Can a diet high in fruits and vegetables really prevent breast cancer recurrence? The most recent data do not support such hopes (Pierce JP et al., Influence of a diet very high in vegetables, fruit, and fiber and low in fat on prognosis following treatment for breast cancer. JAMA 2007; 298(3):289).
It's been widely accepted that such diets are generally healthful, partly because they contain supposedly anticarcinogenic substances, although questions have been raised about the diet-cancer link before this. A group of researchers at seven different clinical centers collaborated to examine this question in over 3,000 women who had been previously treated for early-stage breast cancer. The participants ranged from eighteen to seventy years old when their cancers were first diagnosed. Approximately half of them were assigned to eat a diet high in fruits and vegetables that contained five servings of vegetables and three of fruit, as well as sixteen ounces of vegetable juice and thirty grams of fiber per day; the diet was to contain only 15-20% of calories from fat. A telephone counseling program was supplied, as were cooking classes and newsletters. In contrast, the control group was simply advised to eat the government-recommended "Five-a-Day" fruits and vegetables. The women were followed for an average of just over seven years.
Although the high-produce group did indeed substantially increase their produce intake, they didn't manage to reduce their fat intake to the desired level -- but they did reduce it somewhat. Their body weight didn't change by very much, either.
In spite of the dietary changes, the high-produce group experienced essentially the same number of recurrences of breast cancer as did the control group (256 vs. 262 respectively), and 155 women in the intervention group died from the recurrent cancers compared to 160 control group participants. None of these differences were statistically significant. The authors noted that even women in the intervention group who had not been eating five servings of produce per day at the beginning of the study -- who thus increased their intake the most -- did not have a recurrence benefit, nor were they less likely to die from the disease.
The take-home message for breast cancer survivors? Eating a diet with a reasonable component of fruits and vegetables is a healthful move, but pushing the consumption to extremes is unlikely to provide a benefit. This is another vote for moderation.
Ruth Kava, Ph.D., R.D., is Director of Nutrition at the American Council on Science and Health (ACSH.org, HealthFactsAndFears.com).
See also: ACSH's 2000 report on Chemoprevention of Breast Cancer.
