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Branched-Chain Amino Acids



What are Branched-Chain Amino Acids (BCAAs)?   There are three branched-chain amino acids (BCAAs), these are: isoleucine, leucine, and valine.  BCAA’s are considered essential, as unlike other amino acids they cannot be manufactured in the human body, and they can only be obtained in our diet.  In total there are nine essential amino acids, but, BCAAs account for 35% of all the essential amino acids found within muscle protein.  They are needed for protein building and can be metabolised and used as an energy source during aerobic exercise.  BCAAs are present in all protein rich foods, but are found in the greatest amounts in red meat and dairy products.  Whey protein contains particularly high levels of BCAAs.   


Who might benefit from BCAA supplements?   The main benefits of BCAAs are: A reduction in the amount of muscle breakdown, improved preservation of muscle glycogen stores, improved immune health, and a possible improvement in endurance performance.  Therefore anyone who trains intensively, wants to recover more quickly from training, increase lean muscle size, reduce muscle soreness, and improve endurance performance may benefit from BCAAs.


Summary of BCAAs physiological effects:

  • Stimulates muscle protein synthesis (muscle building)

  • Decreases muscle protein catabolism (muscle breakdown)

  • Helps to increase lean muscle mass

  • Reduces muscle damage and soreness following exercise

  • Improve immune function

  • May enhance endurance exercise performance


What does research say about BCAA supplements?   In skeletal muscles and the heart, BCAA supplementation alone, has the same benefits of stimulating protein synthesis and reducing muscle breakdown, as is the case when the supply of all amino acids is increased (May and Buse, 1989).  BCAAs supplementation has been demonstrated to preserve and even increase muscle size under extreme physical conditions where there would normally be a net loss of muscle tissue (Schena et al., 1992; Bigard et al., 1996).  Research looking at the effect of BCAA supplementation during prolonged skiing at altitude, found that the consumption of BCAAs helped to prevent a loss of body mass (Bigard et al., 1996). Research has also demonstrated a positive effect on immune function with BCAAs supplementation (Bassit et al., 2000; Bassit et al., 2002).   

During aerobic exercise, or any prolonged exercise session, BCAAs can be oxidized within the mitochondria of skeletal muscles to produce aerobic energy – the six other essential amino acids are mainly catabolized within the liver (Shimomura et al., 2004).  It is well known that during aerobic exercise – endurance exercise in particular – the level of BCAAs metabolised to produce energy increases significantly (Rennie, 1996; Kobayashi et al., 1999).  Therefore, during any prolonged period of exercise, a significant amount of BCAAs, may be metabolised and may lead to a depletion of BCAAs within muscles.  

Research looking at the effect of BCAA supplementation has found that taking 77mg of BCAAs, per kg of bodyweight, before exercise results in a significant reduction in the amount of muscle breakdown (MacLean et al., 1994).  So to reduce muscle breakdown during exercise a 70kg athlete would consume around 5g of BCAAs.  It has also been demonstrated that the consumption of BCAAs before and after exercise reduces the levels of serum creatine kinase activity – which indicates reduced levels of muscle breakdown (Coombes and McNaughton, 2000; Nosaka, 2003).  BCAA supplementation before and after exercise also appears to increase the recovery rate from exercise, as indicated by a reduction in muscle soreness following exercise (Nosaka, 2003).  Therefore, BCAA supplementation, before and after exercise, appears to be beneficial for reducing the level of exercise-induces muscle damage and for increasing muscle protein synthesis (muscle building) and enhancing the recovery process following exercise. 

A further benefit, is the positive effects that BCAAs supplementation appears to have on endurance performance.   BCAAs compete with the amino acid trytophan for uptake into the brain.  During prolonged exercise BCAAs are used for fuel and this leads to a decreased level of BCAAs in the blood.  The decreased levels of BCAAs in the blood means there is a greater ratio of tryptophan uptake into the brain.  High levels of tryptophan in the brain, are associated with increased feelings of tiredness and fatigue, and hence, reduced exercise performance.  Supplementation with BCAAs during exercise keeps the levels of BCAAs elevated in the blood and helps to delay the build up of tryptophan in the brain.  Research suggests that supplementing with BCAAs during exercise may have a positive effect on exercise performance by reducing fatigue (Blomstrand et al., 1991). 


Are BCAAs effective?  Research has shown that BCAAs are effective for enhancing muscle growth and recovery from exercise.  They also improve immune health and may enhance endurance exercise performance.


How should I take BCAAs?   The general recommendation for enhancing exercise performance, improving recovery, and increasing lean muscle size, is to consume 3-5grams of BCAAs 30 minutes before exercise, and a further 3-5g within 30minutes of completing exercise. On non-training days the recovery rate may be enhanced, and lean muscle mass maintained, by consuming 3-5g of BCAAs, 1-2 times during the day – consider taking one serving first thing in the morning and one last thing at night.  There are no reports of any side effects associated with BCAA consumption (Shimomura et al., 2004).



Bassit, R. A., Sawada, L. A., Bacurau, R. F. P., Navarro, F. and Costa Rosa, L. F. B. P. (2000) The effect of BCAA supplementation upon the immune system of triathletes. Medicine and Science in Sports and Exercise. 32, 1214-1219. 

Bassit, R. A., Sawada, L. A., Bacurau, R. F., Navarro, F., Martins, E. Jr, Santos, R. V., Caperuto, E. C., Rogeri, P. and Costa Rosa, L. F. (2002) Branched-chain amino acid supplementation and the immune response of long-distance athletes. Nutrition. 18 (5), 376-379. 

Bigard, A. X., Lavier, P., Ulmann, L., Legrand, H., Douce, P. and Guezennec, C. Y. (1996) Branched-chain amino acid supplementation during repeated prolonged skiing exercises at altitude. Int J Sport Nutr. 6 (3), 295-306. 

Blomstrand, E., Hassmen, P. and Ekblom, B. (1991) Administration of branched-chain amino acids during sustained exercise-effects on performance and on plasma concentration of some amino acids. European Journal of Applied Physiology. 63, 83-88.  

Coombes, J. S. and McNaughton, L. R. (2000) 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. 

Kobayashi, r. shimomura, Y., Murakami, T., Nakai, N., Otsuka, M., Arakawa, N., Shimizu, K. and Harris, R. A. (1999) Hepatic branched-chain alpha-keto acid dehydrogenase complex in female rats: activation by exercise and starvation. J Nutr Sci. Vitaminol. 45, 303-309. 

May, M. E. and Buse, M. G. (1989) Effects of branched chain amino acids on protein turnover. Diab Metab Rev. 5 (3), 227-245. 

MacLean, D. A., Graham, T. E. and Saltin, B. (1994) Branched-chain amino acids augment ammonia metabolism while attenuating protein breakdown during exercise. Am J Physiol. 267, E1010-E1022. 

Nosaka, K. (2003) Muscle soreness and amino acids. Training J. 289, 24-28. 

Rennie, M. J. (1996) Influence of exercise on protein and amino acid metabolism. In: Handbook of Physiology, Sect 12: Exercise: Regulation and Integration of Multiple Systems (Rowell, L. B. & Shepherd, J. T., eds), Chapter 22. 995-1035. American Physiological Society, Bethesda, MD. 

Schena, F., Guerrini, F. and Tregnaghi, P. (1992) Branched-chain amino acid supplementation during trekking at altitude. The effects on loss of body mass, body composition, and muscle power. European Journal of Applied physiology. 65, 394-398. 

Shimomura, Y., Murakami, T., Nakai, N., Nagasaki, M. and Harris, R. A. (2004) Exercise Promotes BCAA Catabolism: Effects of BCAA Supplementation on Skeletal Muscle during Exercise. J Nutr. 134, 1583S-1587S.


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Last modified: 01/05/06