Stimulatory influence of soy protein isolate on breast secretion
in pre- and postmenopausal women
Petrakis
NL, Barnes S, King EB, Lowenstein J, Wiencke J, Lee MM, Miike R, Kirk
M, Coward L
Cancer
Epidemiol Biomarkers Prev 1996 Oct 5:10 785-94
Abstract
Soy foods
have been reported to have protective effects against premenopausal
breast cancer in Asian women. No studies have been reported on
potential physiological effects of dietary soy consumption on breast
gland function.
We
evaluated the influence of the long-term ingestion of a commercial soy
protein isolate on breast secretory activity.
We
hypothesized that the features of nipple aspirate fluid (NAF) of
non-Asian women would be altered so as to resemble those previously
found in Asian women.
At monthly
intervals for 1 year, 24 normal pre- and postmenopausal white women,
ages 30 to 58, underwent nipple aspiration of breast fluid and gave
blood and 24-h urine samples for biochemical studies.
No soy was
administered in months 1-3 and 10-12. Between months 4-9 the women
ingested daily 38 g of soy protein isolate containing 38 mg of
genistein.
NAF volume,
gross cystic disease fluid protein (GCDFP-15) concentration, and NAF
cytology were used as biomarkers of possible effects of soy protein
isolate on the breast. In addition, plasma concentrations of estradiol,
progesterone, sex hormone binding globulin, prolactin, cholesterol,
high density lipoprotein-cholesterol, and triglycerides were measured.
Compliance was assessed by measurements of genistein and daidzein and
their metabolites in 24-h urine samples. Excellent compliance with the
study protocol was obtained.
Compared
with NAF volumes obtained in months 1-3, a 2-6-fold increase in NAF
volume ensued during months 4-9 in all premenopausal women. A minimal
increase or no response was found in postmenopausal women. No changes
were found in plasma prolactin, sex hormone binding globulin,
cholesterol, high density lipoprotein cholesterol, and triglyceride
concentrations.
Compared
with concentrations found in months 1-3 (no soy), plasma estradiol
concentrations were elevated erratically throughout a ''composite''
menstrual cycle during the months of soy consumption. No significant
changes were seen in plasma progesterone concentrations. No significant
changes were found in plasma estrogen levels in postmenopausal women. A
moderate decrease occurred in the mean concentration of GCDFP-15 in NAF
in premenopausal women during the months of soy ingestion.
Of
potential concern was the cytological detection of epithelial
hyperplasia in 7 of 24 women (29.2%) during the months they were
consuming soy protein isolate.
The
findings did not support our a priori hypothesis. Instead, this pilot
study indicates that prolonged consumption of soy protein isolate has a
stimulatory effect on the premenopausal female breast, characterized by
increased secretion of breast fluid, the appearance of hyperplastic
epithelial cells, and elevated levels of plasma estradiol.
These findings are suggestive of an estrogenic stimulus from
the isoflavones genistein and daidzein contained in soy protein
isolate.
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