Eating more than five servings of fruits and vegetables--the amount recommended by the U.S. Food and Drug Administration (FDA)--doesn't provide any additional protection against breast cancer, a new study finds. However, eating the recommended amount still appears to help protect against the disease.
Worldwide, breast cancer is the leading cause of cancer death among women, claiming some 500,000 lives each year. Previous research suggested that diet can significantly lower the odds of developing the disease. In particular, some foods contain antioxidants, compounds that prevent damage to DNA that is thought to cause mutations and contribute to triggering breast cancer. Doctors have been keen to determine whether increased amounts of antioxidant-rich fruits and vegetables can reduce a woman's risk even further.
To find out, John Pierce of the University of California, San Diego, and colleagues tracked the health of more than 3000 women who had previously been treated for early-stage breast cancer. Half the women received literature promoting the FDA-approved target of five servings of fruits and vegetables per day, and the other half received this plus counseling and literature promoting significant additional intake of fruits, vegetables, and dietary fiber coupled with a reduced-fat diet.
After monitoring each volunteer for about 7 years, the researchers compared the rates of relapse and new breast tumors in the two groups, as they report this week in the Journal of the American Medical Association. In both categories, the rates were the same, indicating that subjects got no extra benefit from the additional produce. Although overloading on fruits and veggies might not lower your risk, Pierce notes that in previous studies his group found that eating at least the recommended amount and getting regular physical exercise does. "You don't need to go overboard," Pierce says.
The result isn't ironclad because the researchers had to assume that people followed the promoted diets; giving people literature doesn't necessarily translate to behavioral changes, says JoAnn Manson, an epidemiologist at the Harvard School of Public Health in Boston, Massachusetts. However, Meir Stampfer, a nutritionist and epidemiologist also at Harvard's School of Public Health, says the results aren't surprising, because the evidence that overloading on produce would have an additional benefit was modest to begin with. And even though the extra produce doesn't help with cancer, it might help women live longer anyway, Stampfer notes, perhaps by reducing the odds of cardiovascular disease.