"isoflavones found in soy (like genistein and diadzein) block some receptor sites where estrogen binds to cells. The effect is to prevent estrogen from accumulating in your body. "
Effect of protein source and resistance training on body composition and sex hormones.
Kalman D, Feldman S, Martinez M, Krieger DR, Tallon MJ.
Miami Research Associates, Nutrition/Endocrinology Division, Miami, Florida, USA.
dkalman@miamiresearch.com.
ABSTRACT: BACKGROUND: Evidence suggests an inverse relationship between soy protein intake and serum concentrations of male sex hormones. Anecdotal evidence indicates that these alterations in serum sex hormones may attenuate changes in lean body mass following resistance training. However, little empirical data exists regarding the effects of soy and milk-based proteins on circulating androgens and exercise induced body composition changes. METHODS: For 12 weeks 20 subjects were supplemented with 50 g per day of one of four different protein sources (Soy concentrate; Soy isolate; Soy isolate and whey blend, and Whey blend only) in combination with a resistance-training program. Body composition, testosterone, estradiol and sex hormone binding globulin (SHBG) were measured at baseline and week 12. RESULTS: Protein supplementation resulted in a significant increase in lean body mass independent of protein source (0.5 +/- 1.1 and 0.9 +/- 1.4 kg, p = 0.006, p = 0.007). No significant differences were observed between groups for total and free testosterone, SHBG, percentage body fat, BMI or body weight. The Testosterone/Estradiol ratio increased across all groups (+13.4, p = 0.005) and estradiol decreased (p = 0.002). Within group analysis showed significant increases in the Testosterone/Estradiol ratio in soy isolate + whey blend group (+16.3, p = 0.030). Estradiol was significantly lower in the whey blend group (-9.1 +/- 8.7 pg/ml, p = 0.033). CONCLUSION: This investigation shows that 12 week supplementation with soy protein does not decrease serum testosterone or inhibit lean body mass changes in subjects engaged in a resistance exercise program.
Dietary soy protein containing isoflavonoids does not adversely affect the reproductive tract of male cynomolgus macaques (Macaca fascicularis).
Perry DL, Spedick JM, McCoy TP, Adams MR, Franke AA, Cline JM.
Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.
dlperry@wfubmc.edu
Short-term dietary studies of soy-protein-derived isoflavonoids, using rodent and nonhuman primate models, have documented variable effects on the reproductive tract. Long-term effects of dietary soy and/or isoflavonoids on the reproductive tract of nonhuman primates have not been determined. The objective of this study was to assess the effects of long-term consumption of dietary soy isoflavonoids on histomorphology of the mammary glands and prostate gland, testis, and sperm counts in adult male cynomolgus macaques. Ninety-one adult male cynomolgus macaques (Macaca fascicularis) were fed diets for 3 y differing only in protein source: 1) a soy-free, casein-lactalbumin-based diet or 2) a low-soy isoflavonoid diet ( approximately 6 mg . kg(-1) . d(-1)) or 3) a high-soy isoflavonoid diet ( approximately 12 mg . kg(-1) . d(-1)). Serum isoflavonoids were measured by liquid chromatographic-photodiode array electrospray MS. Mammary gland, prostate gland, and testes were obtained at postmortem and evaluated histopathologically and histomorphometrically. Epididymal and testicular sperm counts were performed. Serum isoflavonoid concentrations at 4 h postfeeding differed among all groups (P < 0.001) and were (means +/- SEM) 67 +/- 23 (soy-free diet), 799 +/- 44 (low-soy isoflavonoid diet), and 1458 +/- 80 nmol . L(-1) (high-soy isoflavonoid diet). Diet did not alter serum estradiol and testosterone concentrations or epididymal and testicular sperm counts. Organ weights and histologic indices did not differ among treatment groups. Mammary gland histopathologic and histomorphometric analysis revealed no abnormalities and no indication of gynecomastia. We found no evidence of an adverse effect of soy isoflavonoids at physiologically relevant doses within the reproductive organs of adult male macaques.
PMID: 17513396 [PubMed - indexed for MEDLINE]
Good for Prostate:
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.
Hamilton-Reeves JM, Rebello SA, Thomas W, Slaton JW, Kurzer MS.
Department of Food Science and Nutrition, University of Minnesota, Minneapolis, MN 55455, USA.
The purpose of this study was to determine the effects of soy protein isolate consumption on circulating hormone profiles and hormone receptor expression patterns in men at high risk for developing advanced prostate cancer. Fifty-eight men were randomly assigned to consume 1 of 3 protein isolates containing 40 g/d protein: 1) soy protein isolate (SPI+) (107 mg/d isoflavones); 2) alcohol-washed soy protein isolate (SPI-) (<6 mg/d isoflavones); or 3) milk protein isolate (0 mg/d isoflavones). For 6 mo, the men consumed the protein isolates in divided doses twice daily as a partial meal replacement. Serum samples collected at 0, 3, and 6 mo were analyzed for circulating estradiol, estrone, sex hormone-binding globulin, androstenedione, androstanediol glucuronide, dehydroepiandrosterone sulfate, dihydrotestosterone, testosterone, and free testosterone concentrations by RIA. Prostate biopsy samples obtained pre- and postintervention were analyzed for androgen receptor (AR) and estrogen receptor-beta expression by immunohistochemistry. At 6 mo, consumption of SPI+ significantly suppressed AR expression but did not alter estrogen receptor-beta expression or circulating hormones. Consumption of SPI- significantly increased estradiol and androstenedione concentrations, and tended to suppress AR expression (P = 0.09). Although the effects of SPI- consumption on estradiol and androstenedione are difficult to interpret and the clinical relevance is uncertain, these data show that AR expression in the prostate is suppressed by soy protein isolate consumption, which may be beneficial in preventing prostate cancer.
PMID: 17585029 [PubMed - indexed for MEDLINE]
Serum prostate-specific antigen but not testosterone levels decrease in a randomized soy intervention among men.
Maskarinec G, Morimoto Y, Hebshi S, Sharma S, Franke AA, Stanczyk FZ.
Cancer Research Center of Hawaii, University of Hawaii, Honolulu, HI 96813, USA.
gertraud@crch.hawaii.edu
BACKGROUND: Low prostate cancer incidence and high soy intake in Asian countries suggest a possible protective effect of soy foods against prostate cancer. The goal of this pilot study was to evaluate the feasibility of a randomized, crossover soy trial among men and to investigate the effects of daily soy intake on serum prostate-specific antigen (PSA) and testosterone levels. METHODS: We randomized 24 men to a high or a low soy diet for 3 months. After a 1-month washout period, the men crossed over to the other treatment. During the high soy diet, the men consumed two daily soy servings; during the low soy diet, they maintained their usual diet. During the entire study each man donated four blood samples and five overnight urine samples. Dietary compliance was assessed by soy calendars, 24-h dietary recalls, and urinary isoflavone excretion measured by high-pressure liquid chromatography with photodiode array detection. Blood samples were analyzed for serum testosterone and PSA by radioimmunoassay. When necessary, variables were log transformed. Two sample t-tests compared the two groups before each study period. Mixed models incorporating the repeated measurements were used to evaluate the effect of the soy diet on urinary isoflavone excretion and serum analytes. RESULTS: Twenty-three men aged 58.7+/-7.2 years completed the study. The compliance with the study regimen was high according to self-reported soy food intake and urinary isoflavone excretion. No significant between-group and within-group differences were detected. During the high soy diet, dietary isoflavone intake and urinary isoflavone excretion increased significantly as compared to the low soy diet. A 14% decline in serum PSA levels (P=0.10), but no change in testosterone (P=0.70), was observed during the high soy diet in contrast to the low soy diet. CONCLUSION: The high adherence as shown by three measures of compliance in this pilot trial demonstrated the feasibility of an intervention based on soy foods among free-living men.
PMID: 16775579 [PubMed - indexed for MEDLINE]