of total salt, including the "chloride" or whatever else.

It's possible to use very common, inexpensive sources for these salts.  Sodium can be consumed as table salt, or alternatively from baking soda.  Potassium is most typically encountered as potassium chloride, although there must be other forms.  Magnesium is more complicated, since many people report experiencing strong laxative effects from some forms.  It all requires more consideration and review than I'll try to support here.  In theory food-grade versions of epsom salt could supplement magnesium, but that form, magnesium sulfate, may really act as a stronger laxative than other compound versions.

That Reddit sub wiki recommends making up a "snake juice" daily supplementation mix and drinking that, along with extra water intake.  That does work, but drinking salt water can seem a bit rough, even diluted forms.  I've experimented with variations of that practice, and for me it works best to drink a good bit sort of as meals, 3 to 4 times a day.  For sure even sodium and potassium can act as a powerful laxative if you ingest too much too quickly; everyone taking up fasting has that experience at some point.  I can't stand the taste of baking soda in such a mix; that kind of factor enters in.  

Flavoring that mix might be promising, but many people adjust to tolerating it without that step.  There are two schools of thought about stevia and artificial sweetener input, which could relate to this.  One take is that it can cause an insulin release response, and the other is that it probably doesn't.  I don't drink much for sweetened tisanes or diet sodas but I've not noticed any related effects when I have, any problems of any kind.

Muscle cramps are one clear sign that your electrolyte balance is off, or trouble sleeping could be.  I sleep well while fasting, in general, but while exploring electrolyte supplementation I often didn't.

Drinking a lot of water seems crucial.  Some people report good results from drinking an awful lot, much more than 2 liters a day, so I suppose it comes down to personal judgment and experimentation.

Limitations of fasting, related practices

You can exercise while fasting; that seems to work.  I keep intensity moderate, and have evolved practice to use it as a good time for a break from running, but I do tend to walk a lot while I fast.  It keeps my energy level up, and helps me shift over to the experience ketosis faster over the first two days.

In fasting circles discussion the main restriction is on discussing that you are fasting, with anyone, under any circumstances.  I don't observe this, but I get it.  Some people are put off by it, and in one discussion account their company's HR department required them to stop the fast.  It's a judgment call.  People do have an aversion to practices that are completely unfamiliar to them, so in general discussing fasting isn't met with acceptance or interest.

I work well while fasting; the busier I stay the easier it is, and my productivity level can be even higher than when I'm not fasting.  The extra mental clarity, after you adjust to it, is really something to experience.  Flashes of creative insight and productivity can be quite an experience, surpassing what I almost ever go through at other times.

How long someone can or should fast is relatively open, or duration over time.  It depends on the purpose.  People trying to lose weight describe fasting for up to 3 weeks or so in that fasting group; beyond that many report relatively severe side effects, or some in even less time.  Most people there adopt periodic fasting instead, like rotating 3 or 4 day fasting and eating periods (rolling 48s or 72s).  

This is just my take, but it would intuitively seem necessary to eat a very nutritionally balanced diet while trying to pull that off, during the days that one eats, including plenty of protein, healthy fats, and micronutrients.  Additionally supplementation through multi-vitamins might make a lot of difference.  I wouldn't undertake such a practice myself, but then I've not been trying to lose weight.

I fast for 5 days at a time, generally 4 times per year.  For someone trying to maximize or optimize the types of inputs I'm going after, improved general health, and experience of autophagy (cellular recycling), that might be sufficient, or alternating 4 day fasts every other month could be a next further step.  Maybe someone could obtain most of the same benefits only fasting every 6 months, for that same period, 5 days.  To me it helps to not go too long in between fasts to retain the acclimation to the experience.

Other sub-themes

There are so many other related sub-themes one might venture into.  Is it dangerous to break a fast by eating a lot of sugar, or too much food?  Yes, but not so much for shorter fasts, for a period of a week or less.  You definitely should break a fast by eating healthy food though, no junk food, fast food, or high sugar content foods.  Even very high fiber it would be best to avoid, resetting your digestive system with easy to process, balanced foods.  I often broke fasts by eating a healthy version of a burger and fries, so it doesn't need to be so healthy, or as easy to digest as rice soup.  Then I tried it using McDonald's food once, when time was tight, and it took days for my digestive system to recover.  I guess I had that coming, for straying so far from common sense.

Drinking bone broth comes up as a topic, both in relation to a question about whether it would break a fast (it would; even minimal calorie input breaks a fast), and related to a potential input to re-start digestion.  If someone fasts for two weeks or longer you need to re-feed in a much more careful, controlled way, or it really can be quite dangerous.  In such a case using bone broth as a gradual resumption of digestion could work well, according to plenty of discussion input.  But this is a topic I have no first-hand experience with, to be clear; I've only ever fasted for five days at a time.

People ask about what can offset hunger when fasting, if drinking water or salt-water might work, or if there are other "hacks."  It can't hurt to drink a little water or salt-water, but in general the hunger experience is just part of it, kind of unavoidable.  It subsides after 2 or 3 trials, but in those first rounds it's rough.  Your stomach might rumble or produce some gas, and thoughts of food don't quiet down.  Again I think gradually building up to longer periods--5 days; not multi-week fasts--might help.  To me there is no reason why one would need to go further, why fasting for a week or longer would make sense.  Autophagy is said to peak at or after 48 hours, so a 5 day break goes plenty beyond that.

Even though I've said that I've not used fasting for weight loss I can pass on speculation about how that might work.  I reset my diet to be just a little cleaner and healthier after every fast, and I think an approach like this could work.  You could reset, re-start eating, at a slight calorie deficit, switching to 1800-2000 calories per day, if you normally eat more.  You might just reset your metabolism to be slower, instead of inducing gradual weight loss, so it might work as an option to try dropping to 1500 calories for a couple of extra weeks.  Given that fasting could cause micro-nutrient gaps restarting diet to be much healthier than normal would make sense, especially if the idea is to eat less.  If you wake up and eat a few frozen waffles with syrup and then skip eating until dinner your diet will be essentially empty.

One main theme that people lean into in a fasting sub (group) is drawing on support from others to continue a fast, often supported by using an app to track fasting time.  I don't do any of that.  I wouldn't need a timer counting down hours across a period of five days, because I already know exactly when I started.  It wouldn't help me to know that a few internet strangers were also not eating at the same time.  But I don't think that my own approach and preferences are necessarily better for any reason.

I'm also not careful about making sure that I fast for the entire 120 hours (5 days); I tend to start a fast after dinner the first day, and eat a normal dinner on the last, so I would really only fast for 4 days and 22 hours, or so.  These types of practices and preferences vary by person; I get it why crossing the actual finish line makes a lot of difference for most people, as a personal victory.  I would just as soon not re-start eating right before sleeping on that last day, so those kinds of concerns also factor in.

I've not mentioned when I would stop a fast, under what circumstances.  If I feel sick I might, unless symptoms are very mild.  If something feels off I would stop.  I've started to get sick before, the stage prior to the normal symptoms, sore throat and such, and resuming eating a day or two early has seemed to cut short that illness experience to follow.

The only times fasting has seemed to cause atypical health issues seemed to relate to getting electrolyte supplementation wrong, early on.  Experience of an irregular heartbeat is especially concerning; when that occurs I would stop the fast.  I have experienced plenty of hunger, of course, and energy level fluctuation and limited dizziness is normal.  If I feel off drinking a round of tisane (herb tea) seems to correct for that.  In some cases I may just be getting behind on hydration, so that it's really the water in the herb tea that's making the difference.  Drinking a bit of salt water, supplementing some extra sodium and potassium, will often make a difference.  I tend to take magnesium as tablets or capsules, a couple of times a day, so it's easy to keep up with that input.

Conclusions

I don't tend to recommend fasting often because it's just too extreme a practice for most people.  Maybe not as much in other cultures with that practice as a component, but most Thais and Americans certainly can't relate to it.  Since I don't really recommend it for weight loss, as covered here, it's hard to suggest with certainty that it's great for general health, even though that is my understanding.  I think my general mental clarity has improved since fasting, and again I lost the experience of greying hair, which may well connect with other forms of internal systems health that is less obvious.

It's a little harder than I've let on, especially for the first 2 or 3 fasts.  Hunger experience is profound.  I think someone could avoid most of that by using a staged, progressive approach, as I've described.  Now when fasting I can go hours of the day without thinking about food at all.  The sharp, intense experience of hunger no longer occurs, and a dull empty feeling is quite diminished.  It does add some tension, or light underlying mental stress, that never completely goes away.  I find this comparable to the off feeling related to being jet-lagged; something isn't completely normal, for days.  Over time being jet-lagged seems normal to you though, and so does fasting experience, to an extent.

Optimum timing would vary by schedule demands, and how someone relates to different phases of the experience.  To me the first day is very easy, the second sometimes relates to the most experience of hunger, and on day three adjustment of energy level can occur.  Then days 4 and 5 tend to be easier, but mental tension can increase a little.  It seemed to work out well to start fasting on a Wednesday, on work-weeks, because that day is the easiest, and weathering Friday was the main concern.  Then fasting on off-work days was easy, because I could add a nap to offset energy issues, or make the time go faster, and watch more video content to stay distracted.

I think in the future fasting will become much more accepted, in "the West," but not any time soon. We're just not there yet.  Isolated positive accounts will continue to enter into public awareness, but it will probably take years for this kind of experience to become more mainstream.  It's trending more lately, and plenty of health-guru types now recommend it, especially more science-oriented examples of that broad type, like Huberman and the like.  Even so I think people will take up easier versions of their trend-oriented recommendations first, like trying to get some sun exposure in the morning, or ice baths.  It's much easier to exercise than to fast, and a little of that exposure goes a long way for general health.