Pea Protein vs Soy Protein: A Dietitian Compares

Last Updated: June 9, 2024

Pea protein vs soy protein: they’re two popular plant based protein powder options, but which is better? As a dietitian, I know that choosing the right protein supplement can feel overwhelming. 

That’s why in this post, we’re diving into what they are, their nutritional benefits, and their impact on muscle growth. Plus, we’ll see how they compare to whey protein. 

Whether you’re a fitness enthusiast or just looking to boost your plant protein intake, keep reading to get the scoop on which protein might be the best fit for your lifestyle and goals. 

What is Pea Protein? 

Pea protein is made from yellow split peas, a sustainable crop known for its lower environmental impact. 

These peas are harvested, dried, and ground into a flour, which is then mixed with water to create a paste. This paste is then filtered and dried to isolate the protein from the fiber and starch and made into a fine powder (1).

This powder is what we know as pea protein isolate. The isolation process ensures the final product is high in protein while being low in carbohydrates and fiber.

Types of Pea Protein

There are two main types of pea protein powder available on the market: isolate and concentrate.

  • Pea Protein Isolate: Contains 80-90% protein and is lower in carbohydrates, ideal if you’re looking for a pure protein source.
  • Pea Protein Concentrate: Has 70-80% protein, retaining more of the natural fibers and starches from the peas. It’s often used in food products for added texture and nutrition.

Most protein powders are made with pea protein isolate because it’s a purer protein source.

What is Soy Protein?

Soy protein also has a relatively low environmental footprint compared to animal based proteins. 

Soy protein powder is made by harvesting and cleaning mature soybeans to remove the oil content. This leaves behind the soybean meal, which is rich in protein.

Similar to pea protein, the soybean meal undergoes a series of steps to isolate the protein from the carbohydrates. 

Types of Soy Protein

Like pea protein, soy protein comes in the form of isolate and concentrate. 

  • Soy Protein Isolate: Contains around 90% protein and is low in fat and carbohydrates, achieved through extensive processing.
  • Soy Protein Concentrate: Contains about 70% protein, retaining more natural fibers and carbohydrates, and is less processed than isolate. It’s often used in a variety of food products for its texture and nutritional benefits.

Pea Protein vs Soy Protein Nutrition

Whatever your protein goals are, pea protein and soy protein are both good options to help you meet them, as most varieties pack about 25 grams per serving. However, they do have some differences in their nutritional properties. 

Macronutrients

Both pea and soy protein contain around 90% protein, with low levels of carbohydrates and fats.

Amino Acids

Both pea and soy protein contain all nine essential amino acids (the building blocks of protein we need to obtain from our diet), making them complete protein sources. 

However, pea protein is relatively low in the essential amino acid methionine. This can be compensated for by including other protein sources throughout the day. 

Micronutrients

  • Pea Protein: Contains some vitamins and minerals, such as iron and calcium, but in lower amounts compared to whole foods. 
  • Soy Protein: Contains iron, calcium, magnesium, and potassium. Soy also contains beneficial compounds like isoflavones, which have antioxidant properties.

Isoflavones

Isoflavones are a unique nutrient in soybeans that have been linked to multiple health benefits, including potential antioxidant properties, support for heart health, and reducing the risk of certain cancers. 

Foods like tofu and soymilk are richer sources of isoflavones than soy protein isolate, because the processing can reduce isoflavone content by 80-90% (2). 

This loss means that while soy protein isolates are an excellent source of protein, they may not provide the same health benefits associated with isoflavones as minimally processed soy foods​. 

Leucine

Leucine is a branched chain amino acid essential for muscle building. Optimal leucine intake for muscle growth is around 1-3 grams per meal (3).

Soy and pea protein isolates are both good plant-based sources of leucine. Both provide roughly 2 grams of leucine per 30 grams serving (4), although the exact number varies from brand to brand. 

Nutritional Comparison (Per 100 grams)

NutrientPea Protein Isolate (5)Soy Protein Isolate (6)
Protein Content78 grams83 grams
Carbohydrates7 grams0 grams
Fats5.5 grams2 grams
Essential Amino AcidsRich in lysine, lower in methionine and cysteineComplete protein with balanced amino acids
Iron23 mg12.5 mg
Calcium74 mg804 mg
Fiber4 g0 g
IsoflavonesNonePresent

Effects on Muscle Growth

Pea Protein

Studies have shown that pea protein can effectively help with muscle growth. 

One study found that pea protein resulted in comparable muscle thickness gains to whey protein over a 12-week period in men who resistance trained (7). 

However, a randomized control trial concluded that compared to pea protein, whey protein might be better for post-exercise recovery in older adults (8).

Overall, it appears that pea protein isolate can provide the necessary leucine to support muscle growth, especially when taken in adequate amounts throughout the day.

Soy Protein

Soy protein has been studied pretty extensively for its effects on muscle growth. 

A meta-analysis compared the effects of soy protein to whey protein and found that soy protein can support muscle growth and strength gains similarly to whey when consumed in sufficient amounts​ (9)​. 

This doesn’t mean you should limit your protein source to only soy, but diversifying your protein sources and ensuring you’re getting the right amount of total protein and leucine in a day can help you meet your goals. 

Comparison to Whey Protein

Whey protein is often considered the gold standard for muscle growth due to its high leucine content and quick digestion rate. 

Studies have shown that whey protein supplementation leads to significant increases in muscle protein synthesis and overall muscle mass, especially if resistance training. 

When compared to plant-based proteins like pea and soy, whey generally results in greater muscle protein synthesis, but the differences can be minimized with adequate total protein and leucine intake.

Digestibility and Absorption

The PDCAAS (Protein Digestibility-Corrected Amino Acid Score) is a score that shows how well your body can use the protein.

Pea protein isolate has a high PDCAAS of around 0.8, indicating that it’s highly digestible and its amino acids are readily absorbed by the body​ (10)​​.

Soy protein is also highly digestible and has a PDCAAS of 0.9-1.0, making it similar to that of whey (11). 

Both are processed to reduce anti-nutritional factors, making them highly digestible.

Comparison to Whey Protein

Whey protein is often considered the benchmark for protein digestibility and absorption, with a PDCAAS of 1.0 and rapid absorption rates. 

This rapid digestibility and high leucine content make whey protein particularly effective for promoting muscle growth and recovery.

You don’t need to make a choice based on PDCAAS scores since most meals include more than one protein source, which impacts the overall score.

Pea Protein vs Soy Protein: Which is Better? 

Like many things in nutrition, neither is necessarily better than the other for everyone. 

Choosing the right protein supplement depends on your dietary preferences, fitness goals, and any dietary restrictions. Both pea and soy protein isolates offer high-quality protein sources that support muscle growth and recovery.

Pea protein is ideal for those with soy allergies, while soy protein offers additional health benefits like isoflavones.

If you’re still unsure which one to choose, try both to see which taste and texture you prefer in the foods/beverages you’ll be using them in. 

Eating a variety of protein sources ensures a well-rounded intake of amino acids. The quality of a single protein source matters less when your diet includes proteins from many different sources.

Final Thoughts

Pea protein and soy protein isolates are excellent plant-based options that provide high quality protein to help you meet your daily needs.

Incorporating either one of these proteins into your diet can help you meet your daily protein needs, and support muscle strength and recovery, making them viable alternatives to whey protein, especially when consumed in the right amounts. 

Just remember to consume a variety of protein sources into your diet for a well-rounded intake of amino acids and nutrients.

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