Category: Nutrition

The Facts on Fasting

If you follow my work and message, you know that I’m a champion of brain-derived neurotrophic factor, or BDNF. A protein that plays an integral role in stimulating the growth of new brain cells, and the performance of existing neurons, BDNF is best described as the brain’s “growth hormone.” Given that, stimulating the production of BDNF is easily one of the best things you can do for your body and your brain. One of the ways I recommend doing that is by engaging in intermittent fasting. If you’re looking to incorporate fasting into your regiment, I recommend fasting once or twice a year for 24-48 hours at a time. As hard as it may be, during this time you must cut out everything except water (which you should drink plenty of). Remember, fasting may be a stressful activity, but it’s one that acts as a very positive stressor for your body, as it instantly activates life-altering genes. Of course, before engaging in any type of fasting, you should consult your physician.

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  • Karl Allen

    Looking forward to reading more about fasting in the book tomorrow. I’d love to get your input on doing a daily fast (my current routine) and only eating from about noon to 8pm every day. And just as importantly, if I drink coffee with heavy cream during my fast, does the intake of calories from the cream negate the positive effects of the fast?

    • Liana

      Hi Karl, I’m doing the same thing. Dr Mercola has a lot of info about this on his site. I’ve read that it’s best not to have any calories when doing this type of fasting (have water, black tea or coffee, herbal teas) so save the coffee with cream (which I also love) to when you break your fast.

  • Mark

    Fasting known for hundreds of years as one of the methods to release toxins and loose weight and bring body to its normal healthy state.
    To loose weight you should fast once a week 24-36 hours. Drink water with lemon juice and a little raw honey(if you feel exhausted). I tested this method. It works. But one thing before testing you should clean up your guts by taking 2-3 pills of senna or castor oil (2-3 tablespoons).If you have some comments you can email me at cureyourself@mail2expert.com.
    Thank you . Mark.

  • Mark

    Hello Dear Karl Allen. Dr. Perlmutter is correct. During fasting is better to drink only water (pure or with lemon juice, 1/2 tea spoon of honey). Otherwise you will disrupt all purpose of fasting. If you have any questions I am ready to answer. Mark: cureyourself@mail2expert.com

  • Chris Ferguson

    I began 5:2 fasting in April in a desperate attempt to help my brain find it’s way out of PTSD which had a crippling hold on me for 3 years. As I began fasting two days per week I also discovered Paleo for improving brain function and so began on that path a short time after starting fasting. For the first few weeks I had horrible back of the brain headaches during the later part of my fast days, I think this had something to do with my brain being weaned off sugar onto fat.

    Within a month my PTSD symptoms had disappeared and my brain function began to improve drastically. 6 months on and I have lost 15 kg and my brain is well and truly FIRING! So much so that I am thinking of going back to study. I haven’t experienced any more PTSD symptoms and have been able to turn it into Selligman’s post traumatic Growth- this was something I was unable to do before changing my diet and beginning fasting.

    I still fast for 2 days most weeks, consuming under 500 calories for the day. Some days it doesn’t work out but it is no big deal as I can do it tomorrow!

    I wish I could explain what has happened in my brain. I went from very foggy brain, feeling like my intelligence had deserted me, unable to focus on anything other than things related to the trauma. Always an avid reader I was unable to finish a book, my ability to concentrate had deserted me. Now I feel like me again. My love of learning has returned and creative thought is part of my life again at long last.

    I know that fasting started the healing process, it seemed to shake my brain out of a rut and get it going again to find it some food. Going grain and sugar free and eating more fat has no doubt helped the process along. I plan on maintaining these dietary habits for the rest of my life and would encourage everyone to try fasting- its not as hard as it seems and the rewards are there. Perhaps there is room to use fasting to treat brain disorders like PTSD- it worked for me.

    • David Perlmutter

      Thanks for sharing an incredible story Chris. Would you mind emailing it to me at Success@DrPerlmutter.com? I’d love to feature it here on the website.

    • Ani Bravo

      I have a similar story. I suffered very worrying brain damage after a lot of sleep deprivation ( I had a circadian disorder known as Non 24). For a person with an intellectual, creative career whose brain was her source of work and excitement, to suddenly not be able to remember my relatives’ names or follow the plot of the simplest films (I would not be able to remember what had happened a minute ago, so I couldn’t follow the story) was terrifying at different levels. I was very afraid.

      I spent a long time asking doctors and researching whether I could reverse this damage. None of the doctors I visited even knew of my disorder. (Neither did I, for a long time.) A few years and doctors later, I finally learnt of the paleo diet, fish oil, fasting, meditation. I put all of that to use.

      It’s a long, detailed (and to me very exciting) story, but, to make it short, I have turned my life around in the most incredible way. Not only cured myself of this brain and life wrecking disorder, seen a rapid improvement of memory and concentration which has made me become happy and functional again, but have gotten out of a very low place into a level that often feels exhilaratingly perceptive and clear.

      • Rich

        Thanks for sharing this Ani! Really inspirational. Do you have any more details or links you could point to regarding the approach you took?

        Would love to learn more, I’m embarking on a similar journey myself.

        Kind regards,

  • David

    Why is caffeine prohibited while fasting?

    • David Perlmutter

      David: The prohibition during fasting extends to all foods/beverages besides water, it’s not just caffeine.

  • Beth

    I don’t see how a person could totally eliminate carbs from their diet. Is there an acceptable level of grams/day that I could target?

  • stevenjoseph

    Would having psyllium husk and vitamins be counter effective to a fast ? I find it helps with alleviating hunger.

  • Julie Shafer

    Okay..here I go Dr Perlmutter, after many months of avoiding the idea of fasting, I decided to take the plunge. I listened to your podcast with Dr Mercola yesterday, (loved it btw), and now I have a better understanding of how important fasting is to the brain. I think I’ve done a pretty good job of reducing my carbohydrate intake, but now it’s time to take this to a different level. So, here I go….. bring on the water!!!!

    • David Perlmutter

      Great to hear Julie. Wishing you good health. Be sure to undertake this in consultation with your physician!

  • DougECKS

    Is there a limit to how many times you would recommend a 24 hour fast? I see you’ve said a 4 times a month minimum, but is there a maximum?

    Thanks for your time and your fascinating book. I follow it and feel great.

    • David Perlmutter

      Good question Doug. Unfortunately I can’t comment on that, as it’s something that is deeply driven by a person’s health state. You will need to consult with your doctor before looking at a lifestyle with intermittent fasting.

  • Pingback: Intermittent Fasting SuperCharges Your Brain - Primal Docs()

  • Jim

    Dr. Perlmutter, I like some of your message to society about the brain but if I may vent for a second please.
    saddens me to see that you have a quote from Plato on your website.
    Plato taught the west how to live as a slave state. Cuba is a text book
    reproduction of Plato’s Republic. The Chinese flag is based on Plato’s
    Republic. Most of the governments in the world today and since Plato
    have been some form of Plato’s Republic. Plato’s Republic is not based
    on reason and reality. Plato could never give a good reason for adopting
    his utopian slave state. So in the end he just said that he had divine
    inspiration which no one else had.
    Fortunately for the west Aristotle
    conducted a massive study on the politics of over 100 Greek city states
    and had impirical data which helped him create a form of government
    based on reality and reason, individual rights and freedom. Aristotle’s
    politics was not perfect but it was far superior to Plato’s slave state.

    Thank you for letting me vent.


    • mike

      this is a joke, plato believed tyranny to be the worst form of government followed by democracy and oligarchy. plato’s ideal state is basically a meritocracy. if you read about the training of philosopher kings in the republic, you find that it takes 50 monitored years with specialized training in both physical and mental education and they cannot own property.

  • Pingback: 10 Transformational Practices You Don’t Need To Be “New Age” To Benefit From.()

  • David T

    I have just finished reading grain brain and want to start my fast tomorrow, is there an advantage to going 72 hours instead of just 24 or 48? I would really like to commit to this change and feel this would be a good way to prove my commitment

    • David Perlmutter

      It depends on how you feel, when your body enters ketosis, and should be discussed with your physician.

  • Julia

    Dear Dr. Permlutter,

    thank you for your time and work. I am a
    biologist and truly belief in a low carb lifestyle. In a discussion with
    a nutritionist some points came up which I had no answer to. It would
    be great if you could answer it.

    1) Fatty acid metabolism needs more oxygen than glucose oxidation and is decreasing cardiac efficiency


    2) In a paper from 2013

    J Cereb Blood Flow Metab. 2013 Oct;33(10):1493-9. doi:
    Epub 2013 Aug 7. Why does brain metabolism not favor burning of fatty
    acids to provide energy? Reflections on disadvantages of the use of free
    fatty acids as fuel for brain. Schönfeld P, Reiser G. http://www.ncbi.nlm.nih.gov/pu

    Their conclusion: Three particular
    problems: (1) ATP generation linked to β-oxidation of fatty
    acids demands more oxygen than glucose,
    enhancing the risk for neurons to become hypoxic; (2) β-oxidation of
    fatty acids generates superoxide, which, taken together with the poor
    defense in neurons, causes severe oxidative
    stress; (3) the rate of ATP generation based on adipose tissue-derived
    fatty acids is slower than that using blood glucose as fuel. Thus, in periods
    of extended continuous and rapid neuronal firing, fatty acid oxidation cannot
    guarantee rapid ATP generation in neurons. We conjecture that the disadvantages
    connected with using fatty acids as fuel have created evolutionary pressure on
    lowering the expression of the β-oxidation enzyme
    equipment in brain mitochondria to avoid extensive fatty acid oxidation and to
    favor glucose oxidation in brain.

    Thank you and looking forward to your answer

  • clarekaylene

    I am following Grain Brain, but would like to begin some fasting using maybe a 8-10 hour window of eating. However, in the mornings I take a powder probiotic 30 min. before food, and then also right now, am taking a capsule detox 30 min after the probiotic and another 30 min. before food. Would either of these cancel out the benefits of the fast? I would so appreciate your input!

    • Ömer Ömer

      I don’t know what detox does (because I haven’t used any kind of medication for 15+ years) but it’s likely to interfere with a healthy fasting and so does the probiotic. It’s best to refrain from all of those together not for fasting, but for a better life too

  • Rachel

    Hi, I have become quite unhealthy since back surgery a year ago, I drink a lot of coffee with a lot of sugar, should I try to cut down first, or is it okay to try a day fast? I want to stop coffee and sugar but when I tried before the headaches were pretty bad. Is there maybe a supplement or do I just go cold turkey? I’ve been drinking coffee for 30 years! Can someone help, please

    • David Perlmutter

      Fasting is quite healthful, but I always advise it be done in conjunction with a physician.

    • Mina

      Hello, I know this is an old post but if you still want help with this…I have successfully cut my caffeine intake/addiction over the years from coffee, to black tea, to one cup of green tea per day. You can cut it gradually, or take the leap. For me, the headaches went away after a day or two. My brain would feel foggy for a couple of weeks but that went away too.

      If I were you, I’d focus on cutting the sugar down and then you will probably crave the coffee less. I’m not sure coffee itself is that bad for you, unless you are noticing particular things going wrong.

  • Amit Kumar

    Hello Dr Pearlmutter. I wanted to ask you if you know how I can recover the “injury” that I’ve had on my brain from having ptsd. I have troble concentrating and worries too much about everything. I have read your book and taking these supplements: Cocunut oil, DHA, Tumeric, Vitamin D3 and priobotics. Would I benefit from taking less/more of your reccomendation of these supplements? Is there any more supplement I could take?

    And yes, I am going to try to fast some days every month, and see if that helps.


    • Dying_in_this_Crap_World

      Suicide obviously.

  • Andrea

    Dear Dr. Perlmutter,
    I believed and have experienced the healthy effects of Intermittent fasting, skipping every day the breakfast, since six months. But, do you think that in this state the body could detox the brain from the heavy metals like mercury? I mean, eliminate them and not sweep them under the rug.
    I know it is difficult to know because of lacking of studies. But it could be possible according to you? I have seven amalgamas. I used to be sometimes depressed and moody, suicidal thougths, etc., I have never went to a dr., because I think the culprit is that I am a capricious person. Anyway, fasting makes me energetic and relaxed. That is enough!

  • Green Deane

    I fast one day a week, 24-hours straight, usually a Saturday lunch to a Sunday lunch. Some times I extend it to 32 hours, Saturday breakfast to Sunday lunch. This includes four hours of walking (or eight hours of walking if it is extended to 32 hours.) Fasting is not difficult. What is difficult managing social events so one is not being expected to eat.

  • Julia Gavilanes

    Do you have any specific recommendations for women on Intermittent Fasting? (I´ve read we might need a wider eating window, since our hormones play a huge role in our body regulation) xoxo

  • Rhett Shipp

    I read Brain Maker and LOVED it. I’m thinking about doing a 7 day water fast. Do we know much about how this would impact the gut? I would take a good multivitamin while doing it and I may take probiotics/fiber supplements if needed to keep from damaging my microbiome. I already do a 24 hour fast once a month generally.

  • Metin

    Is it allowed to drink mineral water during the fasting hours?

  • R Holtslander

    Why should I consult my Dr before engaging in a fast? If I’m otherwise healthy what value is there in talking to my Dr about it? Are there any dangers associated with a fast that I’m not aware of?

  • hugh welte

    Hi, I’m just coming of a 7 day water fast. What would you recommend for breaking it. I’ve heard you should gradually increase start slow and nothing solid for a bit.

  • Javier Mejia

    do senna tablets break a fast????

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