Hello everyone, everything good? In today's post we're going to talk about something that's in our meals every day: protein!

Do you know how to measure the quality of a protein and what makes a protein high or low quality? Keep reading and I’ll explain!

Protein quality considers factors that influence the magnitude and speed with which we can produce new proteins (protein synthesis rate) after consumption. It seems complicated, but it's not. These factors include the essential amino acid (EAA) content, leucine content, and the digestion/absorption kinetics of a given protein source. As training adaptations are supported by a positive net protein balance, protein quality is considered an important aspect of protein nutrition to improve such adaptations.

What distinguishes high-quality proteins from low-quality proteins?

There are 9 essential amino acids (those that the body cannot produce) that must be obtained from the diet in sufficient quantities to stimulate protein synthesis. One EAA worth highlighting is leucine , as it acts as a “building block” for the formation of new skeletal muscle proteins, but also as a signal for protein synthesis to be “turned on”. After ingestion, proteins must be broken down into constituent amino acids, which are then absorbed and then delivered to peripheral tissues (e.g., skeletal muscle) for protein synthesis to occur.

Therefore, high-quality proteins are those that:

1) Provide all 9 EAAs in sufficient quantities

2) They are abundant in leucine and

3) They are easily digested and absorbed into the circulation.

It is generally believed that proteins of animal origin are superior to sources of plant origin in terms of protein quality. However, there are exceptions and this should be considered a general principle and not a rule.

Gabi, so high quality is good and low quality is bad?

More or less. Protein quality is considered most important when the total dose of protein consumed is low to moderate. For example, let's say you consume 10g of low-quality, low-EAA, low-leucine protein. The amount of amino acids provided here is unlikely to maximally stimulate the protein synthesis response, even if digestion and absorption were optimal. Therefore, combined with poor digestion and absorption kinetics, we are unlikely to see an increase in protein synthesis with this lower quality source. On the other hand, consuming 10g of high-quality protein, with a more favorable EAA profile and leucine content, as well as better digestion/absorption kinetics, would probably induce a more intense increase in protein synthesis. However, simply consuming more than one low-quality protein source can compensate for the aforementioned inadequacies.

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In short: when consuming “low quality” protein, in order to have significant protein synthesis, it is necessary to consume it in greater quantity.

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Regarding digestion: Fast or slow? It depends.

Fast-digesting proteins (like whey protein) are believed to be more effective in promoting a rapid increase in protein synthesis, which may be the ideal post-workout strategy. On the other hand, slow proteins (such as casein) may be beneficial in scenarios where frequent protein feeding is not possible, such as at night, on a busy day or during intentional fasting.

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Another consideration is total protein intake and/or protein consumption pattern. For example, in the presence of a moderate to high daily intake of total protein (1.6-2.2g protein/kg/day) or frequent protein feeding (≥20g every ~3 hours), the importance of protein quality protein for synthesis likely decreases. On the other hand, a low total protein intake and an altered consumption pattern may emphasize the role of protein quality. Therefore, quality must be considered in the context of all aspects of protein nutrition.

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There are also other non-protein aspects of a food or drink that can influence the effect on the acute protein synthesis response. For example, the food matrix (i.e., the constituents that make up a food, including water, fiber, macronutrients, micronutrients, etc. and how they interact) can enhance or impair muscle response to protein consumption. While much of the research on protein quality uses isolated protein sources (usually powdered supplements), most of us get a large proportion of our protein from whole food sources (meats, grains, cheeses, eggs, etc.). Therefore, whole-food protein quality is an emerging area of ​​research, and we will undoubtedly have more answers about its importance in the coming years.

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In summary, protein quality considers essential amino acid content, leucine content, and digestion/absorption of a protein source. These factors influence the muscle’s immediate response. High-quality proteins appear important for increasing the protein synthesis response to a given protein source. However, it is still unclear how significant this is for there to be measurable differences in muscle-related adaptations (e.g., hypertrophy).

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Thanks for reading and we’ll see you in the next post!

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Gabi

References: Jeukendrup AE, "What is protein quality?" - Available at " What is protein quality? (mysportscience.com) "