Whey Protein Versus Soy Protein—Which Is Better?

Body builders and other athletes as well as everyday people looking to improve their levels of fitness have been turning to protein supplements in greater numbers than ever before. Two of the most commonly used sources of protein are whey and soy.

Despite the fact that of these sources do have similar effects and that each can be used effectively to build lean muscle mass, there are subtle differences. In order to determine which is best it is important to understand what each one actually is and their respective values, benefits, and side effects.

What Is Whey Protein?

Whey protein comes from cow milk and is considered to be high quality and complete. It contains all of the essential amino acids including branched chain amino acids like leucine, isoleucine, and valine.

These acids are incredibly important since the body strips them from the muscles during exercise. Additionally, whey protein has a very high absorption rate that leads to muscle rebuilding very quickly after its ingestion. This is also why whey protein is a great post workout supplement.

What Is Soy Protein?

Soy protein comes from soy beans and is, therefore, plant-based rather than animal based. This is also considered a complete form of protein, containing all the essential amino acids. Unlike whey, soy protein is rich in glutamine and arginine. These amino acids help muscle formation, especially the formation of new muscle tissue. It is less effective in rebuilding muscle tissue. Obviously, this would likely be the better option for those who have dairy allergies.

Whey Vs. Soy Protein

One method of comparing different forms of protein is to use the Biological Value or BV. This is a way to measure the amount of nitrogen retained after consumption versus the amount of nitrogen consumed with an empty stomach.

Whey protein has a BV of around 100, while soy protein has a BV of 74. This is most likely related to the ease of absorption, with whey protein being the clear winner.

Another method of comparison between these two forms of protein is called the net protein utilization. This is simply a measure of how much of the consumed protein is actually used by the body. In the case of soy protein approximately 61 percent of the protein is actually used. With whey protein, this rating is approximately 92 percent. Whey protein is the clear winner when judged by this standard as well.

The amino acid score is another way to quickly compare two different protein sources. This is a way to compare based on the most limiting amino acid found in the studied protein. The exact method of testing is a bit complicated, but whey protein wins in this regard again, 1.14 to 0.99.

Soy protein does have three major factors in its favor. First, this is a better choice for those with milk or other dairy allergies. It also contains more of two critical amino acids (the glutamine and arginine already mentioned) which are incredibly important in the formation of new muscle tissue.

Whey vs Soy Protein Side Effects

There are some concerns with the isoflavones in soy protein disrupting the natural hormonal balance of the body. Another criticism is that some of the inhibitors found in soy change testosterone or estrogen levels. Whey protein can aggravate milk and dairy allergies. Then again, this is not true for everyone and you should just monitor yourself for any of these potential side effects. 

Ultimately, the best course may be to try both whey and soy protein sources to see how your body responds. If you are lactose intolerant or lactose sensitive, it may be best for you to stick to soy protein. Otherwise, most individuals use whey protein for its superior nitrogen retention and protein absorption.


Statements found within have not been evaluated by the Food and Drug Administration. These dietary supplement products are not intended to diagnose, treat, cure or prevent any disease. Always consult a physician if you are unsure about taking a new supplement. Do not take this supplement if you are under 18, if you are pregnant, nursing, or have any cardiovascular issues.

Scientific studies cited are not conclusive and have limitations, due to of their closed environment nature. Referenced studies will not necessarily determine your experience with a supplement, since there are many unaccounted variables, which fall outside the scope of the studies.

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