UC Davis researchers, with colleagues at the USDA Western Regional Research Center in Albany, Calif., assessed tumor size in mice fed different diets for 9, 18 and 24 weeks. They found that the mice that consumed the human equivalent of 2.4 ounces of whole walnuts daily, gained weight at the same rate as mice fed a soybean diet formulated to match the nutrients, fat levels and fatty acid profiles of the walnut diet. At 18 weeks, however, the tumor weight of the walnut-fed group was approximately half that of the mice consuming the soybean oil diet. Overall, the rate of tumor growth was 28 percent lower in the walnut-fed mice.
A low-fat diet is frequently recommended for reducing a man’s risk for developing or slowing growth of existing prostate cancer, but the UC Davis study suggests that excluding walnuts, which are high in fat but rich in omega-3, antioxidants and other plant chemicals, may mean foregoing a protective effect of walnuts on tumor growth.
“If additional research determines that walnuts have the same effect in men as they do in mice, adhering to a diet that excludes walnuts to lower fat would mean that prostate cancer patients could miss out on the beneficial effects of walnuts,” said lead author Paul Davis, a research nutritionist in the Department of Nutrition at UC Davis and researcher with the UC Davis Cancer Center.
Prostate cancer is the second most common cancer in American men. One in six men will be diagnosed with the cancer, most commonly in later life. But relatively few — one in 36 — will die from the disease because most tumors do not spread beyond the local site, according to the National Cancer Institute.
“These characteristics of prostate cancer make adding walnuts to a diet attractive as part of prostate cancer prevention,” Davis said.
The findings were published in the British Journal of Nutrition