Fasting for Three Days Could Reboot Your Immune System

Fasting diets have been slowly growing in popularity. But are they just a fad, or are there real health benefits behind them?

Dr. Valter Longo, Professor of Gerontology and Biological Sciences and Director of the Longevity Institute at the University of Southern California (USC), has been studying the effects of fasting for several years. In a study published in the journal Cell Stem Cell, Longo and his team found that fasting for 3 days had an effect similar to rebooting the immune system. 

The Effects of Prolonged Fasting

During prolonged fasting, our bodies change fuels. They turn from burning glucose to burning fat and ketone bodies. But fasting also causes a reduction in the number of white blood cells, which are in charge of helping us fight against infectious agents.

When you starve, the system tries to save energy, and one of the things it can do to save energy is to recycle a lot of the immune cells that are not needed, especially those that may be damaged.” said Dr. Longo. What we started noticing in both our human work and animal work is that the white blood cell count goes down with prolonged fasting. Then when you re-feed, the blood cells come back. So we started thinking, well, where does it come from?”

It turns out that fasting activates the stem cells that are in charge of replenishing our blood cells. Fasting reduces the concentration of PKA, an enzyme linked to aging, and IGF-1, a growth factor associated with an increased risk of cancer and tumor growth. Reduced levels of these two molecules encourages the stem cells to proliferate.

This, the authors note, could be especially useful for people with a weakened immune system, like elderly patients or patients receiving chemotherapy. Fasting cycles could kick-start the regeneration of their damaged immune systems.

Potential in Cancer Therapy

Dr. Longo’s group found that fasting protected mice against some of the negative effects of chemotherapy. What’s more, they found that after six cycles of fasting and chemotherapy, only the mice that had undergone fasting recovered their white blood cell numbers.

A similar effect was observed in a Phase I clinical trial with human cancer patients. The patients were asked to fast for 2-4 days within a six month period, apart from receiving chemotherapy. Like in the mice, fasting helped the patients recover their normal white blood cell counts.

However, the length of the fasting period is important. The authors write, “(…) the results from a Phase I clinical trial indicate that 72 but not 24 hr of prolonged fasting in combination with chemotherapy were associated with normal lymphocyte counts and maintenance of a normal lineage balance in white blood cells.”

Should You Fast?

Although fasting can seem extreme in our modern lifestyle, Dr. Longo points out that it was, until relatively recently, part of the normal human experience.

If you look at [people in medieval times in Italy] it’s amazing how many times they were without food (…) They could be without food for months and this was very, very common for everybody,” he said, in an interview with Dr. Rhonda Patrick from FoundMyFitness. “So fasting is part of the normal world. It is the normal world.”

Nonetheless, the authors advise that dietary interventions such as this should only be adopted under the close supervision of a physician.

These are exciting results although, as the authors mention, further testing is needed to confirm and expand them. “We are investigating the possibility that these effects are applicable to many different systems and organs, not just the immune system.” said Dr. Longo.

Following the positive results of his research, Dr. Longo has developed a fast-mimicking diet, designed to help consumers “get all the benefits of a 5-day fast…with food.” It is sold under the brand name ProLon and requires overview by a healthcare practitioner.

It will be exciting to see what new things their research uncovers.

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