Flaxseed Supplementation (Not Dietary Fat Restriction) Reduces Prostate Cancer Proliferation Rates in Men Presurgery

Randomized presurgical controlled trial in men with biopsy-confirmed prostate cancer scheduled for prostatectomy. Participants were middle-aged men enrolled at Duke University Medical Center, Durham Veterans Administration Medical Center, and five University of Michigan CCOP Research Base sites between July 5, 2002 and April 17, 2006.

Men in the flaxseed arm received 30 g/day of ground flaxseed orally, stepped up over 7 days (10 g on days 1–3, 20 g on days 4–6, 30 g/day from day 7 onward) with at least 64 oz/day of fluids. The flaxseed plus low-fat arm used the same flaxseed regimen plus a low-fat diet targeting less than 20% of energy from fat. The low-fat arm received dietitian-supported fat restriction.

Flaxseed supplementation was associated with lower prostate tumor cell proliferation before surgery, whereas low-fat diet alone did not show a clear antitumor effect. Median Ki-67 proliferating cells per total nuclei x100 was 1.66 in the flaxseed group and 1.50 in the flaxseed plus low-fat group, compared with 2.56 in the low-fat group and 3.23 in controls; flaxseed arms showed lower proliferation with P < 0.002, and reported flaxseed-effect P values ranged from 0.0007 to 0.02. There were no consistent between-arm differences in apoptosis or most serologic endpoints. The low-fat arm significantly reduced serum cholesterol (P = 0.048), and other biomarkers such as PSA, testosterone, IGF-I, IGFBP-3, and C-reactive protein generally decreased across all arms without clear between-arm differences.

The intervention period was short, averaging 30.7 days and ending within 3 days of surgery, so long-term clinical relevance is uncertain. The trial was relatively small and focused on biomarker outcomes rather than cancer recurrence or survival, and there was no strong evidence of interaction between flaxseed and low-fat diet. Adverse events occurred and the findings may not generalize beyond presurgical men with localized prostate cancer.