• A 2-year randomized double-blind placebo controlled clinical trial found that soy isoflavones can reduce fibroglandular breast tissue (FGBT) in premenopausal women.
• Urinary excretion of isoflavones in adherent subjects was significantly related to changes in breast composition.
• After an average of 1.2, 2.2 and 3.3 years of supplementation, a mean decrease of FGBT by 5.3, 12.1, and 19.3 cc, respectively, and a mean decrease of FGBT% by 1.37, 2.43, and 3.50%, respectively, were estimated for isoflavone exposure compared to placebo treatment.