Is Soy Protein Bioavailability Better Than Pea Protein?

November 24, 2025 •

4 min read

While soy protein has traditionally earned a perfect Protein Digestibility Corrected Amino Acid Score (PDCAAS), suggesting superior bioavailability, newer metrics like the Digestible Indispensable Amino Acid Score (DIAAS) provide a more nuanced picture when questioning if is soy protein bioavailability better than pea protein. The answer depends heavily on the specific processing and form of the protein.

Quick Summary

This article provides an in-depth comparison of soy and pea proteins, analyzing how digestibility scores and processing methods affect their bioavailability. It examines amino acid profiles, anti-nutrient impacts, and practical differences for consumers deciding between these popular plant-based sources.

Key Points

Soy Generally Edges Pea in Scores: While both are excellent plant proteins, soy protein often receives slightly higher bioavailability scores on metrics like PDCAAS (1.0 vs. ~0.9 for isolate) and DIAAS.
Processing is Key: The bioavailability of both proteins is significantly enhanced through processing into isolates, which removes anti-nutrients like phytates and improves digestibility.
Amino Acid Profiles Differ: Soy provides a complete and well-balanced amino acid profile, while pea is particularly rich in arginine and BCAAs like leucine, but is slightly lower in methionine.
Consider Allergies and Digestion: Pea protein is hypoallergenic and generally considered easier on the stomach, making it a safer option for those with soy allergies or sensitivities.
Small Difference for Most: For the average person with a varied diet, the practical difference in bioavailability between high-quality soy and pea protein isolates is often minimal.
Complementary is Optimal: For pea protein users, combining it with other plant sources like rice protein can effectively compensate for the lower methionine content, ensuring a complete amino acid intake.

Understanding Protein Bioavailability

Protein bioavailability refers to the proportion of a protein that is absorbed and utilized by the body for various functions, including muscle repair and growth. The quality of a protein is determined by both its amino acid profile and its digestibility. For decades, the primary method for evaluating protein quality was the Protein Digestibility Corrected Amino Acid Score (PDCAAS), but it has since been challenged and improved upon by the Digestible Indispensable Amino Acid Score (DIAAS).

The Old Standard: PDCAAS

PDCAAS measures protein quality by correcting for fecal digestibility and comparing the amino acid profile to an ideal human requirement. Under this system, soy protein isolate is typically given a perfect score of 1.0, similar to animal proteins like whey and egg, indicating it is a complete and highly digestible protein. Pea protein isolate, in comparison, usually receives a slightly lower PDCAAS score, often around 0.9. However, the PDCAAS has several limitations, including the truncation of scores at 1.0, which obscures the higher quality of some proteins, and its reliance on fecal digestibility, which can overestimate how much amino acid is actually absorbed by the small intestine.

The Newer Metric: DIAAS

Recognizing the limitations of PDCAAS, the Food and Agriculture Organization of the United Nations (FAO) recommended the adoption of DIAAS in 2013. DIAAS offers a more accurate measure of protein quality by using ileal digestibility, which measures absorption at the end of the small intestine where most amino acid absorption occurs. Unlike PDCAAS, DIAAS scores are not truncated and evaluate the digestibility of each individual indispensable amino acid. In studies using DIAAS, animal proteins like milk generally outperform most plant proteins. For plant-based options, soy protein isolate often scores higher than pea protein concentrate, though specific values can vary based on processing. One study showed a DIAAS of 0.87 for soy protein isolate compared to 0.69 for pea protein concentrate in adults.

Soy Protein vs. Pea Protein: A Side-by-Side Comparison


Feature	Soy Protein	Pea Protein
Completeness	Complete protein, containing all nine essential amino acids.	Complete protein, especially when in isolate form.
Limiting Amino Acid	Methionine and cysteine are slightly lower compared to animal sources, but not typically a limiting factor when consumed as an isolate.	Methionine is the main limiting amino acid, but can be complemented by other proteins like rice protein.
High-Concentration Amino Acids	Good source of glutamine and arginine.	High in branched-chain amino acids (BCAAs) like leucine, as well as arginine.
PDCAAS Score	1.0 (isolate form).	~0.9 (isolate form).
DIAAS Score (Adults)	~0.87 (isolate form, example).	~0.69 (concentrate form, example).
Anti-nutrients	Contains phytates and trypsin inhibitors in raw form, which are largely removed during processing.	Contains some anti-nutrients like phytic acid, minimized in isolate form.
Digestibility & Allergies	High digestibility, but is one of the most common food allergens.	High digestibility and hypoallergenic, making it gentle on the stomach and suitable for many people with food sensitivities.

What Impacts Bioavailability?

Multiple factors influence how effectively your body can absorb and utilize protein. For plant-based proteins like soy and pea, these factors are particularly important to consider.

Processing Methods: The manufacturing process plays a crucial role. Techniques like heat treatment, fermentation, and protein isolation break down anti-nutrients and cellular barriers, dramatically improving digestibility. A soy or pea protein isolate will always have higher bioavailability than its less-processed concentrate or flour form. Fermentation, in particular, has been shown to boost the nutritional value of soy.
Anti-Nutrients: Plant-based proteins contain compounds like phytates and tannins that can inhibit digestive enzymes and bind to minerals, reducing overall bioavailability. The effectiveness of processing in removing these compounds directly impacts the final product's quality.
Food Matrix: The other components of a meal, known as the food matrix, can affect protein absorption. For instance, consuming pea protein with a source of methionine, such as rice protein, can create a more balanced amino acid profile and enhance overall utilization.
Amino Acid Profile: The proportion of essential amino acids relative to human requirements is a key determinant of quality. Soy's profile is complete, while pea's is often deficient in methionine, requiring supplementation from other food sources.

The Practical Takeaway: Which Should You Choose?

For the average person, the slight difference in bioavailability scores between high-quality soy and pea protein isolates is often negligible. Your final choice should be based on individual dietary needs, preferences, and sensitivities. If you have a soy allergy or sensitive digestive system, pea protein is the clear winner due to its hypoallergenic nature. If you're looking to maximize specific amino acids for muscle synthesis, pea's higher BCAA content may be an attractive feature, though both are proven effective for muscle growth. For those not avoiding soy, its complete profile can offer excellent and well-rounded nutritional support.

In conclusion, while processing and metrics like DIAAS reveal that soy protein may be more bioavailable than pea protein, the difference is not a deal-breaker for most. The key is to select high-quality isolate forms and, for pea protein, to ensure a complementary diet to cover all amino acid bases.

Conclusion

The question of whether is soy protein bioavailability better than pea protein is complex, with traditional PDCAAS scores favoring soy, while newer DIAAS metrics provide a more detailed, though still variable, picture. While soy isolate typically boasts a slightly higher absorption rate, modern processing has improved pea protein significantly. For most individuals, especially with a varied diet, the marginal difference in bioavailability is less important than other factors like potential allergens, specific amino acid needs, and digestive comfort. In the end, both represent high-quality, effective plant-based protein options, and the 'better' choice is a personal one rooted in individual health and fitness goals. FAO/WHO Expert Consultation on Protein Quality Assessment

Frequently Asked Questions

Yes, soy protein isolate has a perfect PDCAAS of 1.0, similar to animal proteins. Pea protein isolate typically receives a slightly lower PDCAAS score, often around 0.9.

DIAAS measures protein quality more accurately using ileal digestibility. Studies using DIAAS have shown higher scores for soy protein isolate compared to pea protein concentrate, though values can vary.

Soy protein has a complete and balanced amino acid profile. Pea protein is particularly rich in BCAAs like leucine and arginine but is slightly lower in the sulfur-containing amino acid, methionine.

Yes, especially in its isolated form, pea protein contains all nine essential amino acids necessary for the body's functions.

Yes, processing methods such as heat treatment, fermentation, and isolation significantly enhance the digestibility and bioavailability of both soy and pea protein by reducing anti-nutrients.

Pea protein is hypoallergenic and generally considered easy to digest. This makes it a preferred option for individuals with allergies or sensitivities to common allergens like soy or dairy.

Both proteins are effective for muscle growth. Some studies suggest pea protein, with its higher BCAA content, might have a slight edge in stimulating muscle protein synthesis, but the overall difference is often small.

It is not necessary, but combining pea protein with another plant source like rice protein can complement its amino acid profile, particularly for methionine, ensuring a complete intake of all essential amino acids.