Bile acids are associated with increased risk CRC. Reduced colonic transit time has been suggested as important in the aetiology of CRC. Dietary factors – including meat, fat, cereal, vegetables, fruit, milk and olive oil-influence colonic transit time and the volume of secondary bile acids in the colon. We have carried out an ecological study in which the association of dietary factors with CRC, and their interrelations, were examined. Our study differs from other ecological studies, such as Armstrong and Doll, as we have included data on olive oil, which features significantly in the diet of southern European countries, and has been suggested as an important regulator of cancer in these countries. We also suggest a possible mechanism for the effect of diet on CRC.