Determining Protein Quality

Protein quality is typically defined as a protein’s capacity to supply all essential amino acids (EAAs) to an individual.  There is a total of 9 EAAs which cannot be produced by the body and can only be obtained through eating whole food sources or supplementation. As a whole, research has shown that dairy based (i.e. whey) and animal proteins contain the highest percentage of EAAs which results in greater hypertrophy and muscle protein synthesis following resistance training than a vegetarian-matched control (i.e. plant proteins), which typically contains less total proteins and EAAs on a gram for gram basis.

Of the 9 EAAs, three are unique in their ability for their roles in muscle protein synthesis, neural function, and blood glucose and insulin regulation. These are commonly referred to as the Branched Chain Amino Acids (BCAAs) which are leucine, iso-leucine, and valine. Of particular importance is the BCAA leucine which can stimulate MPS by itself; however, when combined with the other two BCAAs it is increased to a greater extent.  Ideally, if a protein supplement is to be consumed, choose one that contains 2-3 grams of naturally occurring leucine as this will optimize the muscle protein synthesis response.

Please view that chart below for an EAA comparison of various protein sources per 100 grams:

EAA Hydrolysate Whey Isolate Whey Concentrate** Egg Casein Soy
Isoleucine* 5.5 6.1 5.8 5.7 4.7 4.9
Leucine* 14.2 12.2 10.8 8.4 8.9 8.2
Lysine 10.2 10.2 9.6 6.8 7.6 6.3
Methionine 2.4 3.3 1.9 3.4 3 1.3
Phenylalanine 3.8 3 3.3 5.8 5.1 5.2
Threonine 5.5 6.8 7.2 4.6 4.4 3.8
Tryptophan 2.3 1.8 2.1 1.2 1.2 1.3
Valine* 5.9 5.9 5.8 6.4 5.9 5
Total BCAAs 25.6 24.2 22.4 20.4 19.5 18.1
Total EAAs 49.8 49.2 46.5 42.3 40.7 36

** 80% Whey Protein Concentrate

Bottom Line on Protein Quality

Dairy and animal based proteins are superior to plant-based proteins as determined by their respective EAA values and their ability to stimulate muscle protein synthesis.  If an individual follows a vegetarian/vegan diet and supplements with plant based protein powders, it is recommended to add additional leucine (to achieve 2-3 grams of leucine per serving).

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