Broccoli and cauliflower helped one part of the colon more, while carrots and apples helped in another part.
Australian researchers have found a link between different types of fruits and vegetables and cancer risk in different parts of the colon. Specifically, the study found that the risk of cancer in the part of the large bowel that runs up the right side of the abdomen and across was not associated with total combined intake of fruits and vegetables or total intake of either one. However, the family of vegetables that includes cabbage, broccoli, brussels sprouts, and cauliflower was linked to a lower risk of cancer in that part of the colon.
On the other hand, total fruit and vegetable intake and total vegetable intake alone were associated with a lower risk of cancer in the part of the colon that runs down the left side of the abdomen. That finding could have been due to chance, though, the scientists write. But they did find a significant connection between eating more apples and dark yellow vegetables, such as carrots and pumpkin, and a lower risk of cancer in the right side of the colon.
Why fruits and vegetables would affect various parts of the colon differently is not known, the study researchers write.
"Our study was based on the hypothesis raised by our colleague Barry Iacopetta, who suggested that the left and right sides of the colon had different cancers," researcher Lin Fritschi, PhD, a professor at the Western Australian Institute for Medical Research in Perth, says in an email.
Iacopetta, a co-author of the study, "has published a few papers showing that left and right colon cancers have different genetic makeups" and respond differently to chemotherapy, Fritschi says.
Iacopetta is particularly interested in the role of folate, Fritschi says, which is why she and her co-authors also focused on the family of vegetables that includes broccoli and cauliflower, a main source of the vitamin.
They called for more studies that follow larger numbers of people since the findings of this study only show an association, and do not prove cause and effect.
Eating a Variety of Fruits and Vegetables
Fritschi and her co-authors based their findings on a comparison of 834 people who had been diagnosed with colon cancer and a comparison group of 939 people without cancer.
Participants completed a questionnaire about their food and alcohol intake a decade earlier since it takes years for colon cancer to develop, and information about current intake wouldn’t be as relevant. They also answered questions about their health history, such as their height and weight at age 20, their smoking status, and whether they had diabetes. Smoking, diabetes, and obesity are factors linked to risk for colon cancer.
“I think the message is a good one, and that is to eat a variety of fruits and vegetables,” Marji McCullough, ScD, RD, strategic director of nutritional epidemiology at the American Cancer Society, tells WebMD.
Meat Intake Might Have Played a Role
However, noted McCullough, who was not involved in the study, the authors did not account for the amount of red and processed meats in the study participants’ diets.
The World Cancer Research Fund International says there’s "strong evidence" that such meats increase risk of colon cancer, and people who eat lots of them usually eat fewer fruits and vegetables, McCullough says. The American Cancer Society also states that diets high in processed meats and red meat can increase the risk of colon cancer. So, she says, meat consumption, not fruit and vegetable intake, might explain the Australian researchers’ findings.
Fritschi says she and her co-authors looked in detail at meat consumption in only a subset of study participants, not enough to take into account in their analysis.
McCullough also says this type of research -- relying heavily on recall of diet in past years -- tends to find a stronger relationship between fruit and vegetable intake and colon cancer risk than studies that collect dietary information from people before they’re diagnosed.
The authors note that limitation in their study. “The problem of bias and memory is a real issue with dietary measurement,” Fritschi says. “We tried to do what we could, but it is a real problem for all these retrospective studies.”
The study appears in the October issue of the Journal of the American Dietetic Association.