Features of soy protein

Author: Frédéric Delavier and Michel Gundill: Chapter from the book "Sports Supplements for Athletes".
2011-10-27

Soy proteins contain a lot of isoflavones, which have estrogenic properties. This means that men are advised not to consume soy for long periods and in large quantities. Daily consumption of 32 grams of soy protein for a month reduces testosterone levels by about 10% (B. Dillingham, 2005). Although this decrease is temporary, the levels of female hormones continued to rise in subjects for 57 days (the entire time they consumed soy). It turns out that the ratio of testosterone to female sex hormones shifted in favor of the latter. However, athletes are always interested in the opposite effect.

Apparently, isoflavones serve as a fundamental factor that determines the ability of these proteins to resist free radicals. Thus, for 30 days, men continuously received either soy protein, whey protein, or a placebo at a rate of 0.6 grams of protein per kilogram of body weight daily. Neither soy nor whey caused a decrease in testosterone levels. However, soy was noted to enhance protective antioxidant mechanisms. This ability of soy protein was confirmed by a study from E. Brown.

This protective mechanism undoubtedly mitigates the process of muscle breakdown that begins after consuming soy protein rich in isoflavones. In one study, men engaged in sports were given either 40 grams of soy protein or 40 grams of whey protein every day for 21 days. Soy improved the antioxidant status in the subjects, while whey protein worsened it. Soy reduced the increase in muscle catabolism markers by 42% that occurred after aerobic physical activity, where intensity increased over two hours. Whey protein, on the contrary, increased catabolism by 38%.

The inhibition of muscle depletion caused by physical exercise allows for more frequent training sessions and faster recovery. This property is very beneficial for almost all athletes except those aiming to increase muscle mass. The thing is, by preventing catabolism, soy, unlike whey, partially inhibits muscle hypertrophy as well. Indeed, the more reliably our muscles are protected from destruction, the less often they need to strengthen themselves by increasing the thickness of their fibers.

On the other hand, soy protein represents increased interest for women. Research conducted among elite gymnasts found a positive effect of soy protein (V. Stroescu, 2001). A daily supplement of 1 gram of soy protein per kilogram of body weight for 4 months helped maintain muscle mass. In contrast, with placebo, muscle mass gradually decreased due to prolonged and intense daily training.

Note from the administrator

The cheapest and most effective soy protein that I have tried is RPS: Soy Protein. You can try it yourself. However, it has no flavor additives.