Protein provides the building blocks for tissues such as muscle mass.
Ingested protein is digested into amino acids. Subsequently, these amino acids are:
- Absorbed in the gut
- Released into the circulation
- Taken up by tissues
- Incorporated into tissues (protein synthesis)
Protein synthesis allows tissues such as muscle to recover, adapt, and grow. Therefore, many athletes consume a high protein diet. Protein and (free) amino acids supplementation are also common strategies to increase protein intake.
But is there a difference between protein and amino acids supplements? If protein is digested into amino acids, is it simply the same? Or perhaps amino acid supplements are more effective because they don’t require digestion?
While protein powders have a high absorption (>90%), amino acids are thought to have essentially 100% absorption. In addition, amino acids will be absorbed more rapidly and result in a large spike of amino acids into the circulation. Such a spike is thought to be an anabolic signal that triggers muscle protein synthesis.
So theoretically, a free amino acids supplement could potentially be more efficient than a protein powder that contains exactly the same amount and composition of amino acids.
Therefore, we designed a study to compare a protein versus amino acid supplement.
Study design
We investigated the impact of a:
- 30 g milk protein supplement
- 30 g free amino acid supplement (matched for amino acid content with the milk protein)
We measured how much of the ingested amino acids were released into the circulation, muscle protein synthesis, and whole-body protein net balance (more outcomes in the paper).
Results
As expected, the amino acid supplement resulted in a faster release of amino acids into the circulation (indicating a faster absorption rate).
In addition, the total amount of ingested amino acids released into the circulation was higher in the amino acid group. However, it appeared that the milk protein group was still in the process of catching up at the end of the 6-h study period, so the difference may have become smaller.
While the protein supplement resulted in a positive whole-body protein net balance, the increase was lower when compared to the free amino acid supplement.
Whole-body protein net balance strongly correlated with the ingested amount of amino acids released into the circulation. Since the total release of ingested amino acids was still increasing in the milk group, it is likely that the difference between the treatment in whole-body protein net balance would also decrease beyond the 6-h mark. In addition, we believe that people should be careful in drawing practical conclusions based on whole-body protein metabolism but should rather focus on muscle protein synthesis (for a more in depth explanation, see XYZ).
Therefore, we also measured protein synthesis specifically in muscle tissue. Both supplements were effective at stimulating muscle protein synthesis, but there was no difference between the treatment.
Discussion
These data suggest that when matched for amino acid content, the form of supplementation (protein or amino acids) does not impact muscle protein synthesis. However, it is possible that the results would be different in other scenarios.
For example, the subjects received 30 g of protein/amino acids. This may have been enough to maximally stimulate muscle protein synthesis in both treatments. A difference in the efficiency of the supplements may only become clear when smaller (suboptimal) amounts are ingested (<20 g).
In addition, potential benefits from amino acids may become more pronounced when they are compared to less digestible protein sources or in subjects with suboptimal digestion.
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