(OR16-01-24) Anabolic Capacity in Healthy Older Adults Using Compartmental Analysis Is Dependent on the Essential Amino Acid Composition of a Meal

Objectives: There is little understanding of the body’s anabolic threshold and capacity to respond to protein intake in healthy older adults. We applied a novel pulse method of multiple stable isotopes of amino acids to more accurately estimate the body’s efficiency in utilizing a balanced mixture of amino acids (TAA), as present in high quality animal protein, for protein anabolism.

Methods: Eleven healthy adults (5f/6m), aged 60-80 years old, participated in a randomized placebo-controlled single-blind study. On 2 separate study days, 3 days apart, participants consumed a liquid mixture as sips every 20 minutes for 6 hours: a) TAA (45g), or b) Placebo (water). Three hours after the start of the sip feeding, a stable isotope i.v. pulse containing L-[ring-²H₄]tyrosine and L-[ring-¹³C₆]phenylalanine was administered with subsequent blood draws to measure the plasma amino acid enrichments via LC/MS. Both non-compartmental and compartmental analysis from isotope enrichment decay calculations were used to estimate the rate of appearance (Ra) and intracellular net protein synthesis to calculate the anabolic response. Statistical analysis by Ttest (Graphpad Prism). Significance: p< 0.05.

Results: (µmol/min) mean [95%CI].

Results: Per gram consumed TAA mixture, the anabolic response using Ra is 0.36 g protein synthesized/gram protein intake [0.34, 0.41], an efficiency of 36%. However, the anabolic response when estimating intracellular net protein synthesis increases to 0.81 g protein/day [0.73, 0.90] (p < 0.0001 vs Ra calculation), an efficiency of 81%.

Conclusions: The use of the stable isotope pulse approach and subsequent intracellular modeling allows for an accurate estimation of intracellular net protein synthesis and protein synthesis efficiency in response to any type of dietary protein or amino acid mixture in healthy older adults.

Funding Sources: N/A