Can I work out and exercise during a water fast?


(1) Video lecture

(2) Article

  1. Confusion between juice and water fasts
  2. Facing addiction to exercise
  3. Slowing down to heal
  4. Fear of losing muscle mass while fasting – and why this is a misguided concern
  5. Water fasting and human growth hormone (HGH)
  6. What kind of exercise is okay during a water fast?
  7. What kind of exercise isn’t okay during a water fast?
  8. When is working out okay during and after a water fast?

Video lecture (13:55)

Whether or not it’s a good idea to work out during a water fast is a question which crops up surprisingly frequently on In general, most FAQs to do with water fasting usually lack a ‘one-size-fits-all’ answer, because it depends on the individual circumstances of the individual fast, along with the reasons that the individual person is fasting. In this case, though, the answer is clear-cut and applies to everyone: do not plan on working out or any serious exercise during a water fast!

I know this won’t be a popular answer, and many of my water fasting clients also resist the idea before they know any better. But there are several important reasons to rest while fasting. We’ll cover these below, in order of ascending importance, saving the most important – which is actually a question of preventing damage to your health – until last!

Confusion between juice and water fasts

Most people who approach water fasting do so after having done some juice fasting first. Juice fasting often permits a good degree of exercise because the calories they contain provide energy. Most of these calories also usually come in the form of simple sugars, which are easily burnt. In contrast, water fasting obviously provides no calories at all, and this changes everything (see below). In addition, water fasting induces higher levels of cleansing than juice fasting. This leaves less energy left over for other activities, such as working out and exercise.

Facing addiction to exercise

If you enjoy working out in everyday life, then it’s almost certainly going to be hard to shake the habit – even though a fast hardly counts as ‘everyday life’. I know. It took me years to learn to let go of the desire to exercise while fasting. Even though I did rest while fasting because I knew it was bad for me, something nevertheless continued to resist the idea of slowing down. Part of it is societal. Quite simply, the modern world glorifies busy-ness and work, work, work. But I also had to face the fact that I was addicted to the endorphins. It’s also true that most people who work out are equally addicted to endorphins.

Fasting is a time to face your addictions (more detailed information can be found in my article: ‘Overcoming addictions through water fasting’). Through fasting you learn how to be without the need for external distractions and frills. Allowing your hormones to reset without extra endorphins, caffeine, nicotine or any other drug, you learn that life is already good as it is.

Slowing down to heal

If you’re like most people in the modern world, you’re too busy for your own good, suffering from stress in everyday life. A limited amount of stress is actually good in many circumstances, but the problem is that most of us don’t get enough down time to balance this out. Fasting is a perfect opportunity for this!

More importantly, any energy spent on working out is going to take away from the energy available for healing. It’s that simple.

Fear of losing muscle mass while fasting – and why this is a misguided concern

Perhaps more than anything else, people feel compelled to work out during a water fast because they are afraid of losing muscle mass. Logically, this makes total sense. As the saying goes: use it or lose it! The problem is that working out during a water fast leads to a greater degree of muscle loss than not exercising at all. This is due to the metabolic changes which take place while fasting.

In everyday life, your body exists in a so-called anabolic state. Most people have heard of this word in relation to anabolic steroids: hormones which are designed to build muscle in order to enhance athletic performance. In general, anabolic simply refers to any state in which the body grows or builds itself up. In everyday life you eat, and the nutrients from food allow your body to build itself up.

While water fasting, though, your body exists in a so-called catabolic state. With no intake from food, your body changes priorities. Rather than building things up, it uses the available materials it already has to engage in cleansing and healing instead. Simply put, you can’t build up muscle when there’s no protein going in! Furthermore, working out while fasting actually reduces muscle mass. This is because exercise inherently causes a degree of micro muscle damage. It is precisely this damage which causes your body to build muscle when in an anabolic state. Your body detects the damage, and then builds additional new muscle in the area in order to prevent damage in the future. In a catabolic state, though, there is no protein to build new muscle. Instead, working out while fasting causes muscle damage which cannot be replaced with new, additional muscle. The damage is simply cleansed by the immune system, and you end up with less muscle than before.

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Water fasting and human growth hormone (HGH)

Fortunately, there’s no need to worry about muscle loss while water fasting. Fasting is one of the best ways to naturally promote the production of growth hormone. Elevated levels of HGH continue long enough after the fast to allow your body to easily make up for any loss of muscle during the fast. You don’t need to hysterically exercise after your fast – it will all return naturally. In fact, you can capitalise on the extra growth hormone in order to reach new levels of fitness and personal bests during the period after your fast (see below).

Similarly, there’s no need to start eating an extra high-protein diet after the fast in order to compensate for what you’ve lost. In fact, high-protein diets are the number one cause of problems during refeeding after fasts of up to about 10 days. When clients come to me with problems in refeeding, nine out of tens times it’s because they have reintroduced too much protein too soon after the end of their fast.

What kind of exercise is okay during a water fast?

Although hardcore workouts are downright damaging while water fasting, gentler forms of exercise can and do have a beneficial effect – so long as they don’t cause micro muscle damage in the process. For instance, gentle walking, stretching, yoga, as well as gentle cardiovascular exercise in general all help to promote detox. By burning more calories than usual, your body releases toxins stored in fat cells. The increased circulation of gentle exercise also helps to flush these and any other toxins out from the tissues, from where they can be cleansed from the body.

More generally, any exercise which feels good is probably good for you. While fasting, your body offers very clear signals about what kinds of exercise it is happy to do. The key is to listen and to respect this! Especially for those addicted to working out, though, it’s tempting to override these messages and force the kind of performance out of yourself which only causes damage. In everyday life you can get away with pushing through the pain. While water fasting you can’t!

What kind of exercise isn’t okay during a water fast?

It’s very simple. Any exercise which feels difficult, laboured, painful or unpleasant during a water fast is probably causing you damage. You never want to get to the point of sore muscles the next day, because in the catabolic state of fasting your body simply cannot repair and replace the damaged muscle cells.

Also, it’s important to avoid any activity which approaches the so-called anaerobic threshold: the point beyond which your circulation is unable to provide enough oxygen to power your muscles. (This basically means panting, a pounding heartbeat, and not being able to sustain the given activity for an extended period of time.) Although the ketosis of water fasting is able to provide enough energy for aerobic activity, anything approaching the anaerobic threshold requires your carbohydrate metabolism to kick in as well. Given that your glycogen stores are depleted during a water fast, anaerobic exercise quickly leads to accelerated muscle damage. While water fasting, you’ll also reach the anaerobic threshold much faster than in everyday life. Even if you’re just walking, ascending a hill can easily leave you out of breath. So slow down and feel into what the right, sustainable pace is for you!

Exercise of any kind is to be avoided on Day 2 of a water fast. At this point, your glycogen stores have already run out and ketosis is not yet fully engaged. This means that the main source of fuel are your muscles themselves, because the protein in muscle can be broken down into carbohydrates for energy. In fact, this is the primary reason why people often have sore muscles on Day 2 of a water fast – even without doing any exercise at all!

When is working out okay during and after a water fast?

Although working out is almost always something to be avoided during a fast, the one and only exception to this is on Day 1. At this point you still have glycogen reserves to provide carbohydrate based energy, and your body is still harvesting the nutrients from your last meal. This means that you haven’t fully entered a catabolic state yet (see above). Although it’s probably not a good idea to push yourself through an exceptionally hard work out, normal daily exercise on Day 1 is fine. In fact, burning more calories compared to resting helps you to consume your glycogen stores faster, which helps to accelerate the process of getting into ketosis. I often go for an easy, long run on Day 1, and it’s never a problem.

After a fast, it’s important to resist the temptation to start working out too soon. Remember: there’s no hurry to return to serious exercise due to the continuing elevated levels of growth hormone afterwards. Immediately after a fast the body’s priority is to work on your inner organs and body systems – and not the muscles! The liver, kidneys, lymphatic and immune systems all work overtime while water fasting. Once you’re taking nutrients on board during refeeding and you return to an anabolic state (see above), your body focusses first on rejuvenating and rebuilding them, and not muscles.

If you start working out too soon, you’ll only damage your muscles in the same way as during a fast. Also similar to during a fast, your body will continue to give you signals if exercise isn’t a good idea by making it feel difficult, laboured or unpleasant. In my experience, I find this period tends to last up to half the length of the fast, after the end of the fast itself. In other words, after a 3-day fast you’ll need to wait 1-2 days before working out, and after a 7-day fast you’ll need to wait 3-4 days.

After this point, the body turns from the core of the body to the periphery, and it quickly starts building back muscle through elevated levels of growth hormone. I usually return to my full pre-fast strength by the time the length of the fast has elapsed after the end of the fast itself (eg. 7 days after the end of a 7-day fast).

This isn’t the end of the story, though. Elevated levels of HGH continue significantly longer, allowing increased athletic performance beyond pre-fast levels. After a 7-day fast, for instance, I usually find that my performance (in terms of both strength and endurance) increases by about 5% for about a month afterwards.

Good things come to those who wait. So get the best of both worlds: slow down and relax while fasting, and then enjoy working out again afterwards!

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52 responses to “Can I work out and exercise during a water fast?”

  1. What sort of cardio can you do? Running, cycling and rowing machine? Should I do a lower level on these machines at the gym? Lastly, can I drink a protein shake or would that break the water fast?
    Thank you.

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

      Hi Mahir,
      Thanks for writing. When doing a water fast, it’s important to respect the limitations of your body. For the vast majority of people this means not doing a usual, everyday workout. It will simply feel too draining, and you’ll feel a lot of resistance towards forcing yourself through it. Walking and gentle yoga is enough for 99% of people!
      If you’re doing a zero-calorie water fast, then a protein shake most definitely breaks both ketosis and your healing metabolism.
      All the best

  2. Hi, this was one of the most informative articles I’ve ever read about water fasting. I have a question. Have you seen your clients with IBS improve their symptoms after a 3-day cleanse? I’ve been suffering day in and day out to the point where I am sick of eating, everything triggers a reaction out of my stomach, even low fodmap foods. I feel hopeless!

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

      Hi Yazmine,
      Thanks for writing. I have a lot of clients with IBS issues, and in my experience water fasting is the best thing you can possibly do to return to full health. Unfortunately, though, 3 days is unlikely to make much difference. It just doesn’t give you enough time to heal. (It is, however, a good introduction to fasting which provides a good preliminary cleansing.) Especially if everything is triggering a reaction in your case, you’ll probably need an extended fast. But don’t give up hope: you just need to commit a little more time. If you feel you don’t have the strength to get through it without support, that’s why I’m here!
      All the best,

  3. So im currently in day 6 of my 21 one day water fast. Ive been working out lightly. Im a 6 foot 220lbs man. Im using vey light weights, 5lbs and no more than 10lbs. A lot of compound movements and like i said before nothing to heavy. Ive been able to keep working out and i feel great. I did a 14 day fast last year and i didnt do anything and i felt really drained. should i Stop? I mean im mostly doing body weight exercises like small sets of 10 push ups, small sets of squats and lunges. am i doing this wrong?

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

      Hi Rafael,
      Thanks for writing. The main thing is to listen to your body. Most people feel fatigued by doing even only a few push-ups or squats – and so they shouldn’t! I always say about exercise (while fasting) that if it feels good, it probably IS good for you. If it doesn’t feel good, then it probably isn’t. Who am I to argue with you if you feel great? 🙂 You might just be one of those lucky exceptions who can work out while fasting and enjoy it!
      All the best,

      1. Thanks for your answer! I will do that! The moment my body starts to feel like it can handle it then i will stop. Also Thanks for being so open minded on this topic. I have found that a lot people like to go to the extremes of the arguments in fasting, its either “youre with us or against us” type of dynamic. Thanks again.

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

          Yes, I’m afraid there’s a lot of dogma in fasting, which leads to the ‘with us or against us’ attitude. I’d argue that, especially in fasting, dogma is dangerous. Dogma is driven by the mind, whereas fasting is something which takes place first and foremost in the body. It’s the body we need to listen to more closely!

          1. Completely agree. Thanks for your help. Have a great one!

  4. William Butcher Avatar
    William Butcher

    What are the differences between two water only fasts… one that has just distilled water and one that uses boiled distilled water where fruits/vegetables are added in the boiling process (so you are drinking water infused with whatever the boiling process takes out of the fruit/vegetable). Are there significant differences during the fast and after?

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

      Hi William,
      Apologies for the delay in responding. There’s been a glitch with messaging on the website.
      There are definitely differences! One is a zero-calorie fast and the other is not. Even if both are good for you, this is going to make a significant difference in terms of the cleansing and healing.
      All the best,

      1. William Butcher Avatar
        William Butcher

        thank you for your thoughtful reply. Are you able to elaborate more on what happens to the body when it is a zero calorie fast vs a very low calorie fast?

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

          There are lots of articles on this website to discuss what exactly happens to your body while water fasting. Just go to the homepage and scroll down! Compared to low-calorie fasting, zero calories facilitate much deeper cleansing and healing, but you’ll almost certainly feel much lower physical energy as a result. In my opinion it’s a price worth paying!

  5. Great article. Wish I read it this morning when on day 4 of my waterfast I decided start out the day with a 20minute HIIT-Training followed by a 14km(9miles) jog because I did not sleep last night and thought this will help me sleep tonight (also in 27celsius/81 fahrenheit without water because “I*m on a fast – my body can gain water from my fat cells”). I made my way home. After 6 hours, faining two times and vomiting countless times… I will only walk around the blog tomorrow. thanks for making clear why I felt this way.

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

      Hi Kristin,
      Thanks for sharing. Sorry to hear about what happened. Just listen to your body – which means if it doesn’t want to walk around the block today, you should just rest and recuperate from what happened yesterday!
      All the best,

  6. Such an interesting article. I would love to know if an extended fast, like 21+ days, would heal or improve the symptoms of a herniated disc. Have you had anyone who may have rhealed from this type of injury?

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

      Hi Chip,
      Thanks for writing. Herniated discs are tricky to predict… I’ve had both clients for whom there is longer term healing as well as clients who experience pain relief only during the fast itself (due to the anti-inflammatory effects of the fast). A lot is going to boil down to the degree of herniation. A fast can certainly heal tissue and even nerve damage, but when the disc has already begun to physically shift out of its normal position, there’s less scope for a fast to be effective.
      All the best,

  7. Thank you, I’m finding your articles really helpful! I just had a quick question about prolonged fasting and medication:
    I’ve been prescribed an SSRI (paroxetine) for depression but haven’t been taking it for about 3 weeks now, and the withdrawal side effects subsided also.
    I’m currently on day 4 of my water fast and will go back to taking them as they do make quite the difference. Do you suggest I start taking them again after my fast is over, especially as I haven’t been taking them for the last weeks, or is it safe to start them again still during the fast?
    I’m aiming to do around 20 days unless it feels right to end it sooner. My goal is to heal my joints and my lungs (I’ve been a smoker for a number of years now and have cut down significantly in the last week or so, especially now during the fast). I’m within a healthy BMI range and 21 years old.

    Thank you so much!

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

      Hi Agnes,
      Thanks for writing, and glad that you’re finding the website useful.
      I’m afraid there’s never a one-size-fits-all answer when it comes to SSRIs. After a fast as long as 20 days, you may even find you don’t need them, or that the dosage should be reduced. In my experience, SSRIs are frequently over-prescribed anyway – which isn’t to suggest that they’re not appropriate in individual cases. I’d suggest working through the possibilities with your doctor. If you’ve not been taking them before or during the fast, I personally don’t see any need to start taking them again before the end of the fast at the earliest.
      Hope this helps,

  8. Patricia Mustafa Avatar
    Patricia Mustafa

    I fasted for 10 days, awesome experience, I lost 20 pounds in those 10 days my only problem was not to have a back up plan after my fasting time and I end up having the same bad habits. I planning on going to do 10 days water fasting again with a better plan after I am done, like eating healthier and exercising more. Do you have any recommendations?

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

      Hi Patricia,

      Yes, eating habits can easily run into problems after a fast – fort many people this is in fact the hardest thing about fasting. In case you’ve not seen it, I deal with the issue in this video:

      Otherwise, different people have different bad habits in their eating – and these all require different solutions. So it’s hard for me to suggest specifically what you could try. A couple of things do apply to pretty much everybody. (1) Have a smart and reasonable plan for how you’ll eat after your fast well before you begin the fast itself. (2) After the fast, stick to this structure!

      It’s true that fasting helps you to feel what your body truly needs to eat. Unfortunately, though, the problem is that most people have so many addictions around food and eating, that usually a fixed structure is still easier to follow than your natural inclinations.

      This is also where exercise comes in. Along with fasting, exercising regularly will also help your body to show you what it truly needs to eat.

      When it comes to improving eating habits, I always say “2 steps forward, 1 step back.” Most people can’t totally fix their eating habits with just one fast. Addictions are simply too strong. This applies to people with both eating disorders and those whose addictions are less obvious. What I do find with my clients, though, is that each fast does make it easier to gradually give these addictions up. It just takes time, patience and willpower.

      Hang in there!

  9. Alice Vicaire Avatar
    Alice Vicaire

    Excellent video. ALL the replies I was looking for!!

    Thanks a lot!

    1. Tallis Shivantar Avatar
      Tallis Shivantar

      Glad it helped!

  10. hi Tallis,

    Once again i am very grateful for all the love and wisdom that you share with us , thank you from the bottom of my heart. This last year via water fasting I’ve been healing things that were holding me back for years, been as far as going to past life traumas …my last fasting my body asked to heal my broken heart ( harder fast ever, had to break it at day 4; due to arritmia and very low blood pressure, but it all made sense from a numerology point of view as well, It was a very hard decision for me , but I had to interrupt a pregnancy last year, and day 4 of the fast was the day that 9 months were due…the body remembers. so I am deeply humbled by this experience . Semi related to the video too, water fasting and period? This time around I feel that my body is asking me to fast now and my period is due now, I always struggle with it, lots of pain, but I’m curious if the” feeling good” hormones that kick in while fasting will help reduce my lower back pain ( when I fast it all goes away )…. thank you again for this new videos, learning so so much.

    much love Ju

    1. Tallis Shivantar Avatar
      Tallis Shivantar

      Hi Ju,

      Yes, the body does remember, and I’m not at all surprised by the anniversary bringing things up. As far as fasting when your period is due: depending on the length of time that you’re fasting, a fast which coincides with when your period is due can interfere with your cycle. Short fasts are unlikely to make any difference, but for fasts of between 4 and 10 days it’s generally best to time them to begin in the middle of your cycle, especially in the days following ovulation.

      Thanks for your kind words, and I wish you all the best for fasting in the future too 🙂


      1. Hi Tallis, thank you for your advise again, i will keep in mind the tip about the cycle for longer fasts , this time around is only a 3 day and i’ve been feeling ok, less pain for sure too, but thats also due to when I’m fasting im much kinder with myself and the way i move too 😎

  11. Thank you for all your wonderful information. I am a ultarunner also and was wondering how to add fasting to my training schedule. I started with 24 hr fasts then 36 hr and now I am doing 31/2 day fasts. I plan on doing 3 1/2 day fast twice a month with 24 hr fast the other weeks.
    Gary Sheets

    1. Tallis Shivantar Avatar
      Tallis Shivantar

      Hi Gary,

      That’s great you’re discovering fasting as counterweight to running :-). Sounds like you’ve made a good start at it too!

      You’ll see what works best for you – my only advice is not to treat your fasting schedule too strictly in terms of its regularity, especially when it comes to fasts of more than 24/36 hours. There are natural periods when the body wants to detox more, and natural periods when it wants to train more. For instance, you might find that you end up fasting more in the winter and less in the summer. Depending on where you live, you can also take advantage of being snowed in during certain times, so rather than force yourself to get outside to run, you can just stay inside and fast. Another natural time to fast is after an injury. I talk about all this at greater length in these articles:


      Also, in the long run you might find that doing one or two annual 7 day fasts works out better than more frequent 3-day fasts, in terms of their impact on your running schedule. I certainly do! Everything will find its own natural rhythm. In the meantime, just enjoy it!


      1. Thank you, Thank you, Thank you Tallis for sharing your knowledge on fasting and running! My last 2 runs have been full of energy, didn’t get tired and felt like I could run further but didn’t, don’t want to over train. I am 66 yrs old and you have given me the confidence to know that I have many years left of running. I hope you realize how much you help people through the sharing of your knowledge.
        You are AWESOME.

        1. Tallis Shivantar Avatar
          Tallis Shivantar

          Thanks for your kind words, Gary :-). I wish you many more years of running, fasting and health!

  12. The video is really interesting. Thank you.

    Quick question, do you know is water fasting is good for someone without a gallbladder? I’ve done a 3day fast but not longer and would like to increase that to 7, then 14 and possibly 21days.

    1. Tallis Shivantar Avatar
      Tallis Shivantar

      Hi Silvia,
      Thanks for writing, and glad you like the video. Fasting without a gallbladder shouldn’t be a problem, considering that its main function is to act as a container for bile. In the early days of a fast, the liver often secretes more bile than usual before reducing production and eventually switching off almost entirely.

      My advice, therefore, would be to precede your fast with a low-fat diet, in order to reduce the amount of bile secreted in the days leading up to the start of your fast. Another possibility might be (also) to try a liver cleanse or citrus diet beforehand. By lowering fat intake before the fast, you’ll maximise the chances of keeping bile production down (and any related symptoms such as acid reflux) in the early days of your fast. If you get past this stage, it should be clear sailing ahead afterwards.

      All the best,

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