(NaturalNews) A diet high in walnuts may significantly decrease a person's risk of breast cancer, according to a study conducted by researchers from the Marshall University School of Medicine and presented at a conference of the American Association for Cancer Research.Researchers fed mice that had been genetically engineered to develop breast tumors either a normal diet, or the same diet supplemented with a daily dose of walnuts. Typically, 100 percent of these mice would have developed breast tumors by the age of five months. In the mice who had been fed walnuts, however, tumors did not develop for an extra three weeks. In addition, mice in the walnut group had fewer tumors, fewer cancerous glands and their tumors were smaller.Researcher Elaine Hardman noted that three weeks is a significant chunk of a mouse's average six-month lifespan."Since most cancers develop when you're older, if you could increase the time until the cancer develops even 15 percent, then that's a considerable delay, and you might die from something else before the cancer ever showed up!" she said.A chemical analysis showed that omega-3 fatty acids, antioxidants and phytosterols contained in walnuts all contributed to the mice's tumor resistance."The omega-3 fatty acid, the phytosterols and antioxidants individually have been shown to prevent or delay cancers," Hardman said. "So if you add them all together, it looks like it may be really good."In another study, Hardman found that feeding mice a diet enriched with the same omega-3 content as that contained in the walnut dose given in the current study was not as effective as eating the whole walnut."It did reduce cancer incidents," she said, "but not as dramatically as the walnut-containing diet did. So it's something else other than the omega-3 in the walnut that's contributing to the suppression of cancers."Hardman noted that the effect of the whole food was probably greater than the sum of its parts."With dietary interventions, you see multiple mechanisms when working with the whole food," she said.Sources for this story include: health.usnews.com; www.voanews.com