Flaxseed, but not soy, significantly altered urinary estrogen metabolite excretion in healthy post-menopausal women


Brooks, J., Ward, W.E., Hilditch, J., Lewis, J., Nickell, L., Wong, E. The Faseb Journal: Official Publication of the Federation of American Societies for Experimental Biology. 16(5):A1005. Abstract.


Phytoestrogens found in flaxseed and soy have been suggested to provide protection against breast cancer and osteoporosis. The present study examined the effect of flaxseed or soy supplementation on urinary estrogen metabolites 2-hydroxyestrone (2OHE1) and 16α-hydroxyestrone (16αOHE1), bone metabolic markers urinary deoxypyridinoline crosslinks and serum bone specific alkaline phosphatase and urinary phytoestrogens (lignans and isoflavones) in postmenopausal women in a randomized, double blind, placebo controlled study. Postmenopausal women (n=48) were randomized into three groups and supplemented their diets with either a placebo muffin (control) or a muffin containing 25 g flaxseed or soy daily for 16 weeks. Analysis of 24-hour urine collected at 0 (baseline) and 16 weeks showed that flaxseed, but not soy and placebo, significantly increased 2OHE1 and the 2/16αOHE1 ratio. No significant change in bone metabolic markers was observed in any of the three groups. Total urinary phytoestrogens at 16 weeks in the placebo, flaxseed and soy groups were 7, 51 and 31 μmol/day, respectively. The authors conclude that flaxseed supplementation at the same daily dose as soy has a greater antiestrogenic effect on estrogen metabolism, and therefore may be more cancer protective. Furthermore, neither flaxseed or soy affected the bone metabolic markers suggesting tissue specific action of the phytoestrogens.