Soy Contains Plant Estrogens
Soy contain isoflavones – a plant estrogen (also called phytoestrogen) (Harvard, 2021).
Soy isoflavones bind to estrogen receptors in the body & can cause weak estrogenic effects (Harvard, 2021).
High soy consumption can lead to symptoms of high estrogen in men. (PubMed, 2021)
According to a 2020 study, high estrogen in men:
- Suppresses testosterone production (Nature, 2020)
- Leads to premature ejaculation (Nature, 2020)
- Contributes to erectile dysfunction. (Nature, 2020)
Does Soy Lower Testosterone In Men?
A 2020 meta analysis found:
- In 33 studies soy consumption had no significant effect on testosterone in men. (PubMed, 2021).
- In 8 studies soy decreased free testosterone by 6% (PubMed, 2021).
Soy Decreases Sperm Count
A 2008 & 2021 study found a diet high in soy can significantly decrease sperm count & contribute to infertility & erectile dysfunction in men (PubMed, 2008; PubMed, 2011).
The 2008 study found the negative impact of soy on sperm count and fertility was higher in overweight men than athletic men with a lower body fat percentage. (PubMed, 2008)
A 2011 study found a vegan diet (high in soy) can significantly decrease free testosterone. (PubMed, 2011).
The Testosterone levels returned to normal healthy range after the subjects switched back to an omnivore diet (a normal diet consisting of eating meat, fruits and vegetables) (PubMed, 2011)
Another study conducted on mice found consuming phytoestrogens significantly decreased testosterone levels and prostate weight for the mice (PubMed, 2001)
Does Soy Protein Isolate Powder Reduce Testosterone?
Soy Protein Isolate Contains Less Phytoestrogens
Soy protein isolate powder contains less soy isoflavones and phytoestrogens (plant estrogens) than soy beans and food derived from soy (PubMed, 2010)
This is due to processing which removes anywhere from 30 to 90% of soy isoflavones to create the concentrated soy protein powder. (PubMed, 2010).According to AHA, “Soy isoflavones remain in soy protein preparations that are not extracted with alcohol. During the preparation of soy protein isolate, the soy is washed with alcohol, removing a substantial amount of the isoflavones.” (AHA Journals, 2006)
Therefore, soy protein isolate should have less of an impact on Testosterone than ordinary soy products.
But what do the studies say?
Soy Protein Isolate Decreases Testosterone
A 2005 study in 35 healthy young men looked at the effects of drinking soy protein isolate for 54 days on Testosterone.
The study found:
Soy Protein Isolate (with low concentration of soy isoflavones and low phytoestrogens):
- Decreased Testosterone by 9%
- Decreased DHT by 9.4%
- Increased Estrogen levels
Soy Protein Isolate (with high concentration of soy isoflavones and high phytoestrogens):
- Decreased Testosterone by 14%
- Decreased DHT by 15%
- Increased Estrogen levels
(PubMed, 2005).
Soy protein isolate decreased Testosterone by 9 to 15% and decreased DHT by 9.4 to 15% in 54 days in healthy young men while increasing Estrogen levels.
Soy Bean Oil Decreases Testosterone
Soy Bean Oil Increases Inflammation & Blood Glucose
A 2017 Chinese study found soy bean oil significantly increased inflammation & blood sugar levels in mice – contributing to metabolic disease and increasing risk of Type 2 diabetes (Taylor, 2017)
A high soy bean oil intake also resulted in increased body fat (Taylor, 2017).
Although the study was conducted in mice, similar negative effects can be experienced in humans. (Taylor, 2017)
High levels of inflammation & high blood sugar are linked to low Testosterone in men (American Society of Endocrinology and Metabolism, 2018)
Although soy bean oil can have negative effects on Testosterone, a 2006 study found that soy bean oil can decrease LDL in monkeys and had cardiovascular benefits. However in humans, soy bean oil and soy protein had no effect on improving HDL or LDL (AHA Journals, 2006).
Final Verdict
Removing soy from your diet is essential to maximize Testosterone levels, increase sperm count & improve fertility.
Studies show there are mixed conclusions on the impact of soy on Testosterone.
- Some studies have no impact on Testosterone.
- Other studies show consuming soy decreases Testosterone by around 5 to 15%.
- Soy protein isolate powder decreased Testosterone by 9 to 15% and decreased DHT by 9.4 to 15% in 54 days while increasing Estrogen levels (PubMed, 2005).
However, many studies agree that consuming soy can reduce sperm count, decrease quality of sperm, and contribute to infertility (PubMed,2008; PubMed, 2011). The negative impact of soy on sperm and fertility was increased in individuals with higher body fat percentage (PubMed, 2008).
Removing soy from your diet is essential to maximize Testosterone levels, increase sperm count & improve fertility.
