A diet rich in fruits, vegetables and whole grains, and low in sweets and processed meats, may help lower the risk of breast cancer in some African-American women.

In a study of more than 50,000 African-American women, researchers found that thinner and younger women who ate a generally “prudent” diet were less likely to develop breast cancer than their counterparts who maintained a more Western-style diet.

There was no evidence that healthier eating lowered the risk among overweight women, or those past menopause. However, the prudent diet was linked to a generally lower risk of estrogen receptor-negative breast cancer - an aggressive type of tumor that accounts for about one-third of breast cancers.

The prudent diet is one rich in whole grains, fruits, vegetables and fish, and lower in red and processed meats, sweets and starchy carbohydrates, like white bread. The opposite pattern is true of the so-called Western-style diet.

The new findings, published in the American Journal of Clinical Nutrition, add to the understanding of how these diet patterns may affect breast cancer risk in different groups of women.

Past studies have suggested that the prudent diet may help lower breast cancer risk in at least some women. But there has been a lack of studies focused on black women, according to the researchers on the new work, led by Tanya Agurs-Collins of the U.S. National Cancer Institute.

Their findings are based on a long-term study launched in 1995 that is following the health and lifestyle habits of 50,778 black women from across the U.S. Between 1995 and 2007, 1,094 of those women were diagnosed with breast cancer.

The researchers found no strong evidence that the prudent diet lowered breast cancer risk for the study group as a whole.

However, when they focused on normal-weight women, they found that as scores on the prudent-diet scale rose, the risk of developing breast cancer declined. The 20 percent of women with the most prudent diets were about one-third less likely to develop the disease than their counterparts with the least prudent eating habits.

Similarly, the healthier diet was linked to a lower cancer risk among premenopausal women. Those with the most prudent diets were 30 percent less likely to be diagnosed with breast cancer.

Other studies, according to the researchers, have found that a healthy diet may lower breast cancer risk in normal-weight women, but not those who are overweight.

The reasons are unknown, but taken together, the researchers write, these studies suggest that the protective effect of a prudent diet may be “largely among thinner women.”

The issue of age appears more complicated, however. Agurs-Collins and her colleagues point out that some studies have linked the prudent diet to a lower breast cancer risk in postmenopausal women.

As for why the diet might be protective against estrogen receptor-negative tumors, in particular, the reasons are not clear. But the findings may be particularly important for younger African-American women, as they are more likely than their white counterparts to develop this type of tumor, the researchers point out.

Whatever the effects on breast cancer, though, the prudent diet is one that is recommended for better overall health - including a lower risk of heart disease, the number-one killer of U.S. women.

SOURCE: American Journal of Clinical Nutrition, September 2009.