Leucine supplements boost muscle synthesis by 33% during exercise

In addition to the implications for sports nutrition, results of the randomized crossover study, published in The American Journal of Clinical Nutrition​, may have implications for populations susceptible to muscle loss, such as sarcopenia.

“To the best of our knowledge, this was the first study to assess whether increasing leucine provision during endurance-type exercise by dietary supplementation enhances muscle protein anabolism in recovery,”​ wrote researchers from the US Army Research Institute of Environmental Medicine, Tufts University, and Louisiana State University System.

Resistance vs endurance exercise​

According to the researchers, the effects of resistance exercise on the metabolism of protein in muscles, the effects of endurance exercise on protein metabolism is not well established.

“Increasing the concentration of leucine within an optimal dose of EAA does not have an added stimulatory effect on resting and post-resistance exercise muscle protein synthesis,”​ explained the researchers, led by the US Army’s Stefan Pasiakos.

“In contrast with resistance exercise, sustained endurance exercise is mainly catabolic, yielding simultaneous reductions in muscle protein synthesis and plasma leucine concentrations during exercise, which may be attributed to the metabolic demand for branched chain amino acids in exercising skeletal muscle.”​

The researchers set out to elucidate if leucine-enriched amino acid supplements during endurance exercise had an effect on muscle protein synthesis and whole-body protein turnover during recovery.

Eight volunteers consumed 10 grams of protein drinks with either 1.87 or 3.5 grams of leucine during a cycling test.

Results showed that the leucine-enriched beverage was associated with a 33% increase in muscle protein synthesis, compared with the control beverage.

“[In addition] whole-body protein breakdown and synthesis were lower and oxidation was greater after consumption of [leucine-enriched essential amino acid supplement] than after consumption of [essential amino acid supplement],”​ added the researchers.

“These data indicate that increasing leucine availability during steady state exercise promotes skeletal muscle protein anabolism and spares endogenous protein,” ​wrote Pasiakos and his co-workers.

“Future studies are required to determine the molecular mechanisms associated with leucine on human muscle protein synthesis and whether the observed anabolic effects are influenced by nutrient timing or exercise intensity. ​

“Our findings indicate that increasing the leucine content of protein supplements provided for those populations susceptible to muscle loss, including proteolytic conditions—such as cachexia, sarcopenia, and calorie deprivation—may warrant further exploration,”​ they added.

Source: American Journal of Clinical Nutrition​
Volume 94, Pages 809-818, doi: 10.3945/​ajcn.111.017061​
“Leucine-enriched essential amino acid supplementation during moderate steady state exercise enhances postexercise muscle protein synthesis”​
Authors: S.M. Pasiakos, H.L. McClung, J.P. McClung, L.M. Margolis, N.E. Andersen, G.J. Cloutier, M.A. Pikosky, J.C. Rood, R.A. Fielding, A.J. Young