Pomegranate Extract in Treating Patients With Rising Prostate-Specific Antigen Levels After Surgery or Radiation Therapy for Localized Prostate Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed adenocarcinoma of the prostate * Must have completed prior surgery, cryotherapy, or radiotherapy for the primary tumor * Documented rising prostate-specific antigen (PSA) * Absolute level of PSA \> 0.2 ng/mL after surgery * Absolute level of PSA \> 1.0 ng/mL after radiation or cryotherapy * Absolute level of PSA ≥ 0.4 ng/mL after multiple treatment modalities (e.g., surgery with radiotherapy or radiotherapy with cryotherapy) * PSA must be ≥ 100% above best nadir achieved * PSA doubling time \> 3 months or ≤ 24 months * Patients must have ≥ 3 rising PSA time points above the minimum nadir achieved over ≥ 6 months * The interval between PSA time points must be \> 2 weeks * PSA ≤ 7.0 ng/mL * Patients who underwent radical prostatectomy and never achieved undetectable serum PSA after surgery are not eligible * Gleason score ≤ 7 * No histologically positive lymph nodes * No evidence of metastatic disease by physical examination, CT scan, or bone scan PATIENT CHARACTERISTICS: * Life expectancy ≥ 6 months * ECOG performance status 0 or 1 * No significant concomitant medical or psychiatric conditions that would limit study compliance * No known allergies to pomegranate extract * No known diabetes with hemoglobin A\_1c level \> 7.0% in the past 3 months * Diabetic patients entering study who have not had hemoglobin A\_1c level measured in the past 3 months must have levels measured at study initiation * No clinically abnormal laboratory values \> 2 times the upper limit of normal PRIOR CONCURRENT THERAPY: * See Disease Characteristics * More than 4 weeks since prior and no concurrent experimental drugs, high-dose steroids, or other cancer treatment * No hormonal therapy, with the exception of neoadjuvant androgen-deprivation therapy (ADT), prior to or concurrent with primary therapy * Patients who received prior neoadjuvant ADT must have serum testosterone ≥ 150 ng/dL * No prior or concurrent hormonal therapy for rising PSA after primary therapy for prostate cancer * No finasteride or dutasteride at any time point after primary therapy and during study therapy * No other concurrent commercial pomegranate products * No other concurrent systemic or local therapy for prostate cancer * Concurrent dietary/herbal supplements (e.g., saw palmetto or selenium) allowed provided dose has been stable for ≥ 2 months prior to study entry and there are no plans to change or stop the supplements during study therapy