Drinking soy milk shakes might reduce DHT in men. (Photo by lists&diagrams)
Last month, I wrote about a paper that suggested soy isoflavones reduce DHT and increase testosterone. I also promised to write blog posts about similar studies to get a better understanding of how soy affects androgen levels.
In the second study we'll be looking at, 35 men were given soy protein isolate or milk protein isolate for 2 months to see how it affected their reproductive hormone levels (link). There were two versions of the soy protein diet: the low-isoflavone and the high-isoflavone diet. Each participant was put on each of the three diets with a 28-day washout period in between them.
Composition of the diets
The low-isoflavone soy protein isolate contained 0.02 mg isoflavones/kg body weight, while the high-isoflavone isolate contained 0.72 mg/kg body weight. Mean soy isoflavone intakes were 1.64 mg and 61.7 mg, respectively, with the most abundant isoflavones being genistein and daidzein. The milk protein isolate contained no isoflavones.
A third of the participants were categorized as equol excretors (meaning their bodies were able to produce equol from soy isoflavones), which seems to be consistent with other studies. Especially from a hair loss perspective, equol shows great promise, but it's currently unclear whether it's possible to affect one's ability to produce equol.
Soy protein isolate and testosterone
Halfway through the experiment, testosterone levels were slightly lower in the low-isoflavone diet (19.8 nmol/L) than the high-isoflavone diet (22.0 nmol/L) and the milk protein diet (22.1 nmol/L). At the end of the experiment, there was no statistically significant difference between testosterone levels. Levels of free testosterone were similar during all three diets.
Soy protein isolate and DHT
Serum dihydrotestosterone (DHT) and was decreased by the low-isoflavone diet (1952 pmol/L) and the high-isoflavone diet (1962 pmol/L) compared to the milk protein diet (2155 pmol/L) at the end of the experiment. The ratio of DHT to testosterone was also decreased.
Soy protein isolate and other effects
At the end of the study, serum estradiol and estrone were increased by the low-isoflavone diet compared with the milk protein diet. Levels of SHBG, gonadotropins, and 3-alpha-AG (a marker of 5-alpha-reductase activity), did not vary significantly between the diets. DHEA-S was increased by the low-isoflavone diet, but DHEA levels were not significantly different.
Serum DHT was significantly reduced following the consumption of both a low-isoflavone and high-isoflavone soy protein isolate compared to a milk protein isolate. The reductions were 9.4% and 15%, respectively. The DHT/testosterone ratio was also decreased by 9.0% and 14%, respectively.
The reduction in the DHT/testosterone ratio suggests an inhibition of 5-alpha-reductase. However, 3-alpha-AG, a marker of 5-alpha-reductase activity, was not significantly affected. Levels of sex hormone-binding globulin (SHBG) were also not significantly different between the diets.
For more information on hair growth, see these posts:
Tea Tree Oil vs. Korean Red Ginseng – Hair Growth Battle Conclusion
North African Plant Extract (Erica multiflora) Increases Hair Growth
2% Nizoral Shampoo Increases Hair Growth More than 2% Minoxidil
Lygodium japonicum Promotes Hair Growth by Inhibiting Testosterone to DHT Conversion