If you want to stay healthy, the last thing you’d probably think of doing is fasting. After all, there are so many vitamins and minerals you need to help support your immunity, like vitamin C, zinc, and protein. So how could NOT eating anything at all be good for you and help support immunity?

fasting and the immune system

Well, a new study suggests that a bit of fasting can actually be good for your immune system. Scientists at USC say that fasting for two to four days can regenerate the entire immune system, even in the elderly. 

We could not predict that prolonged fasting would have such a remarkable effect in promoting stem cell-based regeneration of the hematopoietic system,” said author Valter Longo, Edna M. Jones Professor of Gerontology and the Biological Sciences at the USC Davis School of Gerontology and director of the USC Longevity Institute.

The study revealed some interesting information on how fasting periodically may impact the immune system.

Does Fasting Boost the Immune System?

How could not eating be good for your health? According to the USC study, fasting basically helps your body to reset its immune system, kicking it into high gear by the end of your fast and repairing damaged cells.

How does fasting and the immune system connection work?

Fasting for 2 or 3 days can be the key to restoring your immune system! #fasting #immunesystem

When you fast, you basically force your body to work extra hard to keep you going. You burn the fat you have stored around your frame, you use less energy, and so on.

Long-term fasting has been slammed as being unhealthy and of course we do need food to survive and thrive. The truth about fasting is more complicated than that. It is true that it can be a bit unhealthy if you’re not smart about it. Fasting or not providing your body with the nutrition it needs for long periods of time can lead to a number of health problems, not to mention an increase in fat storage.

Avoiding eating for the sake of health is not healthy, but when fasting is used periodically and in a controlled manner, it can have some immune benefits.

Intermittent Fasting and the Immune System

Short-term fasting, sometimes called intermittent fasting, basically kick-starts your immune system. The mild stress of fasting for a short time forces your body to produce new white blood cells, and floods your body with these disease-fighting cells. It’s like fasting hits the reboot button on your immune system, and by the end of those two or three days, you have a completely rejuvenated immune system.

Fasting, the Immune System, and Cancer

The study discussed above found that intermittent fasting can be particularly helpful for patients suffering from a suppressed immune system resulting from cancer treatments. Chemotherapy and other cancer treatments decimate the immune system, killing off most of the body’s natural defenses against disease.

By the end of the treatment, cancer sufferers usually have very little immune function, leaving them at risk for infectious diseases, and forcing them to take medication to boost immune function.

By fasting, though, cancer sufferers can basically force their bodies to reboot their immune system. This may help increase the production of the white blood cells that have been destroyed in the cancer treatment. Fasting regenerates the immune system, making it possible for their body to protect itself even after it is flooded with chemotherapy drugs and radiation. 

A fasting cycle results in the depletion of white blood cells and creates changes that trigger stem cell-based regeneration of new immune system cells. In particular, it reduced the enzyme PKA, which is the key gene that needs to shut down in order for these stem cells to switch into regenerative mode.

“It gives the OK for stem cells to go ahead and begin proliferating and rebuild the entire system,” explained Longo, noting that there are many potential clinical applications that mimic the effects of prolonged fasting to rejuvenate the immune system.

The research on fasting and immunity also has implications for patients afflicted by a wide range of immune system deficiencies, including autoimmune disorders such as rheumatoid arthritis, inflammatory bowel diseases, chronic fatigue syndrome and others.

In summary, intermittent and short-term fasting of 2-4 days regenerates the immune system and may protect against cancer cell formation, reduces free radical damage, and reduces inflammation in the body.

Other Uses of Fasting for Immunity

The effect of fasting on the immune system doesn’t stop there!

When you fast, your body basically has to scramble to find nutrients and energy, so it burns up a lot of what your body has stored in case of emergencies. This means that a lot of the inefficient or damaged parts of the body are eliminated during the fasting, basically resetting your overall health at the same time.

The fasting cycle of two or three days can actually help to restore a system that was severely damaged or decimated. This process is called apoptosis and may have a significant impact in reducing the risk of developing cancer or other diseases.

Fasting may also help fight off infectious diseases. White blood cells are broken down during the fast, which in turn forces the stem cells in your body to produce more. These new white blood cells are not just brand new, but they’re healthier and more effective than the previous cells–meaning they’re more effective at combating disease and illness.

To sum it up, fasting reboots your immune system, regenerates white blood cells for a better immune response, and replenishes any blood cells that have been lost! Pretty awesome reason to fast, right?!

Fasting and the Immune System: How to Fast Safely

If you want to benefit from the effect of fasting on your immune system, it’s important that you go about it the right way. Fasting can have negative effects on the body if sustained for more than a few days, which is why diets like the Water Fast and the Master Cleanse have been highly criticized by nutritionists and dietitians.

In this case, however, you are only going to be fasting for two or three days, which is much easier on your body. It’s not going to be an easy fast to go through with, but if you do it right, you should be able to make it through the 48 to 72 hours of fasting without too much suffering. This type of fasting should not be done more than a few times a year to help reset the immune system. There is no benefit to fasting all the time.

It’s important to prepare yourself for your 2 or 3-day fast BEFORE you start fasting. In the week leading up to the fast, slowly wean yourself off coffee, sugar, alcohol, and any other stimulants. Cut back on meat, fish, and dairy until you are accustomed to just eating fruits and veggies for a few days. Focus on soups, as they are water-heavy and will acclimate your body to getting more liquid. Eat some fruit, seeds and nuts, but focus on veggies.

For the 3 days before your fast, aim to eat as cleanly as possible. Avoid processed foods and sugar. Focus your diet on fruits, vegetables, whole grains and lean means. This will be easier on your digestive system, and will help acclimate you to the fast.

When it comes to the two or three-day fast, you’re going to be drinking your meals. You will not be eating anything, and your liquid options will be fairly limited as well. You can choose to do a water fast only, but that should be limited to only 24 hours. If you choose to add vegetable or fruit juices, you can extend the fast for up to three days.

Here’s what you need to know:

  • Drink at least 8 glasses of water per day in addition to any juices, teas, or broth you drink.
  • Dilute any juice you drink with water to cut acidity.
  • DO NOT drink tomato or orange juices, as they are very acidic.
  • Have at least 2 cups of herbal tea per fast day–particularly chamomile and peppermint, as they are very soothing for your stomach.
  • Squeeze fresh lemon into your water–about 1 lemon per cup of water.
  • Drink room temperature water as much as possible, as it will be easier on your digestive system.
  • Juice fruits and veggies yourself (apples, beets, carrots, cabbage, celery, and grape are the best).
  • Make green drinks with kale, spinach, and collard greens.
  • Optional- one shake per day with whey protein while intermittent fasting.

Once you get through the three days of fasting, it’s time for another 3 days of reintroducing foods. You want to ease your body back into solids, so these three days will help your stomach get accustomed to digesting once more. Start with steamed vegetables and move into whole fruits, grains, meat and then dairy. If you don’t feel well after eating a certain food, don’t try it again for another few days. This may be an indication that you are sensitive to that food.

Follow the instructions above to modify the fast as needed for your personal needs. If you have a medical condition and are trying to use fasting to improve your symptoms, work with a healthcare provider like a dietitian or doctor to determine the right type of fasting for you. The reintroduction part of the fast is just as important as the fast itself and only a knowledgeable healthcare provider can help you determine how to reintroduce foods correctly.

Fasting may help support an improved immune system when done correctly, but may also be dangerous for some people. If you feel extremely light headed, nauseated, or confused, stop your fast immediately and eat something with protein.

Once you come out of the fast, you’ll find that your immune system is all revved up and ready to go!



  1. https://news.usc.edu/63669/fasting-triggers-stem-cell-regeneration-of-damaged-old-immune-system/
  2. Lowe SW, Lin AW. Apoptosis in cancer. Carcinogenesis. 2000;21(3):485-495.
Kade Brittain