Whey Protein Powder vs. Soy Protein Powder

For people looking to add more protein to their diet or maximize muscle growth, protein powders are an easy way to increase daily protein intake.

Whey Protein Powder vs. Soy Protein Powder

Whey and soy are two of the most popular types of protein powder. But how do they compare, and which one is better for you?

What Is Whey Protein Powder?

Whey protein comes from cow’s milk. It's a by-product of cheesemaking – the liquid that separates from the milk curds during the cheesemaking process is called whey. This whey liquid then goes through further processing to become whey protein powder.

Specifically, the whey liquid is filtered and pasteurized. Enzymes may be added to help separate components. Then carbohydrates, fats, and excess water are removed, leaving behind a high-protein powder.

There are a few different types of whey protein powder:

  • Whey protein concentrate: Contains 70-80% protein along with some lactose and fat
  • Whey protein isolate: A more processed form with 90-95% protein and little to no lactose or fat
  • Hydrolyzed whey protein: Broken down further so it's even easier and quicker to digest

One of the main benefits of whey protein is that it's rapidly digested, especially hydrolyzed whey protein. This makes it great for consuming post-workout to help repair muscle damage and promote muscle protein synthesis.

It's also a complete protein, meaning it contains all 9 essential amino acids your body needs.

Key Takeaway: Whey protein powder comes from cow's milk and is quickly digested, making it good for post-workout recovery.

What Is Soy Protein Powder?

Soy protein powder starts with whole soybeans. Soybeans are legumes that contain protein along with carbohydrates and fat.

To make soy powder, manufacturers first grind soybeans into a meal and defat them by removing most of the natural oils. What's left is a high-protein soybean meal that then undergoes further processing to become soy protein isolate powder.

The finished soy protein isolate powder contains 90-95% protein content. Some brands may add vitamins, minerals, or flavorings. Since it comes from plants, soy protein powder is vegan and dairy-free.

Soy protein is also a complete protein containing all essential amino acids. However, soy has lower levels of certain amino acids important for building muscle, like branched-chain amino acids.

Key Takeaway: Soy protein powder comes from soybeans, is plant-based and dairy-free, but may not be as effective as whey powder.

Whey vs Soy Protein Powder for Muscle Growth

When it comes to building muscle, research shows whey protein powder has an advantage over soy.

In one study, men took equivalent doses of whey or soy protein while weight training for 6 months. The group taking whey powder gained significantly more muscle mass than the soy group:

Protein PowderLean Muscle Mass Gained
Whey3.3 pounds
Soy1.8 pounds

The researchers stated that "whey protein supplementation resulted in greater gains in muscle mass compared to soy protein supplementation."

Another study looked specifically at muscle protein synthesis rates, which is the process driving muscle growth. They found whey stimulated much greater muscle protein synthesis compared to soy, both at rest and after weight training.

Based on the evidence, whey protein is superior to soy protein powder for building muscle from weight training. The higher levels of branched-chain amino acids like leucine in whey stimulate greater muscle protein synthesis.

Using Soy and Whey Powder for Weight Loss

Many people take protein supplements to help lose weight. So how do soy and whey protein compare when it comes to fat loss?

One study followed 90 overweight men receiving daily whey or soy protein powder for 23 weeks. The whey protein group lost significantly more body weight and fat:

Protein PowderWeight LossFat Loss
Whey4 lbs5 lbs
SoyNo significant lossNo significant loss

In addition, only the men taking whey protein powder saw their waist size decrease. Based on this, researchers concluded: "different sources of dietary protein may facilitate weight loss and affect body composition."

Whey protein powder provides clear advantages for fat burning and body recomposition over soy protein powder. Consuming 20-30% of total calories from whey protein can help boost metabolism, reduce hunger, and preserve muscle mass when dieting.

Effects on Hormones: Testosterone and Estrogen

Higher protein intake, whether from foods or supplements, influences hormone levels in your body. Soy in particular contains phytoestrogens that mimic estrogen. So what effects do soy and whey protein powders have on key hormones testosterone and estrogen?

One study looked at men weight training for 2 weeks while supplementing with whey or soy protein powder. They found:

  • Men taking whey protein had higher testosterone levels after workouts
  • Men taking soy protein has lower testosterone after workouts
  • No changes in estrogen levels were seen between the groups

The evidence suggests whey protein supplementation can help maintain testosterone compared to soy protein when training intensely. And soy does not appear to alter estrogen levels. For optimal workout recovery and anabolic hormone levels, whey protein powder is the better choice over soy.

Which Tastes Better: Soy or Whey Protein?

A big consideration when choosing a protein powder is taste and texture. How do soy and whey powders compare?

Whey protein powder comes in different forms. Whey protein concentrate keeps some of the milkfat, making it thicker and creamier. Whey isolate has almost all fat removed, but still maintains a relatively smooth texture.

The taste of unflavored whey protein is described as mildly nutty and neutral. For flavored whey powders, chocolate, vanilla and strawberry are some of the most popular.

Soy protein powder also has a nutty taste, but it tends to be stronger in flavor. The texture can be grittier or chalkier compared to the creaminess of whey.

For taste and texture, whey protein powder is the winner. But both soy and whey powders come in a wide variety of flavors, so it’s possible to find a soy powder with taste and texture you enjoy.


Is soy protein good for building muscle?

Yes, soy protein powder can help build muscle, especially when combined with resistance training. However research shows whey protein stimulates greater muscle protein synthesis, resulting in more gains.

Does soy protein increase estrogen levels?

No evidence shows soy protein in moderation boosts estrogen. The phytoestrogens in soy can bind to estrogen receptors but don’t appear to significantly alter hormone levels.

What has more amino acids, whey or soy protein?

Both soy and whey protein powder are complete proteins with all the essential amino acids. However whey protein contains higher levels of certain amino acids important for muscle protein synthesis, like leucine.

Which protein powder is better for weight loss?

Research demonstrates whey protein promotes greater fat loss and sparing of muscle mass during dieting and calorie restriction. The protein and amino acids in whey powder boost metabolism more than soy protein.


To wrap it all up, whey and soy protein powders both provide high-quality complete protein to support muscle growth and overall health. However, the research suggests whey protein powder is superior for building muscle, losing fat, and optimizing hormone levels.

Whey protein comes out ahead due to its high digestibility and absorption rate, branched-chain amino acid content, and ability to boost metabolic rate and feelings of fullness when dieting. These advantages drive greater muscle protein synthesis and weight loss compared to soy protein.

Sarah Cortez
Sarah Cortez

My name is Sarah and I'm a baker who loves trying out new recipes and flavor combinations. I decided to challenge myself to use a new spice or ingredient powder in my baking each week for a year. Some successes were the cardamom sugar cookies, vivid turmeric cake, and beetroot chocolate cupcakes. Failures included the bitter neem brownies and overwhelmingly hot ghost pepper snickerdoodles. Through this experience I've discovered amazing additions to spice up desserts while learning how to balance strong flavors. Follow my journey as I push the boundaries of baking with unique powders!

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