A recent study at the Western Australian Institute for Medical Research has provided evidence that the effects on colorectal cancer (CRC) of eating fruits and vegetables varied according to the malignancy's site of origin, the scientists claimed.
The researchers have documented their findings in a paper set to be published in the October issue of the Journal of the American Dietetic Association, indicating eating brassica (or cruciferous) vegetables, such as cabbage, cauliflower, broccoli and Brussels sprouts, decreased the risk of distal and proximal colon cancers, and eating apples also lowered distal colon cancer risk, but drinking lots of fruit juices increased the risk of rectal cancer.
Lead author epidemiologist Lin Fritschi explained,
"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. 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."
He also called for further, larger studies to attempt to replicate these results.
The team, which included Deakin University researchers, investigated the effects of eating fruits and vegetables on three cancers originating in different bowel sections -- distal colon cancer, proximal colon cancer and rectal cancer -- through a case-control study of 918 subjects diagnosed with CRC and 1021 controls with no CRC history.
All participants, who were assigned a socioeconomic level by the home addresses they listed, completed extensive nutritional and medical questionnaires.
Unlike earlier CRC studies, according to the researchers, this survey set out to distinguish between cancer sites of origin because distal colon and rectal tumors have been shown to follow different courses from cancers originating in the proximal colon, and it has been established that risk varies within the colorectum according to the subsite where the cancer started.
But no mechanism that could be causing different results for different foods at different sites has been identified yet.
In this study the team found: brassica vegetable intake was associated with a lower incidence of proximal colon cancer; total vegetable and fruit intake, total vegetable intake and dark yellow vegetable and apple intake were associated with lower risk of distal colon cancer; but total vegetable and fruit, total fruit, and total vegetable intake were not associated with higher or lower risk of rectal cancer and proximal colon cancer, though drinking fruit juice appeared to increase rectal cancer risk.
The authors concluded it is easier when considering public health to translate analyses of food intake into dietary recommendations rather than focusing on single nutrients.
ScienceDaily reported in April 2010 that an international research team found only a weak cancer-protective effect at best from increased consumption of fruits and vegetables in a study of over 400,000 women and men, and a review of a decade of evidence at Oxford University in December 2010 failed to find a definite association between fruit and vegetable intake and lowered risk of cancer, but two separate studies in 2007 suggested eating fruits and vegetables protected against head and neck cancers, and eating cruciferous and dark green vegetables lowered prostate cancer risk.