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Glycogen Sparing Effect of BCAAs

The branched-chain amino acids (BCAAs) leucine, isoleucine and valine are considered essential amino acids. That is, you need to consume them in your diet since your body can't produce them endogenously. BCAAs are utilized as a fuel source during prolonged exercise by the working muscle.

In essence, BCAAs are released from the liver and skeletal muscles. The carbon skeleton of these amino acids is used as fuel while the nitrogen residues form the amino acid alanine. Alanine is then shuttled to the liver, where it's converted to glucose (gluconeogenesis). Consequently, this glucose is shuttled back to skeletal muscle to he used as fuel. This mechanism by which blood glucose homeostasis is maintained is called the glucose-alanine cycle. Thus, the ingestion of BCAAs may result in a net decrease in the amount of skeletal muscle protein that is broken down, which has applications to both endurance and strength-power athletes. Minimizing the rate of muscle-fiber breakdown is paramount for strength-power athletes such as bodybuilders. In addition, new evidence suggests that in a carbohydrate-depleted state, the ingestion of BCAAs may spare muscle glycogen use.

Scientists at the department of biochemistry at Oxford University, England, examined the effects of sustained exhaustive cycling exercise on plasma levels of amino acids as well as muscle glycogen concentration. Subjects performed cycling exercise at 70% of maximum oxygen uptake for 60 minutes followed by 20 minutes of maximal cycling (that is, the subjects were encouraged to cycle as hard as possible). Immediately before exercise and after every 15 minutes of exercise, each subject drank a solution containing either 90 mg of BCAAs per kilogram of bodyweight or a flavored placebo. The two drinks had a similar taste.

The ingestion of the BCAAs resulted in a significant increase in blood and muscle concentrations of these amino acids, and muscle glycogen concentration decreased much less in the BCAA group (about 10%) vs. the placebo group (about 35%). Furthermore, BCAA ingestion resulted in a significantly greater increase in blood and muscle alanine levels. The researchers suggested that alanine may have been converted to glucose in the liver and then transported to the working muscle to be used as fuel. This would make sense, since less muscle glycogen was used in the BCAA supplemented group.

This study may be relevant to both endurance and strength athletes, because the ingestion of BCAAs may diminish the loss of muscle glycogen and alleviate the loss of muscle volume, not to mention the positive effects on energy production. Written by Jose Antonio, PhD.

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