The one-day (36-hour) water fast

Most people in the modern world have never gone 24 hours without eating. You too? If so, the one-day (36-hour) water fast is the perfect way to begin your journey into water fasting.

I remember when I did my first one-day water fast. My plan was to eat dinner, then fast through all of the following day, breaking my fast with breakfast on the day after this. This format is ideal for anyone wishing to try out a 36-hour fast.

Psychologically, the experience was hugely challenging. Like most people, I’d hardly ever even skipped a meal in my life, and the idea of not eating anything for a whole day seemed almost inconceivable. Every time my stomach rumbled, it felt like the end of the world: I was going to starve! Of course, logically I knew that I wouldn’t, but the rational mind so easily collapses when your deeper, instinctive emotions emerge from out of the subconscious. By the evening, all I could think about was food… In the end, though, I did it. And so can you. Anyone can survive 36 hours without food!

So why put yourself through such a terrible ordeal 😉 ? (By the way, contrary to my own experience, many people do actually enjoy their first one-day fast, feeling full of energy and without existential worries.)

The benefits of a 36-hour water fast:

There are two reasons to face your fears and reap the benefits of a 36 hour water fast. The first is psychological. Precisely by facing your fears and emerging victorious on the morning following the fast, you become a stronger person. We all have a built-in survival response. By breaking the psychological barrier of no food for a whole day, you’ll find that the next 36-hour fast goes much more smoothly. Equally important, it also then becomes much easier to move on to longer water fasts in which you fully unlock the body’s healing metabolism.

The second reason is physical. At the very least, you give your digestive system a break for a day. It can rest and recuperate. This is hugely beneficial for maintaining health and to prevent aging. Mahatma Gandhi, for instance, used to fast one day every week. Following his assassination at the age of 78, the doctors at his autopsy described how Gandhi’s inner organs looked like those of someone half his age.

Perhaps even more importantly, by fasting for 36 hours you prompt the body to begin unlocking its healing metabolism. This can take place only when the body is burning fat for fuel, in a state otherwise known as ketosis. In everyday life you normally burn carbohydrates, either directly from digested food or from the glycogen stored in your liver. When you stop eating, though, your glycogen stores run out after about 24 hours, and your body must begin switching over to ketosis in order not to run out of energy. (This process is described more fully in the article on the 3-day water fast.) There are two main reasons that you can heal while in ketosis. Firstly, the body stores toxins in fat cells, where they can’t cause damage. Only through ketosis can these toxins (continued below)

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be released and expelled from your body. Secondly, the immune system gains extra energy to repair and replace damaged cells when you stop eating, and the energy normally used for digestion can be used instead for healing.

Beyond the 36-hour water fast:

To complete the switch over to ketosis you need about three days, which is why it’s so important to learn the 3-day water fast at some point. But don’t rush into anything too soon! If you don’t feel ready to fast for three days, keep practising the 36-hour fast. If 36 hours feels too long, then try 24 hours instead. You can begin a 24-hour fast after eating dinner and then break the fast with dinner the next day (lunch to lunch is another option). 24 hours does less to nudge the body into ketosis, but still allows you to benefit by flushing out the toxins accumulated from the air you breathe, the water you drink, the food you eat – not to mention any medications and drugs you take. If a weekly or fortnightly 24-hour fast feels too much, then perhaps you should try intermittent fasting instead. Whatever you do, your body will thank you for it!

Dietary transition and refeeding:

One final note: there’s no need to prepare for a one day fast by changing your eating habits beforehand. Likewise, you don’t have to transition gradually back to eating normally afterwards.

Related articles:

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135 responses to “The one-day (36-hour) water fast”

  1. Wonderful blog. It is a blessing you are providing this information. I’ve completed a 3 day fast fast twice. Are herbal teas like peppermint, roboos or cinnamon allowed? I visit a local wellness natural hot spring resort and it helps w daily yoga as a break from my normal routine of hikes and kickboxing classes. I find that gerolsteiner and the fresh spring water work nicely. Should I be adding more electrolytes? I’m 300# at 27% body fat. I have some fat to lose, but lots of muscle mass. I’m also a chemist so feel free to answer technically.

    1. Tallis Barker, D.Phil. Avatar
      Tallis Barker, D.Phil.

      Hi Michael,

      Thanks for writing, and glad you’re finding the website useful. There’s nothing wrong per se with using herbal teas during a water fast. The question for me, rather, is why you’d want to use them… Is it because of their medicinal properties? Is it because you find plain water ‘boring’? (This is obviously one of issues once you start to delve into the more spritual aspects of fasting.) The main thing is to be clear about the reasons you might – or might not – want to use them. There’s a time and a place for everything.

      In terms of adding electrolytes, there’s absolutely no need for the vast majority of people, and it’s one of the misplaced myths about fasting!!! Electrolytes reduce cleansing and slow the rate of healing. When there’s time, I need to write an article which goes into this in more depth!

      All the best,

  2. Should I be taking electrolytes whilst on longer water fasts? Is there any benefit in drinking distilled water during the fast? Is eating once every 24 hours everyday, better or worse long-time than a 36-48 hour fast every 2 weeks or so? Cheers, Chris.

    1. Tallis Barker, D.Phil. Avatar
      Tallis Barker, D.Phil.

      Hi Chris,
      Except for those suffering from certain health issues, electrolytes are neither necessary not desirable during an extended water fast.
      Distilled water can be fine, but natural spring/mineral water is better for you – and it also tastes better!
      It’s hard to compare OMAD with longer fasts. Different things work for different people, and it also depends on what you’re trying to achieve through you fast.
      All the best,

  3. Hi Tallis,

    I pinched a nerve in my neck a few days ago and am working with my doctor, but I’m wondering if you think a 36-hour fast could help foster healing? I’m experiencing some mild tingling and pain. I’d appreciate any info or opinions. Thank you!


    1. Tallis Barker, D.Phil. Avatar
      Tallis Barker, D.Phil.

      Hi Joe,
      Thanks for writing. I’m afraid that a 36-hour fast isn’t going to be long enough to make much difference in healing. Water fasting does work wonders for pain. This is usually caused by reducing inflammation and accelerating healing. Reduction of inflammation is likely to start soon after 36 hours, but the problem here is that the pain would return when you start eating again, and inflammation levels return to normal. In order to effect the kind of healing which would really deal with the cause of the pain, you’d need to fast for much longer: anywhere from about a week or more. The exact length of time required for a full healing, however, would depend on the severity of the case, and it’s possible that you might need considerably more than just one week.
      Sorry not to be able to give you better news!

      1. No problem, thanks for the thoughtful response! Hoping to work up to some longer fasts down the road 🙂

  4. How many times in a week/7days would you recommend to do the 36 hour fast?

    1. Tallis Barker Ph.D. Avatar
      Tallis Barker Ph.D.

      Hi Blair,
      Thanks for writing. To be honest, I’m not really a fan of setting up a strict schedule, because it doesn’t take into consideration what your body is actually telling you. Rather, it’s a plan worked out by the mind – which often has very little to do with the body’s true needs. However, many people are happy to fast once a week, and others even practise alternate day fasting, which involves eating only every other day. These are both safe and healthy options for the vast majority of people. But if you feel like fasting only once a month, this is still something your body will thank you for!
      All the best,

  5. How much water should I drink during the 36 hour fast?

    1. Tallis Barker Ph.D. Avatar
      Tallis Barker Ph.D.

      Hi Cathy,
      Thanks for your question. Whether a 36-hour fast or a 40-day fast, the best default setting is to drink according to thirst. You can read about drinking large amounts of water every day – and there are definitely certain circumstances when this is prudent – but the best is usually to just trust in your body. Thirst is there for a reason, so just listen to it!
      All the best,

  6. Christina Pongracic Avatar
    Christina Pongracic

    Hello Tallis,

    Thank you for all this information. I would like to try the 36-hour fast to “wet my feet”. How many cups (actual measurement) of water should I consume during this period (waking period, of course) to make sure that I do not become dehydrated, and would you say that I should drink a cup of water every hour? two hours? How would you space them?

    Best wishes,

    1. Tallis Barker Ph.D. Avatar
      Tallis Barker Ph.D.

      Hi Christina,

      Glad you’ve benefited from the information here on the website. Good idea to start slow, by dipping your feet in the water. I always say the tortoise beats the hare when it comes to getting into fasting!

      When it comes to drinking, the default position for a generally healthy person should always be to drink to thirst, which can then be modified if and when detox symptoms appear. The truth is that your body could easily manage 36 hours without drinking anything at all (a SHORT dry fast). If you’ve not been eating a healthy diet recently, though, you might want to drink a little more than usual. There’s no need to flood yourself with water, though, as most of this will only be passed out immediately as urine.

      All the best for your first 36-hour water fast :-),

      1. Thank you! A wealth of information 🙂

  7. Just been reading through this post as I am about to start a 36hr fast. I was wanting to know if it is ok to drink coffee and tea while on the fast. Thanks. Nigel

    1. Tallis Barker Ph.D. Avatar
      Tallis Barker Ph.D.

      Hi Nigel,
      I’d always avoid coffee while fasting. First there’s the caffeine, which is best to avoid if possible while fasting, so your body can slow down and rest. Second – and in my view more importantly – coffee is extremely acidic in the GI tract. This elicits a mucous response in the gut, in order to protect the sensitive lining of the intestines. Much better to stick to tea: ideally green tea, as this is mildly alkaline and won’t cause digestive issues.
      All the best for your fast,

  8. You spoke about Gandhi having an autopsy and his organs appearing like someone half his age. There is no record I could find of an autopsy being performed on his body after his death. Only a forensic investigation of the bullet wounds. Can you please show the source for this information so that others may read it?

    1. Hi Chris,
      This is an anecdote I’ve read on multiple occasions – although I don’t know the original source. Do you have the source for the records of the forensic investigation? I should think there would be reference to it in there, as obviously the pathologists would have seen his organs when they opened him up.

        1. Tallis Barker, D.Phil. Avatar
          Tallis Barker, D.Phil.

          Thanks Gary, I appreciate the link. I’ll look into it and change the text accordingly!

  9. I currently follow a 16:8 time-restricted eating programme 7 days a week. Would I benefit from adding weekly/bi-weekly longer fasts?

    Also, I visit the gym 4-5 times a week. If I were to include extended fasting periods, should I avoid training during these?

    One final question!! Following on from the previous comment about chewing gum, does using toothpaste during a fasting period trigger the digestive system in any way?

    1. Hi Thomas,

      Thanks for your question. You’d almost certainly benefit from longer fasts – the main question is exactly how you could fit this into your lifestyle. I would think of the main benefit of 16:8 as giving a daily rest to your digestion, whereas that of longer fasts is detox and cleansing. In that sense, it makes more sense to go for less frequent but longer fasts.

      If you regularly go to the gym, it IS important to back off on working out while fasting for anything longer than 24-36 hours. This video goes into the question in depth:

      Toothpaste probably does minimally trigger the digestive system. Comparing it to chewing gum, though, you won’t be swallowing so much saliva, which means that the stimulus from brushing your teeth comes only from the mouth, and not the mouth plus the stomach. To be honest, I wouldn’t worry about it!

      All the best,

      1. Thanks, Tallis.

        So would daily 16:8 fasts with a once-weekly 36hr fast work well or is this is some way detrimental?

        Also, despite the clear health benefits, as a naturally lean body type, I am a little concerned about losing weight (muscle mass) from missing a day’s worth of calories – should I be increasing my calorie intake over the remainder of the week to make up for the ‘lost’ calories during a 36hr fast?

        1. Tallis Shivantar Avatar

          Hi Thomas,

          There’s no reason why 16:8 plus a weekly 36hr fast shouldn’t work if you’re eating a nutritious diet in between. The most important thing, though, is not to turn the 36hr fast into a weekly drudgery, but rather do it because you can feel your body asking for it – which itself may require a few fasts in order to be able to tune into what your body is saying.

          If you’re already very lean, then eventually your body is going to start cannibalising muscle mass to compensate for any long-term calorie deficit. This isn’t going to be related directly to the weekly 36-hr fast but rather the overall calorie intake versus output. So to answer your question: yes, it does sound like you should be compensating for the lost calories of a 36-hour fast over the rest of the week.


  10. Hello! Great source of information, thank you!

    I was wondering, if a drink in the morning with juice from half a lime, few drops of apple cider vinegar and some salt following with some coffee and spoon of butter is a good way to go?

    Also, should I be taking my supplements (Vitamin D3 and K2) during a fast? Are there other specific supplements that would help during fast?

    Thank you again!

    1. Tallis Shivantar Avatar

      Hi Rimatas,

      Glad you’ve found the website helpful.

      About the juice, lime, vinegar, salt, coffee and butter: I’m not sure what context you’re thinking of. This isn’t for a water fast, is it? Water fasts are supposed to be zero calorie!!! In every day life, a big glass of water with some lime and apple cider vinegar is definitely a good way to start the day. Not so sure about the spoon of butter though…

      About supplements during a water fast: if you’re a healthy person who has been eating a healthy diet, there’s no need for supplements – even for long extended ones. Here is an article with plenty of information:

      Hope this helps,

  11. Adrienne Amato Avatar
    Adrienne Amato

    Just found your site. Great info. I was wondering, is it ok to chew gum on a fast? I’ve read some sites that say it’s not helpful because it can stimulate your appetite but will it actually interfere with the process? I get really dry mouth and oddly enough the more water I drink, the more noticeable it becomes. Gum and mints help a lot.

    1. Tallis Shivantar Avatar
      Tallis Shivantar

      Hi Adrienne,

      Chewing gum isn’t the end of the world but it’s not the best either. It doesn’t involve ingesting calories and therefore doesn’t interfere with ketosis, but it IS going to stimulate your digestive juices to a degree. This usually does prevent appetite from receding as quickly, and, of course, keeping your digestive system awake is going to divert some of your energy away from the healing process – but, quite honestly, the degree to which a little piece of gum is going to decrease your ability to cleanse and heal isn’t going to be very significant.

      All things considered, I’d avoid chewing gum and instead sip from a glass of water when you really need to. The dry mouth is a detox symptom, and this is why drinking often doesn’t help – because another glass of water simply isn’t enough to complete the cleansing process. But this doesn’t mean you shouldn’t drink. Quite the opposite. Without any doubt, the dry mouth (like thirst) is a signal from the body to drink more, because fluids help to facilitate cleansing. Chewing gum, on the other hand, isn’t going to help you cleanse at all. It just hides the body’s message to you that you should be drinking!

      The situation here is similar to taking a paracetamol for a headache. All it does is suppress symptoms without addressing the root cause.

      I know having a dry mouth feels annoying, but, in terms of detox symptoms, at least it’s not uncomfortable. If you continue your fasting journey it will pass – either on this fast on during future fasts. My advice would be to follow your body’s first instinct and drink instead of chew 🙂

      All the best,

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