For more than two decades American and international health organizations have promoted eating five or more servings of fruits and vegetables a day as a way to prevent cancer by as much as 50 to 70 percent. A new study says the impact is much less, only about four per cent.
The eight-year study took place in 10 European countries between from 1992 to 2000. Participants ate about 400 grams of fruits and vegetables a day and the results show the diets had only a minor effect against developing cancer.
Published in the current issue of the Journal of the National Cancer Institute, the study found ''no conclusive evidence'' of a link between cancer and fruit and vegetables.The authors found a small inverse association between high intake of fruits and vegetables and reduced overall cancer risk. Vegetable consumption also afforded a modest benefit but was restricted to women. Heavy drinkers who ate many fruits and vegetables had a somewhat reduced risk, but only for cancers caused by smoking and alcohol. The authors caution against attributing any risk reduction to diet and they conclude that any cancer protective effect of these foods is likely to be modest, at best.
"In this population, a higher intake of fruits and vegetables was also associated with other lifestyle variables, such as lower intake of alcohol, never-smoking, short duration of tobacco smoking, and higher level of physical activity, which may have contributed to a lower cancer risk," they write.
During the 1990s health professionals and government officials started campaigns to encourage people to eat more fruits and vegetables to reduce the risk of many cancers. In 1991 the National Cancer Institute adopted the Five-A-Day program which promoted increasing the average consumption of fruits and vegetables to at least five servings a day. People with family histories of cancer were told these diets could help prevent their chances of getting cancer by as much as 50 percent. Cancer patients were taught to eat more fruits and vegetables to support their recovery.
In recent years those recommendations have been questioned in several studies. The new international study "strongly confirms" the findings of other prospective studies that concluded that a diet rich in fruits and vegetables has little or no effect on cancer risk, Dr. Walter C. Willett, chairman of the Harvard School of Public Health, wrote in an accompanying editorial.
Willett said earlier researchers were misled by bias built into the survey methods. “Even more problematic,” he said, “participation rates in surveys have fallen sharply over the past 50 years so that those…interviewed…over represent health conscience persons who smoke less, exercise more, and eat more fruits and vegetables compared with those who do not participate.” Willett says nutrition studies have compared healthier individuals against cancer patients causing results that show “an exaggerated apparent benefit of fruits and vegetables, even if both groups report their past diets perfectly.”
Is eating “Five-A-Day” good for your health? Yes, your cardiovascular health. A 2004 study in the same journal found eating five daily servings of fruits and vegetables resulted in a 28 percent lower risk of heart disease and stroke, compared to people who eat fewer than 1.5 servings a day. That study, by the way, did not find a link between eating fruits and vegetables with either cancer incidence or cancer deaths.
What’s next for fruits, veggies and cancer prevention? More studies. Willett said while the study shows a broad adoption of these foods in the diet does not have a major impact on cancer prevention there is a need to determine whether specific components have value – for example, whether lycopene in tomatoes reduces the risk of prostate cancer. Willet also advocates studying the effects of fruit and vegetable consumption at earlier periods of life. What does he think will help prevent cancer? “For prevention of cancer, the primary focus at present should be heightened efforts to reduce smoking and obesity because obesity in the United States has become similar in magnitude to smoking as an avoidable cause.”
Sources:
Article: Boffetta P. et al.Fruit and Vegetable Intake and Overall Cancer Risk in the European Prospective Investigation Into and Nutrition (EPIC). J Natl Cancer Inst 2010;102(8)
Editorial: Willett WL. Fruits, Vegetables, and Cancer Prevention: Turmoil in the Produce Section. J Natl Cancer Inst 2010;102(8)
About the author: Pat Elliott is a journalist and blogger who has written about health issues for more than 20 years. She is also a cancer survivor who coaches people on how to manage their transition and take control of their new future.