Plant foods are known to contain phytochemicals, many of which have been identified and shown to have potential health benefits. Carotenoids and flavonoids are plant derived compounds that have been investigated for their antioxidant and gene regulatory effects, and it is possible that they may affect cancer development via both of these mechanisms. Animal and cell culture studies have identified particular inhibitory mechanisms by which flavonoids and carotenoids may inhibit carcinogenesis. However, while epidemiological studies suggest that consumption of fruit and vegetables may play a protective role in the development of cancer, many studies have shown inconsistent results. It is unclear why the results are not consistent, but it may result from the fact that some phytonutrients are protective from certain cancers but not others. For example, citrus fruits, legumes, dry beans and green leafy vegetables may protect from colorectal adenoma development.
Research published in the Journal of Nutrition in 20091 investigated the association between fruit and vegetable consumption and the risk of developing adenomatous polyps. Subjects were recruited from a colonoscopy-based case-control study being conducted in the US, and recruitment included subjects between the age of 40 and 75 y who had been invited for a colonoscopy, but who had not had previously been diagnosed with inflammatory bowel disease, skin cancer, adenomatous polyps or genetic colorectal cancer syndromes. Control subjects were those that had colonoscopy and were free of polyps in the caecum. Dietary intake was assessed using a frequent food questionnaire. The researchers used a multivariate analysis of 764 cases and 1517 controls and the results showed that increased intakes of total fruits, berries, fruit juice and green leafy vegetables were associated with reduced adenoma risk. Plant based foods may therefore be protective of colorectal adenomas.
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