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The myth that eating soy leads to feminizing effects in men has been perpetuated to dissuade people from consuming plant-based meat & dairy replacements for far too long;
a necessary thread:
a necessary thread:
Our story begins with a highly-cited isolated case study from 2008 of an elderly man suffering from gynecomastia (male breasts) that was attributed to his consumption of excessive amounts of soy milk https://pubmed.ncbi.nlm.nih.gov/18558591/
It is important to point out that case studies cannot be used to draw scientific conclusions for obvious reasons (n=1). Case studies simply alert researchers that they should go check something out. So let’s examine the research that looked into this...
A study on Japanese men found that drinking 1.5 cups soy milk/day had no statistical effect on testosterone. https://pubmed.ncbi.nlm.nih.gov/11303585/
Another study fed groups of young men various protein shakes (soy concentrate, soy isolate, whey, or a soy isolate/whey blend) and found similar testosterone levels and lean body mass gains for all groups. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1997115/
“But these studies were just on young men, what about older men?”
A 3-month study on men 50 years+ fed them soy in similar amounts to Asian countries and found no effect on testosterone. https://pubmed.ncbi.nlm.nih.gov/16775579/
A 3-month study on men 50 years+ fed them soy in similar amounts to Asian countries and found no effect on testosterone. https://pubmed.ncbi.nlm.nih.gov/16775579/
Another 12-week study on men between 50-65 had them consume 50 g of soy yogurt daily and also found no effect on testosterone. https://pubmed.ncbi.nlm.nih.gov/22066824/
“But wait, aren’t there rat studies showing changes in testosterone from soy consumption?”
Yes, this is true. However, the rats had to be fed exorbitant amounts of soy for any response to be observed. Additionally, a rat is a pretty poor approximation of human biology.
Yes, this is true. However, the rats had to be fed exorbitant amounts of soy for any response to be observed. Additionally, a rat is a pretty poor approximation of human biology.
One rat study did observe a small decrease in testosterone, but the rats were fed 20 mg isoflavones/kg bodyweight. When adjusted to the avg human male bodyweight, this is the equivalent of 3.5 gallons of soy milk per day! https://pubmed.ncbi.nlm.nih.gov/17673432/
In contrast to this isolated rat study, a literature review of both human and rat studies concluded that soy isoflavones do NOT exert feminizing effects on men, even with relatively high levels of consumption. https://pubmed.ncbi.nlm.nih.gov/20378106/
Finally, and most powerfully, a meta-analysis that compiled work from 32 different studies concluded that the intake of soy isoflavones, the phytoestrogens found in soy, had no significant impact on testosterone concentrations in men. https://pubmed.ncbi.nlm.nih.gov/19524224/
Based upon the research I’ve highlighted in this thread, it appears there is only logical takeaway here: Stop stressing over soy and go enjoy yourself an impossible whopper!
If you liked this thread, keep an eye out this summer for my upcoming book titled: The Living Machine: Engineering Strength and Mass on a Plant-based Diet
