By Alok Jha in London

Guardian News Service: Short-term fasting could help protect cancer patients against the effects of chemotherapy, a study suggests.

Scientists found that fasting toughens up healthy cells but not cancer cells, raising hopes that, if the finding can be confirmed in clinical trials, it could be used to improve cancer treatment.

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.

Valter Longo, of the University of Southern California, led a group of researchers who found that a short period of fasting deprived healthy cells of oxygen, causing them to enter an emergency mode that made them highlyresistant to stress.

But cancer cells, when deprived of oxygen, did not enter this emergency mode, making them more vulnerable 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 the next stage for their work was to test the results in humans, and they warned cancer patients not to try starving themselves.

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. These mice lived, whereas half of the control mice, which had not fasted, died.

Test-tube experiments with human cells confirmed the different resistance of normal and cancer cells to chemotherapy after a short period of starvation. The results were published online yesterday in the Proceedings of the National Academy of Sciences.