LETTERS TO THE EDITOR Olive oil and colorectal cancer

EDITOR,—In a recent article on diet and colorectal cancer, Stoneham et al reported that 76% of the variation in incidence rates between 28 countries could be explained by three significant dietary factors (meat, fish, and olive oil). The authors concluded that olive oil may have a protective eVect on the development of colorectal cancer. While a plausible mechanism is proposed, it is worth noting that 21 of the 28 populations included in the ecological study were essentially non-consumers of olive oil (<0.01 kg/year per capita) and the inverse association between consumption and colorectal cancer risk is therefore based on a relatively small number of influential data points (fig 1). Regional colorectal cancer rates in Italy and Spain (for example, Trieste and Mallorca) are among the highest in Europe despite high levels of olive oil consumption, while lower rates in Greece are consistent with a diet characterised by intermediate meat and high fibre consumption. The authors have demonstrated a strong positive association between meat supply and colorectal cancer risk, which persists after controlling for a range of potential dietary confounders. The association is supported by a plausible causal agent in the form of heterocyclic amines produced in the cooking of meat and fish products and shown to be both mutagenic in the standard Ames’ test and carcinogenic in animal studies. Further studies on olive oil are clearly warranted, including research on the possible inhibition of heterocyclic amine formation by constituents in olive oil such as oleic acid and vitamin E. Nevertheless, the data presented suggest that meat consumption may be a more important determinant of colorectal cancer risk at the population level and also warrants further investigation.