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Soya protein reduces androgen's side effects, leaves anabolic effect intact

If chemical athletes react to soya proteins in the same way that rats do, then a high soya diet could be of interest to athletes who are worried about their prostate. French researchers discovered that the phyto-oestrogens in soya soften the androgenic side effects of testosterone without reducing the anabolic effects.

Soya protein reduces androgen's side effects, leaves anabolic effect intact

The French were actually interested in the way experiments are set up. More and more animal research is being done on substances in the environment that disrupt hormone balances. But for studies to be done accurately, researchers need to know whether these substances are also present in the feed the animals get. The most powerful hormonal substances known to be found in lab animal diets are the phyto-oestrogens genistein and daidzein, both present in soya.

The French therefore gave rats a diet consisting of feed from which all phyto-oestrogens had been removed, or a diet consisting of 23 percent soya proteins. The exclusively male rats were given these diets for their whole life.

At the age of 21 days the rats' testes were removed. After that the rats were given injections of testosterone propionate, in doses of 0.1, 0.2, 0.4 or 0.8 mg per kg bodyweight per day. The lowest dose mimics the natural production of testosterone propionate. A control group was given injections containing oil instead.

The figure below shows the effect of the different testosterone doses on the different diets. A soya diet inhibits the androgenic effects on the prostate and seems to slightly increase the anabolic effect on the sphincter muscle. Very, very, very slightly.

DO3 = 22.5 percent soya protein; L5 = diet with no phyto-oestrogens. BC/LA = sphincter muscle, the weight of which is an indication of the muscle-strengthening effect of hormones.

Soya protein reduces androgen's side effects, leaves anabolic effect intact

The researchers also did experiments with the anti-androgenic vinclozolin. Vinclozolin reduced the growth of the sphincter muscle, but the soya diet inhibited the size of the reduction. So phyto-oestrogens are also very slightly anti-anti-androgenic.

The researchers think that this effect is caused by inhibiting the enzyme 5alpha-reductase type 2, which converts testosterone into DHT. But, they also add, it may be that the phyto-oestrogens have a more indirect effect, for example affecting the functioning of the androgen receptors.

Food Chem Toxicol. 2003 Aug;41(8):1175-83.

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