Adding walnuts to your diet could help lessen the growth and spread of breast cancer, according to a study conducted at Marshall University in Huntington, West Virginia, and published in Nutrition Research. The new research expands on existing data showing that walnuts could help slow breast cancer growth and lower breast cancer risk in mice.

The Marshall study involved women with breast cancer who were randomized into a group that ate walnuts or a control group that didn’t eat walnuts. After undergoing biopsies to confirm breast cancer diagnoses, the women in the first group began eating 2 ounces of walnuts per day until their follow-up surgery, which included taking addition tumor specimens. Women in the control group had the same follow-up surgery but didn’t add walnuts to their diet.

According to the researchers, tumor specimens from the women who ate walnuts revealed changes in the expression of 456 genes related to cancer cell growth, while these results weren't observed in the control group.