The Interaction of BCAA & Glutamine Metabolism

       Point blank, exercise promotes increased BCAA oxidation (Shirmomura et al., 2004). This increased degradation of BCAA helps maintain energy homeostasis by providing carbon as a direct energy source and glucose homeostasis by providing substrates for the citric-acid cycle and gluconeogenesis (glucose-alanine cycle). Plasma and muscle glutamine levels are also decreased post workout and it can take hours before they are restored (Rowbottom, 1996).

      Skeletal muscle and plasma glutamine levels are decreased during times of increased stress and metabolic demand, such as illness and exercise, while BCAA levels are often unchanged. Some may view this as meaning the BCAAs are not depleted or there is not a lack of BCAA during illness or exercise. But in reality, BCAA levels are not decreased because proteolysis of skeletal muscle and resynthesis of BCAA from branched-chain keto acids (BCKA) in the liver increases BCAA levels (Holeck, 2002). It is not that BCAA levels are not depleted, but rather they are kept elevated by breaking down skeletal muscle and resynthesizing BCAAs.

      According to Houston (2001), "Glutamine content in skeletal muscle and other tissues appears to have a regulatory role in whole body protein synthesis." Glutamine levels inside muscle govern protein synthesis and nitrogen balance and therefore muscle growth (VanAcker et al. 1999). The newly synthesized glutamine is created by using BCAAs obtained from muscle protein breakdown (Holecek, 2002).

      What all this means is Glutamine requirements are trying to be met during/post workout by BCAA catabolism causing BCAA catabolism/muscle protein breakdown to be increased.

      One way to increase skeletal muscle hypertrophy is by decreasing BCAA oxidation and therefore skeletal muscle catabolism. This can be accomplished by supplementing with BCAA and Glutamine.

      Glutamine administration has been shown to decrease leucine oxidation (Holeck, 2002). The mechanism behind this decrease in oxidation is believed to be that glutamine oxidation increases NADH levels (and increases the NADH/NAD+ ratio), thereby inhibiting BCKA dehydrogenase, which is the “key-enzyme” in BCAA oxidation (Holeck, 2002).

      Research on leucine shows that once the minimum requirement of leucine for or to activate various signaling pathways (Layman, 2003), such as the mTOR pathway. It may sound like leucine is free to exert its powerful effect of mTOR activation, but one must remember that protein breakdown and synthesis is occurring throughout the entire body; the body's protein stores are in a constant state of flux.

      The constant body protein flux plus the increased BCAA/leucine oxidation caused by exercise means that leucine is in high demand and therefore may not be able to participate in muscle growth at its full potential. This is where supplementing with additional BCAA (or free-form Leucine depending on your beliefs) and Glutamine comes into play. Supplementing with Glutamine will help keep skeletal muscle and plasma Glutamine concentrations elevated and decrease BCAA/leucine oxidation and therefore muscle catabolism. Supplementing with BCAA will help meet the increased BCAA oxidation caused by exercise by providing substrates for energy production and protein synthesis and serving as precursors for alanine and glutamine. This means there will be more BCAA/Leucine available to stimulate protein synthesis through mTOR-dependent and independent pathways.

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