The study – published in the Journal of the American Dietetic Association – 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 researchers found that brassica vegetables, such as brussels sprouts, cabbage, cauliflower and broccoli, are associated with decreased risk of the cancers, but have differing effects on risk depending on the specific site of cancer.
The team, from the Western Australian Institute for Medical Research, found that 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 colorectal cancer, however, their protective effect has been subject to debate, possibly because of different effects on different subsites of the large bowel," said lead investigator Professor Lin Fritschi, PhD.
"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,” she explained.
Fritschi said the replication of these findings in larger prospective studies could help to determine whether a higher intake of vegetables is a means for reducing the risk of colorectal cancers.
The team analysed dietary information from nearly 2000 people in order to asses the nutritional intake with the risk of the cancers. The case-control study included 918 participants with a confirmed CRC diagnosis and 1021 control participants with no history of the illness.
Fritschi and her colleagues found that consumption of brassica vegetables – like broccoli and 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, they said – noting that distal colon cancer risk was significantly decreased in by intake of dark yellow vegetables and apples.
They also showed that consumption of fruit juices was associated with an increased risk for rectal cancer, whilst the risk of proximal and rectal cancer was not found to be associated with intakes of total fruit and vegetable, total vegetable or total fruit.
The team concluded 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."
They added that when examining the relationship between nutrition and the risk of colorectal cancers, future research should take location of the tumour in to account.
Source: Journal of the American Dietetic Association
Volume 111, Issue 10 , Pages 1479-1490, doi: 10.1016/j.jada.2011.07.008
“Fruit and Vegetable Consumption and the Risk of Proximal Colon, Distal Colon, and Rectal Cancers in a Case-Control Study in Western Australia”
Authors: N. Annema, J.S. Heyworth, S.A. McNaughton, B. Iacopetta, L. Fritschi