What Do You Know About Protein Quality?

January 16, 2023

HAVE MORE PROTEIN! This is something athletes have heard all their life. Athletes can easily meet their recommendations for daily protein intake. However, in order to optimize the training effect, it is essential to understand the amount of protein required in each meal but also the quality of protein consumed. But what is exactly meant by quality protein?

What Do You Mean By Protein Quality?

The magnitude and speed with which we are able to make new proteins following protein consumption are taken into consideration when determining protein quality. The essential amino acids content and digestion/ absorption of a given protein source are included in the same. 

What Is The Difference Between High-Quality Protein and Low-Quality Protein?

High quality proteins are those that:

1). Provide all 9 EAAs in sufficient amounts :Essential amino acids stimulate protein synthesis.

2). Are abundant in leucine : An EAA that acts as both, a signal for protein synthesis to be on and as a building block for the formation of skeletal muscle protein.

3). Are easily digested and absorbed into circulation : After ingestion, proteins must be digested into amino acids, which are then absorbed and eventually delivered to skeletal muscle for protein synthesis.

But How Exactly Can We Assess Protein Quality?

The easiest and cheapest way to learn about the protein quality is to study its amino acid composition. Although termed “easy”, most food labels only report total protein and not the EAA value. Protein sources with a more favourable EAA and leucine content are considered more effective for synthesis of protein. Although the exact numbers may vary, the threshold for EAAs and leucine required to optimally stimulate protein synthesis is ~10 g and ~3 g respectively. (“https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/essential-amino-acid”) 

Protein Quality Scoring System.

The next method combines amino acid composition with digestibility of the protein. Protein quality can be ‘scored’ using 2 techniques such as the PDCAAS (protein digestibility-corrected amino acid score) and DIAAS (digestible indispensable amino acid score). Both these techniques compare the digestibility of a dietary protein against a reference protein to determine a score of protein quality; a higher score is equal to a higher quality protein.


Although an outdated method, PDCAAS evaluates the quality of a protein based on both the amino acids and their ability to digest. This method has been adopted by FAO/ WHO as a preferred method for the measurement of the protein value in humans. The highest PDCAAS value is 1.0 , indicating that the protein will provide 100% of the amino acids required in the diet. (or more) Whey,soy,casein and egg have a score of 1.0, indicating they are good quality protein.

The formula to get PDCAAS

PDCAAS % = [mg of limiting amino acid in 1 g test protein / mg of same amino acid in 1 g reference protein x (True digestibility %)]


This newer method takes into account the digestibility of amino acids at the end of the small intestine,in  the ileum, providing a more precise measurement of the body's absorption of amino acids and the protein's contribution to the human requirement for amino acids. Assessing individual EAA is considered a better reflection of the amino acid absorption. However, there are limited number of proteins assessed for quality using the DIAAS

The formula to get DIAAS 

DIAAS % = 100 x [(mg of digestible dietary indispensable amino acid in 1 g of the dietary protein) / (mg of the same dietary indispensable amino acid in 1g of the reference protein)]

The other methods for assessing the protein quality include blood amino acid concentration, muscle protein synthesis and anabolic signalling. 

The best method for determining protein quality is to use a combination of all evaluations. However, for those who want to maximize the effects of protein on protein synthesis, PDCAAS and DIAAS scores probably provide less information. Unfortunately, athletes do not have access to good tools. As a result, it is suggested that athletes look for the EAA and leucine content of their food at the very least in order to determine the quality of their protein sources.

Meryn Aricatt
Sports Nutritionist

Meryn, with a Master’s in Sports Science, is a pivotal member of the 'Evolve' vertical at iThrive, specializing in sports nutrition. She operates under the philosophy that "Nutrition can elevate a good athlete to greatness." Beyond her role at iThrive, Meryn imparts her expertise as an instructor for both the Functional Sports Nutrition and the Functional Nutrition Certification courses at iThrive Academy. She is passionate about helping sportspersons enhance their performance, ensuring they lead healthier, happier lives through the power of sports nutrition.

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