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- 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
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- 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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