Aging does not impair the anabolic response to a protein-rich meal.
BACKGROUND
Sarcopenia is a debilitating condition afflicting the elderly that may be facilitated by insufficient or ineffectual intake of dietary protein. We previously showed that free-form essential amino acids acutely stimulate muscle protein synthesis in both the young and the elderly. However, the ability of an actual protein-rich food to stimulate anabolism in the young and the elderly has not been explored.


OBJECTIVE
We aimed to characterize changes in plasma amino acid concentrations and to quantify muscle protein synthesis in healthy young (41 +/- 8 y old; n = 10) and elderly (70 +/- 5 y old; n = 10) persons after ingestion of a 113-g (4-oz) serving of lean beef.


METHODS
Venous blood samples and vastus lateralis muscle biopsy samples were obtained during a primed (2.0 mumol/kg) constant infusion (0.08 mumol.kg(-1).min(-1)) of l-[ring-(13)C(6)] phenylalanine. Plasma amino acid concentrations were measured and a mixed-muscle fractional synthesis rate (FSR) was calculated during the premeal period and for 5 h after beef ingestion.


RESULTS
Mixed-muscle FSR increased by approximately 51% in both the elderly (mean +/- SE measurements: 0.072 +/- 0.004%/h and 0.108 +/- 0.006%/h before and after the meal, respectively) and the young (0.074 +/- 0.005%/h and 0.113 +/- 0.005%/h before and after the meal, respectively) after beef ingestion (P < 0.001). Plasma amino acid concentrations peaked at approximately 100 min after beef ingestion in both age groups but were substantially higher in the elderly (2185 +/- 134 nmol/mL compared with 1403 +/- 96 nmol/mL; P < 0.001).


CONCLUSIONS
Despite differences in the concentration of amino acids in the plasma precursor pool, aging does not impair the ability to acutely synthesize muscle protein after ingestion of a common protein-rich food.
Division of Rehabilitation Sciences, The University of Texas Medical Branch, Galveston, TX 77555-1144, USA.
T Brock
TB
Symons
Scott E
SE
Schutzler
Tara L
TL
Cocke
David L
DL
Chinkes
Robert R
RR
Wolfe
Douglas
D
Paddon-Jones
D000273:Adipose Tissue / Q000033:anatomy & histology; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000596:Amino Acids / Q000097:blood*; D000601:Amino Acids, Essential / Q000032:analysis; D015992:Body Mass Index; D002247:Carbon Isotopes; D004044:Dietary Proteins / Q000378:metabolism*; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D008460:Meat / Q000032:analysis; D008875:Middle Aged; D010649:Phenylalanine / Q000008:administration & dosage / Q000493:pharmacokinetics
D000596:Amino Acids; D000601:Amino Acids, Essential; D002247:Carbon Isotopes; D004044:Dietary Proteins; D010649:Phenylalanine