The Study
Protein Type, Protein Dose, and Age Modulate Dietary Protein Digestion and Phenylalanine Absorption Kinetics and Plasma Phenylalanine Availability in Humans
This study is like doing 18 small science experiments where people were randomly given different types and amounts of protein, and scientists watched how their bodies absorbed it. Because people were picked randomly, we can say the differences were probably caused by the protein, not something else.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
This study tracks how much of the protein you eat actually gets into your blood to help build muscle, depending on the type of protein, how much you eat, and your age.
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 588 / 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.
- 1Yes, the differences matter—especially choosing milk over pure casein and eating enough protein.
- 2Older adults may need more protein to compensate for reduced absorption.
- 350% of eaten protein shows up in the blood within 5 hours.
- 4Milk protein delivers more (65%) than whey (57%) or casein (45%).
- 5Eating more protein gives more amino acids.
- 6Older people get 6% less from the same protein.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
The Journal of Nutrition
Year
2020
Authors
S. Gorissen, J. Trommelen, I. W. Kouw, A. Holwerda, B. Pennings, Bart B L Groen, B. Wall, T. Churchward-Venne, A. Horstman, R. Koopman, N. Burd, C. Fuchs, M. Dirks, Peter T. Res, J. Senden, Jan M. Steijns, Lisette C P G M de Groot, L. Verdijk, Luc J C van Loon
Related Content
Claims (6)
As men get older, their bodies don't absorb protein from food as well after eating — specifically, older guys get less use out of the amino acids from a protein meal compared to younger guys.
When healthy guys drink milk protein, about half of the protein gets into their bloodstream within 5 hours — that's what muscles can use. The rest is either still being digested or gets used by organs like the liver before it ever reaches the rest of the body.
For healthy guys, drinking regular milk protein gives your body more usable protein building blocks over 5 hours than taking just whey or just casein alone.
When healthy guys drink more whey protein, their bodies absorb more of an important amino acid called phenylalanine—about 10% more when they take a higher dose.
If healthy guys drink more casein protein, more amino acids show up in their blood overall—even though a smaller percentage gets absorbed—probably because their bodies haven’t finished digesting it within 5 hours.
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.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.