From the Guidelines
Soy is considered a complete protein source as it contains all of the essential amino acids in sufficient quantities to support human life. According to a study published in the journal Circulation 1, soy protein contains all of the essential amino acids, making it a complete protein. This is due to its unique composition of amino acids, particularly its high content of lysine, which is often lacking in other plant proteins. Some key points to consider when evaluating soy as a protein source include:
- Soy flour is 50% protein and contains 5% fiber
- Soy concentrate is 65% to 70% protein and contains a small amount of fiber
- ISP is 90% protein with no fiber To incorporate soy as a complete protein source in your diet, consider consuming a variety of soy products like tofu, tempeh, edamame, soy milk, or soy-based meat alternatives. Aim for 2-3 servings per day to meet protein needs, especially if following a vegetarian or vegan diet. As noted in the study 1, several components associated with soy protein have been implicated in its health benefits, including trypsin inhibitors, phytic acid, saponins, isoflavones, and fiber.
From the Research
Definition of a Complete Protein Source
A complete protein source is one that contains all the essential amino acids necessary for human nutrition.
Soy as a Complete Protein Source
- Soy protein is considered a complete protein source because it contains ample amounts of all the essential amino acids, as stated in 2 and 3.
- Studies have shown that soy protein has a nutritional value roughly equivalent to that of animal protein of high biological value, as mentioned in 2.
- However, some research suggests that soy protein may be deficient in the essential amino acid methionine, as noted in 4.
Comparison with Other Protein Sources
- Animal sources of protein are considered complete sources of protein because they contain all essential amino acids, as stated in 5.
- Plant proteins, on the other hand, are often classified as incomplete because they lack some essential amino acids, as mentioned in 5.
- Soy protein is unique among plant-based proteins because it is a complete protein source, as noted in 2 and 3.
Nutritional Value of Soy Protein
- Soy protein has been shown to have numerous health benefits, including lowering cholesterol and improving insulin resistance, as mentioned in 2 and 3.
- The protein digestibility-corrected amino acid score (PDCAAS) is a measure of a protein's ability to provide adequate levels of essential amino acids for human needs, as discussed in 6.
- Soy protein isolates and concentrates have been found to have high PDCAAS values, indicating their high quality as a protein source, as noted in 6.