Our new study: are free amino acids superior for muscle protein synthesis?
Muscle protein synthesis is the process underlying muscle adaptation and is stimulated by protein ingestion and exercise.
Following ingestion, protein needs to be digested into amino acids (the building blocks of protein). The amino acids are then absorbed and released into the circulation and taken up by tissues such as muscle. Finally, the amino acids are taken up and incorporated into functional proteins in those tissues (protein synthesis).
A rapid release of amino acids in the (blood) plasma is an important trigger of muscle protein synthesis. Free amino acids do not need to be digested and can therefore be rapidly absorbed. Theoretically, this makes free amino acids an ideal candidate to stimulate muscle protein synthesis.
In our study, we compared the effect of 30 g intact milk protein vs free amino acids. The amino acid content was matched, so the form of the amino acids was the only variable (free AA vs protein).
As expected, the free amino acids resulted in higher peak plasma concentrations of amino acids. However, the free amino acids stimulated muscle protein synthesis to the same extent as the intact milk protein.
A possible explanation is that the 30 g maximally stimulates muscle protein synthesis regardless of how it’s provided. Our data suggest that the protein form is not a big concern, at least when protein intake is high enough.
It should be noted that milk protein powder has very high digestibility. It is possible that free amino acids would be superior when compared to protein sources with a lower digestibility or in subjects with impaired digestion.
Go to the next infographic in the protein series:
A high dose of slow protein for prolonged muscle growth?
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