"These findings add to our knowledge of the importance of a high vegetable-based diet in the fight against cancer," said study co-author Jennifer Cohen, PhD, MPH, of the Fred Hutchinson Cancer Research Center in Seattle.

Dr. Cohen and her colleagues evaluated the total fruit and vegetable consumption of 1,230 men between the ages of 40 and 64 and found men who ate three or more servings of vegetables a day had a 35 percent lower risk of prostate cancer, compared with men who ate fewer than two servings per day. Of the men studied, half had been diagnosed with prostate cancer and half were randomly selected.

Vegetables in the cruciferous family -- which includes cabbage, broccoli, Brussels sprouts, and cauliflower -- were found to give the biggest benefit because of a certain type of phytochemical they contain. Prostate cancer risk was cut by 41 percent among men who ate three or more servings of cruciferous vegetables per week compared to those who ate less than one serving per week. It is thought that pytochemicals in cruciferous vegetables boost the production of certain types of enzymes called GSTPi, which are most abundant in the prostate and protect against damaging agents associated with prostate cancer, according to Dr. Cohen.

The study confirms the widely held belief among doctors and nutritionists that fruits and vegetables may help protect against cancer. But, in contrast to an earlier study, it found certain components in cooked tomatoes could not protect against prostate cancer. The new study found no link between tomatoes, which contain the carotenoid lycopene, and prostate cancer prevention -- a result in contrast to earlier studies noting that lycopene actually lowers a man's risk.

The authors found "the relationship between lycopene and tomato products with prostate cancer risk remains inconclusive."

"The jury is still out on lycopene," said Colleen Doyle, MS, RD, nutrition and physical activity director for the American Cancer Society (ACS). "Earlier studies have not consistently shown that men who consume more lycopene are at a reduced risk of developing prostate cancer."

However, Doyle points out that despite the inconclusive results on lycopene, tomatoes are still an important part of a healthy diet. "Everyone should eat at least five servings of a wide variety of fruits and vegetables every day and tomatoes are a great way to get in your five daily vegetable servings," she said.

Doyle said this latest research provides further evidence to support the ACS's dietary guidelines. "This is a good study and adds to a wide body of studies that basically say you have to eat your fruits and vegetables to stay healthy. You can't eat enough cruciferous vegetables," she said.

"We don't make recommendations based on one study, but it is exciting to see more studies confirming what the ACS has been saying all along," Doyle concluded.