Soy Protein vs. Whey Protein for Bodybuilding

Lately, there has been an ongoing debate about whether you should rely on plant-based or animal-derived protein powders to gain bigger muscles and maintain a lean physique.

However, if we just exclude bro-science and agenda-pushing from an equation, we quickly come to realize that the answer to this debate is not at all simple.

In light of that, we’ll try and end at least one part of this debate – soy protein vs. whey protein for bodybuilding – which is better?

Let’s figure it out!

What is Soy Protein?

Soy protein is a plant-based protein derived from soybeans. It comes in two forms:

  • Isolate
  • Concentrate

It contains all nine essential amino acids, which makes it a complete protein source, just like an animal-sourced product would be.

For that reason, soy protein is widely used as a whey protein alternative, and it has quickly become many folks’ go-to choice.

Now, we said that soy protein is a complete protein, and while that is true, it’s also worth noting that not every soy protein will be the same, as its amino acid profile will vary greatly from strand to strand, but that’s something we’ll tackle in a few moments.

What is Whey Protein?

Whey protein is a type of dairy-based protein derived from cow’s milk. It contains all nine essential amino acids, making it a complete protein.

Whey protein is the most popular option when it comes to animal-derived powders and supplements, which makes sense, considering that it has been proven to be very effective for muscle growth and recovery.

Unlike soy protein, whey protein is available in three different forms:

  • Concentrate,
  • Isolate
  • Hydrolysate

Depending on your needs or taste preference, you may opt for one over the other, but it is universally accepted that isolate is the best choice.

What’s the Difference Between Soy and Whey Protein?

Aside from the obvious difference of one being plant-based and the other animal-derived, the only conceivable difference between the two is in their taste. Whey is usually very mild and flavorless, while soy protein powder can come across as nutty or even bitter.

The real difference, however, lies in their amino acid profile, which we’ll explore now:


Per 100 grams

Just by quickly glancing over this table, it becomes evident that whey protein contains significantly more amino acids per 100 grams of protein, which would inherently make it the logical choice for bodybuilders and athletes.

However, it is crucial that we understand that these are just averages for soy proteins. According to a study from 2015, the amino acid profile of soy proteins greatly varies depending on the strand. [1] So, the numbers you see here aren’t necessarily representative of every soy protein supplement on the market.

That said, it is nearly impossible to know what you’d be getting unless the manufacturer is completely upfront about their product’s exact amino acid profile.

How Do the Benefits of Soy and Whey Protein Compare for Bodybuilding?

Considering the differences in the amino acid profiles of these two proteins, when it comes to bodybuilding and fitness, both soy and whey protein can be incredibly effective. But it is safe to say that whey protein will turn out to be more beneficial.

In fact, there was a study comparing the two, and after 12 weeks of resistance training, both study groups experienced comparable results with no notable differences between the two. [2]

If you’re confused about how that makes sense, the study was conducted in a way where the participants were given different amounts of protein – 21 grams of whey protein isolate against 29 grams of soy protein isolate. 

This was done in order to match leucine content, so if we were to compare the findings, gram for gram, whey protein comes out nearly 40% more effective than soy protein.

Now, with that in mind, if used correctly, soy protein can also be a very effective dietary supplement, especially if you factor in the cost.

Why Would Someone Choose a Soy Protein Over Whey?

There are two reasons why someone would choose soy protein over whey – dietary or lifestyle restrictions or cost.

The first one is pretty self-explanatory. If you are vegan – whey protein would not be a viable option. In that case, soy protein should probably be your go-to.

One could make a case for lactose intolerance, but since whey isolate is lactose-free, that shouldn’t be an issue.

The other factor is cost. Soy protein is usually more affordable than whey – mostly due to significantly lower production costs. However, it shouldn’t be too hard to find affordable whey isolate – especially if you don’t mind buying in bulk.

Bottom Line: Is Soy or Whey Protein Better for Bodybuilding?

All things considered, whey protein powder is a better option for bodybuilding.

It has a better amino acid profile and is, therefore, more suitable for muscle building and weight loss.

That said, when it comes to plant-based proteins, you really can’t go wrong with soy protein. As long as you hit your daily goals, soy protein will help you achieve the same results as whey.


There you have it – a complete breakdown of the differences and similarities between soy and whey protein. They both have their unique advantages, and if used correctly, they can be incredibly effective for bodybuilding. It’s just a matter of finding which of the two fits your needs best.

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