Fasting for as little as three days can regenerate
the entire immune system, even in the elderly,
scientists have found in a breakthrough described
as "remarkable".
Although fasting diets have been criticised by
nutritionists for being unhealthy, new research
suggests starving the body kick-starts stem cells
into producing new white blood cells, which fight
off infection.
Scientists at the University of Southern California
say the discovery could be particularly beneficial
for people suffering from damaged immune
systems, such as cancer patients on
chemotherapy.
It could also help the elderly whose immune
system becomes less effective as they age, making
it harder for them to fight off even common
diseases.
The researchers say fasting "flips a regenerative
switch" which prompts stem cells to create brand
new white blood cells, essentially regenerating the
entire immune system.
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"It gives the 'OK' for stem cells to go ahead and
begin proliferating and rebuild the entire system,"
said Prof Valter Longo, Professor of Gerontology
and the Biological Sciences at the University of
California.
"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 ageing, fasting cycles can
generate, literally, a new immune system."
Prolonged fasting forces the body to use stores of
glucose and fat but 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 trials humans were asked to regularly fast for
between two and four days over a six-month
period.
Scientists found that prolonged fasting also
reduced the enzyme PKA, which is linked to ageing
and a hormone which increases cancer risk and
tumour growth.
"We could not predict that prolonged fasting would
have such a remarkable effect in promoting stem
cell-based regeneration of the hematopoietic
system," added Prof Longo.
"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," Dr
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?"
Fasting for 72 hours also protected cancer patients
against the toxic impact of chemotherapy.
"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 the USC
Norris Comprehensive Cancer Center and Hospital.
"More clinical studies are needed, and any such
dietary intervention should be undertaken only
under the guidance of a physician.”
"We are investigating the possibility that these
effects are applicable to many different systems
and organs, not just the immune system," added
Prof Longo.
However, some British experts were sceptical of the
research.
Dr Graham Rook, emeritus professor of
immunology at University College London, said the
study sounded "improbable".
Chris Mason, Professor of Regenerative Medicine at
UCL, said: “There is some interesting data here. It
sees that fasting reduces the number and size of
cells and then re-feeding at 72 hours saw a
rebound.
“That could be potentially useful because that is
not such a long time that it would be terribly
harmful to someone with cancer.
“But I think the most sensible way forward would
be to synthesize this effect with drugs. I am not
sure fasting is the best idea. People are better
eating on a regular basis.”
Dr Longo added: “There is no evidence at all that
fasting would be dangerous while there is strong
evidence that it is beneficial.
“I have received emails from hundreds of cancer
patients who have combined chemo with fasting,
many with the assistance of the oncologists.
“Thus far the great majority have reported doing
very well and only a few have reported some side
effects including fainting and a temporary increase
in liver markers. Clearly we need to finish the
clinical trials, but it looks very promising