Walnuts Slow Prostate Cancer Tumor Growth

Diets rich in walnuts or walnut oils slow prostate cancer (PCa) tumor growth in mice, according to a recent study published in the Journal of Medicinal Food.

Paul Davis, PhD, and colleagues at the UC Davis Department of Nutrition, fed either whole walnuts and  walnut oil or controlled fats with the same omega-3 fatty acid content as walnuts to mice for 18 weeks. They wanted to examine which part of the walnut was responsible for its health effects through the mixture of these fats.

“For years, the US government has been on a crusade against fat, and I think it’s been to our detriment,” said Dr. Davis. “While [walnuts] are high in fat, their fat does not drive PCa growth.”

The researchers found that walnuts and walnut oil lowered cholesterol and slowed PCa growth. However, they observed no changes in the controlled fat group, suggesting that it is the other components of the walnut and not the omega-3s that drive the effect.

Additionally, walnut intake showed a link with certain mechanisms in cancer growth, decreasing insulin-like growth factor 1 (IGF-1), the growth hormone implicated in prostate and breast cancer.

“It could be a combination of the omega-3s with whatever else is in the walnut oil,” Dr. Davis said. “It’s becoming increasingly clear in nutrition that it’s never going to be just one thing; it’s always a combination.”

The study, which is published in the Journal of Medicinal Food, notes that previous studies have suggested intake of tree nuts is linked with reduced cardiovascular disease risk factors as well as cancer.

A 2013 study, for example, showed that consuming walnut oil boosts blood vessel functioning and eating whole walnuts helps "good" cholesterol transport and remove extra cholesterol from the body more effectively. Researchers from this latest study, led by scientist and research nutritionist Paul Davis, note that they have been assessing the health impacts of walnuts for quite a while.

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