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In trials, volunteers were asked to fast regularly 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 aging 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 [formation of stem cells] system,” added 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.

‘There is no evidence at all that fasting would be dangerous while there is strong evidence that it is beneficial’

“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.”

Fasting for 72 hours also protected cancer patients against the toxic impact of chemotherapy.

“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.

Referring to the 72-hour fasting period, Chris Mason, professor of regenerative medicine at University College London, said: “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.”

Longo added: “There is no evidence at all that fasting would be dangerous while there is strong evidence that it is beneficial.”