Flaxseed Intake, Urinary or Seminal Lignan Levels and Prostate Cancer Growth

Boyd R. Switzer, PhD, Robin Vollmer, MD, Stephen George, PhD, John Madden, MD, PhD, Denise Snyder, MS, RD, Mack T. Ruffin, IV, MD, MPH, Vera Hars, MS and Wendy Demark-Wahnefried, PhD, RD (USA).

Abstract

The effects of flaxseed supplementation and/or dietary fat restriction on prostate cancer growth were investigated in a phase II randomized controlled trial among 161 men scheduled for prostatectomy.  Flaxseed is the richest plant source of omega-3 fatty acids, as well as the richest source of dietary lignans, both of which have been implicated in hindering cancer growth.  The men were randomly assigned to one of four dietary treatments: 1) a regular diet; 2) flaxseed supplementation (30/day); 3) a low-fat diet (<20% of energy from fat); or 4) flaxseed supplementation with a low-fat diet.  The consumption of 30 grams ground flaxseed supplement/day for an average of 30-31 days was verified by diet records, and by urine and seminal samples.  The prostate cancer proliferation index of men supplemented with flaxseed, with or without low-fat intake, was significantly reduced to roughly 50% of that observed in men consuming regular or low fat diets.  No significant change in prostate cancer cell death was seen among biopsies of men on any dietary treatment.  How the various components of flaxseed, individually or collectively, decrease prostate cancer growth cannot yet be explained and additional study is required.  We speculate that a high-lignan intake, as part of a long-term energy-balanced diet that is also rich in fruit and vegetables, may affect the biology of prostate cancer.