Editor’s note: This article was originally published in 2018 and was updated in April 2026 to reflect Ideapod’s current editorial standards and The Sovereign Mind Framework.
Researchers at the University of Southern California found that prolonged fasting may trigger stem cell-based regeneration of the immune system — a discovery the research team described as “remarkable.”
The study suggests that cycles of extended fasting force the body to break down damaged immune cells and generate new ones, with potential implications for aging, chemotherapy recovery, and overall immune health.
While fasting has traditionally been viewed with skepticism by the medical mainstream, these findings point to a biological mechanism that could explain why temporary food restriction appears to benefit immune function. The key lies in what happens when the body is deprived of its usual fuel sources for an extended period.
The scientists were surprised by their findings
“We could not predict that prolonged fasting would have such a remarkable effect in promoting stem cell-based regeneration of the hematopoietic system,” said Prof Valter Longo, Professor of Gerontology and the Biological Sciences at the University of California.
“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,” Longo said.
“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?”
The implications of these findings are enormous: with a renewed immune system, we are increasing the chances of a long and healthy life. In fact, yogis and sages have done this through the ages as we all know. Western medicine is only catching up now.
How prolonged fasting triggers regeneration
Prolonged fasting forces the body to use stores of glucose, fat and ketones, but it also breaks down a significant portion of white blood cells.
During each cycle of fasting, this depletion of white blood cells induces changes that trigger stem cell-based regeneration of new immune system cells.
In the same research that I cited above, the team from the University of California gathered a group of participants and asked them, in the initial stages, to fast for 2-4 days on a regular basis over a period of six months.
This is where they made a remarkable discovery.
There was a noticeable decrease in the production of the enzyme PKA, a hormone which has been associated with an increased risk of cancer and tumor growth. In addition the immune system of the participants appeared to get renewed.
“PKA 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.
Prolonged fasting resets your immune system
Longo continued:
“And the good news is that the body got rid of the parts of the system that might be damaged or old, the inefficient parts, during the fasting. Now, if you start with a system heavily damaged by chemotherapy or aging, fasting cycles can generate, literally, a new immune system.”
This is truly an incredible finding.
While these results are promising, the researchers emphasized that more clinical studies are needed before prolonged fasting can be recommended as a therapeutic intervention. Any extended fasting should be undertaken under medical guidance.
Prolonged fasting may mitigate the harmful effects of chemotherapy
Prolonged fasting also protected against toxicity in a pilot clinical trial in which a small group of patients fasted for a 72-hour period prior to chemotherapy, which is good news for cancer patients and others who receive chemotherapy for autoimmune diseases.
“While chemotherapy saves lives, it causes significant collateral damage to the immune system. The results of this study suggest that fasting may mitigate some of the harmful effects of chemotherapy,” said co-author Tanya Dorff, assistant professor of clinical medicine at USC.
She added that more clinical studies are needed, and any such dietary intervention should be undertaken only under the guidance of a physician.
Also, it’s possible that the effects of fasting is not limited to the immune system. Scientists are looking into the possibility that these effects are applicable to many different systems and organs in the body.
Additional benefits of prolonged fasting
Scientists are starting to establish the benefits of fasting to the immune system. What are some of the other benefits you could expect from prolonged fasting?
You can expect to experience these benefits:
- You may experience weight loss. There is a number of reasons for this. First, you’ll lose weight because you’ll lose a lot of water from depleting glycogen in the liver and muscles. This is why you’ll often hear that it’s important to increase your water intake during prolonged fasting. In any case, depleting your glycogen levels will achieve a metabolic state of ketosis, turning you into a fat-burning machine. Important note: Prolonged fasting isn’t a permanent method for weight loss, as you’ll likely put it back on when you start eating again.
- Your body will “start to eat itself,” a process known as autophagy. Autophagy recycles waste from the body and repairs any oxidative stress.
- You will likely experience cognitive benefits from prolonged fasting. This makes sense when you think about it. When we were hunters and gatherers, and we hadn’t eaten for a few days, we needed to come up with new ideas in order to find more food. Our ability to think critically would have improved in these circumstances. Some research suggests that ketosis is advantageous for the brain, resulting in more brain-derived neurotrophic factor or BDNF.
Is prolonged fasting the same as intermittent fasting?
Intermittent fasting means you are introducing a schedule of prolonged fasting into your eating routines.
For example, you may fast for 16 hours per day, only eating within an 8 hour window (eating between 11am and 7pm, fasting between 7pm and 11am the next day). Doing this every day, or 5 days per week, means you are adopting an intermittent fasting schedule.
Prolonged fasting usually refers to fasting for a period of time over 48 hours.
The Sovereign Mind lens
Understanding fasting through The Sovereign Mind framework reveals how our relationship with food can become a pathway to deeper self-knowledge and autonomy.
Unlearning: We inherit cultural scripts about constant consumption being necessary for health and comfort, along with medical orthodoxies that have historically dismissed fasting without fully investigating its potential benefits.
Restoration: Fasting creates space for the body’s natural regenerative processes to emerge while developing the mental discipline to distinguish between genuine hunger and habitual eating patterns driven by external cues.
Defense: By understanding how prolonged fasting works, we can resist both the fear-mongering around temporary food restriction and the opposite extreme of treating fasting as a miracle cure, maintaining clear judgment about what serves our individual health needs.
Starting your own fasting journey safely
Given the compelling research on fasting’s regenerative effects, you may want to explore how this ancient practice might benefit your own health. The key is approaching it with both respect for the science and awareness of your individual circumstances.
- Begin with shorter fasting windows: If you’re new to fasting, start with 16-hour intermittent fasting before attempting longer periods. This allows your body to adapt gradually and helps you understand your personal responses to food restriction.
- Work with a healthcare provider: Extended fasting isn’t appropriate for everyone, particularly those with certain medical conditions, eating disorder histories, or those taking specific medications. Professional guidance ensures you’re fasting safely within your health context.
- Pay attention to your body’s signals: True fasting involves learning to distinguish between habitual eating cues and genuine physiological needs. Notice the difference between mental food cravings and actual hunger, and respect severe fatigue or dizziness as signs to break your fast.
- Prepare your re-feeding carefully: How you break an extended fast is crucial for maintaining the benefits and avoiding digestive distress. Plan to reintroduce food slowly with easily digestible options rather than immediately returning to large or complex meals.
- Consider the timing: Extended fasting is best undertaken when you can rest adequately and aren’t facing major physical or emotional stressors. Choose periods when you can listen to your body rather than push through demanding schedules.
