The Study
Leucine supplementation does not attenuate the decline in daily muscle protein synthesis rates or preserve leg muscle mass during leg immobilization in young or older adults: a double-blind randomized trial
This study is like a fair test where two groups of people got either leucine pills or sugar pills while their leg was in a cast. After 3 days, both groups lost muscle at the same rate. So we can say leucine didn't help here — but only for this short cast and these healthy people.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
When one leg was stuck in a cast for 3 days, muscles shrank and stopped making protein as fast — even in healthy people. Scientists gave some people extra leucine (a protein building block) with meals to see if it helped.
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 581 / 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 — losing 1.2% of leg muscle in just 3 days is fast and meaningful, especially for older adults or during illness or injury when muscle loss can lead to weakness.
- 2Muscle protein production dropped 15% in young people and 23% in older people.
- 3Muscle size shrank by about 1.2% in both groups.
- 4Leucine pills made no difference.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
The American Journal of Clinical Nutrition
Year
2026
Authors
T. Churchward-Venne, Philippe J. M. Pinckaers, J. Smeets, G. N. Marzuca-Nassr, Stefan H M Gorissen, C. Fuchs, J. Senden, J. Goessens, A. Gijsen, Will K. W. H. Wodzig, Luc J. C. van Loon
Related Content
Claims (5)
Three days of keeping one leg immobilized reduces muscle protein production by 15% in young adults and 23% in older adults, and shrinks the quadriceps muscle by 1.2% in both groups.
After three days of being immobilized, both young and older adults lose muscle mass at the same rate, even though older adults have a greater reduction in muscle protein synthesis, suggesting other biological processes offset the lower synthesis to preserve muscle size.
Taking 5 grams of leucine three times a day with meals does not stop the decrease in muscle protein synthesis or prevent muscle loss in the quadriceps during three days of leg immobilization in healthy young and older adults.
When immobilized, older adults lose muscle protein synthesis at a rate 0.18% per day faster than young adults.
When humans are immobilized for 14 days, their muscle volume decreases by 2-3%.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.