The Study
Ingestion of Free Amino Acids Compared with an Equivalent Amount of Intact Protein Results in More Rapid Amino Acid Absorption and Greater Postprandial Plasma Amino Acid Availability Without Affecting Muscle Protein Synthesis Rates in Young Adults in a Double-Blind Randomized Trial
This study is like a fair race between two types of protein: one in pieces (free amino acids) and one in a block (intact protein). Scientists watched what happened in the body right after people drank each one. They can say for sure that the 'pieces' version gets into the blood faster and in larger amounts, but both helped make muscle protein just the same.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
This study compared what happens in your body when you drink pure amino acids versus real protein from milk.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 580 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Even though more amino acids entered the blood from the pure form, your muscles don’t build more protein than with real food.
- 2The body uses both well, but differently.
- 376% of amino acids from the pure form got into the blood vs 59% from milk protein.
- 4Muscle building went up the same amount after both.
- 5Insulin went higher with pure amino acids.
- 6More protein building blocks ended up in muscles with the pure form.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
The Journal of Nutrition
Year
2022
Authors
Michelle E G Weijzen, Rob J J van Gassel, Imre W K Kouw, Jorn Trommelen, Stefan H M Gorissen, Janneau van Kranenburg, Joy P B Goessens, Marcel C G van de Poll, Lex B Verdijk, Luc J C van Loon
Related Content
Claims (6)
It's not just how fast amino acids show up in your blood after eating — it's how much your body gets over time that might matter more for building muscle.
If you drink a mix of free amino acids instead of whole milk protein, your body absorbs them faster and more of them—especially phenylalanine—show up in your blood over six hours.
If you're a healthy young adult, drinking a supplement with 30 grams of broken-down amino acids won't help your muscles grow more than drinking the same amount from real milk protein—even though your body absorbs the amino acids faster.
If you drink free amino acids, your insulin spikes more after the meal than if you drink the same amount of protein from milk — 35 vs 24 units on average.
If you're a healthy young adult, your muscles might use amino acids from supplements better than from real milk—scientists tracked this by seeing how much labeled phenylalanine ended up in muscle over 6 hours.
If you're a healthy young adult, drinking amino acids might help your body build more muscle in the hours after eating than drinking the same amount of protein from milk.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.