How to measure protein quality? And why is it important for your muscle growth?

Protein synthesis is the process our body uses to build and repair muscles.

7 min read

March 5, 2023

Protein is important for building muscles and making them stronger. Some proteins are better for your body than others. To decide how good a protein is, we look at three things: how much essential amino acids it has, how much leucine it has, and how easy it is for your body to use. Essential amino acids and leucine are special types of amino acids that your body needs to build muscles. Bioavailability is how easy it is for your body to use the protein. A protein with a lot of essential amino acids, leucine, and that is easy for your body to use is considered a high quality protein. It can help your body build and repair muscles better.

There are a few different ways to figure out how good a protein is. One way is to look at its amino acid composition. This means checking how much of each type of amino acid is in the protein. Some proteins are better because they have more essential amino acids and leucine. We also need to make sure the protein is easy for our bodies to digest and use. To do this, we can use scoring systems like the protein digestibility-corrected amino acid score (PDCAAS) and the digestible indispensable amino acid score (DIAAS). These systems compare the protein to a reference protein and give it a score based on how easy it is to digest. The DIAAS is better because it looks at how well our body can use each essential amino acid, rather than just the protein as a whole.

There are a few other ways to figure out how good a protein is. One way is to look at how much nitrogen is in our body. Nitrogen is a part of proteins and we can use it to figure out how much protein our body is using. Another way is to use a special drink that helps us measure protein synthesis. Protein synthesis is the process our body uses to build and repair muscles. By looking at how much protein our body is using, we can tell how good a protein is for building and repairing muscles.

It's important to remember that everyone's body is different and what works for one person might not work for another. It's also important to make sure we are getting enough protein to support our bodies, but not too much. Eating a variety of protein sources can help us make sure we are getting all the essential amino acids and other nutrients we need.

Here are some practical recommendations for increasing protein synthesis based on the information in the text:

Make sure you're getting enough essential amino acids (EAAs) and leucine in your diet. Aim for at least 10 grams of EAAs and 3 grams of leucine per day.
Choose protein sources that are high in EAAs and leucine. Some good options include meat, poultry, fish, eggs, dairy products, and plant-based proteins like beans, lentils, and tofu.
Consider using a protein supplement, such as a protein powder or protein bar, to help increase your protein intake. Just make sure to read the label and choose a product that is high in EAAs and leucine.
Use a protein quality assessment method, such as the protein digestibility-corrected amino acid score (PDCAAS) or the digestible indispensable amino acid score (DIAAS), to help identify high-quality protein sources.
Incorporate a variety of protein sources into your diet to ensure that you're getting a range of different amino acids. This will help optimize protein synthesis and support overall health.

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Protein synthesis is the foundation of many physical adaptations, including increased muscle mass and strength. And while the quality of a protein source plays a crucial role in boosting protein synthesis, determining protein quality can be challenging. There are several methods for assessing protein quality, ranging from simple and inexpensive to more complex and costly. Here, we'll explore these methods and how they can help us identify high-quality protein sources.

Evaluate protein quality

‍One of the simplest ways to evaluate protein quality is to examine its amino acid composition, specifically the levels of essential amino acids (EAAs) and leucine. While the exact amounts may vary, research suggests that getting at least 10 grams of EAAs and 3 grams of leucine can optimize protein synthesis (1, 2). However, it's important to note that food labels often only list total protein and finding detailed amino acid information can be difficult.

PDCAAS & DIAAS

‍There are also techniques that score protein quality based on both amino acid composition and digestibility, such as the protein digestibility-corrected amino acid score (PDCAAS) and the digestible indispensable amino acid score (DIAAS). These methods compare the digestibility of a given protein to a reference protein and assign a score based on the result. A higher score indicates a higher-quality protein.

The PDCAAS is an older method that has been largely replaced by the DIAAS. One issue with the PDCAAS is that scores are capped at 1.00 (or 100%), meaning that it's unable to distinguish between high-quality proteins that exceed the reference protein (egg protein). In addition, the PDCAAS estimates protein digestibility crudely using feces, which may not accurately reflect amino acid absorption.

On the other hand, the DIAAS compares a dietary protein to a theoretical protein based on current EAA requirements and assesses the digestion of individual EAAs in the ileum (the end of the small intestine). This makes it a more reliable indicator of amino acid absorption and allows for the detection of higher-quality proteins (those with a score ≥1.00). However, it should be noted that the number of proteins assessed using the DIAAS is limited.

Conclusion

‍In summary, both the PDCAAS and DIAAS are methods for scoring protein quality based on digestibility. A higher score indicates a higher-quality protein that may be more effective at increasing protein synthesis. While the PDCAAS is a simpler, cheaper option, the DIAAS is the preferred method due to its more accurate assessment of amino acid digestion and ability to detect higher-quality proteins.

Additional information

Protein quality is a key factor in determining the effectiveness of a protein source in increasing protein synthesis and supporting physical adaptations such as increased muscle mass and strength. While protein quality scoring systems, like the PDCAAS and DIAAS, are based on minimum requirements for essential amino acids (EAAs), there may be additional benefits to consuming protein sources with higher levels of EAAs, particularly leucine, which has been shown to be a key regulator of protein synthesis.
One method for evaluating protein quality is through the measurement of amino acid concentrations in the blood after absorption, known as "feed and bleed" studies. Protein sources with a rapid and greater elevation in blood amino acids are considered higher quality, as they provide a greater availability of amino acids for muscle protein synthesis. On the other hand, sources with a slower and lower rise in blood amino acids are considered lower quality. While these studies provide insight into protein digestion and circulation, they do not directly measure protein synthesis in muscle tissue.
The most relevant and reliable method for assessing protein quality is the measurement of protein synthesis in human tissue, using techniques such as stable isotope tracer methods and the detection of mTORC1 signaling protein expression. These methods allow for the evaluation of the incorporation of amino acids into muscle proteins and the regulation of protein synthesis. However, these techniques are complex and invasive, limiting the number of protein sources that can be investigated.

Conclusion of extra material

‍In summary, there are various methods for assessing protein quality, ranging from simple and inexpensive amino acid composition analysis to more complex and costly techniques involving the measurement of protein synthesis in human tissue. While minimum requirements for EAAs are important for determining protein quality, there may be additional benefits to consuming protein sources with higher levels of EAAs and leucine, particularly for supporting muscle protein synthesis and physical adaptations.

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