The Study
The effect of daily protein supplementation, with or without resistance training for 1 year, on muscle size, strength, and function in healthy older adults: A randomized controlled trial.
This study is like a fair test where different groups of older people tried different things — some drank protein shakes, some lifted heavy weights, some did both. It found that only the group that lifted heavy weights and drank protein got stronger and built more muscle. But it didn't prove protein alone does anything.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
Older adults who drank protein shakes alone didn't get stronger or build more muscle, but those who lifted heavy weights while drinking protein did.
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 570 / 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.
- 1These strength gains are meaningful — they help older adults stand up, walk, and avoid falls.
- 2Heavy lifting + protein: muscles grew by 1.68 cm², leg strength went up by 18.4–23.9 Nm.
- 3Light lifting + protein: strength went up by 13.7 Nm, but muscles didn't grow.
- 4Protein alone: no change.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
The American journal of clinical nutrition
Year
2021
Authors
K. Mertz, S. Reitelseder, Rasmus L. Bechshoeft, Jacob Bulow, Grith Højfeldt, M. Jensen, Simon R. Schacht, M. V. Lind, M. A. Rasmussen, U. R. Mikkelsen, I. Tetens, S. Engelsen, D. Nielsen, A. Jespersen, L. Holm
Related Content
Claims (6)
Resistance training increases the effectiveness of dietary protein in preserving muscle mass and supporting physical function.
In adults over 65, taking 40 grams of whey protein daily for a year without doing strength training does not change the size of the quadriceps muscle, leg strength, or physical function compared to taking carbohydrate supplements.
In adults over 65, doing heavy weight training three times a week along with daily whey protein increases quadriceps muscle size by 1.68 cm² and improves knee extensor strength by 18.4 Nm for dynamic strength and 23.9 Nm for isometric strength over one year, compared to taking whey protein alone.
Among older adults over 65, combining heavy weight training with whey protein is the only approach shown to increase both muscle size and strength over one year; taking whey protein alone or doing light exercise only improves strength or has no effect.
In adults over 65, doing light resistance training three to five times a week with daily whey protein increases knee strength by about 13.7 Nm after one year compared to taking whey protein alone, but does not increase the size of the quadriceps muscle.
Taking 40 grams of collagen protein every day for a year does not change muscle size, strength, or physical function in healthy adults over 65 compared to taking carbohydrate supplements.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.