In the October, 2011 issue of the Journal of the American Dietetic Association, Australian researchers report the outcome of a study which suggests site-specific protective effects of various fruits and vegetables against the risk of colorectal cancer. The finding may help explain inconsistent results from other studies which sought to examine the effects of plant foods against the cancer disease.
Lin Fritschi, PhD and colleagues at the University of Western Australia compared 918 colorectal cancer patients to 1,021 controls who had no history of the disease. Questionnaires completed by the participants were analyzed for the frequency of consumption of 38 different vegetables and fruits.
Total Fruit and Colon Cancer
Total fruit, vegetable, or fruit and vegetable intake were not associated with the risk of proximal colon cancer or rectal cancer, however, the researchers found a protective effect for increased intake of brassica vegetables, including broccoli, cauliflower, cabbage and Brussels sprouts, against cancer of the proximal colon. Total fruit and vegetable intake, total vegetable intake, and the consumption of dark yellow vegetables and apples were associated with a reduction in distal colon cancer risk. While apple consumption was protective against rectal cancer, consuming a high amount of fruit juice was associated with a greater risk of the disease.
The authors note that “Fruit juice may have similar composition to fruit with respect to a range of phytochemicals, but it is low in fiber and some fruit juices contain added sugar. In addition, there is some evidence to suggest that foods containing high amounts of sugars may increase risk of colorectal cancer, and animal studies have shown that glucose and fructose are associated with increased colonic proliferation and aberrant crypt foci.”
“Fruits and vegetables have been examined extensively in nutritional research in relation to colorectal cancer, however, their protective effect has been subject to debate, possibly because of different effects on different subsites of the large bowel,” noted Professor Fritschi, who is the head of the Epidemiology Group at the Western Australian Institute for Medical Research.
She continued, “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 colorectal cancer 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 colorectal cancer.”
Fruit and vegetable intake in the United States remains below recommended levels despite evidence of the health benefits of regular consumption.
Professor Lin Fritschi is a cancer epidemiologist with a particular interest in occupational causes of cancer. Over the past 17 years she has worked in Montreal, Melbourne and Brisbane and currently heads the Epidemiology Group at the Western Australian Institute for Medical Research in Perth, Western Australia. Lin has been an investigator on a number of large case-control and cohort studies and has a total career funding of over $19 million. Lin is interested in improving the way we assess historical exposure to chemicals and has developed a new web-based application (OccIDEAS) to assist in this task (www.occideas.org). She has published over 140 peer-reviewed publications in national and international journals and holds an NHMRC Senior Research Fellowship.
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