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L-Leucine

    leucine

    L-Leucine is 1 of 3 branched-chain amino acids (BCAA) and is credited by researchers as a main cause of benefits associated with BCAA supplementation.

    The “L” in front of leucine –or any other amino acid –stands for “levo,” denoting the spiral rotation of the chemical structure.

    L-leucine, like the other BCAAs isoleucine and valine, is an essential amino acid and differs from other amino acids because it is mostly oxidized in skeletal muscle.[1] Consequently, L-leucine is more readily available.

    Leucine’s oxidation rate is highest of the BCAAs.[2]

    While BCAAs combined are clinically proven to provide ergogenic and exercise-recovery advantages, researchers are becoming more interested in l-leucine when supplemented by itself, as its benefits tend to surpass its BCAA counterparts’.

    Research shows L-leucine plays an imperative role in muscle metabolism and exercise performance.

    Protein Metabolism

    L-Leucine boosts muscle protein synthesis and combats protein degradation by activating a protein complex mTOR, short for mammalian target of rapamycin.[1]

    In one study, researchers administered 2 amino acid drinks containing 3.5 and 1.87 g leucine to test subjects who underwent steady-state exercise. Results show muscle protein synthesis was 33% greater after ingesting the 3.5 g leucine dose.[3]

    Leucine’s effects are said to be “at least in part, associated with the absence of branched-chain aminotransferase (BCAT) enzyme in the liver.”[4]

    Power Output

    Enhanced strength performance is a benefit associated with daily l-leucine supplementation.

    During a 12-week resistance-training program, 26 men supplemented with leucine or a placebo and trained 2 times a week. Test subjects underwent a 5 repetition maximum (5-RM) exercise to measure strength output.

    Results show those who ingested leucine experienced “higher gains in total 5-RM strength (sum of 5-RM in eight exercises) and 5-RM strength in five out of the eight exercises.” These observations lead researchers to conclude l-leucine supplementation might be useful in increasing strength performance.[5]

    There are no reported side effects associated with l-leucine supplementation on its own. An online medical authority indicates BCAAs are generally safe when used for up to 6 months but may result in fatigue and loss of coordination.[6]

    In clinical studies, l-leucine is usually accompanied alongside isoleucine and valine. A common BCAA ratio found in several sports supplements is 2:1:1, meaning 2 parts leucine to 1 part isoleucine and valine.

    In one study, an amino acid drink mixture containing 3.5 g l-leucine was used to study muscle protein synthesis.[4]

    A 4 g l-leucine dose was studied during a study analyzing strength performance.[5]

    • [1] Yoshiharu Shimomura, et al. “Nutraceutical Effects of Branched-Chain Amino Acids on Skeletal Muscle.” J. Nutr. February 2006 vol. 136 no. 2 529S-532S.
    • [2] Mero A. “Leucine supplementation and intensive training.” Sports med. 1999 Jun;27(6):347-58.
    • [3] Pasiakos et al. “Leucine-enriched essential amino acid supplementation during moderate steady state exercise enhances postexercise muscle protein synthesis.” Am J Clin Nutr. 2011 Sep;94(3):09-18.
    • [4] Layne E. Norton and Donald K. Layman. “Leucine Regulates Translation Initiation of Protein Synthesis in Skeletal Muscle after Exercise.” J. Nutr. February 2006vol. 136 no. 2 533S-537S.
    • [5] Ispoglou T, et al. “Daily L-leucine supplementation in novice trainees during a 12-week weight training program.” Int J Sports Physiol Perform. 2011 Mar;6(1):38-50.
    • [6] “Branched-Chain Amino Acids.” WebMD.

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