Total Shape is a reader-supported site. Purchases made through links may earn a commission. Learn more.

Soy Protein vs Whey: Which Is the Better Powder Choice?

Connor Sellers
Published by Connor Sellers | Senior Coach
Fact checked by Donald Christman, BHSc FACT CHECKED
Last updated: February 3, 2023
We personally test every product featured in our reviews and guides. By ordering products anonymously and getting a group of independent testers, we are able to get first-hand experience and provide data-driven recommendations. Learn more.

I've seen quite a few heated debates at the gym in recent months about the pros and cons of different protein sources. In many cases, it mainly comes down to soy vs. whey protein, but there is often a lot of misunderstanding.

From a nutrition perspective, there are important factors to consider; ones that go beyond the ethics of plant-based protein powder.

If you don't understand the differences in nutritional content, then you could end up making a decision that won't get you to your health and fitness goals.

Let's start with some basics.

What Is Whey Protein Powder?

Scoop of Whey Protein

Whey protein powder is most commonly an isolate of milk, used as a supplement to provide a healthy boost of protein.

Whey is the watery part of milk that is left over when the curds have been removed.

The curds mainly contain fat and carbs and are generally used for making cheese.

The remaining whey portion can then be used to make a protein isolate that is commonly used for weight loss, athletic performance, and bodybuilding.

Of all the protein powder products you'll find on the shelves in sports nutrition stores, whey is going to be the most common [1].

Wondering why that is?

1. Health Benefits Of Whey Protein Isolate

Whey Protein

Whey isolate has a few essential fitness-based benefits that support several goals that many people have.

First of all, it provides the complete amino acid profile, including the 9 essential amino acids that the body needs to assimilate through food [2].

These amino acids play an important role in muscle recovery, as well as muscle building.

Secondly, studies have shown that whey protein is one of the easiest and fastest proteins for the human body to absorb [3].

So, for all types of athletic people, whey protein may increase your amino acid levels the fastest, while providing critical nutrients for your muscles.

2. Side Effects Of Whey Protein

The most common side effects of whey protein are down to some form of dairy or lactose intolerance. While whey protein itself is not high in lactose, it may still cause problems when digested.

The other reason I have seen some clients have problems with whey is down to overuse. Yup, I have encountered many people with muscle building and weight loss goals who thought it was a healthy idea to double and triple up on their whey protein intake.

Let me tell you: unless you're a professional athlete and you work with a dietitian, that's not a good idea.

What Is Soy Protein Powder?

Soy Protein

Soy protein powder is a protein that is isolated from soybeans. Of all the proteins sourced from plants, soybeans are among those with a high protein content at about 40% [4].

One of the reasons soy is so popular, especially with vegans, is that it has high levels of iron, which is something that vegans may be lacking in their diet.

But even non-vegans often replace whey with soy protein it contains far less saturated fats.

Which are known to have medical implications for cardiac health. Let's take a closer look at the benefits.

1. Health Benefits Of Soy Protein

healthy woman

I already mentioned the fact that it's low in saturated fat, especially when compared to whey protein.

But from a nutrition perspective, you should also be aware of the high amount of fiber. This may help your digestion and diet efforts as it may make you feel full for longer periods.

What I found particularly interesting is that switching from animal protein to soy has been shown to help with lowering the bad LDL cholesterol levels [5].

Finally, unlike other plant proteins, soy contains all 9 essential amino acids. This may help with muscle recovery and bodybuilding.

2. Side Effects Of Soy Protein

salt and heart

The most common reaction that I have seen with my clients is due to soy allergies, which are probably more common than a lot of people expect.

If you rarely have soy products in your diet, then it may be best to start with a small scoop of protein powder to make sure you don't have a reaction.

However, two main negatives are often raised from a nutrition perspective.

Soy protein has quite a high sodium content. While many athletes may need this electrolyte to stay hydrated, it may have some negative impacts, especially for your heart health [6].

The other thing you often hear is that soy contains isoflavones, which have similar effects as the estrogen hormone.

However, studies have measured these responses to be very weak, so unless you're planning to take very large doses of soy protein powder, this should not be an issue [7].

Check this video out for a further comparison between the two options:


Comparing Soy and Whey Protein Powder

The main difference between soy and whey protein powder is that whey protein is a dairy product.

Whey powder increases testosterone levels and helps gain muscle faster, while soy protein is better for lowering bad LDL cholesterol levels.

You should have a good picture of the benefits of both forms, so let's take a look at how to make a decision.

1. It’s All About The Amino Acid Profile

While soy does contain all 9 essential amino acids, two of them are present only in minimal amounts: methionine and lysine [8]. This means that if you're looking for muscle-building benefits, whey may be the better option.

Essential amino acids can help maximize the hard work we put in at the gym to stimulate muscle protein synthesis. If you're stimulating muscle protein synthesis, you put yourself in a favorable position to gain muscle or at least not break down your existing muscle.

- Kris Gethin, Professional Bodybuilder

2. Taste and Texture

I would say that this is not so much an issue if you plan to use flavored soy or whey protein powder. But if you're going for unflavored, then it's important to note that whey is a bit more creamy, and soy has more of a nutty flavor to it.

3. How Long Will It Last?

Both soy and whey protein products usually have a shelf life of about a year. If you take protein supplements daily, then that won't be a concern.

But for less regular users, keep in mind that the flavor may diminish as you approach the best before date.

4. Dietary Restrictions

Your choice of protein source may very much come down to any dietary restrictions you have. For anyone with dairy allergies or if you stick to a vegan diet, soy protein is going to be your answer.

Just keep in mind that from a nutrition perspective, you may need to stack soy with rice or pea protein powder to get full amino acid exposure.

Now it's time to factor in your goals.

Considering Your Personal Goals

So, assuming that you don't have dietary restrictions that impact which source of protein you choose, there are two main factors that you'll likely need to consider.

1. Bodybuilding

Muscular Man

To gain body weight in the form of muscle, I would generally suggest to my clients that they stick to whey protein.

Because it contains the full profile of essential amino acids, you will have a better chance of providing your muscles what they need on a daily basis.

I have worked with people of all shapes and sizes, and I firmly believe that whey had a contributing factor to them achieving their dream body composition.

You want to keep track of your intake to avoid excessive exposure to saturated fat.

2. Weight Loss

woman's belly

For my clients who have weight loss goals, I have been recommending soy protein for quite a while now.

While it doesn't have enough of all the amino acids like whey protein has, this is only critical if you're aiming to build some muscles.

But if you just want to work on your body composition and lose some fat, then soy has some advantages.

With the added fiber, you may feel full for longer, which may make it easier to bridge the gaps between meals. This may help you with a restricted-calorie diet, making it less difficult to work towards your ideal body weight.


Is whey protein better than soy protein?

Yes, whey protein is better than soy protein for muscle building as it contains larger amounts of essential amino acids. However, soy may be the better choice for weight loss as it contains more fiber and less fat.

Does soy protein affect testosterone?

No, soy protein doesn't affect testosterone levels, no matter how many grams you take daily. However, it may have an impact on the release of other hormones, especially estrogen.

Does soy protein isolate increase estrogen?

Yes, soy protein isolate may increase estrogen in your body. However, your soy protein consumption would have to be in excess of 50 grams daily for this to start showing any impact. At average amounts of about 20 grams, you shouldn't expect any significant estrogen changes.

How much soy protein is too much?

Soy protein intake above 50 grams per day may be too much, according to some studies. At this point, you may start increasing estrogen receptor responses, and your sodium intake may be rising too much as well.

Is soy bad for males?

No, soy is not bad for males unless you're relying on excessive amounts. It doesn't have an impact on testosterone levels, but taking more than 50 grams per day, may have an impact on estrogen levels, which could influence your body composition.

Soy Protein vs Whey Protein: Which is Better?

At this stage, you should have all the information you need to decide whether to go with whey or soy protein powder. If there are dietary reasons that do not allow you to take whey, soy may be your best choice.

However, if your decision is down to weight loss and muscle building, then you can go with soy for losing some pounds and whey for getting ripped.

Don’t forget to join us on social media to let us know how it works out for you.


Was this article helpful?

About The Author

You May Also Like

Write a Reply or Comment

Your email address will not be published. Required fields are marked *