Fruits and vegetables reduce risks of specific types of colorectal cancers

According to new study published in the Journal of the American Dietetic Association

The effects of fruit and vegetable consumption on colorectal cancer (CRC) appear to differ by site of origin, according to a new study published in the October issue of the Journal of the American Dietetic Association. Researchers found that within the proximal and distal colon, brassica vegetables (Brussels sprouts, cabbage, cauliflower and broccoli) were associated with decreased risk of these cancers. A lower risk of distal colon cancer was associated with eating more apples, however an increased risk for rectal cancer was found with increasing consumption of fruit juice.

“Fruits and vegetables have been examined extensively in nutritional research in relation to CRC, however, their protective effect has been subject to debate, possibly because of different effects on different subsites of the large bowel,” commented lead investigator Professor Lin Fritschi, PhD, head of the Epidemiology Group at the Western Australian Institute for Medical Research, Perth, Western Australia. “It may be that some of the confusion about the relationship between diet and cancer risk is due to the fact that previous studies did not take site of the CRC into account. The replication of these findings in large prospective studies may help determine whether a higher intake of vegetables is a means for reducing the risk of distal CRC.”

Researchers from the Western Australian Institute for Medical Research, University of Western Australia and Deakin University investigated the link between fruit and vegetables and three cancers in different parts of the bowel: proximal colon cancer, distal colon cancer, and rectal cancer. The case-control study included 918 participants with a confirmed CRC diagnosis and 1021 control participants with no history of CRC. The subjects completed extensive medical and nutritional questionnaires and were assigned a socioeconomic status based on their home address.

Consumption of brassica vegetables (e.g., broccoli, cabbage) was associated with reduced incidence of proximal colon cancer. For distal colon cancer, both total fruit and vegetable intake and total vegetable intake appeared to decrease risk. Distal colon cancer risk was significantly decreased in association with intake of dark yellow vegetables and apples, although there was an increased risk for rectal cancer with consumption of fruit juice. Risk of proximal colon cancer and rectal cancer was not associated with intakes of total fruit and vegetable, total vegetable or total fruit.

Previous studies on CRC have often failed to distinguish between the different sites of origin of cancers in the large bowel, even though it is now well established that tumors in the proximal colon develop along different pathways to those of the distal colon and rectum and that risk of cancer varies by subsite within the colorectum. The mechanisms for different effects of dietary components on different sites of the large bowel have not yet been determined.

The authors conclude that “from a public health point of view it is easier to translate food-based analyses into dietary recommendations, rather than using the intake of single nutrient.”

A video featuring commentary by Professor Fritschi and colleagues

 

Reference

Annema N, Heyworth JS, McNaughton SA, Iacopetta B, Fritschi L. Fruit and vegetable consumption and the risk of proximal colon, distal colon and rectal cancers in a case-control study in Western Australia. Journal of the American Dietetic Association 2011; 111 (10): 1479-1490.

 

Cooked Green Vegetables, Dried Fruit, Legumes, And Brown Rice Associated With Fewer Colon Polyps

High consumption of these foods may decrease risk for colorectal cancer, says Loma Linda University:

LOMA LINDA, Calif. — Eating legumes at least three times a week and brown rice at least once a week was linked to a reduced risk of colon polyps by 33 percent and 40 percent respectively, according to Loma Linda University research recently published in Nutrition and Cancer. High consumption of cooked green vegetables and dried fruit was also associated with greater protection, the study shows.

“Eating these foods is likely to decrease your risk for colon polyps, which would in turn decrease your risk for colorectal cancer,” says lead author Yessenia Tantamango, MD, a post-doctoral research fellow with Adventist Health Study-2 at Loma Linda University. “While a majority of past research has focused on broad food groups, such as fruits and vegetables, in relation to colon cancer, our study focused on specific foods, as well as more narrowed food groups, in relation to colon polyps, a precursor to colon cancer. Our study confirms the results of past studies that have been done in different populations analyzing risks for colon cancer.”

Colon cancer is the second leading cause of cancer death in the United States and the third most common cancer in both men and women, according to the American Cancer Society.

Results also show that consuming cooked green vegetables once a day or more, as compared to less than five times a week, was associated with a 24 percent reduction in the risk of rectal/colon polyps. Consuming dried fruit three times a week or more, versus less than once a week, was associated with a 26 percent reduced risk.

The protective effects of these foods could be due in part to their cancer-fighting agents, the study reported.

“Legumes, dried fruits, and brown rice all have a high content of fiber, known to dilute potential carcinogens,” Dr. Tantamango says. “Additionally, cruciferous vegetables, such as broccoli, contain detoxifying compounds, which would improve their protective function.”

Past studies examining the effect of meat intake and legumes on colon cancer have shown that people eating meat, associated with an increased risk of colon cancer, may receive some protection when they also consume legumes. Dr. Tantamango says this suggests that besides fiber content, there may be something else present in legumes that provides a protective effect.

Researchers analyzed data from 2,818 subjects who participated in Adventist Health Study-1 (administered from 1976-77) and who answered a follow-up survey 26 years later from Adventist Health Study-2. The first survey asked respondents to indicate how often, on average, they consumed specific foods. The follow-up survey asked respondents who had undergone colonoscopies to indicate physician-diagnosed colorectal polyps. During the 26-year follow-up, 441 cases of rectal/colon polyps were identified.

The study assessed several possible confounding factors, including a family history of colorectal cancer, education, physical activity level, alcohol intake, smoking, constipation, intake of sweets, pain medication, and multivitamins, as well as different food variables. The study then adjusted for those factors that were shown to distort the effect of the foods and food groups under study. About 25 foods and food groups in total were examined.

Dr. Tantamango says there is a need for future studies to examine foods shown to reduce the risk of colon polyps, since it is possible that interactions between various nutrients with anti-cancerous properties will be better able to explain these findings.