Why Fast? Part Four – Brain Health

Pretty much every feature of the human body can be found, in some form or another, on other species. Opposable thumbs? Great for building and using tools, but apes have them, too. Even the giant panda has an opposable sesamoid bone that works like a thumb. Bipedalism? Helped us avoid direct mid-afternoon sun and carry objects while moving around the environment (among other possible benefits), but plenty of other creatures walk upright, like birds and Bigfoot. The human foot? Okay, our feet are quite unique, but every other -ped has feet (just different types), and they all work well for getting around. So, what is it that makes us so different from other animals (because it’s got to be something)?

What truly sets us apart from the rest of the animal kingdom is the human brain. Other animals may have brains big and complex enough to help them procure food, shelter, and water while processing and acting on basic sensorial inputs from the environment (“avoid obstacle” or “this smells like food” or “I am thirsty, where’s the water?”), but they do not share the human brain’s capacity for self-reflection and symbolic thought. It is the fleshy thinking mass of fatty furrows and gelatinous valleys sitting atop our spine that gave and gives us art, literature, architecture, agriculture, nuclear power, syntax, philosophy, advertising, society, this laptop on which I type this post, and the smart phone on which you read it. In short, our brains make us human. Without them, we wouldn’t be us.

I don’t know about you, but I enjoy being a human. I like contemplating my own existence, being entertained for hours by strange scribblings on layered sheets of dried and pressed wood pulp, and playing Ultimate Frisbee, and if I’m going to continue to enjoy those things, I need to protect my brain and keep it healthy. And if I want to enjoy myself on this planet and experience all it has to offer until I drop dead, I’m going to need as much brain function as possible (since, you know, the brain handles all that experimenting stuff) as I age. Luckily, fasting appears to offer three main protective and therapeutic benefits to the brain:

Fasting Boosts Neuronal Autophagy

I’ve cited this study before, but I’ll do it again because it’s central to the theme of today’s post: “short-term fasting induces profound neuronal autophagy.” Autophagy, or “self-eating,” is the process by which cells recycle waste material, downregulate wasteful processes, and repair themselves. Brain health is highly dependent on neuronal autophagy. In fact, a recent paper shows that deletion of an “essential autophagy gene” in the hypothalamic neurons of fetal mice resulted in metabolic derangement (more body fat, poor glucose tolerance) and impaired neuronal development. Another study shows that disruption of neuronal autophagy induces neurodegeneration. Simply put, without the process of autophagy, brains neither develop properly nor function the way they should.

Fasting Increases Levels of Brain-Derived Neurotrophic Factor (BDNF)

BDNF is a protein that interacts with neurons in the hippocampus, cortex, and basal forebrain (the parts of the brain that regulate memory, learning, and higher cognitive function – uniquely human stuff). It helps existing neurons survive while spurring the growth of new neurons (neurogenesis) and the development of synapses (lines of communication between neurons). Low levels of BDNF are linked to Alzheimer’s, and supplementary BDNF prevents neuronal death, memory loss, and cognitive impairment in an animal model of Alzheimer’s disease.

Fasting Increases Production of Ketones

Ketone bodies like hydroxybutyrate are famously neuroprotective, and fasting often induces ketosis.

Increased autophagy and BDNF and ketones from fasting sounds awesome, but do they manifest as actual benefits to neurological health? Let’s see what the research says.

No discussion of fasting and neurological health research is complete (or can even be initiated) without including Mark Mattson. Mattson, chief neuroscientist at the National Institute on Aging, has been releasing paper after paper on the neurological effects of intermittent fasting for the past dozen years, and he’s amassed an impressive body of work that suggests IF can induce neurogenesis and protect against brain injury and disease. In the following sections, I’ll discuss the evidence – from Mattson and other researchers – for the beneficial effects of fasting on neurological health across a spectrum of conditions.


The most common type of strokes are ischemic strokes (composing about 88% of all strokes) – cerebrovascular events in which a blood vessel that supplies blood to the brain is blocked by a clot. Without blood, the brain can’t get oxygen or nutrients, and (often permanent) brain damage can occur. In an animal model of ischemic stroke, fasting upregulated BDNF and other neuroprotective proteins, reduced mortality and inflammation, and increased cognitive health and function. However, it’s worth noting that fasting was most effective against stroke in young animals, who enjoyed a four-fold increase in neuroprotective and neurogenerative BDNF. Middle aged mice saw a two-fold increase in BDNF, while older mice saw no increase. Post-stroke cognitive function had a similar relationship to age and feeding status; young and middle-aged fasted mice retained far more than old mice and fed mice. Fasted mice displayed lower levels of inflammatory cytokines, but this effect was also modulated by age. Overall, fasting increased neuroprotective proteins and decreased inflammatory cytokines in young and middle-aged mice, thereby reducing the brain damage incurred by stroke.

Brain Trauma

Research indicates that fasting is also effective against physical trauma to the brain. It’s not that fasting somehow physically repels impending trauma by generating a magical ketone-powered force field; it’s that fasting reduces the oxidative stress, mitochondrial dysfunction, and cognitive decline that normally result from brain trauma. Employing one of these contraptions, researchers induced a “controlled cortical impact” on fasting rats and found that a 24-hour fast (but not a 48-hour fast) was neuroprotective. Perhaps the reduced appetite that commonly accompanies a concussion is a protective mechanism rather than an annoying side effect?

Cervical Spine Injury

“Every other day” fasting was neuroprotective following an injury to a rat’s cervical spine. Despite extensive trauma, fasted rats improved gait pattern, vertical exploration, and forelimb function (all heavily dependent on brain function). Neuronal integrity was preserved, cortical lesion volume was reduced, and corticospinal axon (nerve fiber) sprouting increased. The same team performed a similar study on mice suffering from a spinal cord injury, but had very different results; every other day fasting failed to confer any neuroprotective or functional benefits to the injured mice whatsoever. How can we reconcile these apparently contradictory findings? Well, in the rats who experienced neuroprotection, fasting increased ketone production by 2 or 3 fold. The fasting mice never reached ketosis. Ketosis was key.

Alzheimer’s disease.

In a mouse model of Alzheimer’s disease, both intermittent fasting and 40% (!) calorie restriction conferred cognitive and behavioral benefits when compared to mice on the control diet. IF and CR mice showed higher levels of exploratory behavior, and, when placed in a Morris water maze, found the escape platform sooner than the control mice. However, only IF mice showed evidence of protection against synaptic pathology – a hallmark of the disease.

Huntington’s disease.

Huntington’s disease is also characterized by a depletion in BDNF levels. In a rat model of the disease, intermittent fasting normalized BDNF levels, while regular feeding kept them low. Fasting rats lived longer and even enjoyed better glucose tolerance than ad libitum fed rats. By all accounts, fasting slowed progression of Huntington’s disease.

Age-Related Cognitive Decline

We’ve all had a grandmother who called us by our sibling’s name, or a grandpa who forgot to unwrap the Werther’s Original before popping it into his mouth – these are the innocent, simple, quaint, seemingly unavoidable declines in cognition that accompany the aging process. Well, maybe they aren’t unavoidable. Although most of the research focuses on neurological trauma and disease, there’s evidence that intermittent fasting is good for basic age-related cognitive decline. I find it interesting that this was “late-onset” intermittent fasting, meaning elderly rats who began fasting only after showing signs of decline still wrought cognitive benefits. Contrast that with the stroke study in which older rodents saw almost no benefit from fasting and a picture emerges: as long as they’re not trying to counter a debilitating event, like ischemic stroke or trauma, older brains can also expect to benefit from fasting.


Depression has long been associated with lower BDNF levels as a prognostic of the disease, but it’s only recently that researchers are entertaining the possibility that low BDNF and depression could be causally related. And indeed – antidepressants actually increase BDNF signaling and synthesis in the hippocampus (the part of the brain where depression “happens”). Could fasting help with depression via upregulation of BDNF and promotion of neurogenesis? Perhaps. I’d say it’s worth a shot, especially since skipping a few meals doesn’t require a prescription.

Obviously, since these are mostly rodent studies, and hard-and-fast peer-reviewed evidence of the neuroprotective and neurogenerative effects of fasting in humans doesn’t exist yet, we’re only speculating. But I’d argue they are plausible speculations worth pursuing. The mechanisms are there. Speculations about IF’s other health effects – to general health and cancer and longevity and fat loss – are being borne out by human research. Both the risk and barrier to entry are low. And it makes sense in light of our evolutionary history as hunter-gatherers. In a recent interview, Mattson even couches the neuroprotective effects of fasting in evolutionary terms, noting that during pre-agricultural times of scarcity, people “whose brains responded best – who remembered where promising sources could be found or recalled how to avoid predators — would have been the ones who got the food” and lived to pass on their genes.

As I age, the risk of my uniquely human brain going screwy and sabotaging my selfish desires to remain cognizant and engaged with life until the very end increases. It is not a foregone conclusion – I know too many quick-witted, sharp-tongued folks thirty years my senior – but the chances do increase. Since I don’t want that to happen, and the occasional fast is a nearly risk-free endeavor with proven benefits in other areas, I’ll continue to miss a few meals every now and then. It hasn’t hurt me yet, it just might be one of the factors that allows me to live long and drop dead, and hey, since I’m fat-adapted it’s not even a struggle to do it.

What say you, readers? Do the potential neuroprotective effects of fasting interest you? Why, or why not?

Thanks for reading.

Here’s the entire series for easy reference:

Why Fast? Part One – Weight Loss

Why Fast? Part Two – Cancer

Why Fast? Part Three – Longevity

Why Fast? Part Four – Brain Health

Why Fast? Part Five – Exercise

Why Fast? Part Six – Choosing a Method

Why Fast? Part Seven – Q&A

Dear Mark: Women and Intermittent Fasting

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

If you'd like to add an avatar to all of your comments click here!

152 thoughts on “Why Fast? Part Four – Brain Health”

Leave a Reply

Your email address will not be published. Required fields are marked *

  1. Sure, they interest me a lot. Based on your beating of the fasting drum lately, I tried my first fast last week and loved it. Easier than expected, and the surprise benefit is that it’s helped to reset my appetite — I used to gorge, and feel hungry if I didn’t, but that may have been more a conditioned response than a true hunger, b/c it was making me a little soft and I really didn’t need that much food. I’m eating less now after the fast, and feel fine. Thanks, Mark.

    1. Contrary to intuition, appetite will decrease during fasting because epinephrine is released to burn fat. Just like caffeine and ephedrine cause an increase in epinephrine, aka adrenaline, and a decrease in appetite, fasting also causes epinephrine to release, which is partly why you’ll see a decrease appetite.

      You’ll also see a rise in norepinephrine, which you won’t see with necessarily see with caffeine, and this will keep you calm and focused.

      1. You may want to read up on the sympathetic NS response. While I would agree with your statement about catecholamines and appetite suppression, the sympathetic response (epi/norepi) does the opposite of keeping you calm…thus it is considered the “fight or flight” response. Also, caffeine does increase norepi. One of the reasons we give patients beta-blockers to keep them calm during stressful events (public speaking, performances, etc.) The same class of drugs (which inhibit norepi/epi effects) are also used to “calm” the heart, controlling hypertension. The biggest major difference between epi and norepi (there are some small receptor affinity differences) is the chief location of production and action. Epi is produced primarily in the adrenal medulla and control many systemic functions. Norepi has a larger role in the central nervous system. While norepi may be comparatively less stimulating in some circumstances, it is hardly calming. In fact, cocaine works by increasing norepi concentration in synapses. I have never heard anyone say “I need to go bump a line and calm down.” LOL

        1. There are varying potentials of sympathetic response. A certain amount of either of those transmitters can lead to an increase in alertness without invoking something like a panic response and have one feeling “calm and focused”, but too much will be very much like a panic attack.

    2. i have the rarest of the neuroendocrine cancers, somatostatinoma, and have outlived all of the experts’ prognosis for me with, of course, refusal to consider chemo; am post whipple & liver resection; have been following the data on fasting and cancer cell ‘suicide’ first published in 1986 & now replicated by valter longo; however, i found that either the fasting or oz’s green drink caused an electrolyte crisis never experiened in my life that left me in tetany with huge purpura and horrific back muscle spasms, near death; my md’s whom i rarely listen to, since they are all so limited, were in total denial as to what was happening; do you think mark, that it is the fasting? did on one day, off the next, or was it oz’s drink?

    3. THat is very true, I am using IF since two weeks, I was very suprised the benefits of it and I am not talking about losing weight cos for this I used 1000 kcalories diet and los over 40 kilos, but it was terrible experience to me, if I know about IF earlier probably I don`t have to go thru this terrible diet …

      THe worst for me was first fasting day, but the strange feeling at the morning next day – I feelt no hunger, it is amazing, my hunger was lowered a lot, it seems like somoething lowered the greline emmision, I never felt that way before, before my hunger was huge, not after two weeks I don`t feel that anymore, fasting days are very easy to me to go thru. ANd the most important for me was – focus and memory improvement, it is really amazing how it works, it seems our organism needs fasting to make necessary repairs.

  2. I’m loving this tribute to fasting. I am a faster myself and have had great success with it. I just wish more people knew the benefits, or were willing to look into it before they pass such harsh judgement!

    1. No, fasting is absolute torture and just plain BULLSHIT! There are no peer-reviewed scientific studies supporting fasting. It is common sense that fasting makes people feel weak, that it is downright irrational if you work at a job requiring physical and/or mental stamina like construction work or work in a restaurant, and it makes people (at least poorer/third world types) more vulnerable to infectious diseases. Mark Sisson and his cavemen crew have blood on their hands and should all be thrown in jail for advocating child abuse.

      1. Thanks for your input Jeremy. Could you direct me to the peer reviewed studies that support your comments? I also believe in fact checking and I must have missed the studies supporting the opinions you’ve cited. Thanks in advance!

      2. Very interesting take on this subject Jeremy ….

        Point of interest:
        I’ve been fasting for 12 months now …. I am an avid adventure racer, kayak, run, swim, mountain bike, road cycle. I alsohave a weight trainn regime which sometimes takes place pre and post fasting. I train in a fasted state twice a week, have dropped over 10% body fat. I have never (or very seldom) felt weak or incapable of performing exercise of my daily work/life routine ….
        I guess that fasting doesn’t work for you, but maybe calling it BS might be a little strong, and as for the rest of your comments, well I think we’ll just ignore them (:-)

      3. Well, while you’re at it… why not throw the whole processed food industry in jail!! After all, that is the main contributor to obesity and diabetes nowdays! Adding unnecessary HFCS, GMOs, sodium, etc… is no different than tobacco companies adding 600 addictive chemicals to their products in order to make extra $$$. I have fasted and continued to lift weights intensly 3x/wk, with more energy than I had when I used live off a high carb diet. I managed to drop from 230lbs of flab to a lean 180lbs. I’ll also add that it has been years since I last caught a common cold after changing my high carb diet to a low carb one with fasting (approx 6yrs ago). The only thing I consume when fasting is a multi-vitamin and water. I suspect that the people having issues with fasting are those on the high carb processed junk food diet, which is understandable. Not everyone responds the same to dietary changes, but don’t rule this one out (IMO).

      4. Jeremy, I agree with most of your post. I too have done extensive research on IF, and also found NO PEER REVIEWED STUDIES ON HUMANS.

        Yet, I think IF can be a good tool, occasionally. When utilized for the right reasons.

        Lastly, I fully agree, for those who have a physically active occupation, it’s foolhardy to fast. Put another way, only an idiot would couple strenuous work with fasting. A bigger fool or idiot would be the person who weight trains in a severe calorie deprived state, i.e. IF.

        On another note, don’t be morons. DO the f****** research yourselves.

      5. Intermittent fasting might not be that bad. However i fasted for 3 days one time and by the third day i felt weak and had more difficulty sleeping.

  3. Interesting.
    However, studies don’t do it for me. I cannot reach conclusions based on studies.
    Experiments with fasting (on myself 😀 ) have showed me that fasting is great for variety.
    You fuel your body with oxygen, water, and sun.
    I feel smarter, more alert, vibrant when food is in my belly. 🙂

  4. So on this fasting thing… I decided to start! My plan is to fast from dinner on Tuesday to dinner on Wednesday…. Not quite 24 hours, but close. My question are… is this enough time? Should I work out that day (I crossfit)? I am 49 – was doing well with the diet (paleo) and exercise till a couple of major life changing incidents occurred and I gained close to 30 pounds. Now I need to get it off! Sooner than later 🙂
    So, back to the paleo – and maybe IF to help boast the fat loss…

    1. That time is enough for a start. And no, don’t exercise on a fasting day. Just do some walking or other low intensity stuff. Take it slow first, else you will fail and get discouraged. Easy does it. Good luck.

      1. Actually exercise some time before you eat helps move things along. Take a look at this study to read more about this…

        Training in the fasted state improves glucose tolerance during fat-rich diet.

    2. For most people, it’s after the 24 hr mark that you will start to be in danger of losing muscle; just under 24 hrs is great, don’t go beyond that.

      Some people like training fasted, others don’t. You could try both ways. If you train fasted, probably eat big soon after, especially protein (recovery’s where you make your gains).

      1. Actually, studies show muscle loss doesn’t begin until about 72 hours without food. – Webber J, Macdonald IA, The cardiovascular, metabolic and hormonal changes accompanying acute starvation in men and women. British journal of nutrition 1994; 71:437-447.

    3. Once you get comfortable with fasting, you can workout a few hours before breaking the fast. I have written two articles on my website, on how fasting and working out can reverse aging by increase autophagy and telomerase avtivity. Check them out!

  5. IF makes me feel light, alert, and powerful. Better than any upper, downer, food, or med could ever make me feel. Thanks for showing me the way, Mark!

  6. My great grandfather fasted one day a week for religious reasons. he was a dairy farmer and ate mostly meat and raw fatty milk. He lived to the age of 106. He never wore glasses, went to doctors or to dentists. Imagine how healthy he could have been if he had added twinkies to his diet!

    1. I am intrigued by the idea of a spiritual connection to the fast. It would be interesting to look into the various religious fasting traditions around the world and see how they were adaptive for the cultures in which they were practiced.

    2. Wow, that’s awesome! I wonder if the fasting really contributed to his longevity. Some people are just genetically programmed to live longer!

    3. Longevity is mostly controlled by our DNA. Your Grandpapy lived that long thanks to his parents. Diet does play a part, but it takes a backseat to our genes.

      Whole, raw, grass feed “fatty milk”, is an awesome source of Omega 7’s. A type of fat most people are lacking.

  7. I’ve only done partial fasting so far (dinner until lunch the next day) but I have to say I like the results. I’ve only been doing Primal for a few months so it’s hard to know whether it’s the change over to Primal eating or the fasting, but I definitely don’t get the brain fog I used to suffer from.

    I find my thinking is a lot clearer and my creativity is back to the way it was when I was much younger – but now I have the added benefit of experience (and I can remember it!). Aging with a well functioning brain is definitely a plus.

    As you say it’s easy, doesn’t cost anything, and seems to have more pros than cons so I think it’s worth making part of the Primal lifestyle.

  8. What time frame are we talking about for fasting? Are we talking about eating dinner at, say, 8 o’clock and then not eating again until noon the next day? Would this classify as a “short-term fast”?

    1. Yes. Check out leangains.com for more about this method. I am doing this right now and am very happy with the results.

      1. I guess I do this naturally. I rarely eat breakfast because I’m never hungry. Usually have my first meal at noon.

      2. But I’m wondering if I should also do a day long fast every once in a while, or is the everyday fast sufficient.

    2. Personally I don’t think it matters too much, I do it whenever I don’t feel like eating, and usually carry that on for between 14-48 hours. Just listen to your body.

  9. Be very careful when talking about “antidepressants.” There are a wide range of drugs that do dramatically different things under the umbrella of antidepressants and I get really annoyed when bloggers and journalists make no effort to draw any distinctions.

  10. Personally i started to IF without knowing that such a term existed. I generally eat my first meal between midday and 1pm and last (3rd) meal between 8pm and 9pm. I’m type 1 diabetic so it makes sense to consume calories within a set time frame and then for 16 hours have (hopefully) steady regulated blood glucose. You can learn more about IF here, w w w .leangains. c o m

  11. Based on this series, I have started generally fasting in the morning until I am hungry, which is usually around noon. It’s OK – not too uncomfortable. I feel a bit clearer and healthier but you still won’t see me beating my chest and swinging from trees about it.

    Days when I wake up hungry, I have some protein, usually bacon and eggs, when I get up. Then I might have a light salad for lunch, or a few nuts and a bit of cheese.

    Forum name Hedonist2

  12. Great info!
    I remember reading not long ago that Alzheimer’s was related to high sugar intake, sort of like diabetes of the brain. Can’t remember the reference though. 🙁

  13. I’ve been doing a little self-experimentation for the past three weeks. I cut out all processed sugar, though I still eat bread and rice a few times a week, as well as some legumes. I try to eat stuff that’s fresh with minimal ingredients if possible. I eat a lot of veggies. And most days I end up stopping food consumption around 5 or 6 p.m. (earlier sometimes) and eating around 9 or 10 a.m. So… inadvertently I guess I’ve been intermittent fasting with something like 15-16 hour fasting period nearly every day.

    I’ve lost almost 6 pounds in three weeks after having been suck at the same weight for months. I’ve gone from 165/6 to 159.8… I haven’t been below 160 since September 2011. I don’t count calories. I’m no longer obsessed with health and stuff. I sleep better. I drink tons of water. I do HIIT cardio and rock climbing and strength training, but not too much. I walk a lot. I feel fantastic. I don’t think I’m honestly going to give up bread completely – the fresh naan at this local Indian place is just too awesome – though I’m currently working on cutting down to twice or three times a week.

    Some of my early investigation into fasting and ditching processed food came from MDA – keep it up! I can’t wait to check back in in a few months.

    1. Do yourself a favor and cut out gluten entirely for at least 30 days! If you don’t notice an improvement you can always go back.

      I suspect that would change your mind about eating bread. I know we all need to walk our own path but I certainly don’t regret cutting my jalapeño bread habit out of my diet.

      1. I’ve been 99% paleo for three weeks now, and lost 13 pounds. I’m 6-1 and went from 203 to 190. The only exercise I did was golfing and went for a few long walks.

        Before that I was trying to be semi-paleo with food, but working out according to the Primal Blueprint. I was stagnant. You have to cut the carbs out completely if you want to lose a substantial amount of weight.

        1. Pretty cool! Congrats on the loss! I think different strokes work for different folks, and what I’m doing is working for me, though I borrow a lot from primal ideology.

          I have several sets of month-long, habit-changing goals. This month its to not have processed sugar, not consume alcohol (though I rarely did anyway), as well as not eat after dinner. I’ve only eaten after dinner once, and it was something like two tater tots. Minimizing bread/gluten/grain consumption is next on my list! 🙂

      2. Thanks for your input! I actually will be cutting out gluten for the next week… thank you, passover! So we’ll see how that feels. I’m sure it will help things.

        I don’t think I’ll ever permanently be rid of bread, and I do plan on having ice cream once or twice this summer on special occasions… good ol’ 80/20 rule! But yeah. I know I don’t need it, but at this stage I’m just making very slow habit changes that I know I’ll really hold onto. Give it time and I’m sure I’ll be eating much less in the way of grains… 🙂

      3. Why??

        Unless you have celiacs disease, eating zero gluten will do nothing for you. Your body has adapted to effectively and efficiently process the glutinous found in MOST grains. Saying otherwise displays a severe lack of biochemistry knowledge.

    2. I know how you feel about bread because I never figured I would EVER give it up, but I have. The trick for me was finding a substitute. I made nut bread and had that for the first month. Probably more than recommended ideally, but it was a good way to transition and now I realize it was an addiction. I have nut bread a few times a week instead and it works great. I have some good recipes if you want to try them. https://www.eatlivegrowpaleo.com/2012/03/yes-you-can-eat-bread-and-still-stay.html.

      1. Oh cool! Thank you! Luckily passover is sort of forcing me to cut out bread for a week. I have one piece of matzah per day or less. I just need to replace it with something else. The recipes look awesome!

  14. Mark,

    I am extremely interested in the benefits of fasting, however I am in a bit of a dilemma. I am what you would call a “hard gainer” I am attempting to gain lean muscle mass and weight. I have added 5X5 and 5X3 heavy lifting into my workout routine (alnog with CrossFit) and have begun using protein supplements. While fasting intrigues me, amd want to implement it into my routine, I am worried it will set me back with regard to my strength/weight goals.

    Any thoughts would be greatly appreciated from all!

    1. Intermittent fasting and gaining muscle don’t go well together at all. Your best bet is to gain as much muscle as want first. Then, once you’re satisfied, you can incorporate fasting.

    2. IF and lean muscle gaining is doable for those of us aiming for six pack abs, but you simply don’t need to fast, if you’ve got them already. I’d say what you need is to exercise correctly. Check out leangains.com for the reversed pyramid method and others, if interested in muscle gain.

    3. Lol, that is a fallacy. There is no such thing as a hardgainer.

      You are probably not eating enough food. particular Protein and Carbs. Up your calories, carbs and protein. Get on the see food diet. If you see it, eat it. Also, don’t be afraid of dairy products or grains.

  15. Absolutely. I fast for 14-16 hours each day. My mental clarity is through the roof. I am awake, productive, and just generally free to enjoy life more.

  16. If you’re going to cover this in a future post then feel free to ignore my question. However, I was wondering about who SHOULDN’T fast? I’m a big believer in IF but, as my wife and I are planning kids so, I was wondering what your thoughts were about potential harmful sideeffects of IF.

    Should pregnant mothers do it?
    Should kids do it?
    Should seniors do it?
    Under what circumstances would you recommend that someone not fast?

    1. i dont see why a preggers gal, a small fella or even an elder shouldnt do it. I understand you should eat plenty of nutrients and protein innthe 8h window and let your body focus on metabolizing everything 16h, or maybe at least 1 day a week, but the only reason someone should not do it is if they need to stop it to have enough nutrients, which should be calculated not for thirds of days, but for whole weeks. If i can think of someone who should not, at all, do it, are babies, lactating babies, who should have free tit access.

    2. We have 2 kids, ages 2 and 5. I find they naturally fast. When they are not hungry, they simply won’t eat. (Even if it is something they enjoy, they will only eat a small amount or sometimes leave it entirely.)

      1. I totally agree with this. I don’t think you should impose a planned fast on a child. I do think you should help them learn to respect and respond to their inner hunger signals by not urging them to eat anyway if they’re not hungry.

        1. My fiancee has a four year-old daughter who won’t even TOUCH food some days. My fiancee and her mom freak out about it, trying to get her to eat, while I idly sit by and roll my eyes. I’ve tried to explain she’s probably just not hungry (they don’t often succeed in getting her to eat until she IS hungry anyhow). They’re also skeptical of this fasting thing and I’ve tried to point at this behavior as an example of how natural fasting really is. They haven’t bought in yet, but we’ll see.

    3. I guess I was fasting when I was pregnant because I was nauseous or throwing up for about 3 months. Babies turned out fine. Good birth weight, healthy and smart.

  17. I recently started the daily 16/8 IF system of leangains, so far it definitely feels good. Easily doable on a daily basis.

  18. Mark, I read your posts every day. About a year ago a co-worker and I would do a “fasting Thursday”. I was trying to lose weight and it helped. I was already almost at my goal weight when we started so after 2 months I stopped fasting. I kind of missed fasting because when I was fasting I didn’t seem to get as hungry that day and I felt freedom from having to decide what to eat and what not to eat. Since reading your first in this series on fasting and following the links you provide to your sources I have begun a 20/4 intermittent fast. It hasn’t caused me to lose any weight, which is fine by me as I don’t want to. I am a little leaner though. It has helped reduce some of the sugar cravings that show up now and then. It is surprising that I don’t get shaky after hard exercise while fasting. If I didn’t eat something while bike riding when i was overweight I used to get the shakes and sometimes headaches. I’m looking forward to all the cognitive and mood benefits to come.

    I sure enjoy your daily apple site.

  19. Hmm, I never thought of IF that way. I do write better when i’m fasting, though. MY father inlaw has some age-related memory issues, i’m getting him to read Paleo Solution right now, and then Primal Blueprint, if i can find a copy around here >_<
    I'll talk to him about fasting later. My mother inlaw would throw a FIT if she knew about that, lol

  20. Certainly seems to be helping me. I have been IF’in for the last 10 weeks. During the work week I only eat one meal a day for dinner.

    1. I know this is an old reply on an old thread, but I feel the need to interject here nonetheless. Be very careful about behaviours like this. I dropped to one meal mon-fri 18 months ago. I got used to it and my appetite soon diminished. Hunger didn’t bother me anymore and I loved the weight loss I was achieving and the sense of achievement I got from being in control of my eating habits and hunger management. I began avoiding dinner whenever I could and eating less on the weekends. My dinners tended to be very low in dairy and I became lactose intolerant. I started presenting symptoms of nutrient deficiencies, too, but I didn’t see my doctor. I didn’t tell anybody that I was fasting. If, for any reason, I ended up eating breakfast or lunch during the week I felt guilty and like I had failed. These meals, as well as any others that I considered too large or unhealthy, made me feel ashamed and petrified of what damage they were doing to my body. I begun throwing up these meals.
      This is an eating disorder.

      Clearly over the course of this last year and a half my brain function has not improved. My concentration has been impaired and I have become depressed, which comes with its own neurological problems. I wasted a lot of time unable to think of anything but food, and I was sick and unable to work or study within a year of taking up my dangerous eating habits.

      Please just be very careful with any fasting or restricting behaviours. It’s a slippery slope.

  21. Great article! Neurology is one of my part time hobbies… always nice to read about. So I must wonder, which came first? Being smart and going primal, or going primal and being smart? I wonder…

  22. I find it interesting that one of the most promising new treatments for depression are drugs that block the action of glutamates (another reason to avoid MSG). But I read some reports that BDNF stimulates the production of glutamates. On surface, those two things seem to contradict each other.

    Could it be the balance of BDNF and glutamates that’s the key? What’s the effect of fasting on glutamate levels in the brain?

    Dang that humanities degree! Any scientists out there that can make sense of this?

  23. I wonder if the same benefits could be obtained by going into ketosis through carb restriction rather than fasting. Ketogenic diets are increasingly used for neurological disorders.

      1. I eat a ketogenic diet (40-70g carbs/day) and I do the leangains version of IF (16/8). So far, my appetite has adapted, but I’m hungrier at mealtimes, I still eat the same amount of food daily, and I haven’t noticed any other benefits (clearer thinking, more energy, more creativity, ability to work out harder). Of course, in evolutionary terms, I’m old (50), so I probably shouldn’t expect significant improvements in these areas.

    1. That’s only one benefit of not eating. I’m all for restricting carbs, esp. wheat and sugar, but there are other effects of fasting:

      > gives digestive system a rest
      > improves insulin sensitivity
      > reduces bodywide inflammation

    2. This is a very relevant question. I’m not so familiar with the studies presented but: In all studies showing benefits of fasting, was fasting compared to high-carb diet or a carb restricted diet?

      It might not be the fasting but the carb restriction that gives positive effects? Or?

  24. It’s definitely something to try. I started intermittent (mostly alternate day) partial fasting last week, and I plan to keep it up at least a couple of months to see what effects it has. On the partial-fasting days, I’m doing 500 to 600 calories, including about 100 calories of MCT oil first thing in the morning.

  25. I would be interested in doing it merely because it is a part of the Primal Diet! My roommate has both your books and I have been a fan of your site for some time now, and I will be happy to get into this!

    Foe one, I have fallen off the Primal wagon, or wheel, if you will; for another, I’m not even 40 and I notice memory loss and it bothers me to no end!

    Time to skip a lunch or dinner!

    (I’m also a scientist, so having links to science articles…gotta give you props for that Mark!)

  26. Fasting just seems to go against nature. Nature wants the strongest to survive and the strongest would be the ones that can get the food. And if I can get food all the time, then you’d think nature would reward me by keeping my body and mind at their fittest.

    Aren’t there studies that show that having sex is healthy? It makes sense, those that have sex must have the more desirable traits that can help the human species survive.

    Fasting seems to be counter-intuitive.

    1. I disagree. It would be the ones that best survived when there was no food that would be passing on genes.

    2. I’m unfamiliar with the rest of this web site. I found this page by googling for Fasting and Brain Health.

      I started fasting after seeing the show on PBS, “Eat, Fast and Live Longer with Michael Mosley”. Michael Mosley is an English physician. The fast he described is a two days a week fast allowing 600 calories a day on the fasting days.

      His blood chemistry was checked before he began the regimen and later after several weeks of fasting. Checked on a non-fasting day, his glucose and triglycerides moved from borderline pre-diabetic to about half of the original values.

      The fact stated in this TV show that convinced me to fast was that cells operate in two modes, growth and repair and that by fasting, cells go into repair mode. As a cancer survivor, I want repair mode to kick in and I want less growth, cancer being unregulated growth.

      Eric’s comment about fasting being counter-intuitive neglects the need cells have for repair. If I had fasted perhaps a mutated gene wouldn’t have caused the cancer I had.

      1. MayI ask if you are still fasting and whether you found the Mosley’s program effective? My health concerns are not the same as yours, but I’m curious whether people are able to stick to the regimen in the long-term.

  27. This is great news for people who don’t like to eat fish. ‘No food’ is the ultimate ‘brain food’, perhaps??

    Great post, Mark! Make’s me feel good about skipping breakfast and eating a late lunch today.

  28. This is interesting. I was just talking to my brother about his fasting, which isn’t IF’ing, but pretty close to it. I’ve noticed that if I do IF, my focus tends to grow stronger. I wonder how helpful IF would have been when I was younger and sustained several head injuries due to bike accidents and no helmet.

  29. This does interest me. Do you have any info on the impact fasting could potentially have with multiple sclerosis? My husband has MS, which is why I ask.
    Thank you.

    1. alana have you seen the video about the woman who ate herself out of her wheelchair? She’s a doctor or a research scientist or something? She has talk on ted.com I think called Minding your mitochondria… or something similar. It was amazing…

  30. Any thoughts about chewing gum during fasting? I have been doing 20-24 hour fasts, usually twice per week. Great results, weight loss, ton of energy for workouts, not overeating afterwards. I just have water and maybe a cup of green tea, but I’ve noticed that i have a piece or two of sugarless gum during the fast. Any thoughts on this? What if its xylitol gum instead of whatever is in regular sugarless gum?

    1. Maybe six months ago I read a book titled “Eat Stop Eat” by Brad Pilon. His approach was you could put practically anything in your body as long as it had no calories — even diet soda! — and you would still get the benefits of intermittent fasting.

      Artificially sweetened gum would certainly be valid under his system. Assuming gum sweetened with xylitol has on the order of 3-5 calories per stick, it would not counteract the benefits of fasting to any significant degree, in my amateur opinion.

      I do one 24 hour IF a week. I am not a total purist on the matter, adding a tablespoon of cream to my morning coffee and eating several naturally fermented pickles at about 5 calories per pop during the day as well. Regarding the later, I figure augmenting my digestive bacteria is worth the few calories.

    2. Drinking diet soda on a fast doesn’t work for me. When I first started IF, seeing how diet soda made me hungry and broke my willpower (and thus the fast) both made me stop drinking soda during a fast, and gave me good motivation to stop drinking it entirely (since this proved to me it’s not doing “nothing”).

      Though, the golden rule here: try it and see if it works for you. 🙂

  31. This is all very interesting information to ponder while considering starting to fast. I do believe it’s only natural that our bodies can fast. I have done it when I was younger and I can see the many benefits to doing it now in my thirties. Just need to try and work it in around my crossfit routines rather than during which has been the struggle to attempt a fasting day. Here’s to hopefully soon!

  32. Skipping a meal isn’t fasting…to me anyways.

    Fasting to me is when you go 24 hours without food…minimum.

    Skipping a meal might seem like fasting to all you new-comers…because your body hasn’t yet switched completely or you’re still lacking some serious nutrition, which needs to be fulfilled first, before even considering to fast.
    Be primal for like 2 years minimum and real fasting happens automatically.

  33. Has anyone tried a juice fast ala Fat Sick and Nearly Dead? I think Joe Cross has a few options for juice fasting on his Reboot for Life website.

  34. it seems funny and somewhat ironic to me that were all looking for the best diet to allow our bodies to function optimally and it turns out that the most potent good we can do for our body is not eat anything (obviously for a period of time and not indefinitely lol)

    1. great series by the way Mark, truly some of my favorite from the blog. thanks for bringing all this information and research to our fingertips.

    2. Glad I’m not the only one who found this hilarious. Sucks, because I was one of those obsessive people for about 2 years before discovering the light.

    3. Yeah its so amazing!!! I begun today, its midday and stil alive!! Lol

  35. I use to eat breakfast every morning and if I didn’t I felt bad until I ate lunch, then dinner with snacks in between. I’d eat and ask, “What’s next for lunch/dinner/whatever was next. When I started going Primal I started fasting a couple weeks in. First two fasts weren’t the best but I kept going. After several months of going primal and after fasting once a week I don’t remember the last time I actually felt like breakfast. Sometimes I do, but now when I wake up I don’t immediately start thinking about food. I eat less too, which is a shocker because up until my first fast I could eat a ton. It’s like my stomach shrank. Only time I ever think about “needing” to eat an extra meal is when I don’t get alot of protein in. I think that’s the only real reason i eat three times a day on some days. Butter and coconut oil for fat is the best…

  36. So I get the reasons to do this, but I want to know how long to fast… One meal, two meals, two days? And does eating less instead of a fast or having a lite snack in the middle of one cancel out what you’d be trying to achieve? Ex.- handful of spinach and an orange over the course of a whole day of fasting.

    1. not tryin to be a dick but i don’t get all these questions about whats acceptable to eat during a fast… the whole idea of fasting is based on the concept that you are not going to be ingesting anything for a period of time (usually from 16 hours on to answer your question)… is it really that difficult to understand or am i just really smart?

  37. Fasting is natural; food wouldn’t always have been available. Fasting is often difficult for people who eat a lot of carbs and far easier for those who don’t. Eating food when it’s available is natural, too, though, and I find that when I conciously decide to fast, I think about food more and usually fail to fast for very long. Unplanned fasts work best for me…when I just don’t feel hungry or am too busy doing something fun or doing something strenuous in hot weather. That’s when I fast. A lot of times for me, it’s just not eating until mid afternoon and this happens much more often on non workdays (less brain power being used on days off/lower energy needs?) I like knowing I am not doing any damage with fasting and am in fact boosting my health. Ah all that bs about how bad it is to skip meals, especially breakfast! I NEVER wanted food early and how my super-sensitive to grains belly ached when forced to eat “at least some toast” early in the morning as a child!

  38. I really like fasting. One thing I have done recently is drink a bit of kefir partway through a 24-hour fast – I’m talking like 1/2 cup at most. This gives the probiotics a chance to act optimally. I know it’s not technically fasting because I have “eaten” something but it seems beneficial to me. My skin and mood and general health seems to really benefit.

    1. Whole Foods now sells a coconut water based kefir if you wanted to try something less “foody” but still get live probiotic. You only drink a tablespoon of it at a time so it’s pretty negligible.

  39. Hi Mark,

    I was wondering whether it makes any sense that the body would cannibalize muscle mass on a prolonged fast if you were using your muscles still, say, still lifting heavy things? I mean, surely if your body thought you needed the muscle it wouldn’t gobble it up? I’ve read a lot of things online and this still seems to be a worry for people. It doesn’t make sense to me that the body would use muscle when there is still fat to use up; is this not the entire point of our ability to store fat anyway?!

    1. You body would start converting the muscles to glucose via gluconeogenesis and you would start feeling very weak.

      If you are fasting you should NOT do heavy lifting.

      A variant of fasting (technically it’s not fasting) which I sometimes do consists in eating coconut oil +BCAA and doing heavy workouts (bouldering in my case). The body still produces glycogen from Leucine but the existing muscle mass is preserved. This form of fast is also heavily ketogenic and so you/your brain should feel quite well.

  40. While this doesn’t have to necessarily do with fasting, I have noticed a large difference in brain performance with regards to chess rating. I am quite streaky, and it goes perfectly along with dietary carbohydrate (ie, high fat diet equals winning streak). I have “accidentally” repeated this multiple times (after a losing streak, I check my food journal). Since it’s been several times, I think the results are pretty clear. And it’s not like some high fat bias to avoid cognitive dissonance, as I get very angry when making a blunder.

  41. Here are my thoughts on fasting I have done the full 24 hour fast first off if you want to attend this fast I would recommend that you do it at the nighttime so you do the first 12 hours for eight hours of sleep so it’s a lot easier to get through so then you only have another 12 hours to do awake. You can drink as much water as you like and coffee but I has to be black. What happens is at the nighttime between three and the four hour you get rapid eye movement sleep and your first growth hormone surge. Then when you fasted for the 16th hour you get a second surge of growth hormone and I cannot recall when you get the third surge of growth hormone its on the 18th hour or 24. I’ve also done 16 hour fasts so I can get the growth hormone surge on the 16th hour I been doing this for about 2 week now and my dead lift has gone up form 120 kg to 135 kg.

  42. I enjoy fasting too. Every now and then i’ll skip meals during the day and i always become happier, more agile and alert. Yesterday in fact i hadn’t eaten from around 7pm the previous night until around 4pm the next day, i literally couldn’t stop talking, i’ve discovered that when i’m fasting my brain feels like it has a short burst of energy and goes at twice the usual speed, love it. :o)

  43. I’m glad you’ve done this series on fasting because, to be honest, I don’t love the idea and needed to be persuaded. I’ve always been an “eater”, for one thing, so skipping a meal is usually a non-starter. But, as someone who has had cancer and who has a family history of age-related dementia, I have to admit I am reconsidering the whole IF thing. And, it makes sense from an ancestral perspective. Grok wasn’t getting his meals on the dot and to order.

  44. This is a great post. I love the cited references, something I used to do more and should do more. At any rate…

    I haven’t done a 24 hour fast in a long time, but I generally have one large meal a day, typically lunch. I learned of your blog from Kurt Harris’ archevore blog, and have been drinking heavy cream in coffee as a good breakfast and dinner alternative on occasion. Avocados and grapefruit are also good in a pinch. I just had half a grapefruit and some decaf with heavy cream for dinner. I feel sated, alert, with that feeling you get when you fast or haven’t had much to eat…I like to call it feeling ALIVE. There’s something about it that is much different than the feeling after eating 3 large meals a day.

    All in all, I feel better eating this way. I can’t say anything about what may or may not be happening in my brain, but I definitely feel better. The 3 squares a day plan is probably flawed to begin with. Eating one big meal a day (lunch) seems to be the best plan. Some days I eat 2, sometimes 3, but those days are becoming more rare and I’m feeling much better.


  45. I always dread my monthly fast but I always love the way I feel afterwards. I fast as a part of my religion and it is cool to see physical benifets also. I love your site

  46. Love it. My mind is much clearer during a fast. I honestly hate breaking the fast because while my mental clarity doesn’t completely evaporate, it does decrease significantly after I get a lot of food in my belly. Bummer. Has anyone else noticed this? If so, have you found any way to deal with it?

  47. I just finished the 3rd day of a 5 day fat fast. It takes some planning but, for me, is much easier to tolerate. I had plateau and couldn’t get anymore weight to move. The most amazing thing is not only my arthritis is mostly gone, but the sciatica I’be suffered for years is gone! I’m walking miles a day. No pain is GOOD!

  48. Been Fasting past couple of months following the Primal Diet and Lean Gains workouts/fasting regiment (leangains.com) and have never felt better good see the additional benefits of fasting

  49. I have been primal for nearly a year.
    I lost 20kg in about 8-10 weeks and have kept it off. I wish to lose another 5kg. I work for a bank, and I have sales targets. I only work two days a week while I study full time. I decided to IF on the days I work. I eat dinner the night before, and then I dont eat til after work the next day. I do this Wed and Fri. I drink green tea and some coffee in the mornings. My weight has dropped from 59kg to 57kg. But the thing that amazed me is this: On days at work when I fast my sales are amazing. My target is just under two sales a day. I have not been meeting this target for years. I now sit at 127% of target. One day last month I did 9 sales events. That’s 2.5 weeks of sales in one day. In addition and the most exciting for me is that I balance at the end of the day. I have a substantial amt of money to count and in three years I have nearly always failed at this. So much so that I had “coaching” over it. I have balance TO THE CENT everytime I fast at work. This to me is incredible. Lastly, as I know this post is too long… I love the way I feel when I fast. I feel alive. If you havent tried it – please do so.

  50. We do all we can to PREVENT Ketosis in our goats. Ketosis is not a good thing. Goats can die from it.

    From Wikipedia, the free encyclopedia
    Jump to: navigation, search
    Classification and external resources

    Ketone bodies
    ICD-9 276.2
    DiseasesDB 29485
    MeSH D007662

    Ketosis ( /k??to?s?s/) is a state of elevated levels of ketone bodies in the body.[1] It is almost always generalized throughout the body, with hyperketonemia, that is, an elevated level of ketone bodies in the blood. Ketone bodies are formed by ketogenesis when the liver glycogen stores are depleted. The ketone bodies acetoacetate and ?-hydroxybutyrate are used for energy. [2]


    Metabolic pathways
    When glycogen stores are not available in the cells, fat (triacylglycerol) is cleaved to provide 3 fatty acid chains and 1 glycerol molecule in a process called lipolysis. Most of the body is able to use fatty acids as an alternative source of energy in a process called beta-oxidation. One of the products of beta-oxidation is acetyl-CoA, which can be further used in the Krebs cycle. During prolonged fasting or starvation, acetyl-CoA in the liver is used to produce ketone bodies instead, leading to a state of ketosis.

    During starvation or a long physical training session, the body starts using fatty acids instead of glucose. The brain cannot use long-chain fatty acids for energy because they are completely albumin-bound and cannot cross the blood-brain barrier. Not all medium-chain fatty acids are bound to albumin. The unbound medium-chain fatty acids are soluble in the blood and can cross the blood-brain barrier.[2] The ketone bodies produced in the liver can also cross the blood-brain barrier. In the brain, these ketone bodies are then incorporated into acetyl-CoA and used in the citric acid cycle.

    The ketone body acetoacetate will slowly decarboxylate into acetone, a volatile compound that is both metabolized as an energy source and lost in the breath and urine.

    [edit] Ketoacidosis
    Main article: Ketoacidosis
    Ketone bodies are acidic, but acid-base homeostasis in the blood is normally maintained through bicarbonate buffering, respiratory compensation to vary the amount of CO2 in the bloodstream, hydrogen ion absorption by tissue proteins and bone, and renal compensation through increased excretion of dihydrogen phosphate and ammonium ions.[3] Prolonged excess of ketone bodies can overwhelm normal compensatory mechanisms, leading to acidosis if blood pH falls below 7.35.

    There are two major causes of ketoacidosis:

    Most commonly, ketoacidosis is diabetic ketoacidosis (DKA), resulting from increased fat metabolism due to a shortage of insulin. It is associated primarily with type I diabetes, and may result in a diabetic coma if left untreated.[4]
    Alcoholic ketoacidosis (AKA) presents infrequently, but can occur with acute alcohol intoxication, most often following a binge in alcoholics with acute or chronic liver or pancreatic disorders. Alcoholic ketoacidosis occurs more frequently following methanol or ethylene glycol intoxication than following intoxication with uncontaminated ethanol.[5]
    A mild acidosis may result from prolonged fasting or when following a ketogenic diet.[6]

    1. I cannot argue with you about goats, but for humans there are many who theorize that at least intermittently moving from glucose metabolism to fatty acid and ketone bodies metabolism is not harmful, and in many cases is beneficial.

  51. Switched to primal about six weeks ago (wasn’t too much of a change, just cut out grains, and cut down sugars/fruit, which I was already trying to do) and started experimenting with alternate day fasting this week. The first day was pretty hard after about 14 hours, I finally broke the fast when my heart started feeling funny. I’m still not sure if it was related. Today, though, I finished an 18-hour fast with NO problems at all, it was pretty easy. Broke the fast with a small burger sans bun and carrots. Feeling pretty good (:

    1. I’ve tried IF 3 times this year, in the form of a “water only” 24 hour food fast. Each was seperated by 1 week.

      It was tough…

      Recently I came across a very interesting variation on the IF theme. It’s called “protein cycling” but I think a better/clearer name is “protein fasting”.

      The idea is simply that to eat all the calories you normally would but on the “protein fast” day make sure less than 5% come from protein. This ensures the protein intake that day is below the bodys critical daily requirement. The result, according to the person proposing it, is the same thing – autophagy is induced.

      Here is a link to an (free) online version of the book promoting the plan:


      and here is a link to a list of low-protein foods:


      I hope everyone that would want to try this version of IF likes bananas and apples…lol!

      I’ll probably try this later this month and report back. But I know this will make IF fasting easier. I’m not sure if it’s still valid.

      Worth trying I think.

  52. And how good is that first meal when you break a fast? “Owwh, these are the best eggs I’ve ever had! You gotta’ try it!”

  53. I do wonder if being “fat adapted” and IF are redundant. By minimizing carbs going into your body, blood sugar levels will tend to stay low, and thus HGH will flow and many of the other benefits you’ve described probably also. Are there any studies out there suggesting that “fat adapted” animals do better adding IF?

  54. The husband and I are fasting every other day through June. After that we will reevaluate and decide if we want to continue.

  55. My sex drive always improves while I fast. Any inflammation goes down and sometimes I get acne while I fast. On one occasion I had acne before I fasted and during the fast it disappeared. I usually get a release of white blood cells through my nose and I believe this is the immune system dealing with a very pathogens.

  56. Its very interesting as Muslims fast for a compulsory 30 days in Ramadan. Also it is encouraged to fast and seems like there are lots of scientific benefits of fasting. We fast from sunrise to sunset which goes back every 10 days and right not that’s from 3.30am to 9.00pm. I think if anyone needs some motivation to fast try buddying up with someone they may know in Ramadan as it will become much easier to follow : – )

  57. I don’t know about the science side of this but as someone who has been using IF (2 days off 5 days on) for the last 4 weeks. I can say that my desire to gorge has gone. When I do eat, I enjoy it more and feel full more quickly. I’ve noticed aromas and tastes more as well. On my fasting days, I don’t really even feel that hungry and I’ve lost about 2 pounds a week so far. I feel much more calm and I seem to be able to solve problems a lot more quickly(This could be my imagination but I don’t think so). My skin looks a lot better. The thing I have really noticed is, the day after my 2nd day of fasting, I feel a little over-energized; to the point where, last week, I was running about the house finding things to clean and vacuum(this is not like me my wife would testify to this). That was odd as I was buzzing and talking much more than usual. But generally I feel a lot better so I’m going to continue and see where it leads.

  58. A very informative site. Amazes me how folks accumulate and become conversant of so much knowledge; makes me feel like a philistine. I fasted as a young man, and the weight came off, though my motivation was spiritual, though delusionary in the sense that I really didn’t know much about the stuff I believed in. So I was fasting too much, unto starvation, and then I would fast w/o water sometimes. I once went 13 days and nights w/o water, and my heart started skipping beats; lucky to be alive. Because I fasted to starvation, I used up nutrients. My hair all turned gray almost overnight, my skin wrinkled above my nose, and these things never came back. Incidentally, when I was in this state, my body wanted to do yoga, ie stretching the joints etc. That and the growth hormones accounts for why starving people grow taller as an evolutionary adaptation — just a theory, but I suspect true. At the extremes of fasting, I had some out of body experiences, but that was also precipitated by the terror related to this cult I was in. / Well, I’m fasting again today for weight loss and to try to get my mind right. You see the problem I have with food is I eat under stress, which I know is evolutionary because I saw animals on the farm doing this, specifically chickens. When they saw their flock being hatcheded heads off, they started eating until their gullets were stuffed with corn, evinced when their heads were chopped off and corn spewed from their gullets. / Where was I? So I have these very strong thoughts of food, like pizza, with smell, taste, and feel included, and my mind wants me to think this is hunger. My body is not hungry in the least, but the compulsive urge to eat, a learned response to stress I guess, is nearly impossible to resist by attending to thoughts of not eating. I can fast, whether this is by awareness or pure will power I’m not sure, but I want to achieve the state that I am moved to eat out of physical hunger and not out of these thoughts of food, really irresistable at times. This is more about the mind than the stomach. If you have any insights on this, let me know.
    I guess at bottom is that one needs something for the mind to do to keep the mind occupied with something other than food, when stressed or bored. I’m also learning about Vipassana meditation, hoping that might be the answer, but it’s all a battle still at this point. I tried a 30 day fast drinking coffee in the a.m. and OJ throughout the day. After 30 days I lost nothing, may have gained a couple pounds. I’m not on a water only fast, and the weight is coming off. I do have, and have suffered some mental health problems over time, due to the usual childhood and later traumas. Too much negative thought in the stream of consciousness. I hope this fast will help my mind become more aware in the now, as E. Tolle would say, but remains to be seen. I do anticipate feeling better just being a lighter weight, as I remember it did feel good when I was. A girlfriend thought I was too thin; she made it her goal to fatten me up, first dinner was lasagna. Somehow I just kept eating. But the real terrible setback was when some [incompetent] psychiatrist put me on that Eli Lilly poison ZYPREXA, gained 50 pounds in a month and became diabetic, and was too out of my mind to know what was wrong. Many young people died on ZYPREXA, the company was pushing the stuff for profits. If there were any justice, they’d be in prison. / Anyhow, sorry for all the excess thoughts, but thanks for the good information on fasting etc. R.

  59. I actually started research on fasting after an unintentional fast last Saturday. I went for a walk and felt particularly perceptive. The enviroment (specially nature in parks) seemed specially beautiful, and a sutil well being sensation growed inside me. It was an interesting experience that got me very interested in this matter.

  60. You should check out the “Hodgetwins” on YouTube. They were once fat and have been working out and IF for 4 years now and look fantastic! Their look went from a “Jack Black” to Arnold Schwarzenegger. They’re now trainers at a gym and very inspiring.

  61. I thought this was very interesting, especially since I love fasting. I fast a couple times a week and I always believed that fasting can cure a lot of things. And I also have a very bad case of depression to where I hear voices and see things in my head and feel feelings in my body that aren’t really real. And because of it I have to take anti psychotics to help it. And this article gives me more hope that I can get this off forever one day. I once fasted from Friday evening to Sunday at 5pm and I actually felt better. Completely no voices or anything I almost wanted to keep fasting that fast. But once things start getting bad in America and the dollar collapses and I can’t get my meds from where I get them. I’m glad I know now from this article that I can start that Long term fasting again. And Thankyou for this article

  62. Hi, I am that type of people that gets irritated when hungry and my eyes see blurry and my hands start shaking. I was told that this is due to the drop of sugar in blood. But I don’t have any disease.
    However, I usually eat as soon as I get hungry, but recently I was getting so busy and had no time to eat every time I get hungry. And I realized that after an hour of starving, the symptoms go away and I feel that I can think clearer than usual. Therefore, I consider starting fasting. But I think fasting the whole day is way too much for me as a start. Especially that I am thin, don’t have much body fat and I have a fast metabolism. Can you please advise on how to start fasting in my case?
    Please answer as a reply not as a new comment so I can get notified.

  63. I have been fasting for 20 years now. I have been doing a 36-hour fast on Wednesdays and most recently added a 24-hour fast on Fridays. I know my complexion and youthful appearance are a direct result of this discipline. (My husband says I look like I’m in my 30s… I’m 53). Recently fasting has become more difficult for me as I teach Kindergarten and it requires lots of energy. Some days however, I can fast and it feels like it’s all uphill all day and some days I can fast and it feels like nothing. I’m not sure why, I suspect this is related to my hormones as I’m in peri-menopause right now. Recently I added Organic Excellence’s Progesterone Cream to my daily supplements and it has helped me immensely. I think when my hormones are in balance the fast is much easier. Just an observation. I like fasting because it gives my body a real rest from digesting. I don’t think we were meant to digest every single day. It’s just too much work for our systems. Anyway. Hope my experience in fasting helps!

  64. This was an absolutely amazing article!!! Thank you for sharing this! Remarkable, some of the data you’ve presented. This makes me want to look more into the fasting routines of Muslims during Ramadan. How amazingly the body and mind respond to fasting….very interesting.

  65. Useful info. Lucky me I found your web site unintentionally, and I
    am shocked why this coincidence didn’t came about in advance!

    I bookmarked it.

  66. Fasting for 1 day has relieved my SAD. I’ve tried everything else and nothing has worked. I’m on my 3rd day post-fast and have incredible energy. I had to check this site to see if I was on the right track. Such a simple no-cost cure, I would cry if I wasn’t so happy.

  67. Muslim already do fasting in the whole month of Ramazan. The benefits of what science is proving now, has been practice of Muslims for more than1400 years.

  68. I seriously had no idea that fasting would help brain function. I would have thought the opposite to be perfectly honest.

    I understand that when you eat too much your exhausted. LOL. Not the same thing, I know. I try not to overeat anyway. I eat seeds, veg and fruit for lunch and breaks, so never overeat anyway unless it is on the weekend or for an event.

    What I do and believe to the fullest extent is drink a serious amount of water everyday. 2 pints in the morning, 3-4 pints throughout the day and another 2-3 after work. Might be too much, but find it keeps me alert and focused.

  69. Mark, I don’t know if you’re still reading comments after six years, but here are mine. Everything I read about brain health, without fail, overlooks the Jupiter-sized elephant in the room – that the brain is a control system that operates based on stored knowledge at all levels of consciousness. It regulates biological systems, movement, social behaviour, immunity and regeneration processes, and cognition itself. It constructs its own functions from genetic instructions, from environmental experience, and from introspection. NONE of these functions are biochemical. Biochemistry can’t account for the level of complexity needed for the brain to do what it does. Improved and regenerated brain function is triggered and supported by a keto diet and by fasting, but the process is a software one. Experts are so intent on discovering the process where diet affects neurological conditions – but more often than not, they proceed on the false assumption that chemistry facilitates the process. It just doesn’t.