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Sept. 11, 2008 -- Does eating fruits, vegetables, and grains really protect against colorectal cancer? Researchers have been studying this question for years, but their findings have been mixed.
Now a new study from the University of Hawaii weighs in on the issue, but it may do little to clear up the confusion.
The investigation found a modest protective benefit for fruit and vegetable consumption in men but not in women. The benefit was stronger for colon cancer than rectal cancer, and eating grains was not linked to colorectal cancer.
The findings raise as many questions as they answer, Abraham Nomura, MD, PhD, tells WebMD.
"Based on our research and some of the other studies, there is a suggestion that men derive more benefit from eating fruits and vegetables in terms of colorectal cancer risk than women," he says. "But at this point it is only a suggestion."
Nomura and colleagues followed close to 200,000 adults between the ages of 45 and 75 for an average of seven years, during which time 1,138 of the men and 972 of the women developed colon or rectal cancer.
All the study participants filled out a food frequency questionnaire when they entered the trial.
Based on those answers, the researchers concluded that men who ate the most fruits and vegetables were 26% less likely to develop colorectal cancer than men who ate the least.
No decrease in risk associated with fruit and vegetable consumption was seen for women.
There is some suggestion that the female hormone estrogen and estrogen therapy helps protect against colorectal cancer. If this is the case, it might help explain why women would derive less benefit from eating fruits and vegetables than men, Nomura says.
When the researchers analyzed data from only women who took estrogen therapy, they found no difference in colorectal cancer risk among those who ate the most fruits and vegetables and the least.
The study is published in the latest issue of the American Journal of Clinical Nutrition.
The investigation is not the first to suggest that eating fruits and vegetables may be more protective for men than for women.
Last year, a joint study by the National Institutes of Health and the AARP concluded that eating vegetables but not fruit lowered colorectal cancer risk in men but not women.
But a pooled analysis of 14 studies of fruit and vegetable consumption on colon cancer risk, also published last year, showed no strong link to colon cancer risk in general and no difference between men and women.
A protective benefit appeared stronger for cancers of the lower colon, with a 26% decrease in risk seen.
Anita Koushik, PhD, who led the study team, tells WebMD that most of the recent studies examining the impact of fruit and vegetable consumption on colorectal cancer risk suggest no more than a modest benefit.
"There are still many unanswered questions," she says. "We don't yet know the effect of fruit and vegetable consumption at younger ages and throughout life. That hasn't really been studied."