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It's official - fasting can regenerate the entire immune system, even in elderly people, and help cancer patients, new research has found.

A study by a team of scientists at the University of Southern California have hailed the discovery as "remarkable" and say it could have major implications in treating cancer patients whose bodies have been damaged by the effects of chemotherapy.

Researchers have found a two to four-day fast involving both mice and humans, "flipped a regenerative switch" in forming new white blood cells, also known as leukocytes, essential in fighting off infection.

Valter Longo, professor of Gerontology and the Biological Sciences at the University of Southern California, said: "It gives the ok for stem cells to go ahead and begin proliferating and rebuild the entire system.

"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."

He added: "Now, if you start with a system heavily damaged by chemotherapy or aging, fasting cycles can generate, literally, a new immune system."

A smaller clinical trial also found fasting for 72 hours before starting chemotherapy protected patients from building up toxins in their system.

"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 Tanya Dorff, assistant professor of clinical medicine at the University of Southern California.

"More clinical studies are needed, and any such dietary intervention should be undertaken only under the guidance of a physician."

The study found fasting also reduced levels of the PKA enzyme, an effect which is known to increase long life in simple organisms, and lowered levels of the hormone IGF-1, which is linked to ageing, tumour growth and cancer risk.

Chris Mason, professor of Regenerative Medicine at UCL, said the data was "interesting" and "potentially useful", but believed it was better to synthesize the effect of fasting with drugs.

"I am not sure fasting is the best idea. People are better eating on a regular basis," he added.

Top 10 Reasons to Fast

1) Cleanses your system

2) Changes bad habits

3) Changes your health for the better

4) Resets your body clock

5) Bring your body into homeostasis (maintains the stability of the human body's internal environment)

6) Increases mental sharpness

7) Makes changing diet easier

8) Understand better how diet can make your body work

9) Improves fat mobilization and physical efficiency

10) Benefit from forced rest