Results of a new University of California study show that men who are at risk of prostate cancer can include more soy products such as tofu and soy milk in their diets. Dr. Ralph deVere White, director of the University of California at Davis Cancer Center, presented the study at a meeting of the American Urological Association here and said that, although the initial tests were conducted on mice and need to be replicated on humans, ``we are encouraged by these results.''