Whey Vs. Soy Protein: Which is Best for Your Fitness Goals

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Whey vs. soy protein – which is the best?

Whey and soy are both good sources of protein. They are also popular choices for building muscles. But-

  • Which one provides better results?
  • Which is ideal for recovery?

Let us tell you, both whey and soy can be made to have almost 90% protein content. They also have all essential amino acids but at varying levels. And both can grow muscle mass. These are the similarities.

In this post, we will go deep into whey vs. soy protein, and tell you which one scores more points. You will get all the information you need, delivered in the most convenient manner.

First, a few words on both forms of protein.

What is Whey Protein

Whey protein comes from milk. It’s the clear liquid you get after separating cheese from milk. The liquid undergoes drying and then sold as supplements.

(Read more about whey protein and how it’s made.)

What is Soy Protein

Soy protein is extracted out of soybeans. Manufacturers dehydrate the soybeans and sell the powder as a muscle-building supplement. Like Whey, you get soy in both concentrates (containing fats, carbs, and nutrients), and isolate forms (contains only protein, no fat or carbs).

Whey and soy protein also contain other nutrients, but they don’t have any significant effects that demand discussion. So, we are going to evaluate the proteins based on their quality and effectiveness for building muscles.

Now, we will provide a head-to-head comparison of both proteins and their profile.

Whey Vs. Soy Protein: A Technical Analysis

In our detailed analysis, we saw whey beat all other proteins that included soy. Here we will lay down the findings in a more simple way. The numbers used in the analysis are all from the second edition of the Reference Manual for US Whey and Lactose Products. So, you can be sure of their credibility.

Let’s see who tops the results on the following metrics:

Protein Quality

Winner: Whey

Scientists use Protein Efficiency Ratio (PER) to express the quality of a protein. The metric measures the relationship between the intake of protein and the weight gain of a subject. The weight gain includes only the volume of muscle mass growth as protein cannot make you gain weight. So, we are talking about lean muscles. 

Let’s see how both proteins score on protein quality-

Whey – 3.2

Soy – 2.2

It shows whey is a higher quality protein than soy. It also means whey protein is more effective in building muscles compared to soy. And maybe it’s the reason why whey is the most popular supplement for muscle-building.


Winner: Whey

The protein we consume helps in protein synthesis. The more protein we can synthesize, the more muscle mass we can build. We have used a metric called Biological Value (BV) that measures how much protein our bodies can synthesize from a given dose of protein. Higher scores mean we can synthesize a greater percentage of that protein.

Here’s how both proteins fare on the effectiveness meter-

Whey – 104

Soy – 74

As you can see, whey can help our bodies synthesize more protein per dose compared to soy.

Protein Utilization

Winner: Whey

Net Protein Utilization (NPU) is another metric related to the effectiveness of a protein. It measures how much amino acids our bodies can convert against a specific dose of amino acids.

All proteins contain amino acids, as you know. So, this a measure you can use along with Biological Value (BV) to determine the reliability of a protein.

Here’s the score-

Whey – 92

Soy – 61

Both soy and whey have nine essential amino acids, as we already said. But whey has a higher concentration of certain amino acids that are crucial for muscle growth.

Now, this metric shows our bodies can convert more amino acids from whey compared to the same dose of whey. That means we get more amino acids in whey, and can also convert more of those amino acids. As a result, we have more protein synthesis that builds more muscle mass.


Winner: Tie

Protein digestibility reflects how comfortably our bodies can digest a protein-based on our amino acid requirements. The name of the exact metric used is Protein Digestibility Corrected Amino Acid Score. Here’s the score-

Whey – 1

Soy – 1

A score of 1 means a dose of protein supplies all essential amino acids. So, both whey and soy protein fulfills the requirement of essential amino acids.

We think now it’s clear that whey-

  • Helps our bodies synthesize more protein
  • Enables us to grow more muscle by utilizing more amino acids
  • Builds muscle faster than soy
  • Has a higher quality than soy

Next, we whether soy or whey is best for your fitness goals.

Whey Vs. Soy Protein: An Analysis Based on Fitness Goals

Muscle Growth and Muscle Building

Research has proved whey to be much effective in muscle building compared to soy protein. A 2009 study evaluated the effect of whey, soy, and casein on muscle growth. What did the researchers find?

  • The group that took whey had more muscle growth at rest
  • The same group had more muscle growth after weightlifting

The study concluded whey to be the best for stimulating muscle growth.

In another study, subjects who took whey recorded 83% more lean body mass than those who ate soy.

Examine.com also notes some interesting facts noted by a study between whey and soy. The researchers found our bodies show much higher levels of amino acids after consuming whey, especially leucine. This finding also supports the results of our protein utilization metric.

Whey also releases 3 times more leucine, the amino acid that facilitates muscle growth. Other studies support the fact that our bodies can absorb whey protein much faster and better than soy.

Muscle Recovery

To recover muscles after exercise, we need a fast-absorbing protein. Now, from our discussion, it’s clear that our bodies can absorb whey faster than soy protein.

In fact, the absorption rate of whey protein is 10 times higher than soy (first 10 minutes after consumption).

As a result, the amino acids from whey reach our muscles the fastest among all proteins. Along with that, whey also helps our bodies synthesize more protein than soy. In addition, whey releases anabolic hormones that aid in muscle growth. It even blunts the production of catabolic cortisol that decreases muscle growth and lean body mass.

All of these make whey protein a much-preferred choice for recovery.

Weight Loss

Whey seems to be the way to go if you are looking to shed those extra pounds. A study measured the effectiveness of whey and soy protein to find out which was better for weight loss.

The 5-month research found that the group who consumed whey protein lost 1.8 kg body fat and 2.3 kg body mass. The group that took soy protein didn’t record any change in body weight.

In our analysis, whey protein is the preferred choice for-

  • Lean muscle growth
  • Effective muscle recovery
  • Losing fat and body weight

Soy Protein and Estrogen Levels: A Word of Caution for Men

Soy contains estrogenic properties and can affect the levels of hormones in the body. Soy is rich in isoflavones that convert to phytoestrogens after metabolism. The phytoestrogens are a class of estrogens and can have weak estrogenic effects on our bodies, especially men.

Estrogen is known as the female sex hormone and plays a role in reproductive and sexual development in women. Studies on male rats show that soy can lead to infertility, and is a leading cause of worry. But those studies are not feasible as humans and rats metabolize isoflavones in a different manner. So the findings of the studies don’t apply to humans.

Also, research says it’s safe to have soy unless you are eating it too much! That’s the story about soy. However, the story with soy protein is a bit different. Soy protein may contain high levels of isoflavones that can lead to feminine effects on men.

Having large doses of soy protein can give men the “man boobs” as it increases levels of estrogen in our bodies.  Your breasts may start getting fuller, and your nipples can become more prominent. So, it’s always best to stick with the recommended dosage when having soy protein.

The recommended dose of soy protein: Not more than 15-grams per day

Final Verdict

Whey protein has been proven time and again to be the best supplement for muscle growth and building lean mass. Soy protein is much less effective than whey and will take a long time to show any results. You will also not get the same level of results, even if you work out or lift weights. So if you want to build muscles easily, go for whey protein.


Why is whey better than soy?

Whey is much better than building muscles for a number of reasons. The quality of protein in whey is better than soy, whey is more effective than soy, and our bodies use whey much better than soy. All of these add up to result in more protein synthesis and muscle growth compared to soy protein.

Can you build muscle with soy protein?

All types of protein, whether meat or soy, will result in muscle growth. However, you won’t build the same amount of muscle from all protein sources. Research shows whey to be far more superior than any plant protein for building muscles. Also, whey packs the highest amount of protein per serving, even more than meat.

What are the negative effects of soy?

Too much soy can have a negative effect on your digestion. Additionally, you may experience feminine effects like male boobs. However, modern research doesn’t agree with this. Stick to 15g of soy per day for safe results.

Is it okay to eat soy every day?

You can eat soy protein every day as long as you stay within safe limits. If you aren’t that active, don’t consume more than 20g of soy protein per day. You can eat more protein if you exercise or lead an active lifestyle. Consult a dietician to know how much protein is okay for you.

Is soy protein bad for testosterone?

Some studies say soy can lower your testosterone levels. However, current research shows those studies to be flawed or lacking credibility. Soy doesn’t affect your testosterone levels. Talk to a doctor if you think you suffer from low testosterone levels.

Does soy cause inflammation?

Soy may cause inflammation as it increases omega 6 in the body. We suggest you stick with 15 – 20g of soy each day to avoid any harmful effects. And if you aren’t lactose intolerant, go for whey protein for better gains.

How much soy is okay per day?

You can eat up to 15 – 20g of soy per day if you are not very active. The exact amount of protein you need depends on a number of factors. Speak to your dietician for an accurate estimate.