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The Effects of Intermittent Fasting on Human and Animal Health (lift-heavy.com)
202 points by joubert on July 6, 2015 | hide | past | web | favorite | 145 comments

I'm not hostile to the concept, of intermittent fasting (IF), quite the opposite, but I don't think there is much useful information (as the public) we can get from this paper. Granted, I've only skimmed, but there are problems. The paper isn't peer-reviewed and the author indicates he doesn't feel inclined to attempt to get the paper reviewed/published. Red flag.

But that doesn't matter anyway because he reaches only weak conclusions, indicating the data in humans is murky. The author clearly believes IF is beneficial anyway and writes as if he is an advocate for it in the intro at the top of the web page, before the paper appears. Even more damning, portions of the paper itself read like they were written by an advocate. He just couldn't help himself. His job there is to attempt to be neutral and discover and summarize what the data shows (with conclusions) for his systematic review.

However, this paper can serves as a handy compilation of references on the subject which could help other researchers. Given the author's advocacy of the subject, if used as such care should be taken to ensure the references are thorough and nothing is omitted.

What part made you believe the author was an advocate for IF? I didn't get that at all.

It is, quite simply, the tagline of his website[1] that the OP linked from: "Strength Training & Intermittent Fasting At Its Best"

[1]: http://www.lift-heavy.com/

I also got that vibe in a paragraph preceding the paper that has a Clickbank affiliate link to a book on the subject of intermittent fasting. The author goes on to state "...it has helped many people get leaner and healthier with a relaxed mindset."

That kind of hinted to me where the bias of the paper would be. However, such bias could've resulted from the information he found during his studies.

The paper itself seems balanced (I didn't read the whole thing) but it seems clear he his allegiance was likely on the "pro" side.

"Without hesitation the best online recourse on the topic is my dear friend Martin Berkhan’s Leangains.com"

And from Berkhan: "I co-sign on pretty much everything"

Besides the proposed health benefits, it is worth also considering the effects on mental/emotional state. It is probably no coincidence that fasting is an element of practically every traditional religious and spiritual practice. As an example, in Islam the recommended practice is to fast two times a week (consistent with the regimen the OP discusses).

Things that work well for the physical body usually has a corollary beneficial effect on mental state, which is no less of an upside than the health benefits.

In this case it seems to be even more than 'just' corollary, there are tons of papers being published about the connection between inflammation (which fasting seems to mediate very effectively) and a whole array of mental diseases

Whether or not it is a coincidence mentioning religion adds nothing to the conversation.

I disagree. It's worth mentioning simply because the practice has survived a long time trough many cultures. Time is a really good curator - if something survives a really long time (thousand of years scale) it is very likely to be of use.

> Time is a really good curator - if something survives a really long time (thousand of years scale) it is very likely to be of use.

This is actually one of the fallacies related to evolution. Selection only happens against negative pressure, not for positive pressure. In other words, adaptation generally only happens for things which harm survival. Things which are neutral or even benefit survival are not selected for.

Therefore, the proper statement to make would be more along the lines of, "Well, it can't hurt too much."

Nothing is neutral. Every activity one undertakes is at the cost of doing something else, hence "neutral" is actually negative - and would get selected against, ex hypothesi. Even things that benefit survival but don't do it strongly enough would be functionally negative, and therefore selected against.

Finally, take activities that are strongly beneficial. Not doing these things will put one at a selective disadvantage against one's rivals.

If you agree with the above, there is no validity at all left in your original claim:

>Things which are neutral or even benefit survival are not selected for.

If I understand correctly, your basic argument is something along the lines of, "Eating is obviously extremely beneficial. Therefore eating must be selected for. Therefore your statement is false."

My rebuttal would be that you are looking at the wrong side of the equation. Eating is not selected for; not eating is selected against. So no, your argument does not counter my original claim. Such reworkings of the argument may seem petty, but they are centered around a deeper understanding of what exactly selection is and how it works.

Sexual selection can be much more powerful than ordinary survival selection (see: peacock tails).

True. Instances of "survival" in my original statement should probably be read as "reproduction". There are, of course, more selection criteria available than just "survival to reproduction age". And selections can work opposing each other.

But, in all, the original statement still stands: Selections only work negatively. That is, a peacock with better plumage might get more chances of reproducing due to sexual selection, but as long as he gets at least one chance of reproduction, he has not been selected against.

Reproduction causes a loss of half of the chromosomes. If he only has one offspring (unless it is a lot more sexually successful than him), his line dies out.

Different organisms have evolved different reproduction strategies through selection:


You're being pretty pedantic at this point. If an individual reproduces, then none of that individual's traits were sufficiently selected against. That's also not a guarantee that all their traits will carry on in new lines. There's also no guarantee that their children will be fit, due to differing traits or changing environment.

> Things which [...] benefit survival are not selected for

Things which impact reproduction will be selected for. Things which kill you before you can finish raising a child will be most strongly selected against. Things that allow you to keep reproducing longer will be less strongly selected for. I guarantee that if there were a gene that let men and woman keep popping out babies for a century, it would be very likely to be preserved.

> Things that allow you to keep reproducing longer will be less strongly selected for.

No. This is the fallacy.

> I guarantee that if there were a gene that let men and woman keep popping out babies for a century, it would be very likely to be preserved.

It would be preserved, yes. The fallacy is that it will not be perserved in preference of lack of the gene, because there is nothing selecting against not having that gene. In other words, both lines will continue to live on, because there is nothing selecting against either of them.

As long as individuals can reproduce, then their traits are not being selected against. If there are multiple variations of the traits, those will become part of the population's natural variation. Which is a good thing to have in terms of the population, because natural variation helps prevent genetic bottlenecks.

> No. This is the fallacy.

I simply don't believe you.

As the one making the preposterously counterintuitive claim, it's up to you to support this with facts, beyond just saying "nope, you're wrong, it's a fallacy."

To elaborate, if Sensible Sally's female descendants all produce one child, and Fertile Myrtle's descendants all produce 10 children each, then Myrtle's genes will multiply faster, and be less vulnerable to being wiped out by the odd plague or war.

You are repeating exactly what I said in the second and third paragraphs. I do not understand what you expect me to respond with. Your very own hypothetical scenario demonstrates that both lines will live on as long as the traits are not selected against.

The fact that death is random and sometimes widespread is selection pressure. Did you read to the end of my comment, where I said "less vulnerable to being wiped out by the odd plague or war"? Ever heard the phrase "don't put all your eggs in one basket"?

Put 9 Smiths and a Johnson on a boat. Now kill half of them. What are the odds that Johnsons are extinct? Now repeat the experiment until my point sinks in.

You are talking about introducing a genetic bottleneck, which I already addressed. Having diversity is good because it helps prevent such bottlenecks from entirely eliminating a population.

Also, you are no longer discussing the fallacy. The fallacy is believing that something that allows an individual to survive better than another individual will be selected for, when in fact individuals can only selected against by preventing reproduction, thereby restricting the expression of those traits in the future population. The mere existence of a Johnson in the first place indicates that Johnsons were not previously selected against. An event killing the Johnson would then be the selection against.

The end result looks like Smiths were selected for, but the actuality is that not-Smiths were selected against.

Okay, now imagine that Johnsons have a weird flap on their genitalia, and 9 times out of 10 it gets in the way during sex, and prevents conception.

Would THAT weird flap trait be selected against? After all, it "prevents reproduction, thereby restricting the expression of those traits in the future population."

And how is that scenario in any way different than the Smiths which merely reproduce 10 times as often, by virtue of the aforementioned century of fertility?

I'm pretty sure at this point that there is not a response I can give you to change your mind. This is my last attempt, because I'm tired and this is pretty simple logic.

If a individual does not successfully reproduce because of an individual trait, then that individual was selected against for not being fit. This is true no matter what the trait. As soon as an individual successfully reproduces, then that individual was not select against. This is a binary proposition: selected-against ⊕ ¬selected-against.

Now if some other individual happens to be capable of reproducing more, then that individual's traits will be proportionately better represented in the next generation. Over time, these different traits will spread throughout a population and become part of its natural variation.

HERE'S THE IMPORTANT PART: BUT they will both continue to exist within the population because there is no such thing as selecting for a trait. More successful traits will carry a higher proportion within the equilibrium than less successful traits, but all traits not selected against will exist in the population.

It's important to realize that this is a GOOD THING. If individuals were selected for, reductio ad absurdum, only the "best" individuals would survive. This would lead to lower variation within the population, which would make it extremely fragile to changes. What was a relatively unsuccessful trait yesterday might become a very successful trait today.

>Time is a really good curator - if something survives a really long time (thousand of years scale) it is very likely to be of use.

Do you have any evidence to support this theory? I very much doubt this holds any truth. Time is not an indication of truth, empirical evidence is.

You are severely misreading what is being said here. "very likely to be of use" is not the same as being provably true. The point being made is that of usefulness and correlation. Those two things are essential to the way humans have and continue to think. In day to day life, nobody does 'studies' to prove every single thing to be true. That is why customs that survive time can sometimes have a grain of truth to them. And what's interesting is that even if they didn't it could be that blindly following something for years has created an evolutionary pressure on the body to adapt.

How is "a practice that has been sustained across multiple cultures over thousands of years" not empirical evidence?

The fact that people have being doing the same thing over a certain period of time makes no indication to the effectiveness of the activity.

People have being praying for thousands of years, yet I have seen no conclusive evidence of its effectiveness.

Have you really never heard of the benefits of the placebo response? Plus there's the social benefits of people focusing on good things and potentially manifesting them, and the community benefit of coming together to pray, and psychological benefits are a possibility, although I don't think that's well-studied (or even measurable?) enough to start that debate.

Prayer is like meat - it isn't for everyone, but if you're not getting it you have to be careful not to miss out on certain things.

>"Have you really never heard of the benefits of the placebo response?"

Do you have any evidence to support the benefits of a placebo effect in relation to religion and/or prayer?

>"plus there's the social benefits of people focusing on good things and potentially manifesting them, and the community benefit of coming together to pray, and psychological benefits are a possibility,"

What social benefits? What good things? What psychological benefits?

>"Although I don't think that's well-studied (or even measurable?) enough to start that debate."

Seems very convenient to me.

>"Prayer is like meat - it isn't for everyone, but if you're not getting it you have to be careful not to miss out on certain things."

What certain things?

Your comment seems awfully shallow in content to me, lacking in any specifics.

> Do you have any evidence to support the benefits of a placebo effect in relation to religion and/or prayer?

So, you are implying that there is a switch that will magically turn off beneficial parts of human biology (such as some well known and researched mechanisms like the placebo effect) for those and only those humans that engage in activities that you find personally disgusting (such as religion and prayer).

That's the most overtly religious belief I have seen expressed by a self professed rationalist, you know...

You've come to some incorrect conclusions.

If someone makes a particular claim, the burden of proof is on them.

I don't think that means what you think it means. The claim that says people get measurable benefits from "cures" and "solutions" that have no physical effect are scientist, medical researchers actually. That claim would probably benefit from closer investigation and a refined understanding of the mechanism that makes that happen would be useful, but the basic claim is probably demonstrated beyond reasonable doubt.

What you are saying is that if the "cure" in question is prayer instead of sugar pill, then this requires extra burden of proof because the universe is somehow bound to not listen to religious people. Or, to put it more bluntly, prayer would have to be extra harmful in order to counter whatever placebo effect might be at play.

This is a very peculiar belief, not rational but political in nature. In the economics of rhetoric there is a zero sum game: "for my argument to win my opponents must be seen to be in the wrong".


tl/dr; inconclusive, hard to get funding.

> People have being praying for thousands of years, yet I have seen no conclusive evidence of its effectiveness.

Praying isn't likely to mess with the metabolism. It is, in fact, entirely difficult to tell what it would mess with. Fasting is relatively easy to observe: if it fails, people starve to death.

Meanwhile, people all over the world incorporate fasting into their world intentionally. Far before civilization, they probably did so unintentionally. I highly doubt the body is not equipped in some form to deal with regular period of not eating. It is only extremely recently that the median human has reliable food sources.

At most you could say that fasting is not obviously harmful, because if it was, at some point someone would have noticed that all the fasting people get sick or die or whatever.

But it's a far jump from there to "very likely to be of use." The body is adapted to withstand all sorts of cultural practices that we no longer think are particularly medically useful, like haircuts, shaving, piercings, circumcision, branding, tattoos, foot binding, neck lengthening, bleeding (leeching), etc.

I dont believe there is evidence for any of those practices predating biologically modern humans. How far back to you have to go to find a life form that did not face constant fear of starvation?

Consider an ailment like a mild flu. What's more beneficial? Going to the temple and asking a man in the sky to heal you or going to someone who calls himself a doctor who performs something way more harmful than the mild sickness like bloodletting or prescribing antibiotics? In that sense, "praying" or, more accurately described, "letting nature take its course" has ample evidence of effectiveness.

It has less detrimental effects as opposed to an inferior alternative, yes.

The question I was asking, and which your response does not address, is whether or not a certain activity that claims to be beneficial becomes beneficial purely on the basis that it is practiced over 'x' period of time. Which I do not believe to be true. If you have evidence to the contrary, please post it.

Surviving the test of time is the ultimate empirical evidence. In fact I'd go so far to say it's the ONLY way we can test the truth of anything at all. This goes for anything, from biological systems (evolution), technical design - the wheel, to research papers. Look in your fridge: most of the food there has been consumed for thousands of years using basically the same cooking method and is for the most part considered healthy. The recent synthetic foods like margarine and recent cooking methods like deep frying are detrimental to health.

Keep in mind, practiced over 'x' amount of time where x > 2000 years.

You have misinterpreted the point of my post. The initial post was:

>"if something survives a really long time (thousand of years scale) it is very likely to be of use."

Whereby time was the factor by which something is considered 'of use'. The things you've mentioned evolution, the wheel, research papers etc. Have more concrete evidence than just time to back them up.

Although on the topic of food, do you have any evidence to support that?

But I think you've misinterpreted the original comment in the first place. Saying something "is likely to be of use" is not the same as "is empirically true".

Very true, my mistake. I was pushing my interpretation 'of use'. That can have many more meanings.

People have been believing lots of things in religious texts for many, many years. Often enough they are flat out incorrect. Just because something is "believed" doesn't make it necessarily true.

You conveniently left out the individual who does neither. Or the individual who uses some sort of herbal "medication". Or the individual who chooses yet another solution to their mild flu. Your argument for prayer is equivalent to "doing nothing".

Whether you believe in divine intervention or not, prayer is really just a ritual to alleviate stress, and it's cracking good at that.

Do you have any evidence to support that?

From an anecdotal perspective, I found that I suffered more stress and frustration via praying than not.

Because cultures and their beliefs can be stupid, and religious/cultural dogma can perpetrate a system that doesn't work. Humans tend towards efficiency only where there is no ideological dogma to hinder this.

Take the example of sacrifice. In dozens of cultures spanning ((in some cases) hundreds of) thousands of years, people have believed that the sacrifice of <insert species here> will stop the rain/volcano/thunder & lightning/etc. we now know this to be completely false, even though many of these cultures have writings and other 'empirical evidence' that says it does work.

There are 7+ billions of "evidences" sitting around. Look at the people alive today, chances are that either their ancestors did something like this, may be as little as 1 or 2 generations ago. Over the last 10 thousand years (or any other arbitrarily large time-frame), there were large number of potential ancestors whose offspring did not make it to the 21st century. So those people must have been doing something right...

But of course, it is really easy to demand more evidence for the facts we "very much doubt" that for those that confirm our preexisting ideas.

Check out the 'Lindy Effect.' https://en.wikipedia.org/wiki/Lindy_Effect Also read about 'Chesterton's Fence.' http://epicureandealmaker.blogspot.com/2012/03/chesterton-fe...

I think it does because it's evidence it's a brain hack of some sort.

"As an example, in Islam the recommended practice is to fast two times a week (consistent with the regimen the OP discusses)."

I was simply trying to point out that this sort of phrasing is constantly being used in a religious context to try to create an argument for the whole of the religion rather than to just stop at "here is something about my culture that might work". These things are constantly being conflated as being scientific evidences of the "deeper" truth lying within religion. Before you know it they become yet another thing that people brow beat as they try to convert the people around them. It simply isn't an interesting argument from my point of view.

I haven't had breakfast since about 2007. Well, of course there are days where I do have it when I'm staying over at a hotel, or I'm at an early work function. But I don't make breakfast for myself at home. My first meal is between 12h30 and 13h30. I don't feel any worse (or better) than when I used to eat breakfast in the past, but it's been so long that I really can't tell. I suppose this can be considered a type of fasting because of the length of time between lunch and supper the previous night.

I've never really understood the idea that breakfast is the most important meal of the day because I've never suffered from any ailments because not eating breakfast. Or maybe I have and I just don't know it? But then I could apply that same logic to times when I got inexplicably ill or just was not performing at my peak and I did have breakfast. My point is that I don't notice any significant changes in my health and or behaviour.

Of course I don't advise anyone doing this (or NOT doing - check with your physician first), but I still firmly believe that there is a lot of about diet and fitness that has to do with the physiology of the individual.

(BTW, if anyone else thought the linked article sounded familiar it might be because you've read it already. It was published 1 year ago)

I started to skip breakfast a few years ago. Now I skip lunch as well. Feel a lot better for it, don't lose energy, and don't get tired in the afternoon. I run everyday in the morning instead of breakfast, and cycle a lot.

If you eat around the same time daily, your body learns to get hungry when the time approaches. Regular breakfast-eaters get hungry if they skip breakfast, while breakfast-skippers like you and me do not. (If I'm wrong and someone in normal health has tried skipping breakfast for a few days without losing the morning hunger -- assuming they're making up for it later in the day -- I'd like to hear about it.)

I started skipping breakfast not for intermittent-fasting benefits but in hopes of better sleep: the anticipatory appetite can contribute to waking up early, and my sleep needed help.

Added: the article supports this. "The rise in ghrelin is independent of meal timing as demonstrated by similar peaks before an anticipated meal in various meal frequencies, thus suggesting that subjective feelings of hunger and energy intake is highly dependent on the individual’s preferred meal pattern (76)."

> I've never really understood the idea that breakfast is the most important meal of the day...

I've always heard that you should have the most calories and greatest diversity of food at the first meal of the day, slightly less so at the midday meal, and a very light/low calorie dinner. This is supposedly because you need that huge energy and mental boost to get your day started, and as the day goes on your caloric intake should taper off as you won't need it as much by the time you get home from work, and a light dinner because within a few hours you'll be sleeping and won't need it either.

Now that being said, it wouldn't work for me. I am up around 6-6:30am, I have breakfast (when I do eat it) at 7:15-7:30am, and my morning at work is decidedly not busy nor does it require critical thinking (I'm basically stuck answering the sales lines in the morning as the rest of the team doesn't roll into work until nearly lunchtime). This is off-season, so I might get ten calls before lunch, and about half of those are non-productive. I take an early lunch, around 11:30am, so I'm available for the larger part of the afternoon. So, the time between breakfast and lunch is usually four hours. That's not enough time to fully digest a large breakfast and be hungry again, so I usually either eat a light breakfast or none at all.

What I've found is that if I eat small meals for breakfast and lunch, with a snack available should I need it in the mid afternoon, I tend to focus better and get more done. The only downside is that by the time I get home and finish cooking dinner, I'm ravenous and I end up eating way too much for that meal. That's the part I'm trying to focus on now and cut down to about half. This will put my overall caloric intake at less than the "maintain" level for my build and age, which will hopefully help me to slowly lose weight.

> I've always heard that you should have the most calories and greatest diversity of food at the first meal of the day, slightly less so at the midday meal, and a very light/low calorie dinner.

This theory seems to ignore how effectively we can run on glycogen reserves, and sounds like it assumes a full night of sleeping takes less energy than a few hours awake. Also, most nutrients don't need to be consumed just before you're most active; the body can figure out when to use what, and a lot of resources go more to "repair/maintenance" than "fuel".

My eating schedule is kind of similar, in that I also eat my first meal around 12:00, but that's also close to when I wake up. I stay up until around 3am most nights, and I usually only eat lunch and dinner (technically breakfast and lunch?). I think this works really well for me. I'm often "in the zone" late at night and don't think about eating. I'm working remotely from Thailand, so I get to have a bit more overlap with co-founders and clients in the US. And I'm a night owl anyway, regardless of my timezone.

I don't know about the long-term side effects of this sleep schedule, but I'm lucky that I have the freedom to sleep as long as I want.

A side-note: Breakfast food is the best food! Nothing wrong with bacon and eggs for dinner. And sometimes I have cereal for lunch.

I started skipping breakfast in elementary school and haven't been eating it at all since then, no issues whatsoever for me and I actually prefer working out fasted.

I don't even get hungry before 1-3pm so I always found it odd when people couldn't function without a breakfast.

Following IF makes it easier to follow a diet since you only have 8h or less to eat all of them.

I started doing the same thing and lost 30 lbs pretty quickly. At times I just eat one very large meal per day. I've found it much easier to control my appetite and make better choices by exercising a little bit of discipline every day this way. Apparently some Romans idealized eating once per day.

I normally don't have any breakfast either, just because I prefer to spend extra time in bed in the mornings.

This haven't prevented me from gaining weight though. So just skipping breakfasts in the long term wouldn't be enough.

I rather often fast for a lot longer than 16h; I think the 'day fast' is a pretty rough deal, as the hunger (ie, the down side of fasting) is strongest on the first day. So really a small fast isnt too interesting, as you get all the disadvantage without much in terms of advantages.

By the second day, you are no longer hungry anyway, so, for me, a 3 day fast is next to ideal. But I can do rather easily 5 days.

I mostly start on the monday morning and finish on friday, or saturday if I feel brave and there's nothing too exciting in the fridge!

As to why do do it? Well I like cooking, and eating, and drinking, and I rather hate counting calories and such, I'm much more of a 'on/off' sort of guy, and I rather like a bit of a challenge. That also helps me control my weight, without having to spend stupid amount of time in the gym.

Also, there /is/ a 'high' to a fast, I feel like on the third and fourth day you feel particularly sharper; it then decline a bit and you can feel a bit woozy. But the high is pretty cool...

Day 1 was always the easiest for me, but I had an eating disorder, I was not going about this in a healthy way.

After 3 days, I could easily do a week, and I managed to do a 30 day fast one year.

I don't recall feeling high, I just remember a lot of laying down, dreaming and thinking about food, baking, and not doing much of anything else.

I really rather prefer being able to eat everything I want, and spend 2-3 hours a week at the gym. But my weight has gone up by 10-15 lbs (and I have also aged from 17 years old to 29).

I can't say I'm the same size as when I was fasting, but I have a defined shape, whereas before I was bone and skinny fat.

A 30 day fast sounds pretty insane to me, and quite dangerous without medical supervision. I would like to ask if you were overweight, and the goal was to lose weight?

I had ED-NOS (eating disorder not otherwise specificed) which mostly means it was a combination of anorexia nervosa and bulimia nervosa (which just means binge-purge cycle - fasting counts as purging).

I dropped from 140 lbs to 110 lbs in a month. I'm 5'4 female, and a 'skinny' weight for me is about 130 lbs as I am fairly muscular.

I used to want to look like a skeleton, I had no medical supervision and this was probably one of my worst eating disorder periods, the other being at college where I ate a microwaved apple or orange and 2 cups of broccoli / carrots only every day, for most of my freshman/sophmore year.

When I was ill, I knew I what I was doing with a disorder in mind, but I didn't admit it to anyone outside of me. I think most people who have an eating disorder know they have it inside, it's just something kept carefully secret.

I've been in recovery for about 2 years now, with healthy thoughts and no food restriction, excess exercising, starvation or purging. When I was sick I really didn't care if I died, as I have major depressive disorder comorbid, which I continue to have more difficulty beating than I did the eating disorder. I've fainted from fasting and I've been hospitalized from starvation. It's hell, pretty much.

I think it's important to take a step back from whatever the goal of these diets are, and look at the bigger picture. My weight only varied between 30 lbs over 15 or so years, and it controlled me entirely. It made me have to put a lot of my life on hold, when I had to focus what little energy I had towards getting better. I would really recommend anyone take a more careful, therapeutic look at their life if the above sounds tempting, and they find themselves going into cycles of fasting and 'losing' control over how they manage their diet.

How the hell do you keep up calorically? I'm interested in IF but I am trying to reconcile it with my daily caloric needs. If I didn't eat anything M-F I would be 13,000 calories behind, and in really rough shape. I already struggle to keep on weight as it is.

Well I suggest you don't try then; I'm in the reverse situation, it seems like I can store energy (fat) very efficiently, and also build muscle incredibly quickly. So this 'diet' or lifestyle is quite suited to me, but I think I'd be careful if I were in your case...

For example my wife can eat is a notch over 5 foot tall, and eat as much as I do, and does not put on weight, however, if she misses a meal, she gets wobbly and dizzy. So fasting is definitely not for her!

I have a pet theory that some people are just very good at extracting energy from food, and some people are very bad at it. Perhaps it's related to a difference in gut bacteria mix or something.

I agree regarding day 2 onwards - the main problem is if anyone else in the house (rest of the family) is cooking, as the heightened sense of smell brings in psychological hunger.

I agree; I try to go out and have a small walk if someone cruel is having curry or anything else strong :-) Also, I'm lucky that I have a separate 'lab' building where I can go and do some hacking during dinner, most excellent excuse to go spend some time with the CNC or 3d printer :-)

So, what does pass your lips during a fast period?

Fruit juice cut with water, and some coffee (there are bleeping limits! ;-))

Fruit juice is sugar. It's debatable then if it's a real IF.

I'm not really trying to do it 'by the book' -- I think it's better that you come up with something that works for you.

Fasting with just water is a bit tough, as you can get a metallic taste in your mouth that is rather disagreeable. So that's my 'fix' for that problem.

That's a sign of ketosis!

Yes I know, and that's why longer fast work quite a lot better than short ones, you do lose weight like /crazy/. I seems to lose nearly 1Kg a day.

1kg of fat would be 9000 kcal. Impressive energy expenditure there. Of course a lot of water weight is lost initially (when fasting or just skipping all carbs) but that rate won't hold for weeks on end.

I thought in ketosis it wasn't energy expenditure, the liver causes fat to break down and pass through your bladder? ... maybe I have that all back to front though :\ Maybe ketones pass through your bladder and they also break down fat cells...

That sounds vaguely like diabetes.

In the absence of metabolic disease, the body breaks down fat to use the resulting energy. Think about it evolutionarily; "there's no food right now, time to jettison my energy stores"?

Ketosis is a pretty weird state brought on by lack of carbohydrates. The liver starts producing ketones, ketones rapidly breakdown fat cells to boost blood sugar.

It is mostly unrelated to diabetes as that relates to insulin response.

Blood sugar is not boosted by ketosis. Ketosis can occur as a result of low insulin (in which case blood sugar will be high).



How do you make sure that your body doesn't burn up muscle while fasting?

Also, how do you keep sufficient energy to perform daily tasks and things like intense programming sessions?

Ever been in the middle of a hard workout and noticed that you smell like ammonia? That smell means you are burning protein, probably from your muscles. I have only ever seen this during extended exercise, but the same thing during a fast would be a clear indicator you are burning muscle.

So that's what that is! I used to notice that a lot when I first started cycling aggressively in college. Once I got into better shape it mostly went away. Thanks for the tip.

I haven't noticed any muscle lost -- but then again I put on muscle /very/ easily (a bit too easily actually, I get hypertrophia if I do too much sport). For energy, it turns out your body /does/ have some to burn, and once you made the switch to burning fat, well, usually there's a nice source of energy... I also wonder if you don't get a small dose of adrenalin in too, which would explain the 'high' you get after a couple of days.. but don't quote me on this..

But as I mentioned, the fruit juice input in the morning does help get the day started. Oh, and the coffee contains some nutrients too, so it's not like I'm totally starving.

You could add a pinch of baking soda to the water to make it more alkaline.

What is the metallic taste? I've experienced this before during fasting periods. Anyway to get rid of it without sugary fruit juice?

As the previous poster replied, it's related to https://en.wikipedia.org/wiki/Ketosis I don't know if you can really get rid of the taste, I'd be curious to know of course; but you kind of get used to it really.

I personally don't mind taking fruit juice, as it does give a small energy boost, especially in the morning.

Not everyone gets it. Fasting puts you in nutritional ketosis as does ketogenic / very-low-carb dieting. But the metallic taste is usually a temporary and harmless keto-adaptation symptom. The body's ketone production and consumption aren't fully balanced at first for quite a while, during which some people flush out most excess ketones in urine while others breathe out more of them. As you keto-adapt (takes from a week to a few months depending on individual), ketone bodies (a byproduct of fat oxidation) are fully utilized in place of glucose by more and more tissues/cells over time, until balance is achieved.

The metallic taste is excess ketones. If your body is not used to using ketones, some will be excreted in the urine and saliva.

If you really goose your ketogenic metabolism, your body gets better at using ketones and the taste will go away. You should also be sure to eat/drink extra salt during a fast or ketogenic diet due to water loss.

It's a shame that by self publishing this, the work has not had any kind of peer review. As a relative layman, I have no idea how much I can trust the method or conclusions presented.

I trust replications more than peer reviews.

With replication, somebody has to actually try and duplicate experiments.

Replication without proper controls is just confirming a poorly designed experiment.

That's true to a point, but replicability really is the cornerstone of science. A replicable result, even if it's ridiculously implausible, at least needs to be properly investigated to see where the mistake lies. There's something there that is investigable (is that a word?). Conversely you can have all the controls and peer review you like, but if the result isn't replicable it's garbage. Just nicely presented, plausible garbage which frankly is the most insidious and dangerous kind.

There have been some interesting studies into replicating results from published research that have found that only a very small fraction of peer reviewed papers present actually replicable results. That's shocking.

How often are research/litrature reviews peer reviewed? All the references are there, you can check them youself with little effort. There are no results that need to be replicated. To verify no bias exists in the presentation of the existing research, you'd basically have to reproduce the entire output of this paper (i.e. go and find and report on every single study out there related to fasting to ensure the results have been fairly presented). That's not so much a review as a replication of the research and I cannot see how a journal would have the resources to do that. What benefits would peer review give in this case?

Yeah I also don't know why this is the case because it would be more credible and prestigious. His reason was:

First, the idea was publication in a scientific magazine. For many reasons, taking time from becoming a good clinician being the most important, but far from single one, I eventually decided not to go that route.

It was his MD thesis, apparently. I think there is some validity in the fact that his university awarded him his medical doctorate based on the quality and content in the work.

Just from completely personal experience I can confirm the positive effects - if paired with good food and exercise. I've been doing IF for roughly 3 months now (16 hours fast per day, which is pretty easy to do by skipping breakfast) and combined it with leaving out all the crappy food I ate. You know, the usual gaming/coding/convenience stuff like chips. That and regular sports (rowing) not only resulted in weigh loss (which most likely was just from reduced calorie count, not IF per se) and strongly improved blood pressure (from high to normal). So, at least in my case, the combination of the three factors made a massive difference.

At the same time, I doubt IF by itself would do much if during the rest of the time you ate 3000 calories from chocolate and chips.

How do you know if IF itself made any difference? You've got too many moving parts to pin it down exactly. There is tons of evidence that cutting junk food, plus rowing would possibly do the same thing without IF. Have you tried to add a small wholesome breakfast to test for any changes to try and pin down a difference for IF?

Same here, although I skip entire days not eating. Also, I think it get's easier to go without food for a day after a couple of months doing it.

I would attribute the improvement in blood pressure to an exercise, not IF (at least this was my case, as I've started going to gym before I started IF and seen the blood pressure drop).

Just out of curiosity: do you substitute your breakfast with something? I'm on a stinging nettle + mate tea combination but slowly need something new for my taste buds

There's a whole world of fine and unusual teas to discover and enjoy. When I fast, I want a tea that provides more meaty aromas and a more complex taste experience – a food substitute that also gives a 'cleansing' sensation. (It's hard to be precise about what I mean by 'cleansing', but something like the opposite of the typical cloying English breakfast black tea). A fine kabusecha or gyokuro with their intense umami flavors can provide that. At the moment I have some Japanese 'bancha goishicha', a wildly different style from the green teas made from the same plants, a strange and strangely delicious double-fermented tea with tangy seaweed and mushroomy notes that is like a meal in itself.

I make a nice tea with Ginger, Fresh Turmeric Root, Cloves and Cinnamon.

It tastes amazing :-)

The BBC produced a documentary on the fasting titled Eat, Fast and Live Longer, it's well worth a watch - http://www.dailymotion.com/video/xvdbtt_eat-fast-live-longer...

Besides the science, IF is great as a 'lifestyle' diet. It's a simple way to balance food and exercise through awareness and knowledge rather than fads or short-term programs. I think that's why it's caught on well with lifehackers.

This. It removes so much of cognitive load compared to other diets.

You don't have to care about choosing your food according to the diet or to count calories.

You don't have to figure out if you are withing the limits of the diet, or feel bad if you've eaten something extra.

On the days you're not fasting, you can eat whatever you want.

The cognitive load is really the hard part of dieting and weight loss. In one sense, weight loss is simple physics - calories in vs calories out. In another, food is fundamentally connected to our motivation centers, and dieting is a ridiculously complicated affair to align your long-term goals with the emotional effects of eating.

I tried fasting last year after reading a book that promised health "miracles".

At first I fasted every Monday for 3 months (no food at all just water), then I fasted for 14 days without interruption.

This is much easier than I was thinking. After 3 days I was not hungry anymore BUT I wanted to eat. What I mean is that I had no pain in my stomach but my mind wanted the comfort of eating something. It grew more and more, at the end I was watching Youtube cooking videos every evening and planning all the great meals I would cook once I restarted to eat ;-)

Physically I could have lasted at least 2 weeks more, but mentally I was tired of it. I'm a software dev I so of course I had it easy compared to someone who has an active lifestyle.

Now for the bad part : no health miracle at all, and all the weight I lost has been regained and then some. And since then I was unable to gather enough willpower to fast again, even for just one day.

> no health miracle at all, and all the weight I lost has been regained and then some

Lifestyle changes that impact health require that one habitual adopt the change to realize their benefits long term. Of course if you followed a fasting program just once and then returned to the same habits you had prior to fasting you should expect to gain weight back.

Really it just means that if you want some health change you need to find something that is appealing so you can form a habit. (I don't find fasting appealing either.)

FWIW, I've done a ~20 hour fast for the last few months.

Eating in a 4 hour window from 6pm to 10pm approx.

This diet isn't practical if you're doing any serious exercise, either in the morning, or late evening (during after the eating window), so I often have to cheat and eat lunch, or otherwise extend the window on days when I'm exercising.

Otherwise it's surprising easy to stick to with a coffee or two for comfort, and I've lost a significant amount of weight:

* It's hard to eat enough calories to gain / maintain my (over)weight in 4 hours, at least if I stick to whole, fresh, real food. Some days I can hit a ~1000 calory deficit according to my calculations.

* I find it easy to go to sleep on a full-ish stomach, which helps a great deal compared to other diets.

I maintained a 1500 calorie diet for a year a few years ago. I'd pretty much just skip lunch every other day, and on the days I ate i'd go to chipotle and get hardshell tacos with just the fajita peppers, lettuce, and the mild salsa. By skipping the cheese, meat, and beans the calorie count is VERY low.

Eventually I lost 30 pounds. It's not the crazy amounts some people lost, but it was significant for me. Today though, 1500 seems to be my normal. If I go much above it, I start to gain. I think that's the risk of doing it this way. Your body seems to get used to the reduced count for some reason.

> Your body seems to get used to the reduced count for some reason.

It's called "starvation response." Being at a caloric deficit for a long period of time makes your body think that it is going to starve to death. Therefore it reduces your metabolism in response to the lack of calories you intake.

This is why having a cheat day every once in a while is actually physically good for your body not just psychologically.

Maybe this reduced metabolism is good for longevity?

A really interesting BBC show on the subject of intermittent fasting: http://www.bbc.co.uk/iplayer/episode/b01lxyzc/horizon-201220...

I've been experimenting with alternate-day fasting for a while now. I allow myself whatever I want for breakfast (usually cereal with fruit, or oatmeal) and then I eat _basically_ nothing until breakfast the next day. If I really want one, I'll eat a banana or a grapefruit after a run.

An interesting observation is that I have absolutely no problem exercising on fast days. In fact a 5m run feels great.

I am 5.8, 135 lbs. I'm convinced I can be lose another 10lbs if I cut down slightly, and keep running twice a week. Down to my college or high-school weight if I drop another 10 lbs.

It would reduce my cardiovascular risk, improve my running (easier on knees).

Am not a Muslim, but this month of Ramzan (or Ramadan) does inspire me to try some light fasting.

Nothing severe, no extremes for me. Happy with incremental, over a period of time, changes.

I'm wondering why you feel the need to lose 10 more lbs? It feels like an arbitrary number. Besides 135 lbs for someone who is 5.8 is a very healthy weight. You are exercising regularly which is great, so you are probably not likely to reduce cardiovascular risk much more, if that can even be quantified realistically at this point. Running is hard on your knees, period. If you want to go easier on your knees maybe take up biking or swimming.

I have done IF as part of a weight loss program (basically I save 90%+ of my allowed calories for a single daily meal).

I also went through more traditional programs, where calories are spread more evenly over different meals throughout the day.

In my experience both methods work very well, especially if paired with exercise, and I couldn't really see any difference in terms of health benefits.

Personally though, I found that the IF works better from a psychological standpoint, and I'm more likely to stick to it longer: the single meal I have tends to be much more satisfying and allows for appetizing foods and quantities that I could not afford if spreading the daily allowance on more meals.

I wonder if anyone has done a study of the health positive/negative effects of fasting on observant Copts and Ethiopian Orthodox Christians. Respectively their fasting days are approx. 220 and 250 days per year :-


https://en.wikipedia.org/wiki/Ethiopian_Orthodox_Tewahedo_Ch... and beliefs

July 2 marked 2 years straight only eating from 6pm-10pm with bullet-proof coffee sometimes during the day. I grew up always needing food and I can attest that my body adapted to eating this way and totally changed when I started eating this way in the sense of strength and lean muscle. Generally I eat pretty clean, lots vegetables meat beans and lentils, with a cheat day once per week, but always within my eating window.

I try to drink a lot of water during the day too. I am conscious that the water is reverse osmosis and then I'll add a pinch of celtic sea salt, some apple cider vinegar, and lemon. I also use active h2 tablets which I highly recommend.

Have you had the same work hours for 2 years straight? That seems somewhat uncommon, unless you've worked at the same place in the same position for that long.

My current schedule, I would be asleep for most of your eating window. In the past 6 years, my working schedule has rotated around the entire 24 hour clock - early morning shifts, midday shifts, swing shift, early overnight shift, late overnight shift. My eating rotates around with my work shift, eating a small meal before work, a small one during (whenever during the day or night the shift is, there's a "lunch" break almost in the exact center) and a large meal after work.

4.6 years was the average tenure of an employee in 2014. 2+ years straight is within the parameters of common.


I wonder if a 12-36 hour period is consistent with the frequency in which predators hunt. I can't imagine a lion eating every few hours. Anyone knowledgable on things like that?

My grandma has been doing IF (without knowing it's IF) for the last 50 years. She's 94 now and apart from her mind, she's in very good health for her age. I know it's completely anecdotal, but I do believe IF is part of her success.

Could you perhaps add more detail to this?

Did she drink? smoke? Was she a pescatarian? or her diet consist of lots of leafy greens? Lived in conditions closesly resembling a blue zone[1]?

Anything else besides the IF that was out of the ordinary in her regimen?

[1] Blue Zone


How did she unintentionally start IF? Just not eating breakfast or dinner I guess, but do you know if there was any particular reason she chose or was required to do that?


That study suggests (i think) that mice on the 24h fast developed insulin resistance in the liver, a sign of prediabetes.

Since I actually like the one-meal-a-day lifestyle, I wonder which study is more applicable to humans...

The biggest problem with these types of theories (e.g. Paleo diet, grazing, micro-eating etc.) is that there is no way to test against a placebo, for obvious reasons. So it is really impossible to completely test the theory scientifically.

> it is really impossible to completely test the theory scientifically.

This shows a misunderstanding of what science is about. You can set up control groups, that use different eating methods, but consuming the same amount of calories (and micro nutrients, etc.) over a given period of time. In some settings, double-blind experiments (with placebos) are indeed "better"; but it is not required to get scientifically valid results.

True, I may have over stated my point. A double blind with placebos test is the gold standard, and difficult to implement with humans when it comes to diets. Which is why I think there are so many different kinds of fad diets that come and go, which is sort of the point I was driving at. It is just really difficult to conclusively prove.

I think the main problem is that people are looking for some kind of silver bullet diet that will make them healthy and live long. So, since there's demand, there are other people providing them with it.

Of course it's just air, there's no such thing as a silver bullet diet. Health and longevity depends on so much more than just diet that there will never be such a thing.

But still, since there's money to be made by selling dummies miracle diets, there are some to sell. And since they can't sell the real thing because it can't be made, they do what they can to convince the customers that it is. Among other marketing tricks, pervert science so it looks like their snake oil is based on something more than just the will to make money from gullible people.

There might be some good science in the nutrition field. Sadly, it's drowned in a sea of wishful thinking, bad science and plain charlatanry...

That is not a problem with animal studies. The control groups typically eat however much they want, whereas the control group is starved.

i havent regulariy eaten breakfast since i was a child. glad to find out what i thought was a bad habit might have been a good one!


There might be something in it but nobody really knows because no one has studied it properly.

That's a very poor TL;DR. There have been many studies involving animal responses to fasting. There have been fewer human studies due to the difficulty of performing controled studies on humans but reading this report will give you an idea of where the data is lacking. Saying 'no one has studied it properly' comes across as a little unfair.

Fair point, maybe I was a little harsh. But I think people reading the headline just want to know if it works. Is there something to it? The answer is, come back in a few years and maybe we will have an answer.

Its the month of Ramadan, fasting for 30 days

An important difference for Ramadan is that it does not allow the consumption of water.

Same here. Half way through. 2 weeks left. Kinda sad it's going by so fast.

When is HN going to get a penalty filter for all these health fad/craze links? They just bring out all the crazies and the articles are typically inconclusive at best and opinionated and divisive at worst.

I agree with you man. For a site that's geared towards technology blogs there's a huge amount of health articles on here. Not only that, but like you said it attracts a lot of fervent personality types who portray a lot of the cult-like attitudes towards a certain diet or program (Keto is especially bad). Way too much speculation from programmers who think they're outsmarting an entire industry of health professionals.

I have a particular hatred for Soylent but thankfully its quick rise to popularity has drawn upon it a lot of scrutiny and with that has alleviated a lot of the bad that it was originally representing. I still think there are superior alternatives on the market that have pre-dated Soylent but the fact that its been iterated and improved by health professionals and not a Software Engineer says a lot for it.

I agree with you although this particular article seems far better than most.

Anecdotally (my personal experience, with zero statistical significance), the last 10 years seems like it had a huge explosion of interest in fad diets among twenty- and thirtysomething tech industry people. Not sure if this is an actual trend or just a consequence of where I live and who I spend time with these days.

I'm solidly middle-aged at this point. When I was in my 20s and 30s, there were just as many fad diets and nutritional voodoo but it was generally super credulous, spacey middle-aged and older people that were into them. The phenomenon of a degreed, professional 23-year-old wanting to have long and enthusiastic conversations with me about the properties of gluten (or whatever) in casual social contexts feels really bizarre.

This is a very roundabout way of saying that for whatever reason, at this point in time there is a big overlap between people who are into voodoo health crazes and the core HN demographic. This seems like a recent trend to me, but that's only anecdotal.

tl;dr ?


An increasing number of animal studies have shown altered markers for health in subjects exposed to intermittent fasting, i.e. regularly and repeatedly abstaining from eating during 12-36 hours per period. It has been hypothesized that the reported beneficial health effects from caloric restriction on excess body weight, cardiovascular risk factors, glucose metabolism, tumor physiology, neurodegenerative pathology and life span can be mimicked by alternating periods of short term fasting with periods of refeeding, without deliberately altering the total caloric intake. Therefore, a systematic review of available intervention studies on intermittent fasting and animal and human health was performed. In rodents, intermittent fasting exhibits beneficial effects including decreased body weight, improved cardiovascular health and glucose regulation, enhanced neuronal health, decreased cancer risk and increased life span – some of the effects independent of the effects attributed to calorie restriction alone. The human studies performed to date are generally of low-quality design. Beneficial effects such as weight loss, reduced risk for cardiovascular disease and improved insulin sensitivity have been observed, but conflicting data exists. The potential health promoting effects of intermittent fasting in humans and applicability to modern lifestyle are discussed. - See more at: http://www.lift-heavy.com/intermittent-fasting/#sthash.HPQDE...

I'm afraid I don't understand your question.

It is for you to decide whether it was too long, and whether you didn't read it because it was too long.

see 'Abstract'

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