So this is shocking stuff.
There have been conflicting studies on this issue for years.
Some say soy protein is bad for you. For example, there has been talk of lowered testosterone levels or testicular shrinkage. There’s a good write up on soy and men’s health here.
Some say it’s not harmful at all, but it’s just not very effective when it comes to building muscle.
My opinion is that you should get your protein from the top 5 sources, none of which are soy.
- Whey Protein
- Eggs (whole)
- Red Meat
However, if you are getting these, then a little soy now and then won’t do any harm.
But on a different note, now a new study  says that supplementing with soy protein may be no more effective than drinking water!
So here’s how the study was set up.
A group of men were given the following soy protein amounts in water after resistance training:
- 0g protein
- 20g soy protein
- 40g soy protein
This was compared with the results of a previous study done on similar-aged men with 0g, 20g whey protein, and 40g whey protein.
- Not surprisingly the 0g protein did nothing for protein synthesis rates.
- 20g soy also did nothing. The same as water alone
- 40g soy did raise protein synthesis levels – a little.
- Both 20g and 40g whey increased protein synthesis rates significantly.
The researchers at McMaster concluded:
The relationship between protein intake and Muscle Protein Synthesis is both dose and protein source-dependent, with isolated soy showing a reduced ability, as compared to isolated whey protein, to stimulate MPS under both rested and post-exercise conditions. These differences may relate to the lower postprandial leucinemia and greater rates of amino acid oxidation following ingestion of soy versus whey protein.
Study shows soy protein may be no more effective than water for build muscle. Click here Click To Tweet
So it’s not just the amount, but the source that’s important, too. And the researchers seem to suggest this is due to the leucine (an amino acid) content found more abundantly in whey than in soy.
Additionally, a higher proportion of the amino acids from soy get oxidized in the body and therefore cannot contribute to building muscle tissue (protein synthesis).
Interestingly, there is also this review  that concluded…
“New data suggest that whey protein is better able to support MPS than is soy protein, a finding that may explain the greater ability of whey protein to support greater net muscle mass gains with resistance exercise. This review focuses on evidence showing the differences in responses of MPS, and ultimately muscle protein accretion, to consumption of milk- and soy-based supplemental protein sources in humans.”
By the way, the protein I recommend for my readers are:
(1) Optimum Nutrition Whey for those in the US
(2) Impact Whey from MyProtein for everyone in the UK/Europe
Also, if you would like easy high-protein recipes to fuel your muscle growth, see my MuscleHack Buff Baking. It makes eating healthy feel like a cheat meal. There’s pancakes, peanut butter cookies, ice cream, “strong man’s” sausage bake, chocolate cake, “popcorn” chicken and many more!
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 Myofibrillar protein synthesis following ingestion of soy protein isolate at rest and after resistance exercise in elderly men.
 The role of milk- and soy-based protein in support of muscle protein synthesis and muscle protein accretion in young and elderly persons.
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