By David Liu, Ph.D.

Sunday Sept 3, 2011 (foodconsumer.org) -- Breast cancer kills about 50,000 women in the United States.  But following a healthy lifestyle like eating walnuts often may reduce the risk of developing breast cancer, a study in the journal Nutrition and Cancer suggests.

The study showed mice eating walnuts for a lifetime were 50 percent less likely to develop breast cancer, compared with those eating a typical diet.

The amount of walnuts the study mice ate was equivalent to 2 ounces per day for humans.  Walnuts are rich in omega-3 fatty acids, which are known to protect against inflammation and cancer to say the least.

Elaine Hardman, Ph.D. of Marshall University and colleagues conducted the study and found mice on the walnut diet had fewer tumors and smaller tumors even if they ended up developing breastcancer, compared with mice on the typical diet.

It remains known which ingredients in walnuts protected against breast cancer.  In the diet with walnuts incorporated, some other types of fat were removed.  It is unknown whether addition of walnuts or removal of other fats or both attributed to the reduction in the breast cancer risk.

At least the researchers found omega-3 fatty acids in walnuts were not the only thing that is protective.  To be specific, they found vitamin E may also protect against breast cancer.

And walnuts affected gene expressions that are with proliferation and differentiation of mammary epithelial cells in mice and humans, the study showed.  Many foods are known to reduce or increase the cancer risk by affecting the cancer genetics of animals and humans.

This is not the first study to suggest that eating walnuts may help prevent breast cancer. Hardman and G. Ion published a study in Nutrition and Cancer suggesting that walnut consumption decreased tumor cell proliferation, but did not boost apoptosis.

In the early study, Hardman et al. injected human breast cancer cells in nude mice to grow breast cancer in the animals and when tumors grew to be 3 to 5 mm in diameter, one group mice were fed ground walnuts.  The diet used in the control had 10 percent energy from corn oil, which evidence suggests boosts cancer risk.

As a result, the tumor growth rate in the mice eating walnuts was 2..9 mm (3) per day compared to 14.6 mm(3) per day.  

The researchers found eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were much higher in walnut eating mice than those that did not eat walnuts. 

These long-chain omega-fatty acids also known as n-3 PUFA3 have been found to induce apoptosis of breast cancer cells, P.A. Corsetto and colleagues from Università degli Studi di Milano in Italy reported in the May 2011 issue of  Lipids in Health and Disease.

Breast cancer rates in the United states are higher, compared to many developing countries.  One in eight American women are expected to develop the disease in their lifetime and an estimated 175,000 women are diagnosed with the disease each year in the country.

Breast cancer is largely a preventable disease.  What may reduce the risk of breast cancer include B vitamins, vitamin D, soy foods, high dietray fiber, physical activity, vegan diet, fish oil, caloric restriction, Mediterranean diet, antioxidants, green tea and bitter melon.