Background: There are a number of theories which place certain types of protein powder, notably whey protein, as being superior to soy protein powders with arguments made that soy can have an estrogenic effect leading to lowered testosterone levels. We went through the arguments on the impact of soy protein on testosterone already so we turn now to examining a new study which compared results with soy and whey proteins. The researchers in this study set this up to explore if the previous inverse correlation shown between soy and testosterone (2) would impact lean body mass gains.

Methods: For twelve weeks, twenty subjects supplemented their diets with one of four different protein sources – A whey blend, whey plus soy isolate, soy isolate, and soy concentrate. The subjects also performed a comprehensive weight training programme and measurements were taken for body composition, testosterone, estradiol, and sex hormone binding globulin (SHBG) at both the start and week 12.

Results: The use of protein supplements led to a significant increase in lean body mass independent of protein source used. No significant differences were observed for total and free testosterone, SHBG, body fat percentage, BMI, or body weight. The testosterone to estrogen ratio increased across all groups. In group analysis revealed the T/E ratio showed significant increases in the soy isolate/whey blend and estradiol was significantly lower in the whey blend group.

Conclusion: The researchers concluded that a 12 week program of supplementation with soy did not decrease serum testosterone or inhibit lean body mass changes.

Our Comments

It appears that providing soy protein consumption is within reasonable quantities and is not used as the sole source of protein in a diet, that there are no negative effects observed on serum sex hormone levels or performance gains. Soy protein has the highest protein content of all protein powders on the market today which has attracted a lot of interest but also drawn criticism from those who believe that the use of soy protein is associated with estrogenic activity in the body. In reality, soy isolate has relatively little estrogenic activity provided and its consumption should not be a concern as part of a mixed protein diet. Given its high BCAA and Glutamine content and fast release it makes for an adequate replacement for whey protein as evidenced by this study. At Predator, we still believe that a superior choice would be consuming protein from a variety of sources including fish, meat, milk protein and whey protein to take advantage of different qualities inherent in each of the sources of protein. Within a diet based around these protein sources though, soy protein has a useful place as a high protein content, easily digestible, and more affordable source of protein as well as one which has been shown to have beneficial health effects.

Leave a Reply

Your email address will not be published. Required fields are marked *

Main Menu