Protein quality summarised
- Protein quality is an important part of optimum protein intake
- The WHO’s recommended intake for protein takes quality into account
- Many adults risk deficiency by ignoring protein quality, despite high intake
- Plant-based proteins often have lower quality than animal proteins
- Nevertheless, combinations of animal proteins can provide the same benefits
The protein craze is well and truly underway. As consumers flock to the popular nutrient, ‘high protein’ claims are ballooning and protein is being added to just about every product you can think of.
It’s clear that consumers want more protein. But when it comes to protein, it’s not just about quantity, but quality as well.
What is protein quality?
The quality of protein is, in many ways, just as important as the quantity.
The function of proteins is to supply the body with amino acids, which are essential for the synthesis of body proteins (the creation of body protein from DNA).
Different sources of protein have different amounts of the most indispensable of these amino acids.
Essentially, protein quality is the ability of a protein source to provide one with those indispensable amino acids.
This means not only the presence of the amino acids, but their availability and digestibility.
What difference does protein quality make to health?
The importance of protein quality to health is often overlooked, although the recommended daily amount given by the World Health Organisation (WHO) and Food and Agriculture Organisation (FAO) take into account protein quality.
The WHO and FAO recommend a daily amount of 0.83 g of protein per kg of body weight, with a Digestible Indispensable Amino Acid Score (DIAAS) score of 100% or more, the score given to the highest quality proteins.
Nevertheless, protein quality is often neglected, which can lead to protein deficiency.
One study exploring the topic suggests that by considering only gross protein consumption, many policymakers thinking about food insecurity fall short of the mark, and may underestimate the protein needed for sustainable diets.
Once the quality of protein is taken into account, the study says, the average adult is found to be deficient in protein.
Even when an abundance of protein is available, if the protein quality is not taken into account one can still be deficient.
A study on protein in the United States, where most people have access to enough protein in terms of amount, found that there was still a risk of protein deficiency due to consumption of low protein quality.
High quality protein mostly found in animal sources
Plant-based sources of protein often, but not always, are of lower quality than animal-based sources, and score lower on protein quality scores such as the DIAAS.
DIAAS
The Digestible Indispensable Amino Acid Score (DIAAS) is considered the most up-to-date rating of protein quality, endorsed to replace the previous Protein Digestibility Corrected Amino Acid Score (PDCAAS) by the UN’s Food and Agriculture Organisation (FAO).
However, it has been criticised for overlooking the increased digestibility of heat-treated and processed plant-based foods, as well as a focus too much on individual, isolated foods rather than the food matrix (food’s structure, and how the molecules within it interact).
Plant-based sources tend to have a lower amino acid profile and less digestibility and availability of amino acids compared to animal-based sources.
However, plant and animal-based proteins are both important, as they provide complementary sources of amino acids.
Diets with less diversity of proteins, especially those more heavily made up of plant-based proteins, have lower protein quality scores.
Soy and quinoa, along with meat, eggs and milk, are “complete proteins”, according to Harvard Health. This means that they contain all the essential amino acids that the body needs.
Other plant-based proteins, however, may not contain all these essential amino acids. Those on a vegan or plant-based diet must therefore ensure they consume a variety of plant-based proteins.
One study found that, according to the DIAAS, the highest quality proteins were pork meat, egg, casein, and potato proteins, with scores of more than 100%. Whey and soy proteins were slightly under 100%, but still high.
A number of plant-based proteins, including canola, hemp, oat, fava bean, rapeseed, pea, rice, lupin and corn proteins, alongside gelatin, were considered to have no quality claim. However, the study stresses that proteins can reach higher quality when complimenting each other.
