Diet and cancer prevention: the roles of observation and experimentation.

Observational epidemiology and experimentation by randomized controlled trials (RCTs) have been used to evaluate dietary factors in cancer prevention; however, consistency in findings has been elusive. In several circles, RCTs are viewed as more credible than observational studies. As the testing of dietary epidemiological findings in RCTs has been more common for colorectal cancer than for other cancers, we use experience with this malignancy to critically appraise the reasons for discrepancies between results of observational and experimental studies.