Walnuts May Fight Breast Cancer

Study Suggests 2 Servings of Walnuts a Day May Keep Breast Tumors at Bay

Medically Reviewed by Louise Chang, MD on April 21, 2009
From the WebMD Archives

April 21, 2009 (Denver) -- Just two handfuls of walnuts a day may keep breast cancer away, a study in mice suggests.

And if you have breast cancer, walnuts may help curb tumor growth, the study suggests.

Researcher W. Elaine Hardman, PhD, associate professor of biochemistry at Marshall University School of Medicine in Huntington, W.Va., credits the disease-fighting omega-3 fatty acids, antioxidants, and in particular, phytosterols, in walnuts.

“Phytosterols bind to estrogen receptors, so they would be expected to slow growth of breast cancers,” she says. Estrogen fuels the growth of some breast tumors.

Eat More Walnuts or Not?

Although the study was done in laboratory animals, people should heed recommendations to eat more walnuts, Hardman tells WebMD.

“Research suggests that walnuts can be a healthful part of the diet for the prevention not only of breast and other cancers, but also diabetes and cardiovascular disease,” she says.

But Peter G. Shields, MD, deputy director of the Lombardi Comprehensive Cancer Center in Washington, D.C., says it’s “outrageous” to recommend that people eat more walnuts based on a study in mice.

He notes that animal studies once suggested that beta-carotene reduced lung cancer. "But when we did the [pivotal] study in humans, smokers given beta-carotene got more lung cancer,” he tells WebMD.

“This is a nice study that calls for more research. There needs to be a lot more understood” about how walnuts might prevent breast tumors, Shields says.

The findings were presented at the American Association for Cancer Research 100th Annual Meeting.

Walnuts Delay Breast Tumors by 9 Years

Hardman and colleagues studied genetically altered mice that were programmed to develop tumors within six months.

Half consumed a diet that contained the human equivalent of two 1-ounce servings of walnuts per day. “One serving fits in the palm of your hand,” she says.

The other half was fed a diet that did not include walnuts.

Standard testing showed that eating walnuts cut the risk of developing breast tumors in half.

“If mice did get breast tumors, the growth rate was also slowed, by 50%,” Hardman says.

Looked at another way, eating walnuts delayed the development of tumors by at least three weeks in the mice. “Extrapolating to humans, this would be about a nine-year delay,” she says.

The researchers are now testing the benefits of the walnut-rich diet in male mice genetically altered to develop prostate tumors.

Hardman says she expected similar results, with the nuts both preventing and slowing the growth of prostate tumors.

WebMD Health News



American Association for Cancer Research 100th Annual Meeting, Denver, April 18-22, 2009.

W. Elaine Hardman, PhD, associate professor of biochemistry, Marshall University School of Medicine, Huntington, W.Va.

Peter G. Shields, MD, deputy director, Lombardi Comprehensive Cancer Center, Washington, D.C.

The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. 

New England Journal of Medicine, April 14, 1994; vol 330: pp 1029-1035.

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