Washington, April 1 : A new study has suggested that short-term fasting can help protect cancer patients against the effects of chemotherapy.
A group led by Dr Valter Longo of the University of Southern California found that fasting toughens up healthy cells but not cancer cells.
Chemotherapy has many side-effects because the drugs also kill healthy body cells. Scientists have long been looking for ways to improve the body's defences against the drugs.
Longo and colleagues found that a short period of fasting deprived healthy cells of oxygen, causing them to enter an emergency mode that made them highly resistant to stress.
But cancer cells, when deprived of oxygen, did not enter this emergency mode, making them more susceptible to drugs than the normal cells.
In theory, the finding could enable more powerful and effective doses of cancer treatment to be used without harming patients, the researchers said.
In one of the experiments, mice were injected with aggressive human tumours and then given a potentially lethal dose of chemotherapy after two days of fasting.
The same dose killed half the normally fed mice and caused lasting weight and energy loss in the survivors. The chemotherapy worked as intended on cancer, extending the lifespan of mice injected with aggressive human tumours.
Test tube experiments with human cells confirmed the differential resistance of normal and cancer cells to chemotherapy after a short period of starvation. In yeast, the difference was up to 1000 fold.
"If we get to just a 10-20 fold differential toxicity with human metastatic (spreading) cancers, all of a sudden it's a completely different game against cancer," Dr Longo said.
"My hope is that many places around the world will carefully design small clinical trials on starvation and protection against chemotherapy," he added.
Dr Longo further explained that the effects of starvation can also be mimicked by a drug and this approach will also be tested.
"We have identified a drug target and drug as well as a modified diet that appear to work almost as well as starvation. Naturally this is the best way to go because a period of starvation longer than 48 hours may be required but would not be possible (in humans) to obtain the same remarkable effects observed in mice" he said.
"This is a very important paper. It defines a novel concept in cancer biology," said cancer researcher Prof Pinchas Cohen, University of California, Los Angeles, UCLA.
The team stressed that fasting is not the same as malnourishment, when inadequate nutrients are taken in, and can easily be tolerated given progress in cancer care.
The initial trial will study if a 48-hour starvation is sufficient to generate protection, without the risk of making the patient too weak and even more sensitive to chemotherapy.
The idea for the study came from the Longo group's previous research on aging in cellular systems, primarily lowly baker's yeast. Dr Longo had been introduced to this idea 15 years ago by the late Roy Walford of UCLA, who showed that a nutritious diet that is low in calories can make a range of species live longer.
However, Longo cautioned that fasting before chemotherapy has unknown risks and benefits for humans and only clinical trials can establish the effectiveness and safety of fasting before chemotherapy.
"Don't try and do this at home. We need to do the studies," he said.
The study will be published online the week of Mar. 31 in PNAS Early Edition.