A high proportion of leucine is required for optimal stimulation of the rate of muscle protein synthesis by essential amino acids in the elderly.
Level 3 - non-randomized controlled study
Controlled clinical trial with age and formulation comparison groups (randomization not specified in abstract)
PubMed 16507602 · doi:10.1152/ajpendo.00488.2005
What was done
Four groups (two elderly and two young) were evaluated before and after ingesting 6.7 g of essential amino acids (EAAs) containing either 26% leucine (standard whey profile) or 41% leucine (enriched). Muscle protein fractional synthetic rate (FSR) and net muscle protein balance were determined using primed continuous infusions of L-[ring-2H5]phenylalanine, vastus lateralis muscle biopsies, and leg arteriovenous blood sampling.
What was found
In young adults, muscle FSR increased significantly following EAA ingestion in both the 26% leucine group (basal: 0.048 ± 0.005%/h; post-EAA: 0.063 ± 0.007%/h; P < 0.05) and the 41% leucine group (basal: 0.036 ± 0.004%/h; post-EAA: 0.051 ± 0.007%/h; P < 0.05). In elderly adults, FSR did not increase significantly with 26% leucine (basal: 0.044 ± 0.003%/h; post-EAA: 0.049 ± 0.006%/h; P > 0.05), but did increase with 41% leucine (basal: 0.038 ± 0.007%/h; post-EAA: 0.056 ± 0.008%/h; P < 0.05). Phenylalanine net balance improved significantly (P < 0.05) in all groups except the elderly 26% leucine group.
Why it matters
This demonstrates that age-related anabolic resistance to standard amino acid mixtures can be acutely reversed by increasing the proportion of leucine in the supplement.
Limits
Total participant count and sex distribution are not reported in the abstract. The study measures only acute, short-term muscle protein synthesis rates following an isolated supplement and does not evaluate chronic adaptations in muscle mass, strength, or function.
Cited by
- supports Consuming proportionately higher amounts of protein can restore a normal muscle protein synthesis response in older adults.