Protein Quality

Protein serves many important functions in the body, with building muscle being its most well-known role.  Athletes often consume protein directly after a training session to improve muscle size and strength as well as help with muscle recovery. But are all proteins equal?

Protein quality is an important factor in increasing muscle protein synthesis. A high-quality protein will increase the magnitude and decrease the time needed to make new proteins following protein consumption. The quality of a protein is assessed by its:

• Essential amino acid (EAA) content
• Leucine content
• Bioavailability (i.e. how much of the protein can be used for muscle protein synthesis)

What makes a protein high quality?

We have 20 amino acids, of which 9 are EEAs (Essential Amino Acids) and need to be consumed in sufficient amounts to stimulate muscle growth. Of these EEA, leucine acts as a building block and trigger to start new muscle formation. Following ingestion, protein needs to be digested into individual amino acids and then absorbed before it can be delivered to the muscle for protein synthesis. Therefore a high-quality protein source will contain all 9 EAAs, have a high leucine content and be easily digested and absorbed into circulation.

Does the quality of a protein really matter?

If you look at your total daily protein intake and it is moderate to high (>1.6g/kg BW per day) and you frequently consume protein throughout the day, the protein quality does not matter too much. When your total daily protein intake is low, the quality of the protein becomes an important factor.  A fast or slow-digested protein will also depend on the circumstance, for example immediately following a training session a fast protein (e.g. Whey protein) will be preferred to optimally stimulate muscle protein synthesis. As a bedtime snack a slow protein (e.g. Casein) may be better.

Animal or planted-based?

Animal-based proteins are seen as higher-quality proteins compared to plant-based alternatives. This is because animal-based proteins contain all 9 EAAs while plant-based proteins are incomplete and generally have a lower leucine content. If you are using plant-based proteins make sure to combine different types to ensure you get all 9 EAAs in.

How much Leucine?

To optimally increase muscle protein synthesis it is recommended to consume ~3g of leucine. While protein powder is convenient it is possible to get this from food, but the amount needed is not always feasible from a single food source.

It may be better to combine various food sources for example a 3-egg omelette, with a slice of toast and a glass a milk.

Digestibility

Proteins can also be scored based on their digestibility. One of the techniques are Protein digestibility corrected amino acid score (PDCAAS). A high score = higher quality, with 1 being the highest score. Eggs, milk, chicken and tuna all score 1, with beef scoring 0.92. Plant-based proteins typically score between 0.3-0.7.

Take home

Eating proteins is important for general health and bodily function, but when it comes to recovery from exercise and the need to increase muscle mass we should take protein quality into account when our total intake is low and less frequent. Also consider protein quality based on when you consume protein, for example immediately after exercise go for a high quality fast absorbing protein, but just before bed the protein quality will be less of a factor.