Dietary fiber and human cancer: critique of the literature.

The relationship between dietary fiber consumption and risk of gastrointestinal cancer in humans is examined using representative studies of several types: international and intranational correlations, case-control analyses, metabolic investigations, cohort studies, and migrant studies. The strongest statistical association between diet and cancer is found in international studies in which numerous environmental variables differ. Studies on smaller groups within a single culture have not given strong support to the findings of international comparisons. Colon cancer rates within regions of the U.S. and other countries vary with sufficient magnitude that diet is unlikely to account for more than a minor proportion of risk. The evidence that a diet containing fiber-rich foods reduces risk of colon cancer must be considered tentative. Foods high in starch and fiber are statistically associated with a high rate of stomach cancer. Examination of the combined rates of colon and gastric cancer shows that the U.S. risk is low relative to countries in which a diet higher in fiber is consumed. It would be premature to suggest that a high fiber diet will confer protection against gastrointestinal cancer.