Posted: November 7, 2006

Science of Sport: Branched Chain Amino Acids and Exercise

Reviewed by Sally Warner, PhD

Introduction: Amino Acids are the building blocks for skeletal muscle as well as digestive enzymes, hormones, antibodies and other body proteins necessary for optimal functioning. Of the 20 amino acids in the body, there are two types: essential and non-essential. There are eight essential amino acids including -- leucine, isoleucine, lysine, methionine, phenylalanine, theonine, tryptophan, and valine. The term essential is used because the body cannot synthesize these amino acids, making it necessary to obtain them from the diet. The twelve non-essential amino acids are equally important, but can be synthesized in the body at a rate that equals demand so dietary intake is not as crucial. Complete proteins include all of the essential amino acids, and are considered higher quality proteins. Animal proteins (including dairy, poultry, eggs, beef, and pork) and soy protein (plant protein) are considered complete proteins. Incomplete proteins are missing one or more of the essential amino acids, and are therefore characterized as lower quality proteins. Eating a variety of animal and plant sources of protein is the best way to obtain all essential amino acids in the diet.

Valine, leucine and isoleucine are the Branched Chain Amino Acids (BCAA's). These three amino acids are named from their molecular configurations that create unique bonds. In addition, this amino acid group is metabolized in a different manner than other amino acids. During prolonged exercise, BCAA's are taken up by the skeletal muscle rather than the liver in order to contribute to energy production (oxidative metabolism). Making up one third of the muscle amino acid pool, BCAA's can become quickly depleted with exhaustive endurance exercise.

BCAA and Central Fatigue Theory
There has been an increased interest in the mechanism behind central fatigue and the influence of BCAA on fatigue during and after exercise. The central fatigue theory suggests that prolonged exercise lowers BCAA plasma (blood) concentration through amino acid oxidation and increases the plasma concentration of free fatty acids (FFA). The increased FFAs compete with tryptophan for binding sites on albumin which is a transporter protein. This cascade effect ultimately leads to an increase in free tryptophan levels in the brain where tryptophan is converted into the neurotransmitter serotonin. Serotonin can have a sedative effect on the central nervous system (CNS) and compromise athletic performance.

During prolonged exhaustive exercise, two mechanisms have been suggested to contribute to an imbalance between BCAA and tryptophan.

1) In the latter stages of prolonged exercise, low blood sugar stimulates gluconeogenesis which is the synthesis of new glucose from non-carbohydrate sources or amino acids. In particular BCAA's are broken down to be used as a fuel source. When this occurs the BCAA/tryptophan ratio is reduced leaving a relatively high level of tryptophan to enter the blood brain barrier and convert to serotonin.

2) FFAs also are broken down in higher amounts as glycogen becomes depleted during endurance exercise. Free fatty acids are water soluble and therefore bind to albumin for transport in the blood. Tryptophan also binds with albumin. Because there is a competition between tryptophan and FFA for albumin binding sites, the excess free tryptophan crosses the blood-brain barrier to convert to serotonin.

BCAA's and Protein Turnover
New evidence supports that oral ingestion of BCAA’s during exercise can have an anti-catabolic effect on skeletal muscle. Specifically, leucine can stimulate muscle protein synthesis (Lynch, 2003). When combined with carbohydrate feeding during exercise, BCAA’s stimulate protein synthesis and maintain whole body protein balance better than carbohydrates alone (Koopman, 2005). When BCAA’s were consumed during resistance training Shimomura et al. (2006) found a significant reduction in delayed onset muscle soreness (a.k.a. DOMS). Additionaly, when swimmers consumed 12g of BCAA’s they had reduced post exercise urinary protein metabolites suggesting that they experienced reduced protein turnover (Tang, 2006). Though more evidence is needed, these findings suggest that intake of BCAA’s may lessen skeletal muscle damage and may promote muscle synthesis in response to exercise.

BCAA's and Immune
Branched Chain Amino Acids also play a role in the immune response following exercise. Researchers have concluded that the administration of BCAA's may improve serum glutamine levels leading to a lesser incidence of sickness following exercise. Following an Olympic Distance Tri or 30K run Bassit looked studied the immune response in a group which was administered BCAA's vs a second group administered a placebo. The results indicate that branched-chain amino acid (BCAA) supplementation recovers plasma glutamine concentration. The amino acids also positively affect the immune response. (Basset, 2000)

A follow-up study again proved the benefit of supplementing with BCAA's during exercise in respect to immune function. Twelve elite male triathletes of swam 1.5 km, cycled 40 km, and ran 10 km (Olympic triathlon) in the Sao Paulo International Triathlon held in April 1997 and April 1998. In both events, six athletes received BCAA and the others, placebo. The athletes from the BCAA group (BG) presented the same levels of plasma glutamine, before and after the trial, whereas those from the placebo group showed a reduction of 22.8% in plasma glutamine concentration after the competition. The BCAA group showed a 33.84% reduced incidence of infection due to improvement in immune response following exercise over the placebo group.

BCAA are commercially available as powder or pill form and are ingredients in various carbohydrate-electrolyte drinks. Studies have investigated the effect of BCAA supplementation immediately before, during, and after endurance exercise. There is some evidence to support BCAA supplementation during endurance exercise but it has been criticized due to methodological errors and lack of control (Davis et al., 2000). It is difficult to separate the effect of carbohydrate and BCAAs on the brain and muscle, but data does exist to support a beneficial role of the two combined on central fatigue during endurance exercise. The evidence is stronger to support supplementation of BCAAs during recovery of endurance exercise and to reduce incidence of infection. BCAAs have been shown to decrease indicators of muscle damage and protein degradation following exercise.

Recommendations
Too much sodium, water or even carbohydrates can cause negative effects. The same holds true for too high levels of BCAA's. These negative effects can include a slowing of water absorption, gastric distress and the reduced absorption of other amino acids. It is recommended that endurance athletes consume BCAA's at moderate levels in order to assure no negative affects. On the positive side supplementing at moderate doses can offer a reduced incidence of infection, improved 'mental energy' and assurance of adequate levels of a circulating amino acid pool.

1. The breakdown of protein, particularly BCAA's occurs as carbohydrate stores decline. This happens primarily in long exhaustive exercise. The first line of defense is to keep a healthy level of blood sugar by supplementing with a carbohydrate drink during exercise that is intense and lasts longer than 1 hour. Supplement with 45-60g carbohydrates in a 6-8% solution per hour of exercise.

2. The release of serotonin (the fatigue hormone) occurs when BCAA's decline and tryptophan increases. Supplementing with BCAA's during exercise may help maintain a healthy ratio. Supplement with a carbohydrate electrolyte drink that contains BCAA during exhaustive endurance exercise. Consume 2 - 6 g of BCAA's per hour of exercise (no ill effects have been shown with up to 30 g per day).

3. Consider supplementing BCAA's following long exhaustive exercise. This will help you remain mentally and physically strong through consecutive days of hard endurance training through improved immune response and reduced incidence of infection. Supplement with 4 - 6 g BCAA's following your hardest workouts.

4. Consider BCAA supplementation if you participate in extensive endurance training and ingest an inadequate amount of carbohydrate in your daily training meals.

5. It has been theorized that supplementing with BCAA's in doses considerably larger than what is recommended can cause some adverse effects like inhibiting the absorption of other amino acids, slowing water absorption in the gut and can potentially increase the need for thiamin. Consume only what is recommended.

For more reading in this area the American Society for Nutrition published the proceedings from the 4th Amino Acid Assessment Workshop in the Journal of Nutrition Volume 136S in 2006.

References:
1. Armsey, T.D et al. Protein and amino acid supplementation in athletes. Current Sports Medicine Reports. 2003, 4:253-256.

2. Bassit RA, et. al, Branched-chain amino acid supplementation and the immune response of long-distance athletes. Nutrition. 2002 May;18(5):376-9.

3. Bassit RA, Sawada LA, Bacurau RF, Navarro F, Costa Rosa LF. The effect of BCAA supplementation upon the immune response of triathletes. Med Sci Sports Exerc. 2000 Jul;32(7):1214-9.

4. Blomstrand E, Moller K, Secher NH, Nybo L. Effect of carbohydrate ingestion on brain exchange of amino acids during sustained exercise in human subjects.Acta Physiol Scand. 2005 Nov;185(3):203-9.

5. Blomstrand E, Celsing F, Newsholme EA. Changes in plasma concentrations of aromatic and branched-chain amino acids during sustained exercise in man and their possible role in fatigue. Acta Physiol Scand. 1988 May;133(1):115-21.

6. Blomstrand E, Hassmen P, Ek S, Ekblom B, Newsholme EA. Influence of ingesting a solution of branched-chain amino acids on perceived exertion during exercise. Acta Physiol Scand. 1997 Jan;159(1):41-9.

7. Blomstrand E, Hassmen P, Ekblom B, Newsholme EA. Administration of branched-chain amino acids during sustained exercise--effects on performance and on plasma concentration of some amino acids. Eur J Appl Physiol Occup Physiol. 1991;63(2):83-8.

8. Castell LM, Yamamoto T, Phoenix J, Newsholme EA. The role of tryptophan in fatigue in different conditions of stress. Adv Exp Med Biol. 1999;467:697-704.

9. Davis JM, Alderson NL, Welsh RS. Serotonin and central nervous system fatigue: nutritional considerations. Am J Clin Nutr. 2000 Aug;72(2 Suppl):573S-8S.

10. Davis JM, Bailey SP, Woods JA, Galiano FJ, Hamilton MT, Bartoli WP. Effects of carbohydrate feedings on plasma free tryptophan and branched-chain amino acids during prolonged cycling. Eur J Appl Physiol Occup Physiol. 1992;65(6):513-9.

11. Davis JM, Welsh RS, De Volve KL, Alderson NA. Effects of branched-chain amino acids and carbohydrate on fatigue during intermittent, high-intensity running. Int J Sports Med. 1999 Jul;20(5):309-14.

12. Davis JM. Carbohydrates, branched-chain amino acids, and endurance: the central fatigue hypothesis. Int J Sport Nutr. 1995 Jun;5 Suppl:S29-38.

13. Gastmann UA, Lehmann MJ. Overtraining and the BCAA hypothesis. Med Sci Sports Exerc. 1998 Jul;30(7):1173-8.

14. Hassmen P, Blomstrand E, Ekblom B, Newsholme EA. Branched-chain amino acid supplementation during 30-km competitive run: mood and cognitive performance. Nutrition. 1994 Sep-Oct;10(5):405-10.

15. Koopman R, Wagenmakers AJ, Manders RJ, Zorenc AH, Senden JM, Gorselink M, Keizer HA, van Loon LJ. Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects. Am J Physiol Endocrinol Metab. 2005 Apr;288(4):E645-53. Epub 2004 Nov 23.

16. Lynch CJ, Halle B, Fujii H, Vary TC, Wallin R, Damuni Z, Hutson SM. Potential role of leucine metabolism in the leucine-signaling pathway involving mTOR. Am J Physiol Endocrinol Metab. 2003 Oct;285(4):E854-63. Epub 2003 Jun 17.

17. Lehmann M, Huonker M, Dimeo F, Heinz N, Gastmann U, Treis N, Steinacker JM, Keul J, Kajewski R, Haussinger D. Serum amino acid concentrations in nine athletes before and after the 1993 Colmar ultra triathlon. Int J Sports Med. 1995 Apr;16(3):155-9.
Mittleman KD, Ricci MR, Bailey SP. Branched-chain amino acids prolong exercise during heat stress in men and women. Med Sci Sports Exerc. 1998 Jan;30(1):83-91.

18. Shimomura Y, Murakami T, Nakai N, Nagasaki M, Harris RA., Exercise promotes BCAA catabolism: effects of BCAA supplementation on skeletal muscle during exercise.J Nutr. 2004 Jun;134(6 Suppl):1583S-1587S.

19. Shimomura Y, Yamamoto Y, Bajotto G, Sato J, Murakami T, Shimomura N, Kobayashi H, Mawatari K. Nutraceutical effects of branched-chain amino acids on skeletal muscle. J Nutr. 2006 Feb;136(2):529S-532S.

20. Tanaka H, West KA, Duncan GE, Bassett DR Jr. Changes in plasma tryptophan/branched chain amino acid ratio in responses to training volume variation. Int J Sports Med. 1997 May;18(4):270-5.

21. Tang FC. Influence of branched-chain amino acid supplementation on urinary protein metabolite concentrations after swimming. J Am Coll Nutr. 2006 Jun;25(3):188-94.

The Endurance Research Board's (ERB) objective is to offer a broad perspective on both innovative and long-standing endurance nutrition. In addition to having advance science degrees, each member of our ERB races at an elite level. Our scientists are professional mountain bikers, professional triathletes and Cat 1 cyclists. Members of the Endurance Research Board include: Sally Warner MA Ph.D., Neal Henderson MS CSCS, Shawn Dolan Ph.D., Bob Seebohar, MS, RD, CSCS

* The ERB is a resource of First Endurance Nutrition

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