Introduction

Does "5 A Day"--five daily servings of fruits and vegetables--reduce a women's risk of breast cancer? Not all by themselves, say the authors of a study in the February 14 issue of the Journal of the American Medical Association.

A role for diet in breast cancer prevention ?

Researchers from the Harvard School of Public Health combined the results of eight US, Canadian, and European studies that measured the effect of fruit and vegetable intake on the incidence of breast cancer in large groups of women. The combined, or pooled, results showed that intake of fruits and vegetables did not appear to reduce the risk of breast cancer in study participants.

Further, intakes of specific kinds of produce, including nutrient-rich choices like green leafy vegetables, broccoli, cabbage, carrots, and tomatoes did not seem to affect disease risk.

Why didn't fruits and vegetables have a clear health effect?

Part of the answer lies in the type of studies included in the analysis. All are cohort studies, in which researchers assess a certain health habit--like fruit and vegetable intake--in large groups of people, and then monitor them over a period of years for a certain outcome, in this case, breast cancer. But it is hard to separate one aspect of a person's diet from all of the other diet, lifestyle, and genetic factors that determine whether an individual will remain healthy or become ill. In these studies, for instance, the people who consumed the most fruits and vegetables tended to consume a diet lower in fat and high in fiber. They were also more likely than others in the study to get regular exercise, and less likely to smoke. All these factors, not just fruit and vegetable intake, combine to affect disease risk.

And, while the authors of this study say that fruit and vegetable intake did not have a major effect on participants' risk of breast cancer, those in the highest intake group were about 3% to 9% less likely to suffer from the disease when compared with those who ate the least produce. While not a large reduction, it is, nevertheless, a step in the right direction.

Prudent advice to consumers

The American Cancer Society reminds consumers that dietary behaviors contribute to about one-third of cancer cases in the US. But this statistic refers to the whole diet, one that limits fat and excess calories and emphasizes produce and whole grains foods. While certain dietary factors appear to have more of an effect on some types of cancers than others, there is no specific diet meant to reduce the risk of any one type of cancer.

With this in mind, the American Cancer Society lists some steps that everyone over age two can take to reduce their risk of this disease:

• Choose most of the foods you eat from plant sources, including at least 5 servings of fruits and vegetables and a variety of whole grain foods
• Limit your intake of high fat foods, especially from animal sources
• Be physically active and maintain a healthy weight
• Limit consumption of alcoholic beverages, if you drink at all