International differences in diet and cancer incidence.

International variations in the annual incidence rates of reproductive organ and gastrointestinal cancers suggest that they have environmental causes and can be controlled by public health approaches. Secular trends in the national incidence rates of these two groups of tumors and the experiences of migrants moving from countries with low rates to countries with higher rates of these cancers increase the likelihood that public health dietary interventions will lower cancer incidence rates. The results of recent correlation analyses of international variations in the consumption of dietary fat and incidence of large-bowel and hormone-dependent reproductive organ cancers suggest that both the total amount of fat and the specific fatty acids consumed are associated with the incidence of these cancers in national populations and that the associations strengthen with age and are strengthened rather than weakened by the inclusion of potentially confounding and modifying dietary and nondietary factors in the analysis. The consistency of estimates developed with coefficients derived from these analyses and the degree to which they agree with independent observations suggest that they can provide useful parameters for the design of trials to test the hypothesis that they measure causal associations.