Protein Quality – The New Measurement Standard That Has Corporations Up In Arms

Readers of this blog know their macronutrients –  carbs, fats, and proteins. You know the difference between simple and complex carbs and the various types of fats. Maybe you even know the difference between short, medium, and long chain fatty acids. However, when it comes to protein, most people don’t look beyond how many grams a day they eat, let alone the quality of their protein. Keep reading to learn about the importance of protein quality.

Protein Basics

What is protein? It is a macronutrient made up from multiple amino acids. Protein is vital for humans. It is a building block for the body which is used for muscle, skin, hair, nails, tendons, etc. Protein can also be converted to glucose to be used for energy (in a process called gluconeogenesis).

Protein is either animal or plant based. Animal based protein sources include muscle meats, organ meats, diary products, and eggs. Plant based protein sources include nuts, seeds, tubers, legumes, lentils, and grains.

Amino Acids – building blocks of building blocks

As mentioned above, protein is vital for life. In particular, the body requires three types of protein molecules,  known as Amino Acids, in order to finction properly. Some amino acids are essential to the body – thereby called essential amino acids (EAA’s), which the body must receive through diet. Non-essential amino acids are made by the body from essential amino acids or protein we eat.. Lastly, conditional amino acids are needed during times of illness, growth, etc. In these situations, the body demands more of these amino acids than can be produced and therefore we must consume them in our diet.  Examples of conditional amino acids include arginine, cysteine, glycine & glutamine.

Researchers have found over 200 amino acids. Of these, 20 are ‘common’  amino acids (mmeaning the body can make protein from them), and 1o are EAA’s. Amino acids act as precursors to neurotransmitters in the brain, and play a crucial role in the bodies metabolic processes and immune function. This is why I recommend supplementing with a quality essential amino acid, such as Thorne Amino Complex

Protein Quality

20 amino acids. A life basis.

Complete Protein

For a protein to be ‘complete’ it must include an adequate proportion of all the essential amino acids. Think back to your Tetris days as a kid – a row required a block in every spot for it to be ‘complete’, and you couldn’t carry blocks over to the empty slots in another row. This is similar for protein. If you have an abundance of 6 EAA’s, but lack other amino acids, you’re stuck with an incomplete protein. The missing amino acids lead to an imbalance, which can lead to all sorts of problems, such as poor skin quality, growth & developmental issues, fatigue & poor concentration.

So what’s the best way to stay in balance? Consume complete proteins. Complete protein sources are generally derived from animal foods such as meat, fish, poultry, and eggs. Plant sources of complete proteins include chickpeas, pumpkin seeds, quinoa, cauliflower, and soy.

However, plant based protein quantity is usually much lower than the animal based protein. That said, don’t think that incomplete proteins are not worth eating. Your body can store the amino acids found in incomplete proteins. If you do eat some peanuts for example, the body will store the amino acids that are present in the food. Ask any vegan, they understand the importance of balanced amino acids and avoid imbalances by eating a variety of protein sources.

Determining Protein Quality

Even complete plant based proteins may not be the best source of protein and can replace meat. 3 key factors are used in determining protein quality:

  1. Amino Acid Profile – how much of each amino acid (EAA, non-essential, conditional) are in the particular food
  2. Absorption – how well are the amino acids absorbed by the body. If the body cannot digest, absorb, and utilize the amino acids in proteins, including complete proteins, the protein is effectively useless. As an example, eggs are a complete protein source but cooked eggs are better digested than raw eggs. In addition, many plant-based proteins are not absorbed well by the human gut, whether cooked or raw, because of substances such as phytic acid. These ‘anti-nutrients’ are commonly found in grains, beans, seeds and nuts, and have been shown to block nutrient absorption. Chris Kresser covers anti-nutrients in detail in his post “Another reason you shouldn’t go nuts on nuts.”
  3. Toxicity – how the body tolerates protein sources. Some protein sources are not tolerated well by the human body and may cause allergic or immune problems.

Measuring Protein Quality

There are numerous ways you can measure protein quality. Let us take a look at each method.

  • Biological Value

This primarily looks at the amino acid makeup of the source. Popular in bodybuilding circles.  Biological Values (BV) are calculated as a percentage and measure the nitrogen uptake of the protein versus the nitrogen excreted. A figure of 100 means that all the protein provided has been retained by the body. Eggs have a value of 94 Cows milk 91, Beef 74, Soy 72 and Wheat is 64 (a higher number means the protein will be more easily used than a low BV value). BV values cannot be higher than 100.

There are a lot of criticisms with BV however BV is measured under very strict scientific settings not everyday conditions. Also it BV does not look at factors that may influence the proteins absorption in the body. Finally, there is a lot of variability in the results of BV testing.

  • Protein Efficiency Ratio

This looks at weight gain of a rat when fed various types of protein. Obviously there are many limitations here and this regarded as an older measurement tool.

  • Net Protein Utilization

NPU looks at the ratio of amino acids converted to proteins from the amino acids consumed. It works by looking at how much nitrogen is absorbed.  The range runs from 0 to 1.0. Eggs and Milk are 1.0 on this scale.  It has limitations in effectiveness as Biological Value.

  • Protein Digestibility Corrected Amino Acid Score (PDCAAS)

PDCAAS has become the standard for evaluating protein quality. Not only does it look at the amino acid content of the food, but also the amino acid requirement by humans AND their ability to digest these aminos. Finally, PDCAAS factors in how much of the protein is excreted as waste in poop. This extra step is why this test is commonly used today.

Using this test we see the following scores for common foods (higher is better):

Milk protein (casein & whey) – 1.0

Egg White – 1.0

Soy – 1.0

Beef – 0.92

Chickpeas – 0.78

Kidney Beans – 0.68

Peanuts – 0.52

Wheat – 0.40

Wheat gluten – 0.25

However, there are still problems with this test. Firstly, any scores above 1.0 are ’rounded down’ to 1.0, as ” as scores above 1.0 are considered to indicate the protein contains essential amino acids in excess of the human requirements” (1). Which I think is a bit silly, its almost like saying ‘thats enough, you don’t need to worry about anything beyond that level’. Also, the amino acid and nutrient makeup between milk & soy is going to be very different, so to have them with identical ratings seems a bit absurd.

PDCAAS also doesn’t identify where the protein has been digested. The body may not use the broken down protein but bacteria in the intestines may consume the amino acids.PDCAAS will see this as being utilized by the body no matter how it was ‘consumed’.

Finally, PDCAAS doesn’t look at anti-nutrients and any amino acids that are blocked due to these anti-nutrient content from food. This may lead to higher endogenous amino acid losses, meaning PDCAAS may lead to inaccurately higher scores (3). For followers of the paleo/primal movement this is the key issue with PDCAAS.


New kid on the block – Digestible Indispensable Amino Acid Score (DIAAS)

DIAAS is a relatively new way of testing protein quality. DIAAS looks at the amino acid digestibility at the end of the small intestine (vs the fecal matter as per the PDCAAS test). Meaning the data is a lot more accurate at seeing what amino acids are absorbed and utilised by the body.

Along with this DIAAS values are not limited to 1.00. Meaning all those people out there that aren’t satisfied with ‘good’ can now see what the best of the best is.

Also, DIAAS uses pigs and humans to perform the test unlike the PDCAAS test which generally uses rats.

The DIAAS method is starting to gain traction as being a lot more reliable than PDCAAS. The UN is pushing it, and an expert from the Food & Agriculture Organization recommended that “the Digestible Indispensable Amino Acid Score (DIAAS) replace the Protein Digestibility Corrected Amino Acid Score (PDCAAS) as the preferred method of measuring protein quality.” (5)

If you are interested in the science behind the test I recommend looking at this presentation ‘Assessing Protein Quality’.

DIAAS table of foods:

Now that we have found the best way to measure protein quality via the DIAAS method, lets look at some food sources and their protein quality score (using the DIAAS Method. Again, higher equals better quality).

Whole Milk – 1.32
Whey Protein Isolate – 1.25
Whey Protein Concentrate – 1.1
Beef – 1.1
Soy Isolate – 1.0
Pea Isolate – 0.95
Chickpeas – 0.66
Peas – 0.64
Barley – 0.58
Kidney Beans – 0.51
Wheat – 0.4

References – 2, 4, 6,


Protein Quality - Whey

The ‘whey’ to go?! Whey Powder, behind whole milk, appears to be the best food source in terms of protein quality


So as you can see from the above table, animal protein remains the clear winner when it comes to protein quality. By using the DIAAS scoring system we can now see the ‘best of the best’. There is limited data available at the time this blog post was produced, but hopefully the DIAAS method gains traction and we start seeing more studies on various food sources to complete the picture. Not only will a more accurate measurement tool benefit us ‘health nuts’ but food manufacturers and health officials will be able to make more informed and reliable decisions.

My takeaway – make animal food a priority in your diet. Eat plenty of muscle meats, organs, diary, eggs, fish etc. Follow the Superhuman Food Pyramid and you can’t go wrong! Ensure that your protein is coming from these sources and not from less superior plant based foods.

If you are a vegan or vegetarian, spend some time researching the amino acid makeup of the foods you are eating, and also look into anti-nutrients and how you can minimise those (soaking, fermenting, sprouting etc). A great article was put together by Ben Greenfield titled ‘How To Be Extremely Active And Eat A Plant-Based Diet Without Destroying Your Body‘ I recommend all vegans and vegetarians check that out, especially if you’re an athlete.

For the bodybuilders and athletes out there, I’m sure this post just reinforces what you were already doing. However, don’t go overboard just because whole milk  is top of the DIAAS list (I recommend raw, unhomogenized milk from grass fed hormone free cows by the way) doesn’t mean that this should be your sole source of protein. Everything in moderation and that includes protein itself – but I’ll save that for another blog post.

What Do I Do?

I personally eat a primal/low inflammation/superhuman food type diet. Plenty of meats, fish, organ meats, eggs and diary. When it comes to whey powder, I actually use a goat milk powder called Deep 30 by Mt Capra. This is because goat milk has been shown to be absorbed even better than cows milk. Hopefully one day someone will do a comparison test between cows milk whey and goats milk whey using the DIAAS method. If you’d be interested in learning the outcome of such a test be sure to subscribe to my newsletter, follow Alex Fergus Coaching on Facebook or keep an eye on my blog and I’ll be sure to share any new findings!


The Future

Despite WHO supporting the new DIAAS method for testing protein quality, it appears that there is a lot of resistance in making the switch. Why? Obviously there would be great expense involved, new testing procedures, new health policies & recommendations, marketing campaigns informing the consumers of the change etc. However, the biggest hurdle for change is due to money. The grain industry is huge, there are a lot of powerful and influential people that would not be too keen on seeing this new method becoming the standard. Dairy companies on the other hand are pushing for change. In researching this article I spoke to a research scientist at New Zealand’s largest Dairy company Fonterra. When questioned about the future of DIAAS, he responded saying that it will be a slow process. There are still a lot of issues in terms of testing techniques that need to be ironed out and that the main limiting factor is government and private regulation authorities.

My thoughts? Delve into the science yourself (or follow blogs such as this that do they reviewing for you!) and make your own informed decisions.


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1. FAO/WHO [1990]. Expert consultation on protein quality evaluation. Food and Agriculture Organization of the United Nations, Rome.





6. Sarah K. Cervantes-Pahm, Yanhong Liu and Hans H. Stein (2014). Digestible indispensable amino acid score and digestible amino acids in eight cereal grains . British Journal of Nutrition, 111, pp 1663-1672. doi:10.1017/S0007114513004273.