Diet and Cancer

Abstract

The large differences in cancer rates among countries, striking changes in these rates among migrating populations, and rapid changes over time within countries indicate that some aspect of lifestyle or environment is largely responsible for the common cancers in Western countries. Dietary fat has been hypothesized to be the key factor because national consumption is correlated with the international differences. However, detailed analyses in large prospective studies have not supported an important role of dietary fat. Instead, positive energy balance, reflected in early age at menarche and weight gain as an adult, is an important determinant of breast and colon cancers, consistent with numerous studies in animals. As a contributor to positive energy balance, and possibly by other mechanisms, physical inactivity has also been shown to be a risk factor for these diseases and in part accounts for the international differences. Although the percentage of calories from fat in the diet does not appear related to risk of colon cancer, greater risks have been seen with higher consumption of red meat, suggesting that factors other than fat per se are important.In many case-control studies, a high consumption of fruits and vegetables has been associated with reduced risks of numerous cancers, but recent prospective studies suggest these associations may have been overstated. Among the factors in fruits and vegetables that have been examined in relation to cancer risk, present data most strongly support a benefit of higher folic acid consumption in reducing risks of colon and breast cancers. These findings have been bolstered by an association between incidence of colon cancer and a polymorphism in the gene for methylenetetrahydrofolate reductase, an enzyme involved in folic acid metabolism. The benefits of folic acid appear strongest among persons who regularly consume alcohol, which itself is associated with risk of these cancers. Numerous other aspects of diet are hypothesized to influence the risks of cancers in Western countries, but for the moment the evidence is unclear. The Oncologist 2000;5:393-404 The Oncologist 2000;5:393-404 www.TheOncologist.com Correspondence: Walter C. Willett, M.D., Dr. P.H., Department of Nutrition, Harvard School of Public Health, 665 Huntington Avenue, Boston, Massachusetts 02115, USA. Telephone: 617-432-4680; Fax: 617-432-0464 Received June 20, 2000; accepted for publication June 21, 2000. ©AlphaMed Press 1083-7159/2000 The great interest during the last several decades in diet and human cancer derives from the large variations in rates of specific cancers among countries, coupled with the dramatic changes in cancer incidence among populations emigrating to regions with different rates. Such observations indicate the importance of potentially modifiable factors in the cause and prevention of cancer, and a role of diet has been suggested by strong correlations between cancer rates and national per capita intake of specific nutrients. In their comprehensive 1981 review of a...

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