A stronger immune system with water fasting

To boost your immune system specifically against coronavirus Covid-19, please see this separate article HERE.


  • Intro
  • How water fasting strengthens your immune system
  • Fasting to heal auto-immune issues
  • How to use water fasting to cure the flu or a common cold
  • How long does it take to fast out the flu or a common cold?


If you suffer from a weak immune system, water fasting is one of the best things you can do to strengthen it.

Similarly, water fasting is one of the oldest and most effective methods to regain health if your immune system is facing an infection such the flu. Personally, it’s what I do the moment I feel a virus beginning to stir inside me. And nine times out of ten the fast does its magic – and, miraculously, I stay healthy.

In fact, in the days before vaccines, fasting was even successfully applied in treating life-threatening diseases such as smallpox and typhoid. And during the era of the bubonic plague, doctors acquainted with fasting did just that in order to raise the chances of not becoming infected by their patients.

How water fasting strengthens your immune system

The secret to why water fasting is the strongest method for strengthening your immune system lies in the intestines. In everyday life, up to 80% of the cells comprising the entire immune system reside in the gut wall. This is because the gut wall is the single most vulnerable part of the human body to pathogens. It’s true that during flu season, airborne bacteria and viruses can and do penetrate the lungs. But every single time you eat – that is, three times a day, every day – your intestines are exposed to pathogens which are capable of breaching the gut wall as nutrients are absorbed into the blood. When you stop eating, however, this systematic exposure to pathogens ceases, allowing your vast army of defense cells to leave their usual guard duty and spread throughout the whole body in search of foreign bacteria and viruses.

In combination with this, the energy which would otherwise have been required for digestion is similarly freed up. This accounts for approximately 30% of the body’s total daily energy requirements. You won’t, however, feel this huge energy surplus in terms of extra physical strength. Rather, your body applies it to boosting detox and cleansing, which are managed primarily by the immune system, the lymphatic system, along with the liver and kidneys.

It takes about 24-36 hours after your last meal to start releasing cells of the immune system from the digestive system, as well as to strengthen detox and cleansing across the whole body. At this point, your immune system searches out and destroys not only the foreign invaders which cause illness and disease, but also the malfunctioning and dying cells of your own body. This process of ‘house cleaning’ is known as autolysis, and begins with the immune system itself. Blood tests, for instance, frequently show that the white blood cell count actually tends to decrease in the first few days of a fast. This doesn’t happen because your immune system is weakening but precisely the opposite: through culling those white blood cells which aren’t operating in top form. In other words, you end up with a leaner and meaner immune system.

This explains why increased levels of immunity continue not only during a fast but also for a significant period afterwards as well. Similarly, immunity against pathogens increases from fast to fast, as the strength of the immune system increases with each successive fast. I’ve noticed such a shift gradually take place within my own body. When I first began water fasting, I was always the first in my family to come down with niggling colds and coughs, but over the years it’s reached the point where I hardly ever get ill at all.

(In a moment we’ll take a look at how you too can strengthen your own immune system to fight off colds and the flu, as well stay generally healthy.)

Fasting to heal auto-immune issues

In addition to the long-term boosting of the immune system, fasting also brings the immune system into balance.  This is the reason that fasting can prove so effective in cases of auto-immune illnesses, in which the immune system no longer functions to protect the body or, in some cases, actually turns against and wages war against the body. I’ve had clients who have suffered from auto-immune issues as wide-ranging as ulcerative colitis, Hashimotos, multiple sclerosis (MS) and chronic fatigue syndrome (ME), and there isn’t a single case which hasn’t at least improved through water fasting. Sometimes you have to be patient, perhaps undertaking a series of fasts over many months – and especially so when a lot of healing must take place – but good things come to those who wait. (For fasting to heal from illness, please see the article ‘Self-healing through water fasting.’)

How to use water fasting to cure the flu or a common cold

Although some aficionados of water fasting might have you believe that every fast can provide an instant and almost magical cure to colds or the flu, this simply isn’t always true. There are a few key points you need to know before diving in the deep end!


I would advise anyone new to fasting not to tackle a common cold or flu this way, because over the first few water fasts a lot of your energy is devoted to clearing out a lifetime’s worth of accumulated toxins. Your kidneys are working overtime. Your liver is working overtime. Fasting with a virus or bacteria in your system only drains your energy further. You’ll feel truly lousy! Instead, begin by building up some water fasting experience while you’re healthy. This will start the process of strengthening your immune system, preparing it to act more effectively when illness does strike. It also means that when you do tackle a virus through fasting, your immune system won’t get dragged down by having to do a lot of maintenance cleansing as well. Instead, your body will be able to focus solely on clearing the pathogen.

As I found out myself, fasting out a minor illness does eventually become easier, but you’ll never feel as good compared to fasting while healthy. In order to reach the point where such a fast doesn’t completely knock you out, you’ll probably need to have enough experience that you’re already comfortable in undertaking 7-10 day fasts. This doesn’t mean you’ll actually need to fast for 7-10 days in order to cure yourself of a flu (see below). But it does mean that you’ll need to have done the kind of maintenance cleansing achieved through one or more 7-10 day fasts. I know I did.


It’s important to begin such a fast as soon as you feel the pathogen in your body. As with so many other things, an ounce of prevention is worth a pound of cure, and starting your fast early on in the illness will accelerate the healing process, reducing the necessary length of the fast.


It’s important to continue the fast at least until all symptoms have stopped. If, for whatever reason, you discontinue the fast beforehand, the pathogen may well regain momentum against you. To be on the safe side, it’s worth continuing the fast for at least an additional 24 hours after symptoms have disappeared, depending on the particular pathogen.

(A more detailed explanation of these three points can be found in the article: Fasting against Coronavirus: how to boost immunity and maximize health.)

Check out the webshop on waterfasting.org

The webshop offers downloadable fasting plans and guides to help make your water fast a success.

How long does it take to fast out the flu or a common cold?

Anyone thinking of applying a water fast to a cold or the flu is bound to ask: ‘how long am I going to have to fast?’ There’s no fixed answer here.

First there’s you. The more experienced in fasting you are, the quicker your body will shut down the digestive system, step up cleansing and begin to fight the illness. Also, the more fasting you’ve done, the less energy you’ll have to waste on maintenance cleansing.

Then there’s the pathogen. The more virulent the pathogen, the longer you’ll need to fast. If you begin the fast early enough, two days may suffice for minor colds. In my experience, this is the minimum time required for any pathogen, because in any case you need 24-36 hours to release the immune system from the gut (see above).

For the flu, I find that three days or so is more likely. For something as serious as typhoid, the famous Dr. Herbert Shelton says that a fast of 7-10 days is enough, with patients stabilizing around the third or fourth day (The Science and Fine Arts of Fasting, p. 429). In any case, it will take experience in applying water fasting to minor illnesses before you’re able to get a better feel for how you react and how long you’ll need. Every illness is different. Every fast is different. The strength of every immune system is different. Practice makes perfect!

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8 responses to “A stronger immune system with water fasting”

  1. Hi Dr Barker
    I love your website. Thank you for giving so much information.
    Two years ago, just 6 weeks after giving birth to my baby, I got an abnormal PAP test result with ASCUS and HPV (high risk) infection. A year later I got the same result. I took a multivitamin, vit D3 ( I was deficient) and Astragalus every day. I also ate lots of meat and fatty dairy against my best judgment. This year, my third PAP test is still showing HPV and now high grade lesions. I was devastated. On top of that, my blood tests showed low white blood cells and high bilirubin and high cholesterol. That would be possibly explaining the slight pain/burning sensation behind my right shoulder for almost a year…perhaps fatty liver? I was advised (more like pressured) to do a colposcopy and been told that it may be cancer. . I refused because I am afraid that a terrible diagnosis would get stuck to my brain, devastate me emotionally which would be even worse for my healing. . Instead I prefer to just do whatever I would do anyway if that was the case. I never take any medications and generally eat organic food. I now stopped eating meat and dairy but eat fish sometimes. I did a 48h fast and the pain/burning behind my right shoulder vanished since then. I am starting a longer fast. Reading some studies, it seems that the virus causes cancer and also prevents autophagy. I was wondering if you’ve ever come across someone with hpv and ASCUS or high grade lesions or cervical cancer and if water fasting worked for this and how long did it take to clear? I am also going to start taking probiotics Lactobacillus Crispatus and L. Gasseri to try to improve the microbiome and I am doing microbiome tests every 3 months to monitor it. Can I take the probiotic while fasting or is it best to not take any supplements?
    Thank you so much 🙏

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

      Hi Sue,
      Thanks for sharing, and I’m glad you’ve found the website useful! Although I’ve worked with numerous clients with different types of cancer, cervical cancer is not yet one of them. What I can tell you is that you will certainly need a much longer fast. Part of the reason is precisely because certain viruses such as HPV – as well as herpes, Epstein Barr, the bacteria which causes Lyme disease and others – do try to hide from and hijack (‘down-regulate’) the immune system, meaning that it takes longer for the fast to ‘find’ them.

      As you mention, trying to improve the gut biome is also an important strategy. Equally important, however, is looking beyond diet: towards the deeper emotional issues which so often underlie chronic illness. This is probably one of the most important aspects when I’m working with clients who suffer from cancer, and it is an essential part of the fast’s healing power.

      Hope this helps,

  2. Sabrina Swainson Avatar
    Sabrina Swainson

    Hi again Tallis,

    Well, it’s been a while since I posted with the toothache and then we had an hour’s conversation when we worked together with a consultation. I jusut t noticed that the posts don’t have dates on them and I didn’t keep track of how long ago I posted and then we talked, but after our conversation, when I told you my tooth was better, well the toothache came roaring back! But it was all in service of health. I realized that even if the pain went away, I needed to keep up with the antibiotics. They are holistic not pharma but they still need time to work so I went ahead and did a full 2 weeks of using collodial silver and garlic. And the pain went away again and has not been back since.
    I credit that to the fact that, I went ahead and did a 3 day fast, starting a few days after my tooth stopped hurting for the 2nd time. After our talk I felt so inspired to break my 48 hour challenge point in a 3 day fast that I went the full 3 days and at the end of that, I was not hungry, not tired or achy or anything so I went another 24 hours. At the beginning of the 5th day, I did feel tired and hungry so I broke the fast after 99 hours.
    I feel that I would not have been able to jump the psychological hurdle from 48 hours to 99 if we hadn’t spoken.
    I now plan to do another 3 day in May to get really comfortable doing so and maybe another in June or July, just so my body gets really comfortable with making the switch from glycogen burning to ketosis.
    I am looking towards eventually being ready to do the 7-10 day with your guidance, to really unlock deeper healing, both physical and psychological. But most of all I hope to have more ease accessing spiritual modes in the way the body gets more at ease in accessing the ketogenic way of metabolizing.

    Thank you for all you do.

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

      Hi Sabrina,
      Thanks for sharing, and congratulations for making it into the 5th day :-). That’s great news! You did the right thing to continue medicating your tooth, because it would probably have taken considerably longer for a fast alone to heal the issue. I’d just like to emphasise – as you’ve done yourself – that it doesn’t always have to be black-and-white fasting alone or medication alone. Fasting and other modalities can often support each other in the journey back to full health.
      All the best,

  3. Hello Tallis,
    I hope that you are well in these trying times of the COVID virus.
    Two nights ago, I came across your blog while researching water fasting. I have now read many of your posts and the comments too. As one of the people who responded said it is rare to find someone actually ‘at home’ and replying to comments, especially with so much knowledge, professionalism and compassion.
    At first, I was just gleaning information but I now want to work with you. Here’s why.

    Right now I have an abscessed tooth which has progressed to the throbbing stage and is involving the neighboring lymph nodes. I knew something was up but I was determined to handle it with collodial silver and garlic and I started a 3 day water fast 50 hours ago.
    Now my partner wants me to go to the dentist and the pressure to do so is growing. But I have a (well-justified) phobia about dentists and don’t want to take pharma antibiotics.

    In reading this post about A Stronger Immune System, it seems that, with an active infection, this may not be the optimal time to fast. Another question that has also emerged with the reading is whether a 3 day fast is long enough. Also, from another post, I learned I should have cleaned my system out more thoroughly and eased into it with green drinks.

    I am going to fill out your intake form for the consultation because I need personal coaching and I know the value of that. But I thought I’d post this here to get things going and to offer it to someone else who is reading your posts and the comments as carefully as I did but who perhaps can’t afford coaching right now.
    I will post again once we’ve worked together and share my experience. I really want to get healthy again!
    After a sickly childhood, and an average adulthood of declining health, I worked hard in my 50s to get healthier and I felt vibrant most of the time! But I supported that with a lot of supplements and I can’t do that right now. At 63 I have lost the connection to that feeling of vibrant health and am now shying away from ‘hard things ‘that I used to tackle full on. I know some of it is feeling the unease and sheer pain that most of us are feeling on a global scale right now, because of the virus. And as you know, present pain like a toothache makes everything seem a bit more bleak.

    I need coaching to help me find my way back to be stronger for whatever is coming and I would also like to feel more connected to my spirit and less connected to my body.

    Thanks for taking the time to read all this. May you continue to be well and happy.

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

      Hi Sabrina,

      Thanks for sharing, and I look forward to receiving the contact form so we can get started. I don’t like to comment on specific cases – especially when they concern specific health problems – in this public space, because so often things can be taken out of context and misapplied by other people.

      No, it’s not an ideal time to fast if you’re concerned with general detox and health, but it’s very much the ideal time to fast if the purpose of the fast is specifically to deal with this problem. I’m going to say here and now, though, that if the abscess is deteriorating quickly, a water fast may not be enough to turn the tide. We’ll just have to see. This will also depend on how quickly your body can access deep healing over the coming days. If we work together, it may also be worth involving elements of dry fasting, as this is even more effective than water fasting in reducing inflammation and strengthening the immune system. I’m not going to go into any greater detail about this here, though, because dry fasting is an extreme practice, and I don’t want anyone to get any ideas about (mis)applying this to their own situation. Dry fasting to address a health issue is always best practised with expert advice alongside.

      In the meantime, please continue your water fast, and I look forward to hearing from you soon,

  4. Does prolonged fasting help fight or possibly cure viruses like hpv? Will the body be able to autolyze warts during a 14-30 day water fast?

    1. Tallis Shivantar Avatar
      Tallis Shivantar

      Hi Jay,

      Prolonged fasting strengthens your immune system, and this is the reason why you can fight viruses more effectively, both while fasting as well as in the months afterwards. Unfortunately, it’s impossible to tell ahead of time whether or not a water fast will actually fully heal you from stubborn viruses like hpv, but it will depend largely on the length of the fast and the strength of your own immune system. In terms of autolyzing warts, there’s a good chance that 14-30 days should be enough, especially if the final length of the fast is closer to 30 days.

      When using fasting to tackle illnesses, I often work with clients using periods of dry fasting within a prolonged water fast in order to maximise healing. I can’t go into specific details here in this public space, as every case is different, every person is different in how easily they respond to dry fasting, and I don’t want to encourage everyone to dive too deeply into dry fasting, because without proper guidance this can easily lead to breaking off the fast too early.

      I would definitely encourage you to aim for the longest possible water fast that you can manage both physically and psychologically, as this will reap the greatest benefits.

      All the best,

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