Selecting A Source of Protein

Dietary protein is well known for its positive effects on health, including weight management, bone health, cardiovascular health, blood glucose control and for the maintenance of lean muscle mass.  More recently, dietary protein has been shown to favorably influence appetite and muscle protein synthesis. Given these important roles, it is important to select high-quality sources of protein in the diet. Protein sources are assessed on their ability to meet the nitrogen and amino acid demands of the body and the most widely used assessment of protein quality is the “Protein Digestibility-Corrected Amino Acid Score or PDCAAS. The PDCAAS was developed by the food and agriculture organization and the world health organization, two very well respected organizations in their own right. The PDCAAS is used to assess the quality of different protein sources, considered by many to be the gold-standard assessment of protein quality.  A PDCAAS score of 100 represents a protein source that, after digestion, provides 100 percent of your bodies required amino acids.

Recall that proteins are made up of chains of individual amino acids, the building blocks. A common mistake many people make is believing Protein, is a stand-alone molecule. Also recall, that amino acids come in two types, essential amino acids and non-essential amino acids. There are the 9 amino acids our body cannot make and include: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.  When it comes to muscle growth and repair, branch chain amino acids are thought to be particularly important. However, on their own, branch chain amino acids have not been shown to improve muscle growth and repair and in-fact some research shows ingesting branch chain amino acids in isolation can be detrimental. Research has also shown, proteins high in leucine have a greater effect on muscle growth than proteins with lower amounts of leucine.  Finally, the selection of protein should also take into consideration the overall percentage of protein per serve. For example if we compare the amount of protein in a serving of milk which is approximately 13% against the amount of protein in a serving of beef which is 25%, despite both containing all of the essential amino acids and having high PDCAA scores, you would need to consume almost two times the amount of servings of milk to obtain the same amount of protein.  So in summary, choosing the best source of protein requires the comparison of 3 important factors:

  1. The PDCAAS score – the closer to 100 the better
  2. The % of protein per serve – again the higher the % protein, the better
  3. The composition – does the source of protein contain all of the essential amino acids, if it doesn’t , this source of protein will need to be combined with another to complete the number of required essential amino acids to support optimal health.  If your goal is to build muscle mass choose protein sources that are high in leucine.

Protein Selection Matrix


Protein Source PDCAAS Score % Protein Contains all the essential amino acids
Milk 100 3% Y
Egg 100 13% Y
Cheese 100 25% Y
Soy protein concentrate 99 85% Y
Tofu 93 8% N
Beef 92 26% Y
Fish 90 25% Y
Black beans 58 21% N
Vegetables 73 1-3% N
Hemp seed 66 37% Y
Peanuts 52 26% N



Yang, H., Guérin-Deremaux, L., Zhou, L., Fratus, A., Wils, D., Zhang, C., … & Miller, L. E. (2012). Evaluation of nutritional quality of a novel pea protein. Agro Food Industry Hi-Tech, 23(8), 10.

Schaafsma, G. (2000). The protein digestibility–corrected amino acid score. The Journal of nutrition, 130(7), 1865S-1867S.


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