Do older adults require more leucine to stimulate muscle protein synthesis?
Do older adults require more leucine to stimulate muscle protein synthesis?
Approximately 17 y ago, 2 studies pointed out that older adults have a blunted sensitivity to exogenous (external) amino acids. Those studies had indeed suggested that the anabolic response to small doses of amino acids, especially with a lower content of leucine, was reduced in older adults compared with younger subjects.
On the basis of the original findings, researchers at the University of Texas Medical Branch (UTMB) Institute for Translational Sciences Clinical Research Center hypothesized that healthy older adults are resistant to the muscle protein anabolic action of a low-EAA dose and that resistance training (RET) would improve the muscle protein sensitivity to EAAs. To test their hypothesis, they designed a longitudinal study, with an increased sample size compared with previous studies. They also decided to focus their treatment on a healthy, moderately active, older adult [aged 65–85 y] population.
Surprisingly, they found that neither hypothesis was correct!
During this larger study, the researchers found no evidence for muscle protein anabolic resistance in older participants to a small dose of EAAs (6.8 g) containing 1.77g of leucine.
FYI, one serving of OptimalAmino contains 1.964g of leucine per serving (in 10g of EAAs).
The researchers concluded that muscle protein anabolic resistance to amino acids may not be a significant problem in healthy older adults. This would indicate that aging per se is not directly linked to anabolic resistance and an adequate dietary protein intake should be sufficient to maintain muscle mass and function in healthy aging individuals.
Read the full-text here: Muscle Protein Anabolic Resistance to Essential Amino Acids Does Not Occur in Healthy Older Adults Before or After Resistance Exercise Training
Moro T, Brightwell CR, Deer RR, Graber TG, Galvan E, Fry CS, Volpi E, Rasmussen BB. Muscle Protein Anabolic Resistance to Essential Amino Acids Does Not Occur in Healthy Older Adults Before or After Resistance Exercise Training. J Nutr. 2018 Jun 1;148(6):900-909. doi: 10.1093/jn/nxy064. Erratum in: J Nutr. 2018 Oct 1;148(10):1699. doi: 10.1093/jn/nxy181. PMID: 29796648; PMCID: PMC6251608.