Early research on mice with cancer shows that fasting may weaken tumors and help chemotherapy work better, scientists said on Wednesday.

While it remains unknown if the same approach could work in humans, or if it would even be safe, researchers said the findings suggest a promising new route of study for improving response to cancer treatment.

In the mice experiments, "the combination of fasting cycles plus chemotherapy was either more or much more effective than chemo alone," said senior author Valter Longo, professor of gerontology and biological sciences at the University of Southern California (USC).

Longo and colleagues previously published findings in 2008 that showed how fasting protected normal cells against chemotherapy in a study that focused on one type of cancer and a single chemo drug.

The latest study expands on that research to show that fasting makes cancer cells more vulnerable, and spanned several different types of cancer in mice.

Types of cancers studied included breast cancer, melanoma, glioma and human neuroblastoma.

All cancers studied showed that fasting combined with chemotherapy improved survival, slowed the growth of tumors and/or limited their spread.

The study appears in the journal Science Translational Medicine.

"We don't know whether in humans it's effective," Longo said, adding that for now fasting should be "off-limits" to cancer patients, although they should feel they can ask their doctors about the possibility.

In 2010, a small study of 10 human cancer patients who tried fasting cycles with their drug treatment showed that they perceived fewer side effects from chemo, according to self-reported data. The study was published in the journal Aging.

The results of a phase 1 trial assessing the safety of fasting two days before and one day after chemotherapy in patients with breast, urinary tract and ovarian cancer, conducted at the USC, have been submitted for presentation at the annual meeting of the American Society of Cancer Oncologists later this year.

"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 said. (AFP)