Russ Howe PTI
Posted in: Supplements

Is Soy Protein REALLY Bad For Muscle Growth?


Is Soy Protein REALLY Bad For Muscle Growth? / 1st January 2018

Don't mention the 'S' word at your gym..

does soy protein build muscle

I'm speaking about soy protein, of course.

Because if you do bring it up in conversation, be prepared for your resident broscientist to dive into a twenty minute lecture about how it's going to "kill your gains, bro."

“Don’t use that type of protein, brah. It’s the worst. It won't build any muscle. It'll give you bitch tits, mate. It's actually really bad for you.”

What's the worst part about all of the above?

None of it is true! There’s nothing wrong with soy protein!

But for many years, soy protein has been bastardized in the fitness world.

It's billed as the ugly duckling that you don't want in your protein shake because it's going to wreck your hard earned results in the gym.

While whey steals all the headlines (it is awesome) and casein takes the plaudits for it’s great supporting role, soy sits in the background, never receiving any praise for the great work it also does.

That’s largely down to the fact that people remain misinformed about myths which have long been debunked by clinical scientific studies.

does soy protein lower testosterone

Soy Protein - What Does Science Say?

The main myth at play here is that soy protein lowers testosterone.

That statement is enough to scare 99% of men away, right?

Lower testosterone means less muscle building, among other things.

And because soy contains isoflavones, which are similar to estrogen (the female sex hormone), many people make the assumption that using soy protein will lead to lower testosterone.

And so the soy protein estrogen myth was born.

Reading the info above, it’s really no wonder guys have long shunned this form of protein, right?

However, there is ample scientific evidence to show that this is just not true.

In fact, a 2010 review study published in Fertility and Sterility reviewed 15 other studies on soy protein supplementation and categorically concluded that soy does not alter testosterone in men. (1)

So don't buy into the nonsense fitness myth.

The next time somebody tries to tell you that soy protein will lower your testosterone, show them your best Arnold Schwarzenegger impression.

Quickly on the heels of that myth comes another one, this time that soy doesn’t promote as much muscle growth as whey or casein.

Once again, this is supplement industry bulls**t.

Again, this is linked to the idea that soy reduces testosterone, which you now know is not true. And this theory about less muscle protein synthesis as a result of supplementing with soy versus whey or casein is also incorrect.

A 2007 study published in the Journal of the International Society of Sports Nutrition confirmed this beyond all doubt.

This trial ran over the course of 12 weeks, where weight training subjects were given either soy protein, whey protein or a soy/whey blend to test the theory that soy was incapable of promoting as much lean muscle growth as whey protein.

The team of researchers from Baylor University discovered that all subjects were able to gain a similar amount of muscle mass regardless which type of whey protein they were using. (2)

A 2009 study published in the Journal of the International Sports of Sports Nutrition then confirmed it again two years later. (3)

soy protein


The wealth of clinical studies has gone a long way to debunk the unnecessary myths surrounding soy protein, and you should have no concerns about using it as your primary protein supplement.

And then there's the cost issue.

It's a well known fact that soy is far cheaper than whey.

This makes soy ideal for those on a tight budget, or those who (like me) like to keep a backup tub of protein in the cupboard just in case you run out of your main product.

If that’s the case, I suggest  Bedrock Pro XL for pure value purposes.

However, there is a superior way.

You see, the question should not be whether soy, or whey, or casein is better for building muscle.

Because the truth is you can promote even more muscle growth by combining various different types of protein into your shake.

Each type yields different benefits, with the different speeds of release (whey = fast, soy = moderate, casein = slow) being the main reason you'll promote more muscle growth than any one kind on it's own. In fact, a protein blend has been shown to elevate amino acid uptake into the muscle and also to prolong muscle protein synthesis, which is great news for muscle growth! That's why I recommend using a protein blend as your main protein supplement. (4, 5)

If you need a protein blend supplement, I recommend  this one or this one.

This article explains more about protein blends.

soy protein testosterone

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  1. Hamilton-Reeves, J.M., et al. Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertil Steril. 94 (3):997-1007, 2010.
  2. Campbell, B., et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2007, 4:8 doi:10.1186/1550-2783-4-8.
  3. DeNysschen, C., et al. Resistance training with soy vs whey protein supplements in hyperlipidemic males. J Int Soc Sports Nutr. 2009; 6: 8.
  4. Reidy, P. T., et al. Protein Blend Ingestion Following Resistance Exercise Promotes Human Muscle Protein Synthesis. Journal of Nutrition 143(4):410-416, 2013.
  5. Reidy, P. T., et al. Soy-dairy protein blend and whey protein ingestion after resistance exercise increases amino acid transport and transporter expression in human skeletal muscle. Journal of Applied Physiology, in press, 2014.