Low-Fat Diet and Fish Oil in Men on Active Surveillance for Prostate Cancer

PRIMARY OBJECTIVES: I. Determine if a 1-year low omega-6, high omega-3 fat diet combined with fish oil results in decreased prostate cancer Ki-67 index as compared to a control group in men on active surveillance. SECONDARY OBJECTIVES: I. Evaluate the effect of a low-fat (LF)/fish oil (FO) intervention on prostate biopsy tissue markers of progression, prostate biopsy pathologic features (Gleason grade, tumor volume ), prostate-specific antigen (PSA), and long-term clinical outcomes (clinical progression, prostate cancer therapies). II. Evaluate potential surrogate biomarkers of proliferation (red blood cell \[RBC\] membrane fatty acid analyses, ex-vivo bioassay). III. Determine if a correlation exists between free fatty acid receptor 4 (GPR120) levels and progression markers in response to the LF/FO intervention. IV. Evaluate effect of the intervention on the National Comprehension Cancer Network (NCCN) risk group V. Evaluate compliance with a 1-year + 2 year extension LF/FO intervention. VI. Evaluate safety of a 1-year + 2-year extension LF/FO intervention. OUTLINE: Patients are randomized to 1 of 2 arms. ARM I: Patients receive no intervention. ARM II: Patients receive dietary counseling with a research dietitian weekly for 1 month and then monthly for 11 months. Patients are given guidelines with recommended meals to follow a high omega-3, low omega-6 diet comprising 30% kilocalories (Kcal) from fat, 15% Kcal from protein, and 65% Kcal from carbohydrates for 1 year. Patients also receive 4 fish oil capsules per day orally (PO) for 1 year. After completion of study, patients are followed up yearly for 15 years.