(NaturalNews) Walnuts are a rich plant source of omega-3s, the fatty acids also found in cold water fish like salmon. Omega-3s are known to lower the risk of a host of health problems from depression to heart disease. Walnuts are also loaded with gamma tocopherol (a form of vitamin E), phytochemicals known as polyphenols, and antioxidants.Scientists from the University of California-Davis just reported their discovery at the 239th National Meeting of the American Chemical Society (ACS), being held in San Francisco this week. "Walnuts should be part of a prostate-healthy diet," Paul Davis, Ph.D., who headed the study, said in a statement to the media. "They should be part of a balanced diet that includes lots of fruits and vegetables."Approximately 190,000 men in the United States will be diagnosed with prostate cancer this year. According to the University of California-Davis scientists, research suggests that diet is among the most important factors in influencing a man's risk for developing prostate cancer. For example, there's evidence that eating tomatoes and drinking pomegranate juice may reduce the chance of ever having prostate cancer.Recently, scientists have found that walnuts could fight cardiovascular disease by reducing levels of endothelin, a substance that increases inflammation in blood vessels. Because men with prostate cancer are known to have elevated levels of endothelin, the University of California-Davis scientists reasoned that eating walnuts could be beneficial in preventing and/or treating prostate cancer.Davis and his research team conducted their study on laboratory mice that had been genetically programmed to develop prostate cancer. One group of the animals ate the equivalent of about 2.5 ounces of walnuts per day in a human diet (equal to approximately 14 shelled nuts) for two months. A control group of mice did not receive any walnuts in their diet.When the genetically induced prostate cancers developed in the walnut-fed animals, their tumors were only about half as large as those of the control mice. What's more, the cancers in the walnut eating rodents also grew 30 percent slower.So what was going on in the bodies of the mice who ate walnuts? The researchers found those mice had lower levels of insulin-like growth factor-1. That's a crucial finding because high levels of this protein are thought to increase the risk of developing prostate cancer To further investigate why walnuts had the ability to fight prostate cancer, the researchers used gene chip technology to track changes in gene levels in the animals' tumors as well as in the livers of the mice. The results showed eating walnuts had a significantly beneficial effect on both tumor and liver genes that have been shown to be involved in controlling the growth of malignant tumors.Editor's note: NaturalNews is opposed to the use of animals in medical experiments that expose them to harm. We present these findings in protest of the way in which they were acquired.