Differences between Soy Protein and Whey Protein

Comparison Article

Soy protein is derived from soybeans, a legume. Whey protein is a mixture of proteins isolated from whey, which is the liquid byproduct of cheese manufacturing. Both are commonly sold as dietary supplements in powder form and are considered complete proteins, meaning they contain all nine essential amino acids required by the human body. However, they differ in their specific amino acid profiles, origin, and the presence of other compounds.

Comparison table

Category	Soy protein	Whey protein
Source	Soybeans (plant-based)	Milk (animal-based)
Amino acid profile	Complete protein; higher in arginine and phenylalanine than whey.	Complete protein; higher in branched-chain amino acids (BCAAs) like leucine.
Digestion rate	Generally slower than whey.	Rapidly absorbed.
Protein quality (PDCAAS)	~0.97–1.0	~1.0
Common allergens	| Milk (lactose in some forms)
Other notable compounds	Isoflavones (phytoestrogens)	Lactose, bioactive peptides

Venn diagram comparing Differences between Soy Protein and Whey Protein

Nutritional profile

Both soy and whey proteins provide all essential amino acids, but in different ratios. Whey protein has a higher concentration of branched-chain amino acids (BCAAs)—leucine, isoleucine, and valine—which are involved in muscle protein synthesis. Soy protein contains higher amounts of the amino acids arginine and phenylalanine compared to whey.

Protein quality is often measured using the Protein Digestibility Corrected Amino Acid Score (PDCAAS), where both soy and whey score highly, at or near the maximum value of 1.0, indicating high digestibility and a complete amino acid profile. Whey protein is absorbed by the body more rapidly than soy protein, leading to a faster increase in amino acids in the bloodstream after consumption.

Production

Soy protein supplements are produced from dehulled and defatted soybeans. These soybeans are processed into three main commercial forms: soy flour, concentrates, and isolates. Soy protein isolate, the most refined form, contains 90% or more protein and is made by removing most of the fats and carbohydrates.

Whey protein production begins with pasteurized milk used for cheesemaking. When milk coagulates, it separates into solid curds (used for cheese) and liquid whey. This liquid whey is then filtered to remove fat and lactose. Further processing results in whey concentrate, which contains 70–80% protein, or whey isolate, a more purified form with 90% or higher protein content and minimal lactose.

Health considerations

Soy protein is a plant-based protein and is suitable for vegans and those with dairy allergies. It contains isoflavones, which are a class of phytoestrogens—plant-derived compounds with a chemical structure similar to estrogen. The effects of isoflavones are a subject of scientific research, with studies investigating their potential role in alleviating menopausal symptoms and effects on cardiovascular health.

Whey protein is derived from dairy and is not suitable for individuals following a vegan diet. Whey protein concentrate contains lactose, which can cause digestive issues for people with lactose intolerance. Whey protein isolate undergoes additional processing to remove most of the lactose, making it a more suitable option for those with lactose sensitivity.