The connection between diet and cancer risk may be astonishing. According to a recent report by the American Institute for Cancer Research and the World Cancer Fund, between three and four million cases of cancer worldwide could be prevented annually through dietary change.

The report, Food, Nutrition and the Prevention of Cancer: A Global Perspective, represents a broad review of scientific evidence on diet, nutrition and cancers. It offers some dietary recommendations that Americans have heard before from leading organizations such as the U.S. Departments of Agriculture and Health and Human Services (USDA/DHHS) and the American Cancer Society (ACS) on reducing cancer risk. However, the report also contains some advice that is not in accordance with these other dietary guidelines.

Finding precise links between diet and cancer is not easy. For example, over 100 different cancers exist, each with its own set of causes. Further, there is a dizzying number of components in the average diet: Some may decrease the risk while others may increase it.

"Diet is difficult to measure precisely and without bias," said Tim Byers, M.D., M.P.H., Professor of Preventive Medicine, University of Colorado. With heart disease there are risk factors like high blood cholesterol, but similar indicators may not exist to suggest cancer.

The fact that experts have agreed on general dietary advice to reduce cancer risk is also significant because it helps ensure that health professionals speak with a united voice on the subject.

The study's key recommendation—to choose a predominantly plant-based diet that includes a variety of vegetables, fruits and grains—echoes the 1996 ACS recommendation to choose mostly plant-based foods. Likewise, the USDA/DHHS Dietary Guidelines for Americans recommends a similar diet. The study noted that lean red meat can fit in a healthy diet. A recent survey showed Americans consume about 2.6 ounnces of red meat per day—well within the study's recommendation of three ounces per day.

The advice on plant-based foods stems from research showing compounds within plant foods may help protect against potential cancer-causing agents. For instance, fiber, which is found only in plant foods, has a beneficial effect on the intestinal tract and may reduce the risk for some cancers.

Plant foods contain more than just fiber—they are also rich in phytochemicals that may be critical in controlling cell damage from free radicals and in regulating cellular proliferation.

Experts note, however, that Americans are not making such simple changes as eating the recommended five servings of fruits and vegetables a day, which could reduce cancer incidence risk. Likewise, trends suggest a decline in physical activity among Americans.

The new report emphasizes the importance of physical activity and a healthy body weight. These recommendations are also in the USDA/DHHS and ACS guidelines. Physical activity not only helps reduce the risk of obesity, which may increase cancer risk, it independently reduces the risk of certain cancers. According to Dr. Byers, "These dietary guidelines represent sound advice to prevent cancer."