July 1, 2008 -- Men who eat broccoli just a few times a week may have a lower prostate cancer risk than men who don't, new research suggests.
Animal studies have long suggested that broccoli and other cruciferous vegetables help protect against prostate cancer. The new research suggests the same thing in humans, albeit indirectly.
Researchers measured changes in gene expression in human prostate tissue associated with eating a broccoli-rich diet.
Compared to men who ate peas four times a week, those who ate four weekly servings of broccoli for a year showed more changes in gene expression suggestive of increased protection against prostate cancer.
The findings appear in the July 2 online issue of the journal PLoS ONE.
"It is important to stress that we did not directly measure cancer incidence," Richard F. Mithen, PhD, of the Institute of Food Research in Norwich, England, tells WebMD. "But the gene changes we saw were consistent with a reduction in prostate cancer risk."
Diet Changes Genes
The study is not the first to suggest that changes in diet can change your genes.
Earlier this month, nutrition researcher Dean Ornish, MD, and colleagues from the University of California, San Francisco reported that men with low-risk prostate cancer showed profound changes in gene expression when they ate a low-fat diet that was high in fruits and vegetables.
They found that more than 500 genes were affected, with genes associated with beneficial effects becoming more active and genes with cancer-promoting properties becoming less active.
The study included 13 men who ate four 3.5 ounce-servings of broccoli a week for a year and eight men who ate the same amount of peas.
Prostate tissue samples were collected before the start of the trial and then after six and 12 months on the broccoli- or pea-intervention diets.
As with the California study, men who regularly ate broccoli showed more changes in gene expression suggestive of a reduced risk of cancer.
"These were extensive changes," Mithen says. "Basically, hundreds of genes changed expression. We were quite surprised by this finding."
Why Not Peas?
Broccoli and other cruciferous vegetables have compounds known as glucosinolates. Peas do not.
Glucosinolates convert to other compounds known as isothiocyanates, which are widely believed to have tumor-suppressing activities.
Studies suggest that about half the population carries a gene called GSTM1, which may make these compounds even more protective.
Study participants who expressed the gene showed the most beneficial gene changes after eating broccoli.
But Mithen says the finding does not mean that only 50% of people derive a benefit from broccoli.
"It may mean that people without the gene need to eat a bit more broccoli to get the same benefits," he says. "But the good news is that nobody has to eat huge amounts. A few portions a week seems to make a big difference."
Benefits Not Proven
National Cancer Institute researcher Richard B. Hayes, PhD, says the new research strengthens, but does not prove, the hypothesis that a healthy diet can protect against prostate cancer.
Hayes' own 2007 study suggested a link between a high intake of cruciferous vegetables -- especially broccoli and cauliflower -- and protection from aggressive prostate cancer.
"There is a fairly consistent body of evidence suggesting that fruits and vegetables are protective against many cancers and other diseases," Hayes tells WebMD. "But it may be stretching the point at the moment to say that broccoli prevents prostate cancer."
Hayes says the suggestion that any one compound or group of compounds is responsible for the protective benefits seen in animal and epidemiological studies is premature.
"We can too easily go down that road of looking to develop a pill based on this compound or that compound to protect against cancer, but the truth is we may never find that," he says.