Protein Quality

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What is the best source of protein?

Short Answer

Animal sources of protein are generally considered a better source of protein when compared to plant proteins.[1] With whey protein typically being seen as the "gold standard" of protein supplementation. If you are on a plant based diet, you should get your proteins from a wide variety of sources, especially soy protein.

There is no need to supplement with protein powder if you are able to get your daily protein intake from whole food sources.

Long Answer

There are several ways to determine the quality of protein, however, the most commonly used assessment is the Protein Digestibility-Corrected Amino Acid Score (PDCAAS).[2] Thus protein will be gaged on its ability to provide essential amino acids to an individual. Based on this assessment we have these results (1 is highest & best):

Protein Source PDCAAS[3]
Milk 1.00
Whey 1.00
Casein 1.00
Egg 1.00
Soy 1.00
Beef 0.92
Black Beans 0.75
Peanuts 0.52
Wheat Gluten 0.25

Dairy Proteins

While drinking milk will provide you with a high quality protein, it may not be the most practical protein source due to the other macronutrients in milk. Therefore, the most common milk proteins are actually bi-products of commercial milk production, whey & casein.

Whey protein is typically taken post workout due to being a fast acting protein. This is because of whey protein can be broken down and absorbed faster than most other proteins. This allows for a spike in muscle protein synthesis that will return to baseline within 300 minutes.[4] Casein is a slower digested protein that is typically taken at night to spread out the protein absorption during sleep. Casein causes a spike in muscle protein synthesis that is still elevated beyond 300 minutes.[4]

What type of protein is best post workout? While that can vary based on each individuals schedule, protein timing, & diet, there is a general recommendation/guideline. Studies conducted in 2004 and 2010 ranked different types of protein based on blood plasma levels of essential amino acids (EAAs), branch chain amino acids (BCAAs), & insulin. Their findings in order of most effective to least effective:

Hydrolyzed whey > Non-hydrolyzed whey > Hydrolyzed casein > Non-hydrolyzed casein > Hydrolyzed soy > Non-hydrolyzed soy[5][6]

Note that at dosages higher that 30g of protein, hydrolyzed whey does not increase plasma concentrations of BCAAs more than non-hydrolyzed whey.[2]

Plant Proteins

Plant proteins are consumed by everyone who eats carbohydrates. For example 100g of oatmeal has 12.64g of protein [7] and 200g of white potatoes has 3.36g of protein.[8]

Now not all proteins are created equally. There is an optimal essential amino profile for a protein to be considered complete[9]:

Essential Amino Acid mg/g of Protein
Tryptophan 7
Threonine 27
Isoleucine 25
Leucine 55
Lysine 51
Methionine+Cystine 25
Phenylalanine+Tyrosine 47
Valine 32
Histidine 18

Plants sources such as potatoes, soy, chickpeas, black beans, lupin beans, pistachios, cashews, & cauliflower are all sources of complete proteins, meaning they contain all of the above amino acids.

Plant sources like yellow pea & brown rice are often missing one or more of the essential amino acids listed above. When following a plant-based diet, it is important to obtain protein from a wide variety of source to ensure a complete amino acid profile.


  1. Tang, JE (Sep 2009). "Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men.". J Appl Physiol. 107 (3): 987–992. 
  2. 2.0 2.1 Smith-Ryan, Abbie E.; Antonio, Jose (2013). Sports Nutrition & Performance Enhancing Supplements. Ronkonkoma, NY: Linus Learning. p. 33, 41. ISBN 978-1-60797-339-3. 
  3. Hoffman, Jay (June 2004). "PROTEIN – WHICH IS BEST" (PDF). Journal of Sports Science and Medicine (3): 118–130. 
  4. 4.0 4.1 Dangin, Martial (Mar 2003). "The rate of protein digestion affects protein gain differently during aging in humans". J Physiol. 509 (Pt 2): 635–644. 
  5. Morifuji, Masashi (2010). "Comparison of Different Sources and Degrees of Hydrolysis of Dietary Protein: Effect on Plasma Amino Acids, Dipeptides, and Insulin Responses in Human Subjects". J. Agric. Food Chem. 58 (15): 8788–8797. 
  6. Calbet, JA (2002). "Plasma glucagon and insulin responses depend on the rate of appearance of amino acids after ingestion of different protein solutions in humans.". J Nutr. 132 (8): 2174–82.