Fasting was as effective as chemotherapy in delaying growth of specific tumors in mice and boosted the effectiveness of chemotherapy on melanoma, glioma, and breast cancer cells. And fasting plus chemotherapy, but neither treatment on its own, resulted in long-term cancer-free survival in mice with neuroblastoma, according to a study published online on Wednesday in Science Translational Medicine.
However, senior author Valter Longo, of the University of South California (USC) in Los Angeles, told the press that only a clinical trial lasting several years will be able to show if humans are likely to benefit from the same treatment.
In animals at least, the study suggests that cancer cells are less resilient when attacked by chemo accompanied by cycles of fasting. Even fasting on its own appears to treat many cancers tested in animals, including those derived from human cells. The study shows that five out of eight cancer types in mice responded to fasting alone: it slowed the growth and spread and of tumors.
Longo, who is professor of gerontology and biological sciences at the USC Davis School of Gerontology and the USC Dornsife College of Letters, Arts and Sciences, said that without exception “the combination of fasting cycles plus chemotherapy was either more or much more effective than chemo alone”.
He and his colleagues found, for example, that repeated cycles of fasting with chemotherapy cured 1 in 5 mice with a highly aggressive form of children’s neuroendocrine cancer, and 40% of mice with a less severe form. In either case, no mice survived when treated only with chemo.
For their study, in which they used used cancer cells and mice, Longo and colleagues found that for all the cancers they tested, fasting combined with chemotherapy improved survival, slowed tumor growth and/or limited the spread of tumors.
They found that fasting without chemotherapy, slowed the growth of breast cancer, melanoma, glioma and human neuroblastoma. In several cases, fasting was as effective as chemotherapy.
However, the study also revealed that cancer cells can become resistant to fasting. In the case of melanoma, this happened after only one cycle of fasting. But that one cycle was just as effective as chemo in slowing the spread to other organs, said the researchers.
They also found that fasting prolonged survival in mice with human ovarian cancer.
Longo pointed out that as with any cancer treatment, fasting has its limitations. They found this to be when they tried to tackle large tumors. Although fasting cycles combined with chemo did reduce their size, it did not result in cancer-free survival.
Longo suggests this could be because cancer cells inside large tumors are protected in some way: perhaps the variety of mutations in a large mass makes it more adaptable.
To try and find out how fasting has an effect on cancer cells Longo and colleagues studied one type of breast cancer in detail.
When normal cells are starved of nutrients, they go into a dormant state, rather like hibernation. But what Longo and colleagues found was that cancer cells don’t do this: instead they try to make new proteins and do other things to continue to grow and divide.
They saw what Longo describes as a “cascade of events” that results in damaging free radicals that destroy cancer cells by breaking down their DNA.
Perhaps a way to beat cancer cells is not to try and find drugs that selectively destroy them, but to “confuse them by generating extreme environments, such as fasting that only normal cells can quickly respond to”, said Longo.
He also cautioned that for the time being, because they don’t know whether this approach is effective in humans, it should be “off limits to patients”. But that doesn’t mean patients shouldn’t go to their oncologist and ask: “What about fasting with chemotherapy or without if chemotherapy was not recommended or considered?”
He also warns that fasting may not be safe for some patients, for instance those who have already lost weight, or who have other risk factors like diabetes. Fasting can reduce blood pressure and cause headaches, which could make driving and other activities dangerous.
Although a trial published two years ago in Aging suggested fasting reduces the side effects of chemo, it did not include patients with these kinds of risk factors.
Funds from the National Institutes of Health, the Bakewell Foundation, The V Foundation for Cancer Research, the Norris cancer center, the Italian Association for Cancer Research and the Italian Foundation for Cancer Research helped pay for the study.
Written by Catharine Paddock PhD