Key Findings
Flaxseed and soy are rich sources of lignans and isoflavones, respectively, and resemble endogenous estrogens and have been shown to exert hormonal effects. The objective of the present study was to compare the effects of consuming a moderate amount (25 g) of ground flaxseed or ground soy flour incorporated into a muffin on the metabolism of estrogen [ie, urinary estrogen metabolites (2OHE1 and 16alphaOHE1) and serum hormones] and biochemical markers of bone metabolism in postmenopausal women. Flaxseed modified estrogen metabolism and may have the capacity to influence tissue estrogen exposure and therefore breast cancer and osteoporosis. No negative effect of changing estrogen metabolism on biochemical markers of bone metabolism were noted.
ABSTRACT
Background: Phytoestrogens, which are abundant in flaxseed and soy, have chemical structures resembling those of endogenous estrogens and have been shown to exert hormonal effects, thereby affecting chronic diseases. Objective: We compared the effects of consuming equal amounts of flaxseed or soy on estrogen metabolism and biochemical markers of bone metabolism in postmenopausal women. Design: In a parallel design, the diet of postmenopausal women (n = 46) was supplemented with either a placebo, soy (25 g soy flour), or flaxseed (25 g ground flaxseed) muffin for 16 wk. Blood and 24-h urine samples were collected at baseline and at the endpoint. Urine samples were analyzed for phytoestrogens, estrogen metabolites (2-hydroxyestrone, 16alpha-hydroxyestrone), and serum hormones (estradiol, estrone, estrone sulfate). Serum and urine samples were also analyzed for biochemical markers of bone metabolism. Results: Urinary concentrations of 2-hydroxyestrone, but not of 16alpha-hydroxyestrone, increased significantly in the flaxseed group (P = 0.05). In the flaxseed group, the ratio of 2-hydroxyestrone to 16alpha-hydroxyestrone was positively correlated with urinary lignan excretion (r = 0.579, P = 0.02). In the soy and placebo groups, no significant correlation was observed. No significant change in serum hormones or biochemical markers of bone metabolism was observed within or between the treatment groups. Conclusions: Supplementation with flaxseed modifies urinary estrogen metabolite excretion to a greater extent than does supplementation with an equal amount of soy. This modification by flaxseed is associated with an increase in urinary lignan excretion. Despite the shift in estrogen metabolism to favor the less biologically active estrogens, a negative effect on bone cell metabolism was not observed.
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