Do you agree that Soy Protein Isolate is the best for Bodybuilders?

[Gohan-X]

soy

soys great, i use it as my primary source of protien, and then just use whey post workout.

 

[MsBeverlyHills]

soy boys-

soy protein doesnt give you gyno or turn you into a pu$$y..lol what it does do is decrease blood testosterone levels-- so you have diminishing muscle gains on soy that you dont have on animal protein...(same goes for soy isolates).

 

[jboldman]

SPI DOES contain isoflavones.

jb

 

[Singleton]

Okay, I did find a link about that seemed to explain concentrations of isoflavones in isolate:
http://www.soyfoods.com/nutrition/isoflavoneconcentration.html

According to the source, isolate does contain isoflavones, though in much smaller concentrations. I was wrong, but not too far off :/

Soy will lower your estrogen levels. It will not lower your T levels. The phytoestrogens in soy are very weak estrogens that will compete with your body's estrogen for the estrogen receptor.


I found a study that analyzed the hormone levels of estrogen and testosterone in men who consumed 400ml of soymilk daily.

This study is relevent because it uses male humans (that's us). Interestingly, the study does not study the isolated effect of daidzein or genistein, but instead the daily consumption of 600ml soymilk. Let's take a look at it.

http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=11303585&dopt=Abstract

Effect of soymilk consumption on serum estrogen and androgen concentrations in Japanese men.

Nagata C, Takatsuka N, Shimizu H, Hayashi H, Akamatsu T, Murase K.

Department of Public Health, Gifu University School of Medicine, Japan.

Soy consumption has been associated with a reduced risk of prostate cancer. The mechanism for this association may involve the effect of soy on the endocrine system. We conducted a randomized dietary intervention study to determine the effects of soy consumption on serum levels of steroid hormones in men. Thirty-five men were randomly assigned to either a soymilk-supplemented group or a control group. The men in the soy-supplemented group were asked to consume 400 ml of soymilk daily for 8 weeks. The men in the control group maintained their usual diet. Blood samples were obtained just before the initiation of the dietary period and thereafter every two weeks for 12 weeks. Changes in hormone concentrations were analyzed and compared between the two groups using the mixed linear regression model against weeks from the start of the dietary period. The mean (SD) soymilk intake estimated from dietary records during the dietary study period was 342.9 (SD, 74.2) ml in the soymilk-supplemented group. There was a significant difference between the two groups in terms of changes in serum estrone concentrations, which tended to decrease in the soy-supplemented group and increase in the control group over time. None of the other hormones measured (estradiol, total and free-testosterone, or sex hormone-binding globulin) showed any statistical difference between the two groups in terms of patterns of change. The results of the study indicate that soymilk consumption may modify circulating estrone concentrations in men.

Interestingly, the soy group had lower E. I quote:

There was a significant difference between the two groups in terms of changes in serum estrone concentrations, which tended to decrease in the soy-supplemented group and increase in the control group over time.

I found another study that concurs with these findings. The study that I am about to present to you is not a controlled experiment. The conclusion can only be stated with a weak degree of conviction.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10798211&dopt=Abstract

Inverse association of soy product intake with serum androgen and estrogen concentrations in Japanese men.

Nagata C, Inaba S, Kawakami N, Kakizoe T, Shimizu H.

Department of Public Health, Gifu University School of Medicine, Japan.

The cross-sectional relationships of soy product intake and serum testosterone, estrone, estradiol, sex hormone-binding globulin, and dihydrotestosterone were examined in 69 Japanese men. Soy product intake was estimated from a semiquantitative food frequency questionnaire. Serum estradiol concentration was significantly inversely correlated with soy product intake (r = -0.32, p = 0.009), and serum estrone concentration was nonsignificantly inversely correlated with soy product intake (r = -0.24, p = 0.05) after controlling for age, body mass index, smoking status, and ethanol intake. Total and free testosterone concentrations were inversely correlated with soy product intake after controlling for the covariates, but these correlations were of border line significance (r = -0.25, p = 0.05 and r = -0.25, p = 0.06, respectively). Similar correlations were observed for these hormones with isoflavone intake from soy products. The data suggest that soy product intake may be associated with the endogenous hormone levels in Japanese men.

however, that conclusion does concur with the findings of Effect of soymilk consumption on serum estrogen and androgen concentrations in Japanese men. (above).

Conclusion: Soy will lower your estrogen levels.