Is soy protein bad for your health?
Regarding the phytoestrogens that naturally occur in soy foods/soy protein, Dr. Bill Misner wrote about this topic in Endurance News #54 (see the article, Soy Protein - Friend or Foe?). Usually the question isn't whether or not soy reduces testosterone but rather if the phytoestrogens in soy raise systemic estrogen levels. Regarding that, here is some information from Dr. Misner that should provide the information you seek and alleviate your concerns. In particular, note these couple of sentences: "If a soy protein is consumed, the weak estrogen isoflavanoids in soy find and occupy numerous target organ cells, effectually blocking stronger estrogens in the circulation. In other words, soy's mild estrogen-like compound blocks the more potent hormonal estrogen compound from compromising health or regenerating mutagen effects in the DNA."
Here's the rest of the information from Dr. Misner...
"Estrogens are hormone steroids produced in female ovaries, by astrocytes in the brain, and in male testes (lesser extent). However as males age, testosterone production decreases, while estrogen levels increase proportionate to testosteone decrease. Most males by age 60-65 have as much circulating potent estrogen as they do testosterone. In general, toxic effects of estrogens begin when the sum of estradiol + estrone exceeds 50% of the body's total estrogens, i.e. when the proportion of estriol is less than 50%. Of the three types of estrogen, estradiol is 1,000 times more potent in terms of its ability to stimulate breast tissue growth compared to estriol. Specific abnormal cell growth estrogens stimulate is trophoblasts which are strongly implicated in cancer when they are produced in situations other than female pregnancy. Excess estrogen in women (or use of exogenous estrogens) is associated with the cause in kidney cancer, ovary cancer, and in men, is implicated in prostate cancer. Excess estrogen is problematic when levels increase later after the age of 35-40 and on..."
"Estrogen toxicity is dependent upon estrogen receptors in target organ cells. If a soy protein is consumed, the weak estrogen isoflavanoids in soy find and occupy numerous target organ cells, effectually blocking stronger estrogens in the circulation. In other words, soy's mild estrogen-like compound blocks the more potent hormonal estrogen compound from compromising health or regenerating mutagen effects in the DNA. Hypothetically, this may be why resveratrol is being acclaimed an anticancer ingredient because as a weak estrogen, it has been shown to preserve the integrity of cellular DNA in animal studies. The isoflavanoids in soy present similar effects. Daidzein & Genistein compete with Estrogens (including Estradiol 17-Beta) for occupancy of Estrogen Receptors. The Phytoestrogen properties of Daidzein & Genistein cause them to be weakly estrogenic. If Daidzein or Genistein bind with an estrogen receptor, it elicits less than one-thousandth the response of endogenous estrogens. The equilibrium dissociation constant for Daidzein & Genistein is 100-10,000 times greater than for Estradiol or DES, meaning that these isoflavanoids generate the ability to stay bound to an estrogen receptor is a fraction of a fraction of that of the more potent harmful estrogens. This goes for both male and females."
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It's important to note that as males age they produce more estrogen-like hormones and less testosterone-like hormones. Now, take a closer look at the info in the second paragraph. It's important because it points out that the phytoestrogens in soy protein act as anti-estrogens, occupying/binding with specific receptor sites, ones that would normally be occupied by endogenously produced estrogens. The benefit to this, as Dr. Misner writes, is that these phytoestrogens "effectively dilute the impact of the body's own production of estrogen, because they occupy the same receptor sites (estradiol receptor sites) that would otherwise be occupied by endogenous estrogen. Therefore plant phytoestrogens protect the body from the detrimental effects of excessive estrogen."
Here is some additional information regarding the benefits of soy protein...
Research supports the following conclusive statements for dietary Soy Protein Isolate (Hammer Soy) during endurance training:
1. Soy protein may lower hematocrit levels (i.e. Soy protein lowers blood thickness (blood viscosity). (1)
2. Soy protein may lower elevated blood pressure in hypertension patients (by inhibiting the angiotensin converting enzyme). (2, 3)
3. Soy protein may retard the progression of chronic kidney failure. (4)
4. Soy protein may help to prevent breast cancer. (5, 6, 7)
5. Soy protein may reduce the risk of colon cancer. (8, 9, 10)
6. Soy protein may help to prevent and treat prostate cancer. (11, 12, 13)
7. Soy protein (17-25 grams per day) may lower total, LDL, VLDL serum "Bad" cholesterols and raises "Good" HDL cholesterol. (14-20)
8. Soy protein (used in conjunction with dieting) may facilitate weight loss in persons afflicted with obesity. (21, 22)
9. Soy protein may lower elevated serum triglycerides levels. (23, 24)
10. Soy protein (indirectly) may facilitate muscle growth (by enhancing nitrogen retention which helps to prevent the catabolism of endogenous proteins in the muscles). (25)
11. Soy protein may help to prevent osteoporosis by increasing bone density. (26, 27, 28)
12. Soy protein (60 grams per day) may reduce the number of hot flashes experienced by women during female menopause. (29)
13. Thyroid compromised persons should ask their physician about the use of soy with a thyroid problem. However, for most healthy athletes, Soy protein isolate alternated with other proteins is not as harmful as some report for healthy thyroid hormone activity. (30, 31, 32, 33, 34)
Alternating use of the GMO-free, vegetable protein, Soy Protein Isolate (Hammer Soy) with other lean protein sources is a healthy anabolic food source during periodic endurance exercise training.
1 Guang, M., et al. Effects of "Supro" high energy beverage powder on physiological function of athletes. The Research Section of Health and Nutrition, National Sports Commission.
2 He, J., et al. Effect of soybean protein on blood pressure: a randomized, controlled trial. Ann Intern Med. 143(1):1-9, 2005. Full text of this study can be viewed at:http://www.annals.org/cgi/reprint/143/1/1.pdf
3 Yang, H. Y., et al. Soyabean protein hydrolysate prevents the development of hypertension in spontaneously hypertensive rats. British Journal of Nutrition. 92(3):507-512, 2004.
4 Fair, D. E., et al. Dietary soy protein attenuates renal disease \progression after 1 and 3 weeks in Han:SPRD-cy weanling rats. Journal of Nutrition. 134(6):1504-1507, 2004.
5 Badger, T. M., et al. Soy protein isolate and protection against cancer. J Am Coll Nutr. 24(2):146S-149S, 2005.
6 Rowlands, J. C., et al. Soy and whey proteins downregulate DMBA-induced liver and mammary gland CYP1 expression in female rats. Journal of Nutrition. 131(12):3281-3287, 2001.
7 Petrakis, J., et al. A clinical trial of the chemopreventative effect of a soy beverage in women at high risk for breast cancer. Department of Epidemiology, University of California, Ca., & Department of Pharmacology, University of Alabama at Birmingham, Birmingham, Al.
8 Badger, T. M., et al. Soy protein isolate and protection against cancer. J Am Coll Nutr. 24(2):146S-149S, 2005.
9 Hakkak, R., et al. Soy protein isolate consumption protects against azoxymethane-induced colon tumors in male rats. Cancer Letters. 166(1):27-32, 2001.
10 Weiqun, W., et al. Dietary soy protein is associated with reduced intestinal mucosal polyamine concentration in male wistar rats. Journal of Nutrition. 130(7):1815-1820, 2000.