Scientists have known since 2007 that intermittent water-only fasting can help patients withstand higher doses of chemotherapy, reduce the side-effects, and protect normal cells against much of the damage done by the drug.
A study published in Proceedings of the National Academy of Science in 2008 found that fasting for two days before chemotherapy protected cancer patients against the toxic side effects by shielding healthy cells while destroying malignant ones. In 2009, a case report study published in the journal Aging, revealed that 10 individuals with cancer who fasted intermittently in cycles experienced less adverse effects from chemotherapy.
A 2008 study at the University of California at Berkeley found that eating every other day decreased cell proliferation rates, an effect known to reduce the development of cancers. In animal models, intermittent fasting was found to reduce cancer growth on the skin and in breast tissue.
In a paper published in 2010 in Cancer Research, a team at the University of Southern California documented the findings of mice with human cancer being treated with fasting. Fasting reduced their IGF-1 levels, an effect which has been found to prolong life. When the mice received chemotherapy, none of the normal-diet control group survived, while 60% of fasting mice lived.
In 2012, a group of researchers found that fasting had the potential to be as effective as chemotherapy for treating some types of cancer. As a result of their research, published in the journal Science Translational Medicine, the scientists concluded that cycles of 2 to 4 days of fasting were as effective as chemotherapeutic agents in delaying the progression of certain tumors. As is typical in this type of research, the mice had been injected with human cancer cells. The results indicated that five out of eight cancer types in mice responded to fasting alone. In response similar to chemotherapy, fasting slowed the growth and spread of tumors. In summation, the researchers said, "These studies suggest that multiple cycles of fasting promote differential stress sensitization in a wide range of tumors and could potentially replace or augment the efficacy of certain chemotherapy drugs in the treatment of various cancers."
The researchers ran a variety of test protocols. In one procedure, multiple cycles of fasting combined with chemotherapy cured 20 percent of mice with a highly aggressive type of cancer that had spread throughout their body and 40 percent of mice with a more limited spread of the same cancer. No mice survived in either case if treated with chemotherapy alone.
The study found that fasting cycles without chemotherapy slowed the growth of breast cancer, melanoma, glioma, and human neuroblastoma. In several cases, the fasting cycles were as effective as chemotherapy.
Fasting also extended survival in mice bearing a human ovarian cancer. In the case of melanoma, the cancer cells became resistant to fasting alone after a single round, however, a single cycle of fasting was as effective as chemotherapy in reducing the spread of cancer to other organs. For all the types of cancer, fasting combined with chemotherapy improved survival rates, slowed tumor growth, and/or limited the spread of tumors.
According to Valter D. Longo, one of the study's authors, "A way to beat cancer cells may not be to try to find drugs that kill them specifically but to confuse them by generating extreme environments, such as fasting that only normal cells can quickly respond to."
Longo and the other researchers examined one type of breast cancer in particular to try to understand the effects of fasting. They noticed that normal cells deprived of nutrients entered a dormant state similar to hibernation, whereas the cancer cells attempted keep growing and dividing. This led to damaging free radical molecules, which in turn caused the cancer cells to self-destruct. Longo said, "The cell is, in fact, committing cellular suicide. What we're seeing is that the cancer cell tries to compensate for the lack of all these things missing in the blood after fasting. It may be trying to replace them, but it can't."
In terms of human research, only a clinical trial over several years will demonstrate whether humans can benefit from the same treatment. Unsupervised fasting should be avoided in cancer patients, especially those who have experienced significant weight loss.