OUTLINE: This is a randomized study. Patients are stratified according to previous treatment (prostatectomy vs radiotherapy) and prostate-specific antigen (PSA) level (less than 5 mg/mL vs 5 or greater mg/mL). All patients complete quality of life, dietary, and other questionnaires before, during, and at the conclusion of the study. Patients are randomized to one of two dietary intervention regimens: Arm I (Intensive Nutritional Intervention): Patients are assigned to follow a low fat, high fiber diet that is also high in soy, fruits and vegetables, green tea, and vitamin E. Patients meet with a nutritionist for nutrition education and dietary counseling weekly for 8 weeks, then every 2 weeks for 2 months, and then monthly for 14 months. Sessions include dietary counseling, meal planning, and instruction in skills necessary to maintain dietary lifestyle changes. Patients record their dietary intake on a regular basis. Arm II (General Nutritional Instruction): Patients are assigned to follow dietary guidelines established by the National Cancer Institute. Patients meet with a nutritionist for dietary counseling and monitoring every 2 months for 18 months. Patients on both arms have PSA levels tested before the study, 1 and 3 months into the study, and then every 3 months thereafter for up to 18 months.