Pea Protein vs. Soy Protein: How Do They Compare?

With a myriad of options on the market, choosing a plant-based protein powder can be downright overwhelming. 

Two of the most common vegan protein powders are pea protein and soy protein. Which of these is the best for building muscle? Which is the healthiest? Do they have any risks?

My goal with this post is to compare pea protein vs soy protein powders and discuss their amino acid profiles, their effects on muscle strength and hypertrophy, considerations for choosing the best option, and misconceptions about their safety.

What is pea protein powder? 

The main ingredient in pea protein powder is generally pea protein isolate. Pea protein isolate is produced from yellow split peas using a wet processing method¹, in which proteins are separated from the other pea components. 

Pea protein powder is sold as a dietary supplement, meaning it is not regulated by the FDA. It is often marketed as a convenient way to add extra protein to the diet, especially for the purpose of building muscle.

RELATED: Are OWYN Protein Shakes Healthy?

What is soy protein powder?

The main ingredient in soy protein powder is usually soy protein isolate. The process of producing soy protein isolate begins with soybean flour or flakes which have had the natural fat removed, and is processed with water and alkaline compounds until the proteins have been separated from other components. Soy protein isolate must contain at least 90% protein².

Similar to pea protein, soy protein powder is also sold as a dietary supplement for the purposes of adding more protein to the diet and promoting muscle repair and growth. Pea and soy protein powders are sold as a vegan, plant-based alternative to animal-based protein supplements, such as whey and casein.

Nutrition profile and ingredients

Protein quality

Protein quality is usually determined by the combination of a protein’s amino acid content and how easily digestible it is. 

A widely used measure of protein quality is the Protein Digestibility-Corrected Amino Acid Score, or PDCAAS. Using this metric, egg, meat, and dairy-based proteins score the highest³ because they are most easily absorbed by the body and contain amino acids at levels that match what is required by the human body.

The Food and Agriculture Organization of the United Nations now recommends using the Digestible Indispensable Amino Acid Score (DIAAS) instead of PDCAAS.

DIAAS⁴ is considered more helpful because it considers the digestibility of individual amino acids, not the protein as a whole. It also focuses on absorption of the amino acids in the ileal portion of the digestive tract instead of the entire digestive tract.

Pea protein contains all nine essential amino acids but is lower in the amino acid methionine than is considered optimal for building muscle. It’s typically considered a lower quality protein than soy since soy protein contains all nine essential amino acids in amounts closer to what is required by the body.

However, these definitions of protein quality are limited because they don’t consider the impact of different protein sources on chronic disease development or the environment. Eating more plant-based proteins is associated with a lower risk of many chronic diseases, and they have less of an impact on climate change than animal proteins³.

Ingredients 

Pea protein powders may be sold with pea protein isolate as the only ingredient, or may be combined with another protein source since it’s lower in methionine.

For example, protein concentrates or isolates higher in methionine made from brown rice, hemp seeds, or chia seeds are often added to pea protein to provide all nine essential amino acids required for muscle growth and repair in proportions required by the human body.

Soy protein powder is typically not combined with other protein isolates since soy is a complete protein containing all the essential amino acids in optimal amounts for building muscle.

Allergens

Soy is one of the 8 most common allergens. Therefore, pea protein may be a safer choice for individuals with a soy allergy.

However, peas and soy are both legumes. So are peanuts, another common allergen. Although individuals with an allergy to one legume are not usually allergic to every other legume, they may experience an allergic reaction to one or two others, which could include peas⁵.

If you’re allergic to a legume like soy or peanuts, be cautious when trying products with pea protein. Consult a licensed healthcare provider if you aren’t sure what products are safe to try.

Reasons for using protein powder 

There are many benefits of vegan protein powder. Some of these include:

• Building muscle. There are many plant-based foods with protein, but depending on the intensity of your training regimen, your fitness goals, or your schedule, protein powders can provide a convenient and easy way to meet your protein needs for optimal muscle growth.
• Poor appetite. Sometimes despite a person’s best attempts to eat enough protein-containing foods, they simply are unable to do so due to a poor appetite. This can happen especially in older adults, where appetite naturally goes down while protein needs increase. People with cancer, depression, gastrointestinal conditions, dementia, or morning sickness during pregnancy may also have a lower appetite and struggle to get enough protein in their diet.
• Making meals more balanced. While including whole plant-based sources of protein at meals is optimal, sometimes hectic mornings and busy schedules make this challenging. Adding protein powder to a smoothie or having a protein shake along with a bagel or piece of fruit in the morning can make these foods more filling and nutritionally balanced, and therefore may help prevent overeating later in the day.

Benefits for muscle

Unfortunately, there aren’t many research studies directly comparing pea to soy protein. 

To determine the effectiveness of different proteins, they are most often compared to whey protein, considered the “gold standard”. This is due to whey’s high leucine content and easy digestibility. Leucine is one of three branched-chain amino acids (BCAAs) and is especially important for stimulating muscle protein synthesis.

Let’s see how pea and soy protein compare to whey for muscle strength and hypertrophy.

Strength

In an 8-week study⁶ of CrossFitters taking either a whey protein or pea protein supplement, there were no significant differences between the groups in strength gains for either maximal squats or maximal deadlifts. 

Additionally, a larger exercise study⁷ comparing the effect of whey vs. pea protein found no significant differences in biceps curl strength between the groups.

Although more research would be helpful, it appears that pea protein is as effective as whey protein for muscle strength, despite its lower PDCAAS score. 

Interestingly, the pea protein used in these two studies was pure pea protein isolate not combined with protein from other sources to make up for its lower methionine content. It would be interesting to see whether a pea protein combined with brown rice protein, for example, would lead to even better results.

Similarly, when comparing soy protein vs. whey protein in strength training programs, the strength gains are about the same regardless of the protein used. This was the case in young men and women⁸ and in older men⁹.

Hypertrophy (muscle size)

An exercise study comparing the effect of pea vs. whey protein found that both supplements increased the size of the biceps with no significant differences between the groups⁷. Another study similarly found no difference between pea and whey protein supplementation on the thickness of two quadriceps muscles after a CrossFit training program⁶.

Interestingly, a 2024 randomized controlled trial¹⁰ found that muscle protein synthesis (MPS) rates after consuming 30 grams of pea protein were the same compared to 30 grams of milk protein concentrate despite leading to lower levels of essential amino acids in the blood. 

The same effect was seen in older men¹¹ taking an additional 50 grams of pea protein or whey protein above the RDA. Measuring MPS rates isn’t the same as measuring true muscle growth, but it’s a good indicator of the potential for building muscle.

In a 2019 systematic review study¹² comparing the effects of soy vs. whey protein during exercise, four research studies found that whey and soy protein equally increased muscle mass, while two studies showed that whey protein had the advantage.

Overall, both pea protein and soy protein appear to be comparable to whey protein in increasing muscle hypertrophy despite both plant proteins having lower PDCAAS/DIAAS scores than whey. It seems the conventional protein quality score for a protein does not always correlate with its effects on muscle.

RELATED: Vegan Sources of BCAAs

Muscle Recovery

Research on the benefits of pea protein for delayed-onset muscle soreness and recovery after exercise is still scarce, so it’s difficult to say whether pea or soy protein is more helpful.

In one study¹³, participants taking an average of 73 grams of pea protein had moderately reduced markers of muscle damage after working out, but this finding wasn’t statistically significant. It’s possible that differences in the protein content of the participants’ normal diets could have made a difference considering the researchers didn’t collect any dietary data.

The authors of a 2023 systematic review¹⁴ concluded that soy protein helps reduce markers of muscle fatigue like lactate and uric acid and may be especially helpful for the recovery of damaged muscles.

Considering the need for protein to repair damaged muscles, it’s likely pea and soy proteins are both helpful for post-workout muscle recovery as long as you’re meeting your overall protein needs.

Potential risks

Heavy metal levels

A recent study by the Clean Label Project found high levels of heavy metals and BPA, an endocrine disruptor, present in 133 different protein powders. Overall, plant-based protein powders had the worst levels, although some whey products scored poorly as well. 

However, it isn’t clear how dangerous these levels are. One study¹⁵ attempted to determine whether these levels present health risks to humans. Even with up to 3 servings per day, the study found that the levels of heavy metals in these protein powders don’t present a risk to human health.

However, if you’d like to be cautious and reduce your exposure to these heavy metals, choose a brand with lower levels. In the Clean Label Project study, the plant-based products highest in heavy metals were:

• Garden of Life Organic Shake & Meal Replacement Chocolate Cacao Raw Organic Meal
• Vega Sport Plant-Based Vanilla Performance Protein

Additionally, organic products had about 2.5 times higher heavy metals than non-organic varieties, so choosing a non-organic product may reduce your exposure. It’s also theorized that chocolate-flavored powders tend to have more heavy metals because cacao plants can easily absorb them from the soil, so choosing other flavors may also help reduce exposure.

Isn’t soy unhealthy?

Some common concerns about soy include:

Genetic engineering

Most soy grown in the US is genetically engineered to be resistant to the herbicide glyphosate and is most often used as crops to feed livestock and to make soybean oil¹⁶.

While genetically engineered foods are tested for safety before being approved for use in the food supply, studies on the long-term health effects of these foods are lacking.

 If you wish to avoid genetically engineered soy, choose an organic brand of protein powder. Organic soybeans are not allowed to be genetically engineered or sprayed with glyphosate.

Glyphosate

Glyphosate (brand name Roundup) is a weed killer frequently sprayed on Roundup Ready soybeans which have been genetically engineered to survive it. Concerns about the health risks of glyphosate are widespread. 

After evaluating glyphosate for safety, the Environmental Protection Agency (EPA) has stated that glyphosate does not pose a risk to human health, is not carcinogenic, and does not act as an endocrine disruptor. They do state that glyphosate poses a risk¹⁷ to land and aquatic plants and birds. 

However, there doesn’t appear to be a worldwide consensus on this stance. In 2015, the World Health Organization International Agency for Research on Cancer¹⁸ classified glyphosate as being probably carcinogenic to humans.

Given such conflicting information, it makes sense that some people prefer to avoid crops heavily sprayed with glyphosate. To best avoid soy sprayed with glyphosate, choose an organic soy protein powder.

Estrogen content 

Soy contains phytoestrogens (“plant” estrogens), also called isoflavones, which are commonly confused with the estrogen found in humans and animals. While similar in structure to mammalian estrogen, phytoestrogens do not always act the same way in the body. 

In fact, depending on the area of the body, phytoestrogens can either have estrogenic or anti-estrogenic effects. The ability of phytoestrogens to block estrogen in reproductive tissues like the breast and uterus may at least partially explain the association between soy foods and decreased risk of cancer¹⁹ in these areas.

But what about processed soy, as in protein powder? Isn’t that harmful?

The available research does not support this fear. While whole or minimally processed soy foods such as edamame, tempeh, tofu, and soy milk contain more vitamins, minerals, and isoflavones, this does not mean that soy protein powders are unhealthy. They simply serve a different purpose in the diet.

Environmental impact

It’s difficult to find studies directly comparing the environmental impact of peas to that of soy. 

Some negative impacts of soy on the environment include its high water requirement and role in deforestation in the Amazon rainforest. However, the negative impacts of soy come mainly from its role in animal agriculture. A surprising 80% of the world’s soybeans are grown to be fed to animals farmed for meat, which requires a huge amount of land.

But as plant-based proteins, both pea and soy protein have a lower environmental impact²⁰ than animal-based proteins. This is due in part to the large amount of land it takes to raise animals and to grow crops for their feed.

What about organic? The information here is a little conflicting. 

Organic soybeans scored more favorably in one study for global warming potential, non-renewable energy use, and other environmental quality markers than non-organic soybeans, but had a worse impact on land use. In contrast, a study in China found that conventional soybean farming was significantly more energy efficient than organic farming.

How to choose a protein powder

When choosing a protein powder, whether pea protein, soy, or other plant-based protein, here are some things to consider:

• Third-party testing. Protein powders are dietary supplements and therefore aren’t regulated by the FDA. So can you know that your supplement actually contains what it says it does, and if it is safe? It should say on the label whether the supplement has been tested by an independent third-party lab (not by the supplement company itself). Look for NSF-certified manufacturers that also follow Good Manufacturing Processes (GMP).
• Total protein content. Different brands of plant-based protein powder have slightly different amounts of protein, but most contain 18-25 grams per serving.
• Leucine content. The amino acid leucine is essential for stimulating muscle growth, so if your goal with a protein powder is to gain muscle you should choose a protein powder with a high leucine content. Soy is slightly higher in leucine²¹ than pea protein, but if you prefer pea protein you can just use more at a time to get more leucine. And as mentioned above, both proteins have fairly equal effects on muscle strength and hypertrophy.
• Flavor. Finding flavors you love and alternating between them will keep your tastebuds from getting bored, and may inspire you to be more creative in how you consume your protein powder. 
• Texture. Some protein powders are chalkier or grainier than others, so try different brands until you find one you like the best.
• Organic vs. non-organic. This is up to personal preference. If choosing soy protein, you may wish to buy organic to avoid genetically engineered soy. On the other hand, organic protein powders were found to be over 2 times higher in heavy metals than non-organic. 

Main takeaway: Is pea or soy protein better?

It’s up to you! In terms of improving muscle strength and hypertrophy, pea and soy protein don’t seem to be too different from each other despite the lower PDCAAS/DIAAS scores and leucine content of pea and soy protein compared to whey.

If you’re looking to improve your protein intake due to poor appetite, older age, or a hectic schedule with limited time for preparing meals, either would be a great choice. If you find yourself already eating a lot of soy products, you may wish to choose pea protein for more variety, and vice versa.

As plant protein sources, both pea and soy protein have less of an environmental impact than whey or other animal-based proteins. If you prefer to avoid genetically engineered soy sprayed with glyphosate, consider buying organic soy protein.

RELATED: The 16 Best Sources of Protein for a Vegan

The scientific information in this article was accurate at the time of publishing but may change over time as new research becomes available.

References

1. Saarela, Maria. Functional Foods: Concept to Product. Woodhead Publishing. Second Edition, 2011. ISBN 978-1-84569-690-0.
2. Berk, Zeki. Technology of production of edible flours and protein products from soybeans. Chapter 6: Isolated soybean protein (ISP). FAO AGRICULTURAL SERVICES BULLETIN No. 97. Food and Agriculture Organization of the United Nations, Rome 1992.
3. Katz DL, Doughty KN, Geagan K, Jenkins DA, Gardner CD. Perspective: The Public Health Case for Modernizing the Definition of Protein Quality. Adv Nutr. 2019;10(5):755-764. doi:10.1093/advances/nmz023
4. Food and Agriculture Organization of the United Nations. Dietary protein quality evaluation in human nutrition: Report of an FAO Expert Consultation. FAO Food and Nutrition Paper 92. ISSN 0254-4725.
5. BSACI. Pea protein and food allergy labeling. BSACI website. Accessed 1/2/25.
6. Banaszek A, Townsend JR, Bender D, Vantrease WC, Marshall AC, Johnson KD. The Effects of Whey vs. Pea Protein on Physical Adaptations Following 8-Weeks of High-Intensity Functional Training (HIFT): A Pilot Study. Sports (Basel). 2019;7(1):12. Published 2019 Jan 4. doi:10.3390/sports7010012
7. Babault N, Païzis C, Deley G, et al. Pea proteins oral supplementation promotes muscle thickness gains during resistance training: a double-blind, randomized, Placebo-controlled clinical trial vs. Whey protein. J Int Soc Sports Nutr. 2015;12(1):3. Published 2015 Jan 21. doi:10.1186/s12970-014-0064-5
8. Candow DG, Burke NC, Smith-Palmer T, Burke DG. Effect of whey and soy protein supplementation combined with resistance training in young adults. Int J Sport Nutr Exerc Metab. 2006;16(3):233-244. doi:10.1123/ijsnem.16.3.233
9. Haub MD, Wells AM, Tarnopolsky MA, Campbell WW. Effect of protein source on resistive-training-induced changes in body composition and muscle size in older men. Am J Clin Nutr. 2002;76(3):511-517. doi:10.1093/ajcn/76.3.511
10. Pinckaers PJM, Smeets JSJ, Kouw IWK, et al. Post-prandial muscle protein synthesis rates following the ingestion of pea-derived protein do not differ from ingesting an equivalent amount of milk-derived protein in healthy, young males. Eur J Nutr. 2024;63(3):893-904. doi:10.1007/s00394-023-03295-6
11. McKendry J, Lowisz CV, Nanthakumar A, et al. The effects of whey, pea, and collagen protein supplementation beyond the recommended dietary allowance on integrated myofibrillar protein synthetic rates in older males: a randomized controlled trial. Am J Clin Nutr. 2024;120(1):34-46. doi:10.1016/j.ajcnut.2024.05.009
12. Silva, Suelen Maiara Medeiros da; Carminati, Bárbara Cristovão; Santos Junior, Valfredo de Almeida; Lollo, Pablo Christiano Barboza. Comparison of the Effects of Soy Protein and Whey Protein Supplementation during Exercise: a Systematic Review. J. health sci. (Londrina) ; 21(4).
13. Nieman DC, Zwetsloot KA, Simonson AJ, et al. Effects of Whey and Pea Protein Supplementation on Post-Eccentric Exercise Muscle Damage: A Randomized Trial. Nutrients. 2020;12(8):2382. Published 2020 Aug 9. doi:10.3390/nu12082382
14. Zare R, Devrim-Lanpir A, Guazzotti S, et al. Effect of Soy Protein Supplementation on Muscle Adaptations, Metabolic and Antioxidant Status, Hormonal Response, and Exercise Performance of Active Individuals and Athletes: A Systematic Review of Randomised Controlled Trials. Sports Med. 2023;53(12):2417-2446. doi:10.1007/s40279-023-01899-w
15. Bandara SB, Towle KM, Monnot AD. A human health risk assessment of heavy metal ingestion among consumers of protein powder supplements. Toxicol Rep. 2020;7:1255-1262. Published 2020 Aug 21. doi:10.1016/j.toxrep.2020.08.001
16. US Food & Drug Administration. GMO crops, animal food, and beyond. FDA website. Accessed 1/2/25.
17. United States Environmental Protection Agency. Glyphosate. EPA website. Accessed 1/2/25.
18. Guyton KZ, Loomis D, Grosse Y, et al. Carcinogenicity of tetrachlorvinphos, parathion, malathion, diazinon, and glyphosate. Lancet Oncol. 2015;16(5):490-491. doi:10.1016/S1470-2045(15)70134-8
19. Pabich M, Materska M. Biological Effect of Soy Isoflavones in the Prevention of Civilization Diseases. Nutrients. 2019;11(7):1660. Published 2019 Jul 20. doi:10.3390/nu11071660
20. Cellura M, Cusenza MA, Longo S, Luu LQ, Skurk T. Life Cycle Environmental Impacts and Health Effects of Protein-Rich Food as Meat Alternatives: A Review. Sustainability. 2022; 14(2):979. https://doi.org/10.3390/su14020979
21. van Vliet S, Burd NA, van Loon LJ. The Skeletal Muscle Anabolic Response to Plant- versus Animal-Based Protein Consumption. J Nutr. 2015;145(9):1981-1991. doi:10.3945/jn.114.204305