Flaxseed influences urinary lignan excretion in a dose-dependent manner inpostmenopausal women

Dietary estrogens, such as lignans, are similar in structure to endogenous sex steroid hormones and may act in vivo to alter hormone metabolism and su bsequent cancer risk. The objective of this study was to examine the effect of dietary intake of a lignan-rich plant food (flaxseed) on urinary lignan excretion in postmenopausal women. This randomized, cross-over trial consi sted of three 7-week feeding periods during which 31 healthy postmenopausal women, ages 52-82 years, consumed their habitual diets plus 0, 5, or 10 gr ams of ground flaxseed per day. Urine samples collected for 2 consecutive d ays during the last week of each feeding period were analyzed for lignan co ntent (enterodiol, enterolactone, and matairesinol) by isotope dilution gas chromatography/mass spectrometry, Compared with the 0-gram flaxseed diet, consumption of 5 or 10 grams of flaxseed significantly increased excretion of enterodiol by 1,009 and 2,867 nmol/day, respectively; significantly incr eased excretion of enterolactone by 21,242 and 52,826 nmol/day, respectivel y; and significantly increased excretion of total lignans (enterodiol + ent erolactone + matairesinol) by 24,333 and 60,640 nmol/day, respectively. Exc retion of matairesinol was not significantly altered by flaxseed consumptio n, Consumption of flax, a significant source of dietary estrogens, in addit ion to their habitual diets increased excretion of enterodiol and enterolac tone, but not matairesinol, in a dose-dependent manner in this group of pos tmenopausal women. Urinary excretion of lignan metabolites is a dose-depend ent biomarker of flaxseed intake within the context of a habitual diet.