Affecting one in six American men, prostate cancer is a disease in which diet is suspected to play a contributing role.  Paul Andrew Davis, from University of California/Davis (California, USA) , and colleagues fed a diet with whole walnuts to mice that had been genetically programmed to get prostate cancer. After 18 weeks, the researchers found that consuming the human equivalent of 2.4 ounces of walnuts per day resulted in significantly smaller, slower-growing prostate tumors, as compared to mice consuming the same diet with an equal amount of fat, but not from walnuts. The team also found that not only was prostate cancer growth reduced by 30 to 40%, but the mice had lower blood levels of a particular protein, insulin-like growth factor (IGF-1), which has been strongly associated with prostate cancer. In assessing the effect of walnuts on gene activity in the prostate tumors using whole mouse gene chip technology, the team discovered beneficial effects on multiple genes related to controlling tumor growth and metabolism.