Naturally occurring chemicals found in certain vegetables can enhance DNA repair in cells, perhaps helping to stop them becoming cancerous, according to a report in the British Journal of Cancer
The researchers, based at Georgetown University in Washington DC, have shown that a compound called I3C found in these vegetables, and a chemical called genistein found in soy beans, both increase the levels of vital DNA repair proteins in cancer cells.
Although population studies have suggested a link between eating such vegetables and protection against cancer before, this study now puts forward a molecular mechanism on how they might work.
The repair proteins, regulated by genes called BRCA1 and BRCA2, are important for preventing damaged genetic information being passed on to the next generation of cells.
If people have a faulty BRCA gene they are at a higher risk of developing some forms of cancer, including breast, ovarian and prostate cancer.
Since decreased amounts of the BRCA proteins are seen in cancer cells, higher levels might prevent cancer developing.
The ability of I3C and genistein to boost the amount of BRCA proteins could explain their protective effects.
Professor Eliot M Rosen, senior author of the report, said: "Studies that monitor people's diets and their health have found links between certain types of food and cancer risk.
"However, before we can say a food protects against cancer, we have to understand how it does this at a molecular level2.
Rosen's research group had already shown that some natural chemicals in food increased the levels of BRCA1.
In this report, the two compounds they studied both acted on BRCA1 and BRCA2.
Rosen added: "It is now clear that the function of crucial cancer genes can be influenced by compounds in the things we eat.
"Our findings suggest a clear molecular process that would explain the connection between diet and cancer prevention".
Professor John Toy, medical director of Cancer Research UK, which owns the British Journal of Cancer, said: "Diet's role in cancer prevention is complex.
"This research explores an interesting hypothesis as to how certain components of diet can affect cancer risk.
"The evidence is building that these chemical compounds act on some of the genes inside cells that help prevent cancer developing.
"We still don't know if this is exactly how these chemicals might act in every day life.
"Cancer Research UK's Reduce the Risk campaign, however, is based on what we do know, including the fact that eating a balanced diet, high in fibre and with plenty of fruit and vegetables, lowers the risks of developing many forms of cancer".
Rosen (2006) British Journal of Cancer 94 (3) - I3C - indole-3-carbinol BRCA genes.
In 1993, an international team of researchers showed that the inherited breast cancer susceptibility gene, BRCA1, was responsible for the vast majority of families with multiple cases of breast and ovarian cancer, and a large proportion of those families with breast cancer only.
In 1995, a second breast cancer susceptibility gene, BRCA2 was identified.
The gene is associated with a substantially increased risk of female breast cancer as well as an increased risk of ovarian, prostate and male breast cancer.
Normal BRCA1 and BRCA2 genes produce proteins (also called BRCA1 and BRCA2) that are involved in repairing damaged DNA.
Cells with defective copies of the genes cannot repair their DNA so well, meaning mutated genes can survive and the risk of cancer developing is increased.
People with faulty versions of BRCA genes are therefore at a higher risk of several forms of cancer.
