Fasting Rejuvenates The Immune System!

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I’ve written about the benefits of fasting before and do recommend fasting on occasion to improve your health. As part of my healthy lifestyle, I fast at least one day per week, usually on the weekend. It’s become a routine now, and I don’t really find it that difficult. On my fasting day, I will drink a lot of green tea! Usually around 10 cups.

Some people might have problems with drinking green tea on an empty stomach because of the high level of tannins. These tannins can cause nausea by irritating the stomach lining. To get the most out of drinking green tea, I also recommend drinking matcha tea instead of sencha. Here is an article which explains the difference between Sencha and Matcha green tea.

Fasting restores immune function

A new study was just released in the Journal, Cell, which showed that fasting has remarkable effects on the immune system. It seems that just fasting for one day is not enough to induce a strong response either. You would have to fast for at least 2 days, but you will get a stronger response with a 5 day fast.

The study found the following changes occurred after repeated fasting cycles:

  • Fasting downregulated the IGF-1 / PKA pathway in stem cells.
  • Fasting protected cells from the effects of chemotherapy.
  • Fasting promoted stem cell renewal and reversed chemotherapy-induced immunosuppress

Initially, the fasting caused a drop in white blood count, but then after re-feeding, the white blood count increased to normal levels. This has effect has also been observed in animals and people on calorie restriction and it’s one of the reasons why it’s important that you get a full blood count test before starting the diet so that you can get a baseline number. I noticed my own WBC drop after starting calorie restriction – especially lymphocyte count.

In the past, researchers have shown that when mice are fasted before given chemotherapy or radiation treatment, they are able to survive much higher doses without any negative effects. This study confirmed what has been found before – fasting protects the mice from chemotherapy drugs.

In fact, 100% of the mice that were fasted survived compared to just 40% of the animals that weren’t fasted [Figure 1B]. They also noticed that the lymphocyte count was normalized in the fasted mice. In animals, and probably humans, repeated cycles of fasting can rejuvenate an immune system that has been damaged by toxic drugs or aging.

What the researchers investigated

The researchers looked at the level of apoptosis to a subpopulation of cells ( LT-HSCs, ST-HSCs, and MPPs) after 6 cycles of prolonged fasting (PF) + Chemo (CP) or chemo alone. Compared to just chemotherapy, they saw that prolonged fasting was able to have a significant effect on preventing cell death.

The researchers looked at the length of time it took to the recovery of lymphocyte count in control mice and found it took 70 days (6 cycles ) before recovery was seen; but in the fasted mice, the count was decreased independently by the fast. Recovery of the lymphocyte count was seen earlier at day 40 (cycle 4), probably because of the increased resistance to apoptosis of progenitor cells. By cycle 5 the fasted mice displayed a more normal lymphocyte / myeloid ratio as well, indicating higher resistance to the toxic effect of chemotherapy.

In a separate experiment, they were looking at the effect of fasting on old mice and populations of LT/ST – HTCs after 8 cycles of fasting. The researchers noted a temporary drop in white blood count during fasting, but an increase, over time, in HSCs above that of Young-AL & Old-AL mice. There was also a return to more normal and youthful levels because of the shift in balance by the end of cycle 8. A rejuvenation effect of the immune system.

Trials in humans

Phase 1 trials on human have been completed. Cancer patients noticed fewer symptoms associated with chemotherapy when they were fasted for up to 72 hours before treatment. The effect on PF + CP on humans is quite dramatic, as it almost ameliorated the significant drop in chemo-induced lymphocyte count as you can see in the table S1 in the supplementary data from the paper [1]. Researchers are currently planning phase 2 clinical trials to expand their research into larger randomized groups of people.

This is an extremely exciting area of research and something we can learn from and apply today. I wouldn’t personally try to fast for 5 days as 3 days seems to be sufficient. I’m considering trying to do a 3 day fast, once per month, in addition to my 24 hour fast each week.

Watch one of the researchers of this study talk about the benefits of fasting on cancer.


[1] Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic-Stem-Cell-Based Regeneration and Reverse Immunosuppression

Article reviewed and updated: February 2019.

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