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I can relate to that "high".

I'm not sure about the science behind this but my best guess is that it's like the opposite of the drowsy feeling you get after a big meal:

You aren't spending energy on digestion, and the whole body and brain "wake up" and become alert, because, well, you need to be alert so you can survive and get more food! haha

Also:

• you've probably entirely emptied out everything in your intestines+colon by then;

• you've possibly starved your intestinal microbiome enough that it's stopped excreting any metabolic byproducts;

• you've probably starved any bacteria hanging out in your mouth/sinuses/tonsils/adenoids, and so breathing + drinking water + saliva has finally had a chance to actually get rid of those;

• any of the inflammatory compounds that get into your bloodstream from your food, have been removed, so your total tissue inflammation is lower than it ever is otherwise (like being on corticosteroids, sort of);

• since your liver/kidneys aren't dealing with a constant stream of input, they can 1. clean themselves for a change, and 2. clean "lower-priority" stuff out of your blood;

• and once they've done that, now they can just shut down and stop spending energy or consuming metabolites.

Presuming you're also drinking a normal amount of water,

• your blood pH and O2 sat. are likely maintained much more closely than they are when you eat food, which allows your organs and your immune system to function slightly more optimally.

Are these personal observations, or empirically established facts? For example - would liver and kidneys actually shut down when they don't have any work to do?

I was intentionally using sloppy non-clinical language. :) "Shut down" in the sense that the liver specifically is full of xenometabolizing enzymes, and those enzymes get replaced by the densely-packed mitochondria in liver cells as they get used up, requiring nutrients to feed said mitochondria. If those enzymes are consumed at a slower rate, those mitochondria consume your body's nutrient stores more slowly.

This sounds made up without any scientific backing. You starve bacteria? That's now how it works, that's now how any of this works :)

It's a gloss: your intestinal microbiome is maintained because bacterial biofilms in the intestines constantly grow, but are also constantly scraped away by fibrous matter travelling through the intestines (the balance is sort of like bone remodelling.) If you eat only fiber while otherwise fasting, the scraping will occur without the regrowth. Combine this with a course of antibiotics beforehand and a course of probiotics (or a foecal transplant) afterward, and you can fully replace your microbiome.

I've been a long time IBS suffferer and I think yeast overgrowth plays a key role in my case. I took anti yeast medicines for a while and felt great. Should've taken probiotics at the same time.

Do you know of a book/source that sums all of these points up? (I'm going to try the 3 (5?) days strategy and understanding what's going on would add to the motivation.)

We know very little about the bacteria in our gut. Take it from someone who had to get surgery because of ulcerative colitis. Things might fuck up in your intestinal system and doctors who have been in the field for 20 years can only shrug. There's no book on that, I'd not suggest trying to fuck with your intestinal system (antibiotics + probiotics) like there's some science behind it. There isn't.

I've never heard of a fiber only fast. What can you eat that only contains fiber?

This is a very bad idea. Some healthy bacteria cannot be replaced once they're gone. You should only use antibiotics when the pros outweigh the cons, which is if you suffer from an infection.

What would happen if the fast includes water, like in the 4-day vision quest fast (no food and no water) practiced by Native Americans?

Many things, but for a short list.

Massive headaches, mucus membranes dry up, hallucinations, and at 4 days there is some risk of death depending on conditions though this is generally minimal unless you involve sweat lodge conditions or where somewhat dehydrated to start with.

These typically start and end with short sweat lodges. I know quite a few people who've went through the experience but no testimonials about hallucinations or death (amongst everyone I know who did this and everyone they did this with).

I was wondering about possibility for kidney damage?

Done correctly there are few issues unless you have other medical conditions. But, you can also really mess things up, so I guess it depends.

I found the same, I've done numerous week long fasts, I think the longest was 10 days, and the first 1 or 2 days are the toughest. After that my body would stop craving, and I'd stop thinking about food altogether.

I've heard that when you get to the "other side" of a fast, that is, you actually begin starving, that hunger returns with an intensity that is incredibly hard to ignore.

The other thing I realised by fasting is how incredibly social the act of eating is.

I tried to work while fasting, but while I feel good and am perfectly able to have conversations, my brain doesn't work nearly as well when I try to think focused or solve hard problems.

So I stopped doing that.

For how long did you fast or when did you notice a decline in mental ability?

I've done up to 7 days. This was probably a 3-5 day fast.

I didn't notice any decline until I tried to solve a programming problem, and the part of my brain that normally jumps in and figures the hard stuff out just wasn't there.

It's an odd feeling.

I can concur. Used to do long fasts when I was in high school, so tried doing it again in the past couple of years, and suddenly I couldn't function at work.

That being said, I've successfully gone 18-24 hours without eating multiple times without any real noticeable detrimental effects on my ability to concentrate on programming or get work done, especially if I time it so I stop eating at 6pm one day and start eating again after 12pm the next day.

That's about when the body enters the ketosis state and the brain starts getting energy again, this time from burning fat.

> The other thing to note is that the 3 and 4th days (might just be me!) I get a 'mental high' that is quite interesting. Everything seems sharper for a while.

That's very commonly reported, actually. And I would say it lasts longer than that. I'm pretty sure this is a major reason why fasting is a common practice associated with meditation techniques, traditionally.

How much do you eat on a fasting day? You don't go zero calorie intake, or do you?

You don't eat. At all. Nothing. It's not that hard really, as mentioned, the first day is a bit hard, but after that you are no longer hungry anyway.. I have sometime a glass of fruit juice in the morning, coffee, and water.

The trick is to try to 'plan' ahead. Don't stock up on nice food, only do that on the friday!

How does your body react to the fruit juice?

That's not 0 calories though.

Fruit juice is a ton of sugar, it's the same as eating.

Personally, I think the maximum health benefit comes from zero calories. I'm able to function and work fairly well for the first 7 days. It's (typically) on day 8 that I start to feel weak and/or sick. I've gone to a twelfth day, and by then I feel like I have the flu. Which is interesting, because it taught something about a flu. I always thought a flu did direct damage, but now I think the worst thing about the flu is the interruption of the production of normal proteins that my body needs. And exactly the same thing must happen after 7 days without food -- the body is increasingly unable to make necessary proteins. It is interesting to me how much the feeling of a long fast resembles a flu.

So zero calories in for 7 days?

Coincidentally, antifolate drugs like methotrexate (which explicitly halt your cells' reproduction, usually for the sake of fighting cancer) also have similar symptoms.

This guy is describing an eating disorder-- Anorexia Nervosa specifically. Do not start doing what he is describing and put yourself on a similar path.

Heh, actually that's one of the few message on HN that wants me to start the message with 'LOL' because I actually did!

I'm french, I cook, I eat, and drink in pretty reasonable amount, and I'm a muscular 90Kg - with a flat belly, thanks to the fasting.

Last saturday I ate a 32 ounces steak in one sitting... Now that's some sort of Anorexia I had never heard of before! I do feel very bad for people who actually have anorexia, but please, don't insult them throwing these claims around.

Excessive fasting followed by binge-eating is literally the description of an eating disorder. I know for certain I won't be able to convince you of it because you already said you don't trust doctors-- but if I can get one person in here to not go down this path then it was worth the time.

You can't actually /binge eat/ after a fast. You can eat a lot, but you will still eat less than an usual day anyway, you can't possibly eat as much as you've missed, it's impossible.

As I mentioned before, I actually eat quite a bit less /in general/ than I used to a few years back.

So nope, you haven't convinced me, far from it. My family is happy, my doctor is happy, and more importantly, I'm happy. You can safely go back to inventing disorders, I personally hope that the stories on this particular topic will convince a few more people to stop trusting the likes of you.

Dude, just stop it. This has nothing to do with anorexia.

I think the difference is that somebody with a true eating disorder such as anorexia nervosa will still see themselves as overweight regardless of how much weight they lose. To the point they look like someone who just walked out of a prison/war camp and they still see fat in the mirror where it just doesn't exist.

The parent comment sounds as though he his happy with his lifestyle and weight. What really defines it being a disorder is that the person is never happy and always feels they need to lose more regardless of what anyone around them says.

I agree with your sentiment that people should enter such fasting regimes with immense caution (it could be a slippery slope for some), but I also agree with the parent that he is probably not suffering such a disorder.

Well, how do you define excessive? The guy seems to have a healthy weight, so it doesn't seem like he starves himself.

I'm not convinced it would be considered an eating disorder if you are physically healthy and fit, socially normal, and emotionally healthy (since the desire to fast isn't triggered by some crazy desire for weight loss but instead to achieve the supposed health benefits that fasting invokes)

After seeing your user name, I'm having a bit of a hard time sharing your level of anxiety regarding intermittent fasting strategies ;-)

A controlled fast is not an eating disorder. It's like calling prescribed medication drug abuse.

...also "(...) prolonged fasting cycles -- periods of no food for two to four days at a time over the course of six months -- kill older and damaged immune cells and generate new ones (...)" [1]

[1] https://news.ycombinator.com/item?id=8831739

You only eat on the weekend? Seriously?

Socially, how does that work for you? I get a lot of enjoyment cooking and eating with my family every night.

Do you do any strenuous exercise during the week?

Well I also enjoy cooking (a lot!), thus the need to 'reset' sometime. What I hate is counting calories, with the fasting I can pretty much eat as much as I like without having to worry, and when I feel I've done a bit too much of that, I fast and 'reset'.

With the years, I actually don't need it that much/that hard because it seems to have helped quite a bit with the amount of food I eat /anyway/ but I can still eat my way into a 32 ounce steak and not feel bad about it :-)

As far as family goes, when I fast, I go to my mancave during meals and do some tinkering so 1) they don't feel bad and 2) I don't smell anything!

Seriously, with just a little bit of preparation, it's surprisingly easy...

How do you work? Are you able to write good quality code while fasting?

Yes, most definitely -- as mentioned you stop being hungry anyway, and you get a bit of a 'high' as well, perhaps due to the typical drowsiness of digestion not being there...

My pet theory is that we evolved it, as hunter gatherers we probably had to develop a way to sharpen the senses in case the family/group was running out of food. Ie the Next Hunt can't fail. I think it's a cute idea. Very likely completely baseless :-)

I love that idea too! I'm going to believe that's the case

You still haven't said unambiguously how often you do this. You implied you can do it once a month, but didn't say if that's empirically roughly how often you fast.

Exercise... workouts... you haven't mentioned these at all, other than sport shooting which certainly requires some exertion but is not a workout workout. No workouts during fasts? No regular workouts at all?

Also, fruit juice is not exactly zero calories. You should figure out how many calories you're consuming. There's a big difference between "I'm not eating solid food but I drink juice and coffee to keep myself functional" and "I drink water for 5 days."

There is no real timeline for me to do it, it mostly depends if I feel bloated or not. So for example I hadn't done one in about 3 months, but I rather coincidently started one yesterday... It's always a mix of thinking I could 'use' one, and having nothing in the calendar that might interfere (social eating and stuff) AND having nothing spectacular in the fridge needing eating.

So, I'd say I'd do one every two months. I don't /workout/ these days, not as a workout might be seen anyway, I do some weights and so on, but more for tone than 'work'. And I don't do heavy cardio or anything like that. I do a lot of walking, and yeah -- shooting is surprisingly exerting: Lifting/shifting a ~4Kg gun around about 200 times with enough speed and precision is a bit of a workout! On a 'training day' I'll do that more like ~450 times. Thats a few repetitions :-)

I /used/ to workout a lot, and for a little while I did fast AND workout, but ultimately the workout seemed a little bit pointless, especially if you work out for controlling weight. It's a LOT harder to burn energy than to take it in, so my conclusion was to fast, instead.

The workout regime over the years has lead to quite a few injuries as well, and as I get older, I'm now paying for that. I'm built more like a rugbyman than a ballet dancer, so all the years of squash, running, weighted abs and so on leads to weak kneejoints, hips starting to play up a bit etc.

I agree, the social aspect is difficult. Going out with friends limits the times when I can fast. For long fasts, of more than 3 days, finding the time is difficult. I am only able to do 2 or 3 long fasts each year, because I only find time away from friends on rare occasions. If I had a family then I assume my fasting would be limited to once a year retreats of some kind.

Still, even once a year, I think there are great health benefits to long fasts. If you can go 10 or more days without food, surely that gives the body the chance to break down and absorb a lot of damaged cells that otherwise might be kept around?

Personally, for the social aspect, I'm just quite open about it -- I just try not to go to the pub/restaurant etc but if the topic comes up, I just claim I'm becoming a shaolin monk and currently working on my kung-fu. Try that with a serious face :-)