New research suggests the risk of developing the cancer decreases with a diet that include a modest amount of walnuts.
The mice used in the study conducted by the Marshall University school of Medicine ate the equivalent of two ounces of walnuts a day.
Scientists say eating walnuts effects genes that are relevant to breast cancer in both mice and humans.
Researchers say the finding highlights the vital role diet plays in a person's health.
"We think now that diet can prevent 30 to 60 percent of all cancers," lead researcher Dr. Elaine Hardman said.
"The healthy diet that we should be eating is what we know is healthy - a lot of fresh fruits and vegetables, whole grains and nuts," she said. "Walnuts can be an important component of that diet."
Hardman believes that the whole walnut, not just one element of the walnut, provides the benefit against cancer.
"If I tried to strip the walnut apart, I wouldn't see the same benefit," she added.
The study's findings were published in the published the Nutrition and Cancer report.