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Working out and exercise during a water fast: is it safe?

A lot of people who ordinarily work out or exercise in everyday life are tempted to continue doing so while water fasting. Usually the reasons revolve around maintaining fitness and the fear of losing muscle mass. But is it wise to continue exercising after your body has exhausted its glycogen stores? Like it or not, there are potential dangers in doing so. This video takes a look at what is safe, what is not, and why.

Please feel free to post comments at the bottom of the page if I haven’t answered any of your questions!


  1. Patricia Mustafa says

    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?

    • Tallis Barker Ph.D. says

      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!

  2. Alice Vicaire says

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

    Thanks a lot!

    • Tallis Shivantar says

      Glad it helped!

  3. ju says

    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

    • Tallis Shivantar says

      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 🙂


      • Ju says

        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 😎

  4. 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

    • Tallis Shivantar says

      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!


      • 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.

        • Tallis Shivantar says

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

  5. silvia kirk says

    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.

    • Tallis Shivantar says

      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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