Current advice in relation to diet and cancer should include recommendations to consume adequate amounts of fruit and vegetables but should place most emphasis on the well-established adverse effects of obesity and high alcohol intakes, finds a mini review in the British Journal of Cancer.

The possibility that fruit and vegetables may help to reduce the risk of cancer has been studies for over 30 years but no protective effects have been firmly established. In the current review Tim Key, from the Cancer Epidemiology Unit at Oxford University, summarised epidemiological evidence on the association of total fruit and vegetable consumption with the risks for major cancer sites.

The key conclusions of his review were:

For cancers of the upper gastrointestinal tract (oral cavity and pharynx) epidemiological studies suggest high fruit and vegetable intakes can moderately reduced risk, with case control studies suggesting a 50% reduction. However there are confounding factors – tobacco and alcohol cause large increases in the risk of these cancers and are associated with low intakes of fruit and vegetables.For oesophageal cancers data is consistent with the hypothesis that adequate intakes of fruit and vegetable reduce the risk, but again it is possible that the association is due to confounding factors with smoking and alcohol.For stomach cancer while data from case-control studies supports the hypothesis that risk may be reduced by adequate intakes of fruit and vegetables, prospective studies have mostly shown weak or null associations.For lung cancer, recent prospective analyses have not shown convincing associations.For colorectal, breast and prostate cancer epidemiological studies suggest little or no association between fruit and vegetable consumption and risk.

"Nutritional principles indicate that healthy diets should include at least moderate amounts of fruit and vegetables, but the available data suggest that general increases in fruit and vegetable intake would not have much effect on cancer rates, at least in well-nourished populations," concluded Key.

Article: TJ Key. Fruit and vegetables and cancer risk. British Journal of Cancer (2011) 104, 6-11.