Does Soy Protein Consumption Reduce Testosterone Levels in Men?

Tuan Tran

Soy products have a profound impact on a vegetarian diet as it is associated with little of the saturated fat compared to meat and none of the moral indigestion that comes with meat.

 The problem arises when soy protein is correlated with reducing testosterone levels and increase in estrogen. Asian are typically in focus as - they are known to have a typically high soy intake in their diet.

 *jump into conclusion, if you're too lazy to read Soy and its relation to Testosterone part (proven studies)

Brief Introduction to Soy Protein

Soy protein is known to be one of the vegetables proteins with the best biological profile. having a significantly rich aminogram, especially in Leucine. However, soy also contains isoflavones, which are compounds that mimic some of the effects of estrogen in the body.

Isoflavones are often called phytoestrogens due to their potential in reducing the symptoms of menopause such as Osteoporosis.

Soy and its relation with Testosterone 

The main reason that makes soy protein notorious in the world of bodybuilding is the belief that soy consumption may lead to an increase in estrogen levels, while reducing testosterone levels at the same time. But what does the scientific research have to say?

• While it is true that certain studies have associated reductions in testosterone levels due to soy consumption, however it is necessary to put them in perspective. For example, one of the tested individuals in one of the studies was a vegetarian whose daily diet included large amounts of soy.

• Another study demonstrated an average reduction of 19% on testosterone levels on individuals who had a higher soy intake. Only one of the tested subjects had a significantly higher reduction. In the beginning of the this study, the individual was registered to have testosterone levels of 200% above the average among tested subjects, and 50% above the general average. With this in mind, and determining that this subject is an exception, we can establish that soy consumption did not negatively affect the testosterone levels in the blood. 

• There are other studies that point towards an inverse relation between soy consumption and testosterone levels in the blood. The studies are suggesting that a reduction in meat consumption, while simultaneously increasing soy consumption, also lowers the testosterone levels. In the study, the reduction in testosterone levels was already expected, since meat was replaced by soy. 

•  When considering the available empirical evidence, we realize that Asian- who are known to consume large amounts of soy- don;t seem to display any fertility problems, which suggest that the high soy intake does not affect sex hormones. 

• A recent research analyzed several studies in which subjects consumed products derived from soy, in a total of 51 tested groups, and found no evidence indicating that soy protein or isoflavones, reduce testosterone levels and increase estrogen in the body.

•  A more relevant research study than the ones previously mentioned - as this one considers not only sex hormones, but also the effects different types of proteins have on the body mass- showed no significant differences in terms of performance, lean mass gains, body fat percentage and levels of hormones in the blood between the subjects who consumed more soy and the ones who limited its consumption. 

Conclusion:

Soy protein has been considered a villain for a long time, However, what the studies show us is that unless we are talking about significantly large daily dosage (50 grams, at the very least), there are no reasons to believe soy protein will reduce testosterone levels and increase estrogen levels. 

Despite of the fact that soy beans and isoflavones have estrogenic activity, the amounts one usually consumes in his diet are insufficient to negatively impact testosterone.

This means soy should be considered a source of complementary protein and not be used to replace meat as a main source of protein in our daily diet.