Olive oil, diet and colorectal cancer: an ecological study and a hypothesis

Study objectives-Colorectal cancer (CRC) is a common cancer in many western countries and is probably caused in part by dietary factors. Southern Euro pean countries have lower incidence rates of CRC than many other western co untries. It was postulated that, because olive oil is thought to influence bile salt secretion patterns in rats, it may influence the occurrence of CR C. The purpose of this study was to compare national levels of dietary fact ors, with particular reference to olive oil, with national differences in C RC incidence. Design-Ecological study using existing international databases. Incidence r ates for CRC, food supply data, and olive oil consumption data were extract ed from published sources, combined, and analysed to calculate the correlat ions between CRC and 10 dietary factors. Associations were then explored us ing stepwise multiple regression. Setting-28 countries from four continents. Main results-76% of the intercountry variation in CRC incidence rates was e xplained by three significant dietary factors-meat, fish and olive oil-in c ombination. Meat and fish were positively associated, and olive oil was neg atively associated, with CRC incidence. Conclusion-Olive oil may have a protective effect on the development of CRC . The proposed hypothesis is that olive oil may influence secondary bile ac id patterns in the colon that, in turn, might influence polyamine metabolis m in colonic enterocytes in ways that reduce progression from normal mucosa to adenoma and carcinoma.