Genes may not be the only way cancer passes down the generations. Feeding pregnant rats a fatty diet puts both their daughters and granddaughters at greater risk of breast cancer.

Sonia de Assis of Georgetown University Medical Center in Washington DC and colleagues had discovered that the daughters of pregnant rats fed an unhealthy diet are more likely to develop breast cancer. Now they have shown that even if these daughters eat healthily, their offspring are still at greater risk of disease.

Rats don’t normally develop breast cancer, so de Assis had to give the granddaughters a chemical that induces tumours.

This put all the granddaughters at increased risk. Crucially, however, rats with grandmothers who ate a fatty diet were even more at risk. Twenty weeks later, half the rats whose grandmothers ate a normal diet developed breast tumours, while 80 per cent of rats with two grandmothers fed a high fat diet got tumours and 68 per cent of the rats with just did one developed cancer.

Non-genetic inheritance

De Assis, who presented the work at the American Association for Cancer Research meeting in Washington DC, says a fatty diet may cause “epigenetic” DNA modifications that can be passed on to future generations.