DENIAL, famously, is good for the soul. It is also good for the body. Scientists have known for decades that animals fed near-starvation diet in laboratories see dramatic boosts in their lifespans. A lack of nutrients seems to spur the activity of cellular repair mechanisms, which help to slow the gradual accumulation of cellular damage that is one cause of aging.

Some humans, too, try to cheat aging by starving themselves. No one yet knows if such forbearance has the desired effect on members of Homo sapiens. In the meantime, though, boosting a body's repair mechanisms may have other uses. One could be in cancer treatment, where fasting seems both to protect healthy tissue and to make tumours easier to treat.

In 2008 a group led by Valter Longo, a biologist at the University of Southern California (USC), published a paper suggesting that a short, sharp course of fasting—not eating at all for a few days, as opposed to months of eating much less than normal—could make ordinary, non-cancerous cells more resistant to the side-effects of chemotherapy, at least in yeast and mice. If the same results were found in humans, it could mean less suffering for cancer patients; or it could free doctors to use higher doses of chemotherapy in an attempt to tackle cancers more aggressively.

But fasting may bring other benefits, too. On February 8th Dr Longo and his colleagues published another paper showing that—again in yeast and in mice—fasting can actually make cancerous cells more susceptible to chemotherapy than they otherwise might be. Cancerous mice treated with a combination of chemotherapy and fasting had better survival chances and smaller tumours, for several different types of cancer, than those treated with either fasting or chemotherapy alone. In some cases, the combination treatment eradicated even metastasised cancers completely.

The researchers suggest that the explanation for this double bill of fewer side effects and more vulnerable tumours is that cancer cells do not do what the rest of the body would like them to. In thin times, normal cells switch their attention away from reproduction and towards preservation, beefing up their repair mechanisms, and hunker down to wait for better days.

Not so cancer cells which, after all, are distinguished by their reckless proliferation. So while ordinary cells become resistant to chemotherapy drugs following a fast, cancer cells do not. In fact, in Dr Longo's study, tumour cells seemed to boost their activity levels during times of famine. That, in turn, boosted the quantity of free radicals, highly oxidising and damaging chemicals produced as a side-effect of metabolism, inside them. Thus stressed, the tumour cells found it much harder to cope with the added battering from chemotherapy drugs.

The usual caveats apply, as they do to all studies of lab animals; mice and yeast cells are not human. But if fasting shows similar effects in humans with cancer—and early-stage clinical trials are already under way—then the attractions are obvious. Fasting is cheap, safe and, in theory, should work against a wide variety of cancer types. Not quite a magic bullet, then, but not far off.

Correction: The original post listed Lizzia Raffaghello as the lead author of the 2008 paper. In fact, Dr Longo was the lead author on both papers, while Dr Raffaghello was a contributing author. Our apologies to both.

