You probably arrived on this article because you’re interested in the comparison of proteins, specifically pea protein vs whey protein. Perhaps you want to know which is better for you? But what do we mean by better? How do we compare proteins? In this article we’re going to evaluate pea protein vs whey protein using numbers and evidence, not shoddy bro science and internet gossip.
Protein quality
Protein is a macro-nutrient which means it’s one of the three dietary nutrient groups (proteins, carbohydrates, lipids) that are needed for humans to function.
The quality of a protein can be simply thought of as how well it can be used by the body, relative to other proteins.
How well a protein can be ‘used’ by the body can be understood through the following points:
- Amino acid composition – is sufficient amounts of each amino acid type
- Digestibility – the net absorption of an amino acid
- Loss of availability due to interfering substances – the presence of substances which inhibit amino acid uptake
The greatest source of variability comes from digestibility.
We’re going to take a closer look at each of these generally, then look specifically at pea and whey protein.
Protein quality – amino acid composition
Refresher on proteins and amino acids
As discussed elsewhere on this site, all proteins are made of amino acids. So whether you eat animal or plant-based protein, your protein is made up of simpler substances called amino acids.
There are 21 amino acids. The human body can make 12 of these itself, but the remaining 9 amino acids must be obtained from our diets. These 9 amino acids are called essential amino acids (EAAs); histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. If a food contains all the EEAs we call it a ‘complete protein’.
Although proteins are all made of the same types of amino acids, different proteins contain different amounts of each type of amino acid. For example, peanut butter will contain a different amount of methionine compared to cow’s milk.
Amino acid composition
When considering a protein’s quality, we assess whether it contains a sufficient amount of each type of amino acid.
An ideal protein contains a specific amount of each amino acid. The World Health Organisation (WHO) advises that a good typical protein should contain a certain amount of each amino acid per 100g of protein. This can be seen in the graph below.
If the protein you eat is lower in one amino acid (as shown below for Lysine, where there is 1/2 the quantity of Lysine available compared to the WHO requirement), the general understanding is that this will limit the use of all amino acids by the factor of the deficient amino acid. So, Lysine becomes rate-limiting. This would mean your body could only utilise 1/2 of all the other amino acids in the protein too.
This rate-limit effect can be countered by eating proteins that have complementary amino acid profiles. For example, we could eat a protein that is low in Lysine and high in every other amino acid, with a protein that is high in Lysine and low in every other amino acid, and have a meal with complete proteins that could be 100% utilised by our body.
Amino acid composition – pea protein vs whey protein
So what about pea protein vs whey protein? The graph below shows the essential amino acids for:
- WHO’s requirement for protein
- Average for whey protein
- Average for pea protein
You can see that:
- Pea protein and whey protein both generally meet the WHO guide requirement for protein. So they’re both generally good sources of protein.
- Whey protein and pea protein are both deficient in methionine compared to the the WHO requirement. Pea protein is more deficient.
- Whey protein provides more EAAs than pea protein for most amino acids, however the usability of these abundant EAAs will still be rate limited by the other EAAs.
So, whey protein is slightly better in terms of general availability of all amino acids compared to pea protein.
Protein quality – digestibility – pea protein vs whey protein
Digestibility can be thought of as how well the body absorbs EAAs. Simply put, it’s the ratio between how much of an EAA you ingest compared to how much you excrete. Ideally, you would digest all the EAA as food passed through your mouth, stomach, small intestine and large intestine. Ideally the digestibility would be 100%. In reality, digestibility varies but typically is in the 90+% range for good quality protein powders.
We must note that researchers state that, “digestibility is not a fixed attribute of a food but reflects an interaction between the food and the person eating it and so may be subject to individual variation.”
So what values do we see for pea protein vs whey protein?
In the 2019 paper, ‘Nutritional quality evaluation of commercial protein supplements‘, the authors found that pea protein isolate powder and whey protein isolate powder had very similar digestibility factors of 90.0% and 89.8% respectively. They note that these results are similar to that in the research literature.
In the 2015 paper, ‘Protein digestibility-corrected amino acid scores and…’, the authors found that for pea protein concentrate and whey protein concentrate the mean amino acid digestibility was 98% for each protein source. This average figure is slightly higher than the previous paper (90%), as different products and methodology are being used. But the digestibility values for pea protein and whey protein concentrates are very similar.
When it comes to digestibility of pea protein powder and whey protein powder, they’re very similar and highly digestible.
Protein quality – anti-nutritional factors – pea protein vs whey protein
Foods can contain substances which limit the absorption of nutrients that are contained in the food. Examples of naturally occurring anti-nutritional factors include:
- glucosinolates in mustard and canola,
- trypsin inhibitors and haemagglutinins in legumes,
- tannins in legumes and cereals,
Processing food with heat will can affect these anti-nutritional factors; yielding a reduction in anti-nutritional factors for some foods like beans, but a an increase in anti-nutritional factors for other foods like soy and casein.
The 2019 paper, ‘Nutritional quality evaluation of commercial protein supplements‘, the authors note that often plant proteins are considered less digestible than animal proteins due to the presences of anti-nutritional substances, however these are likely to have been reduced due to the processing of the powder.
Frankly, it’s hard to obtain good information on how the bioavailability of pea protein and whey protein may be affected by the presence of anti-nutritional factors. It’s not something we can obtain a robust numerical answer for.
Metrics for assessing protein quality
There are short-cuts and metrics enabling quick comparisons of proteins, the most recent and widely used are discussed below.
PDCAAS – protein digestibility corrected amino acid score
The protein digestibility corrected amino acid score (PDCAAS) was employed by the US FDA and World Health Organisation in the 1990s to determine protein quality.
PDCAAS score = ( rate-limiting amino acid test protein / reference protein ) * digestibility
We’ll explore this below. Despite its complicated name, it’s easy to understand.
Reference profile
First, PDCAAS defines a standard amino acid profile – the ‘reference’ profile. We then select a protein to compare against the reference profile. The ratio (‘example’/’reference’) then shows how much of each amino acid is contained in the example protein relative to the reference protein. If this number is less than 1, it means there’s less amino acid in the example protein than the reference protein.
| Essential Amino Acid | reference protein g/100g | example protein g/100g | example / reference |
| Isoleucine | 2.5 | 2.4 | 1.0 |
| Leucine | 5.5 | 5.6 | 1.0 |
| Lysine | 5.1 | 5.0 | 1.0 |
| Methionine + Cysteine (SAA) | 2.5 | 2.5 | 1.0 |
| Phenlyalanine + Tyrosine | 4.7 | 4.7 | 1.0 |
| Threonine | 2.7 | 1.0 | 0.4 |
| Tryptophan | 0.7 | 0.8 | 1.1 |
| Valine | 3.2 | 3.3 | 1.0 |
| Histidine | 1.8 | 1.8 | 1.0 |
The lowest ratio number identifies the rate-limiting amino acid. In the above example, Threonine is the rate-limiting amino acid.
Rate-limiting amino acid profile
As explained above, the lack of one amino acid is understood to limit the body’s use of the other amino acids. So if you have a protein that displays a profile that matches a perfect reference protein, except it’s missing one essential amino acid, the body won’t be able to process and use the other amino acids, therefore the protein is considered lower quality.
This rate-limit effect can be countered by eating proteins that have complementary amino acid profiles. For example, we could eat a protein that is low in methionine and high in every other amino acid, with a protein that is high in methionine and low in every other amino acid, and have a meal with complete proteins.
Digestibility
Finally PDCAAS uses a multiplication factor based on the digestibility of a protein, as discussed earlier in this article.
PDCAAS conclusion
PDCAAS accurately shows the absorption of an individual protein. But it is a limited measure that doesn’t capture what happens what proteins are eaten together. Most people will eat multiple sources of protein in a meal or day. If two proteins are complementary, i.e. one protein is high in amino acids that the other protein is deficient in, their combined PDCAAS scores can be much higher than individually. This isn’t captured in the PDCAAS scoring system. Therefore PDCAAS can easily be misunderstood and misrepresent protein quality.
PDCAAS for pea protein and whey protein
The PDCAAS score for pea protein concentrate powder is around 0.89, and the score for whey protein concentrate powder is around 0.99
DIAAS – digestible indispensable amino acid score
The digestible indispensable amino acid score (DIAAS) is similar to PDCAAS, except there is more emphasis placed on measuring digestibility more accurately, at an earlier stage in the digestion process through the body.
The DIAAS score for pea protein concentrate powder is around 0.83, and the score for whey protein concentrate powder is around 0.97.
The same issue with PDCAAS exists for DIAAS regarding not capturing what happens what complementary proteins are eaten together.
The conclusion – pea protein vs whey protein
If you’re using concentrated protein powders, then whey protein has a slight edge when eaten in isolation of other protein sources. If you’re like most people and you eat a mixture of proteins and foods, pea protein is likely to be just as good. It’s not a big compromise, especially if you’re trying to follow a plant-based diet.
Need some protein, pea protein or whey protein?
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The link to MyProtein is an affiliate link, so if you buy something from there, I’ll get a small % of the sale. Hopefully you don’t mind, as you found the article valuable and it won’t cost you anything additional.
