How a 3 Day Fast Resets the Immune System

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3 day fast, How a 3 Day Fast Resets the Immune System

3 day fast, How a 3 Day Fast Resets the Immune SystemHow a 3 Day Fast Resets the Immune System

Your immune system is your body’s defense system against bacteria, viruses, parasites, toxins, and other harm. To function properly, your immune system needs your support through a healthy diet and lifestyle – including fasting. According to research, embarking on a 3 day fast can reset your immune system and make an enormous difference in your health.

In this article, you will learn more about fasting and the immune system. I will share with you some new exciting research explaining how fasting may benefit your immune system. You will learn what to expect during your 3-day fast, how to prepare for your fast, and how to properly break your fast.

3 day fast, How a 3 Day Fast Resets the Immune System

Fasting and the Immune System

The immune system is the basis of your health and survival. It is your body’s defense against infections. If you didn’t have an immune system, your body would be vulnerable to attack and harm from viruses, bacteria, parasites, toxins, and more.

Thankfully you have your immune system to look out for you. It is a network of cells and tissues working together. They are on a constant lookout for invaders. When they encounter any pathogen or harm, they send an immune response in order to fight off the harm and protect you.

However, stress, unhealthy foods, and exposure to toxins can weaken your immune system. You can use all the help to boost your immune system and protect your body. According to research, fasting, a period of not eating, may help to boost your immune system. As little as a 3-day fast may make a tremendous difference. Let’s learn how.

3 day fast, How a 3 Day Fast Resets the Immune System

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I could not be happier with the content in this book that you can review here.   It is by far the best book on fasting the world has ever seen and I have read them all!  It is now, my great honor to present this to you and I am deeply appreciative of your support!

3 day fast, How a 3 Day Fast Resets the Immune System

3 Day Fast Resets the Immune System 

According to an exciting 2019 study recently published in the Cell: Stem Cell research journal, prolonged fasting lasting from 48 to 120 hours can benefit your immune system and activate pathways that enhance resistance to toxins and stress. Mice and phase 1 human trials on chemotherapy patients both suggest that a period of fasting may significantly lower white blood cell count.

Fasting may help to activate regeneration and signal pathways to hematopoietic stem cells that allow the generation of blood and a healthy immune system. During fasting, your body tries to save energy. In order to do that it ends up recycling old and damaged immune cells allowing room for new ones.

The study also found that fasting may also lower IGF-1 growth hormone levels that have been linked to cancer, tumor growth, and aging. These findings support previous research that found that fasting and chemotherapy may be more effective than chemo alone. Fasting 72 hours before chemotherapy may boost the immune system and benefit chemotherapy patients (1, 2, 3)

3 day fast, How a 3 Day Fast Resets the Immune System

3 Day Fast For Brain Health and Inflammation

Fasting, however, is not only potential good news for cancer, but it has many other immune-system and health benefits. Research has shown that fasting may reduce autoimmunity of the body. According to one study, fasting may reduce the risk of Parkinson’s and Alzheimer’s disease by stimulating messaging chemicals such as Brain Derived Neurotrophic Factor (BDNF) that plays an important role in the creation of new brain cells.

Fasting may also reduce overall inflammation in the body.  According to a 2017 study, fasting for only 24 hours may help to deactivate the human NLRP3 inflammasome. The inflammasome is a multiprotein intracellular complex. It is part of your body’s innate immune system that is in charge of activating inflammatory responses. Results suggest that fasting may enhance mitochondrial resilience, prevent inflammation, and have an anti-inflammatory effect on your body (4, 5).

3 day fast, How a 3 Day Fast Resets the Immune System

What To Expect on a 3 Day Fast

Periods of fasting is natural for your body. If you think about it, our ancestors have gone through periods of famine when food was simply not available for a few days. In our modern world, we are used to everything being readily available. If our fridge is empty, all we have to do is go to the nearest grocery store, go to a restaurant, or order in. 

When food is so easily available, we need to do intentional fasting to reduce the stress on our digestive system and body. A 3-day fast allows your body to rest, repair, and renew.

While a 3-day fast will certain bring many positive changes to your physical, mental, and spiritual health, a 3-day fast is also new and stressful to your body. You may experience some unwanted symptoms associated with your 3-day fast.

I want you to know that some unpleasant symptoms are normal and natural. This is what you may expect on your 3-day fast:

3 day fast, How a 3 Day Fast Resets the Immune System

Day 1

Unless you are already keto-adapted from practicing a keto diet and intermittent fasting, your body is used to using sugar as a primary fuel source. During your 3-day fast, your body will adapt to using fat as fuel resulting in an initial rise in your ketone levels the second half of your first day and a period of adjustment. Don’t worry, becoming keto-adapted allows higher levels of autophagy and cellular cleansing.

On your first day, you may experience some fatigue, mental lethargy, hunger, cravings, mood changes, increase urination, headaches, and sleep disturbances. This is nothing to be concerned about. These are all happening because your body is adapting to burning fat instead of sugar, detoxifying and cleansing, and beginning to repair months or years of damage.

3 day fast, How a 3 Day Fast Resets the Immune System

Day 2

Going on a 3-day fast helps to de-weed your gut flora. It gets rid of bad bacteria helping to balance your microbiome. By day 2, there is increased cellular cleansing, autophagy, a rise in human growth hormone (HGH) to preserve muscle mass, and a stem cell rise to help cellular repair. This 3-day fast also helps to reset your DNA turning off ‘bad’ genes that may increase inflammation and chronic degeneration. It also helps hormone optimization and detoxification.

On day 2, you may continue to experience similar symptoms as on the first day. Your hunger levels may diminish but emotionally you may have a more difficult time. You may experience more fatigue, brain fog, and mood changes. As your body is cleansing itself and getting rid of bad bacteria, fungi, and toxic substances, you may notice a white, yellow, or even black tongue, or skin rashes.

Your body will also begin to downregulate your thyroid hormone resulting in feeling colder than normal. This simply means that your 3-day fast helps to rest hormone sensitivity. Your body is learning to need less thyroid hormones and insulin to function well (7, 8, 9)

3 day fast, How a 3 Day Fast Resets the Immune System

Day 3

On day 3 you will have a large rise in ketones. There will be a further rise in autophagy, HGH, and stem cells. Your blood sugar levels become more balanced. What does this mean for you? You will be feeling better!

You may notice pain reduction and more energy. Your brain loves using ketones for energy so you will be feeling mentally better, sharper, and more alert. If you were not keto-adapted before, you may still experience occasional tiredness, brain fog, or other unpleasant symptoms. By the time you will be ready to break your fast, chances are that you will be feeling better than ever.

If you want to learn more about what to expect on your 3-day fast or other extended fasts, I recommend this article

3 day fast, How a 3 Day Fast Resets the Immune System

How to Prepare for a 3 Day Fast 

While going on a 3-day fast is beneficial and healing for your body, it can also be a huge shock and stressful if you don’t prepare your body and mind well for your fast. To prepare for a 3-day fast, I generally recommend going on a ketogenic diet and practicing intermittent fasting for at least 2 to 3 weeks before your 3-day fast.

This will help you to become keto-adapted and put your body into a fat-burning mode which will reduce your negative symptoms and ramp up your benefits. Trying one of two 20 to 24-hour fasts the couple weeks leading up to your 3-day fast may also be beneficial. 

To learn more about the ketogenic diet, read this article. To learn more about intermittent fasting, I recommend this articleI also recommend a few other strategies to help you prepare for your 3-day fast.

3 day fast, How a 3 Day Fast Resets the Immune System

Create a Low-Stress Schedule

During your fast, your body will be cleansing and repairing. Stress can be incredibly draining on your body, mind, and soul. A 3-day fast is time for healing. Find ways to reduce stressors in your life. Meditate, pray, journal, do breathwork, and relax.

Do Your Best to Avoid Negative People

Negative people in your life can increase your stress levels and drag you down. During your 3-day fast, try to distance yourself from people who bring you down. Surround yourself with supporting individuals and practice the attitude of gratitude for the loving people in your life.

3 day fast, How a 3 Day Fast Resets the Immune System

Get Plenty of Filtered Water

Hydration is key when you are fasting. As your body uses up stored sugar from your muscles and liver and your insulin levels drop, you may experience dehydration. This is why it’s crucial that you drink at least an ounce of water per pound of your body weight. 

Have Some Good Salts Available

Using good quality salts, such as Himalayan sea salt, Celtic sea salt, or Redmond’s real salt helps to maintain electrolyte balance while fasting. If you feel tired or dizzy during your 3-day fast, mix a pinch of salt with 4 to 8 oz of water or simply put it under your tongue (10).

Schedule a Spa Day

During your 3-day fast, you will be saving money on food. Use this money to pamper yourself. Get a massage. Go to a sauna. Relax.

3 day fast, How a 3 Day Fast Resets the Immune System

Avoid the Kitchen if Possible

The kitchen can be a tempting place and remind you of all the good food you are not eating. Avoiding your kitchen is the best way to reduce emotional cravings and temptations. If you have cravings or feel hungry, drink some water or herbal tea. If you are normally in charge of cooking for your family, ask for help for three days or cook for them ahead of time.

Drink Strategically

During your 3-day fast, the most likely you will feel hungry is around your normal meal and snack times. Make sure to drink plenty of water or herbal tea during these times. 

3 day fast, How a 3 Day Fast Resets the Immune System

Try a Sweet Drink

If you are missing flavor or feel deprived during your 3-day fast, try a calorie-free lemonade by adding organic lemon juice and a bit of stevia to your water. A bit of sweetness can make your 3-day fast much easier.

Get Grounded Daily

Grounding has many benefits, including more energy, relaxation, mental clarity, and feeling of connection. Stand or walk barefoot outside. If it’s cold outside, try a few minutes in your socks, as long as you can tolerate it. To learn more about grounding, read this article.

Get Sunshine Each Day if Possible

Sunshine helps to stimulate vitamin D, enhances fat burning, and boosts your mood. As long as the sun is out, make sure to get some sunshine. You may combine this with your grounding practice and walks.

Move Your Body

While I recommend that you stay away from serious exercise during your 3-day fast, going out and talking some easy walks can be helpful. It stimulates your circulation and lymphatic system and boosts your mood as well. Aim for 10 to 15 minutes 3 to 5 times a day or whatever feels best for your body.

3 day fast, How a 3 Day Fast Resets the Immune System

Give Yourself Permissions to Rest

Our society puts so much emphasis on productivity and hustle. Give yourself permission to take it easy during your 3-day fast. Take naps, take a warm bath, try some essential oils, journal, meditate, and simply relax.

To learn more about how to prepare for your 3-day fast, I recommend this article.

3 day fast, How a 3 Day Fast Resets the Immune System

How to Properly Break a 3 Day Fast 

Breaking your 3-day fast properly is just as important as preparing for it and experiencing it. Your body has been resting, detoxing, repairing, and most importantly, living without food for 3 days. Eating too much too fast can lead to uncomfortable symptoms, including digestion issues or fatigue. Refueling with heavy, sugary, or junk foods can be counterproductive to the healing that just took place. In rare cases, eating too much food too quickly after a period of calorie-restriction can result in refeeding symptoms, a potentially fatal condition resulting from electrolyte and fluid imbalances (11)

Though refeeding syndrome is less likely to happen after a short 3-day fast, you want to avoid any discomfort and health issues. To make it easier on your body and to set yourself off for a healthy path, it is important that you know how to properly break your 3-day fast.

For every 2 to 3 fasting days, you should have at least one recovery day aiming to gradually increase your calories without overburdening your system. For the first day after your 3-day fast, I recommend about 50 percent of your normal caloric load.  On the second day, you should be back to your normal diet and caloric load.  

It’s more than just the calories though. The foods you eat after your 3-day fast matter too. Make sure to eat organic real foods to avoid any toxic chemicals or unhealthy ingredients. Be easy on your stomach by focusing on liquid foods, such as green juice, green smoothies, protein shakes, soups at first. As you are ready to move onto solids for your second or third meal, try steamed vegetables, fermented foods, fruits, and healthy fats, such as avocados, coconut oil, and olive oil. Hold off on meat, dairy, eggs, nuts and starches until your normal eating days.

Once you are ready to presume with a normal calorie intake, I recommend that you continue eating an anti-inflammatory diet. You may benefit from practicing intermittent fasting as well. To learn more about how to break a fast properly, I recommend this article. To learn more about an anti-inflammatory ketogenic diet, read this article. You may learn more about intermittent fasting here.

3 day fast, How a 3 Day Fast Resets the Immune System

Final Thoughts on The 3 Day Fast

The purpose of your immune system to protect you against bacteria, viruses, parasites, toxins, and other harm. To help its proper functioning, it’s important that you support your immune system through a healthy diet and lifestyle.

New research has found that a 3-day fast can reset your immune system and make a great difference in your health and well-being.  Follow my tips and experience the benefits of a 3-day fast yourself.  For more info, feel free to check out my complete Fasting Transformation Quickstart Program.  

3 day fast, How a 3 Day Fast Resets the Immune System

Sources in This Article Include:

1. Cheng, CW, Adams, GB, Perin, L, Wei, M, Zhou, X, Lam, BS, De Sacoo, S, Mirisola, M, Quinn, DI, Dorff, TB, Kopchick, JJ, Longo, VD. Prolonged Fasting reduces IGF-1/PKA to promote hematopoietic stem cell-based regeneration and reverse immunosuppression. Cell Stem Cell. 2014 Jun 5; 14(6): 810–823. PMID: 24905167
2. Wu, S. Fasting triggers stem cell regeneration of damaged old immune system. USC News. Link Here
3. Marziali, C. Fasting weakens cancer in mice. USC News. Link Here
4. Buono, R, Longo, VD. When fasting gets tought, the tough immune cells get going-or die. Cell. 2019 Aug 22;178(5):1038-1040. PMID: 31442398  
5. Anft, M. Don’t feed your head. John Hopkins Magazine. Link Here
6. Traba, J, Geiger, SS, Kwarteng-Siaw, M, Han, K, Ra, OH, Siegel, RM, Gius, D, Sack, MN. Prolonged fasting suppresses mitochondrial NLRP3 inflammasome assembly and activation via SIRT3-mediated activation of superoxide dismutase 2. J Biol Chem. 2017 Jul 21;292(29):12153-12164. PMID: 28584055
7. Haas JT, Staels B. Fasting the Microbiota to Improve Metabolism? Cell Metab. 2017; 26(4): 584-585. PMID: 28978420
8. Pietrocola F, Pol J, Kroemer G. Fasting improves anticancer immunosurveillance via autophagy induction in malignant cells. Cell Cycle. 2016; 15 (24):3327-3328. PMCID: 5224452
9. Mihaylova MM, et al. Fasting Activates Fatty Acid Oxidation to Enhance Intestinal Stem Cell Funciton during Homeostasis and Aging. 2018 May; 22(5): 769-778. PMID: 29727683
10. Brands MW, Manhiani MM. Sodium-retaining effect of insulin in diabetes. Am J Physiol Regul Integr Comp Physiol. 2012; 303(11):R1101-9. PMCID: 23034715
11. Mehanna HM, Moledina J, Travis J. Refeeding syndrome: what it is, and how to prevent and treat it. BMJ. 2008; 336 (7659):1495-8. PMCID: 2440847

3 day fast, How a 3 Day Fast Resets the Immune System

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Dr. Jockers

Dr David Jockers is passionate about seeing people reach their health potential in mind, body and spirit. He is the host of the popular “Dr Jockers Functional Nutrition” podcast and the author of the best selling books, “The Keto Metabolic Breakthrough” and “The Fasting Transformation.


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  1. Thanks for the tips on the “sweet drink” to help with fasting. I’m kind of sensitive to stevia though. Can I substitute kombucha (diluted) instead? Thanks!

    1. Unfortunately not if you are trying to do a water fast as the sugar in the kombucha will elevate your insulin. If you are doing a juice fast or a partial fast this is fine!

  2. Thanks, this is a good concise and clear set of guideliness.

    What are your thoughts on whether fasting is contraindicated in cases of the following conditions: chronic fatigue, high toxic load, hyopthyroid, fatty acid oxidation disorder, adrenal dysregulation?

  3. I take a lot of supplements should I curtail them? And I also start my morning with a drink of warm water a squeezed lemon some squeezed ginger and apple cider vinegar should I stop that too. Thank You

  4. Hope you had a nice birthday, Dr. Jockers!

    The very first fast I ever did, I couldn’t stop reading – cookbooks! Eventually I found some Christian prayer and fasting books, like those by Jentezen Franklin. I find a tongue scraper to be very helpful. I got mine on Amazon very inexpensively. It’s a stainless steel U-shaped, flexible little device for getting the fur off the tongue. In a pinch, a spoon will work as well. Also, dry skin brushing with a natural bristle brush feels lovely. I think the bone broth fast would be easier.

      1. but the indians recommend a copper scrapper or if you are rich, a silver one.. i don’t wash my hands before eating, even after public transport and touching money…doesn’t matter what…and never had a problem until i was at hospital, went in for an unrelated condition A, there i gained a condition B and got poisoned and started vomiting..lesson learned.. there wouldn’t be a problem if hospitals still used copper surfaces, but since they maliciously stopped that, there is the place where you definitely have to wash…

  5. I didn’t make it to a 3 day water only fast. I did perhaps 2+. I had to stop because of elevated heart rate, dizziness even with mg, K and NaCl in plenty of water. I checked my blood glucose and it was 19! Ketones of course were high ca. 4.5
    I had resorted to sips of bone broth on day 2, which I sorely needed. Of course I was cold, but I understood that.

    1. Sorry to hear that! It appears that your body is glucagon resistant and isn’t raising up your blood sugar where it needs to be. I think a bone broth fast would be best for you to keep your blood sugar more stable!

  6. Anyone have any info on as to why my blood sugar drops so low while fasting…..I do not have diabetes. Normal blood sugar is around 80-90. Usually after fasting for 48 hrs blood sugar dips in the 60’s. This last time 54.
    Only Med I take is levothyroxine.
    Thanks for any comments !

    1. This is completely normal on a fast. Your body will increase its energy production from fat/ketones and your blood sugar will drop down. For some people, it gets into the 40-50’s which is ok, as long as they feel good. If you feel excessively tired, have anxiety, trembling, headaches, nausea, etc. than that would be a sign your body isn’t getting the ketones and the sugar is dropping and causing problems.

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