Branched-chain Amino Acids (BCAA)
What are BCAAs?
Branched-chain amino acids include leucine, isoleucine and valine. These amino acids are oxidised during exercise. The metabolism of BCAAs takes place in skeletal muscle rather than the liver. In the muscle BCAAs are a major nitrogen source for glutamine and alanine (two amino acids) synthesis. BCAAs are essential amino acids, in that the body can not make them, they need to be obtained from dietary sources.
Proposed Benefits of BCAAs
It is claimed that BCCAs will enhance recovery after exercise and also reduce the onset of "central fatigue". In addition to this it is claimed that the supplementation with BCAAs during prolonged exercise may reverse the exercise-induced reduction in glutamine levels which may in turn improve immune status.
Mechanism of Action of BCAAs
For Muscle Recovery
It is suggested that BCAAs have a protein-sparing effect during recovery after exercise. It is hypothesised that the effect is due to either a stimulation of protein synthesis and/or a reduction on protein degradation.
The central fatigue hypothesis
Central fatigue has been described as the fatigue resulting from the nervous system rather than the muscle. It is hypothesised that central fatigue is due to increased levels of serotonin in the brain, which result from greater amounts of free tryptophan crossing the blood brain barrier. BCAA and tryptophan compete for the same transporter into the brain. Therefore when BCAAs decrease during exercise (because they are used as a fuel), more tryptophan can cross into the brain. It is therefore theorised that supplementation with BCAAs during exercise might prevent the drop in blood BCAA levels and therefore attenuate the exercise-induced increase in the free tryptophan:BCAA ratio which would thereby reduce the likelihood of fatigue arising from an increase in blood serotonin levels.
Immune Function
It is thought that supplementation with BCAAs will lessen the exercise-induced decrease in glutamine concentrations, and this may translate into an improved immune status
Research on BCAAs
For Muscle Recovery
Several studies have shown that the ingestion of protein in general following exercise increases muscle synthesis and aid muscle recovery (1). Other studies have shown that BCAAs in particular may aid in exercise recovery.
Blomstrand looked at the effects of ingesting 100mg/kg of BCAAs on muscle recovery (2). This study showed that the release of certain amino acids from the muscle during the recovery period was lower for the supplemented group compared to the placebo. This indicates a reduced net rate of protein degradation. It should be noted however, that subjects in this study began exercise in the glycogen-depleted state (most athletes would not begin exercise in this state) and so it is not known whether this would affect BCAAs during recovery.
A study by Coombes also recently looked at the effects of BCAA supplementation during exercise on recovery (3). This group measured levels of blood creatine kinase (CK) and lactate dehydrogenase (LDH) which are indicators of muscle damage from exercise. Results showed significant reductions in CK and LDH after exercise when supplemented with BCAA. This may help reduce delayed-onset muscle soreness. Although no athletic performance benefit have been proven, research continues in this area.
The central fatigue hypothesis
Early field studies suggested that the ingestion of 7.5-21g of BCAAs prior to or during exercise was associated with small improvements in physical and mental performance in some subjects (4,5). These studies however have several methodological problems. For example, subjects were not appropriately matched prior to randomisation, blinding of treatment was not always possible, and failure to control for important variables such as exercise intensity, food and water intake. These methodological problems make it difficult to ascribe benefit to BCAA or to inherent differences in study subjects or uncontrolled variables. Subsequent well-controlled laboratory studies have failed to demonstrate beneficial effects from BCAA supplementation (6-8).
Research suggests that the amount of branched-chain amino acids required to be ingested to reduce the free tryptophan:BCAA ratio results in an increase in ammonia concentrations. Ammonia is toxic to the brain and muscle and may in itself produce negative effects on exercise performance and increase fatigue (9-11). Doses lower than 100mg/kg do not appear to increase ammonia levels. Administering large doses of BCAAs during exercise is likely to slow water absorption and cause gastrointestinal disturbances.
For Immune Status
Bassit et al recently investigated the effects of BCAA supplementation upon immune response in a group of triathletes (12). Half of the group studied were given BCAA for 30 days before and 10 days after the completion of an Olympic-distance triathlon. Athletes in the placebo group (n=6) showed a 23% reduction in plasma glutamine levels after competition and also showed a 34% increase in the number of symptoms of infection 1 week after competition. The supplemented group showed similar plasma glutamine levels before and after the event.
Rating of Efficacy for BCAAs
There is promising data suggesting that BCAAs may aid muscle recovery. Further studies should provide more definitive evidence.
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References
1. Rasmussen B.B., Tipton K.D., Miller S.L., Wolfe S.E. and Wolfe R.E. An oral essential amino acid-carbohydrate supplementation enhances muscle protein anabolism after resistance exercise. J Appl Physiol. 88:386-392, 2000.
2. Blomstrand E.F. and Saltin B. BCAA intake affects protein metabolism in muscle after but not during exercise in humans. Am J Endocrinol Metab. 281:E365-E374, 2001.
3. Coombes J.S. and McNaughton L.R. Effects of branched-chain amino acid supplementation on serum creatine kinase and lactate dehydrogenase after prolonged exercise. J Sports Med Phys Fitness. 40:240-246, 2000.
4. Blomstrand E.F., Hassmen P., Ekblom B. and Newsholme E.A. Administration of branched-chain amino acids during sustained exercise - Effects on performance and on plasma concentrations of some amino acids. Eur J Appl Physiol. 63:83-88, 1991.
5. Blomstrand E.F., Hassmen P. and Newsholme E.A. Effect of branched-chain amino acid supplementation on mental performance. Acta Physiol Scand. 136:473-481, 1991.
6. Galiano F.J., Davis J.M., Bailey S.P., Woods J.A. and Hamilton M. Physiologic, endocrine and performance effects of adding branch chain amino acids to a 6% carbohydrate electrolyte beverage during prolonged cycling. Med Sci Sports Exerc. 23:S14, 1991.
7. Varnier M., Sarto P., Martines D., Lora L., Carmignoto F., Leese G. and Naccarato R. Effect of infusing branch-chain amino acid during incremental exercise with reduced muscle glycogen content. Eur J Appl Physiol. 69:26-31, 1994.
8. Verger P.H., Aymard P., Cynobert L., Anton G. and Luigi R. Effects of administration of branched-chain amino acids vs glucose during acute exercise in the rat. Physiol Behav. 55:523-526, 1994.
9. Bannister W.W. and Cameron B.J.C. Exercise-induced hyperammonemia: Peripheral and central effects. Int J Sports Med. 11:S129-S142, 1990.
10. Wagenmakers A.J.M., Coakley J.H. and Edwards R.H.T. Metabolism of branched-chain amino acids and ammonia during exercise: Clues from McArdle's disease. Int J Sports Med. 11:S101-S113, 1990.
11. Wagenmakers A.J.M., Bechers E.J., Brouns F., Kruipers H., Soeters P.B., Van der Vusse G.J. and Saris W.H.M. Carbohydrate supplementation, glycogen depletion, and amino acid metabolism during exercise. Am J Physiol. 260:E883-E890, 1991.
12. Bassit R.A., Sawada L.A. and Bacurau R.F.P. The effect of BCAA supplementation upon the immune response of triathletes. Med Sci Sports Exerc. 32:1214-1219, 2000.
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