UPDATE: This post was updated to clarify the amount of whole walnuts the mice were fed each day.
According a press release from the California Walnut Commission, a new study suggests that eating walnuts may reduce a man's risk for prostate cancer. The researchers, led by a team at the University of California, Davis, fed whole walnuts to mice with prostate tumors and found that their tumors shrank about 50 percent, and grew about 30 percent slower than prostate tumors in control mice. The mice were fed a diet that contained 155 grams of whole walnuts per kilogram of total diet, says lead researcher Paul Davis. In human terms, that amounts to about 80 grams of whole walnuts per day.The study, published in the British Journal of Nutrition, shows that the walnut-fed mice had lower levels of prostate cancer biomarker IGF-1, lower levels of LDL cholesterol, and had differences in their liver metabolome compared to controls. "Davis believes that their findings are not a result of one isolated component, but due to the multiple ingredients found in walnuts that work together," the press release says. "Walnuts are a whole food that provides a rich package of healthful substances, including omega-3 fatty acids, gamma tocopherol (a form of vitamin E), polyphenols, and antioxidants. These likely then work synergistically," Davis tells the California Walnut Commission.