April 16, 2007 (Los Angeles) -- Sure, you've heard it a thousand times, but three new studies cement mom's advice to eat your fruits and veggies: It may help ward off a host of cancers.
One study of 183,518 men and women suggests that a diet high in flavonol-rich apples, berries, kale, and broccoli may help cut the risk of pancreatic cancer, especially in smokers.
Another study of about 500,000 people aged 50 and older shows eating an additional two servings a day of fruit and vegetables -- no matter how many servings you now eat -- can reduce the risk of developing head and neck cancers.
The third study suggests that chemicals in cruciferous vegetables and soy reduce production of two proteins necessary for the spread of breast and ovarian cancers.
The studies were presented here at the annual meeting of the American Association for Cancer Research.
Flavonols Lower Pancreatic Cancer Risk
Pancreatic cancer is one of the deadliest of all cancers, killing 95% of victims within five years of diagnosis, says Ute Nothlings, DrPH, a researcher at the German Institute of Human Nutrition Potsdam-Rehbruecke in Nuthetal, Germany.
But her study shows that people who eat the largest amounts of flavonols -- antioxidants ubiquitous in plant-based foods -- are 23% less likely to develop pancreatic cancer than those who ate the least.
Smokers gained the most benefit. Those who ate the most flavonols reduced their risk of developing pancreatic cancer by 59%, compared with those who ate the least, says Nothlings, who conducted the study as a postdoctoral fellow at the Cancer Research Center of Hawaii in Honolulu.
While the findings support recommendations to eat your veggies, a flavonol-rich diet isn't going to protect smokers against developing pancreatic cancers, says Alan Kristal, DrPH, of Fred Hutchinson Cancer Research Center in Seattle.
Smoking raises your risk of developing pancreatic cancer by twofold, he tells WebMD. And no matter how many trips you make to the salad bar, "you're not going to ameliorate that risk."
For the study, the researchers asked participants about their diet and estimated consumption of three flavonols: quercetin, which is most abundant in onions and apples; kaempferol, found in spinach and some cabbages; and myricetin, found mostly in red onions and berries. Over the next eight years, 529 developed pancreatic cancer.
Kaempferol offered the most protection: Those who consumed the most were 22% less likely to develop pancreatic cancer than those who ate the least. Risk was reduced 73% among smokers.
Fruit, Vegetables Lower Head and Neck Cancer Risk
While several studies have suggested that fruits and vegetables may lower the risk of head and neck cancer, many suffered from poor design as they asked people who had already developed cancer to recall their dietary habits years before, says Kristal, who moderated a news conference on the findings.
To help settle the issue, National Cancer Institute researchers asked 490,802 AARP members about their typical dietary habits and then followed them for five years. During that time, 787 of them developed head and neck cancer.
Results showed that participants who ate about 12 servings of fruit and vegetables per day were 29% less likely to develop the cancer than those who ate three servings per day. Increasing consumption by just two servings of fruit or vegetables per day was associated with a 6% reduction in head and neck cancer risk, researcher Neal Freedman, PhD, a cancer prevention fellow, tells WebMD.
One serving equals approximately one medium-sized fresh fruit, 1/2 cup of cut fruit, 6 ounces of fruit juice, 1 cup of leafy vegetables, or 1/2 cup of other vegetables.
Broccoli Curbs Breast Cancer Spread
While studies have shown that broccoli and soy offer protection against breast and ovarian cancer, how this occurs has not been well understood, says Erin Hsu, MS, a molecular toxicologist at the University of California, Los Angeles.
Her team's laboratory experiments offer one potential clue, showing that diindolylmethane (DIM), a compound resulting from digestion of cruciferous vegetables, and genistein, a major isoflavone in soy, reduce production of two proteins whose attraction to each other is necessary for the spread of both cancers.
In the experiments, the researchers exposed breast and ovarian cancer cells to purified DIM or genistein. Levels of two proteins known as CXCR4 and CXCL12 that promote breast and ovarian cancer spread dropped.
"In other words, DIM and genistein make the cancers more treatable," Hsu tells WebMD.
Both DIM and genistein are being developed for use in the prevention and treatment for breast cancer, although more extensive toxicological studies are necessary, she says.