Isoflavone-rich soy protein isolate suppresses androgen receptor expression without altering estrogen receptor-beta expression or serum hormonal profiles in men at high risk of prostate cancer.
Level 2 - randomized trial
Randomized controlled trial
PubMed 17585029 · doi:10.1093/jn/137.7.1769
What was done
Fifty-eight men at high risk for developing advanced prostate cancer were randomly assigned to consume 40 g/d of protein from one of three isolates for 6 months: isoflavone-rich soy protein isolate (SPI+, 107 mg/d isoflavones), alcohol-washed soy protein isolate (SPI-, <6 mg/d isoflavones), or milk protein isolate (control, 0 mg/d isoflavones), taken twice daily as a partial meal replacement. Serum samples collected at 0, 3, and 6 months were analyzed by radioimmunoassay for estradiol, estrone, sex hormone-binding globulin, androstenedione, androstanediol glucuronide, DHEA-S, DHT, total testosterone, and free testosterone. Pre- and post-intervention prostate biopsy specimens were evaluated for androgen receptor (AR) and estrogen receptor-beta expression by immunohistochemistry.
What was found
Consumption of SPI+ for 6 months significantly suppressed prostate AR expression without altering estrogen receptor-beta expression or circulating hormone concentrations. Consumption of SPI- significantly increased estradiol and androstenedione levels, and tended to suppress AR expression (P = 0.09). The abstract does not provide exact numerical values, effect sizes, or confidence intervals for any outcome.
Why it matters
This study provides randomized evidence that dietary soy isoflavones can directly suppress androgen receptor expression in human prostate tissue without disrupting circulating sex hormone profiles, highlighting a potential mechanism for prostate cancer chemoprevention.
Limits
Sample size was small (58 men across three study arms), and the abstract omits quantitative point estimates, baseline values, and variance measures. The intervention evaluated surrogate tissue and endocrine biomarkers rather than clinical prostate cancer incidence or progression, and the clinical relevance and mechanism of the hormonal shifts observed in the low-isoflavone group remain unclear.
Cited by
- supports Isoflavone-rich soy protein isolate suppresses androgen receptor expression without altering estrogen receptor-beta expression or serum hormone profiles in men at high risk of prostate cancer.