Branched-Chain Amino Acid Supplementation for Athletes
Protein, together with carbohydrates and fat, is one of the three macronutrients that provide the vast majority of energy to the body. As the major structural component of all tissues there are approximately 50,000 different types of protein containing compounds in the human body-65% of which are found in skeletal muscle. The main purpose of dietary protein is to supply raw materials for the construction and maintenance of bodily tissues, especially muscle. In addition, proteins play a vital role in human health including hormone regulation, immunity defense and oxygen delivery to tissues and organs.
Although protein is involved in almost every cellular function, the human body does not store protein. Therefore, there is a constant turnover of protein in the body; some proteins are always being synthesized while others are being degraded. Proteins are actually very large, complex molecules, or macromolecules, made up of individual amino acid units. Often referred to as the ""building blocks"" of protein, amino acids can fall into one of two categories: nonessential and essential. The term ""nonessential"" can be deceiving-while these amino acids are necessary for survival they can be created within the body and do not have to be acquired from outside sources. Essential amino acids, however, must be obtained through the diet. Of the 20 amino acids, 11 are considered nonessential and the other 9 are essential. Good sources of dietary protein like meat, fish, milk and eggs are known as ""complete"" proteins because they contain all 9 essential amino acids. ""Incomplete"" proteins are usually found in plant foods such as rice, beans and wheat, and only contain some of the essential amino acids.
Within the essential and nonessential categories, individual amino acids are characterized by their molecular structure. Of the essential amino acids, there are three ""branched chain amino acids"", or BCAAs, that constitute one third of all muscle protein. The three BCAAs, leucine, isoleucine and valine, are a major factor in the formation and maintenance of muscle tissue. Unlike most amino acids that are metabolized in the liver, BCAAs are broken down in skeletal muscle where they can be used for energy, or to form new amino acids and proteins.
Like all amino acids, BCAAs that enter the body are absorbed through the small intestines for transport in the blood to tissues and organs. Most BCAAs, especially during and after a heavy resistance workout, are taken up by muscle tissue. When skeletal muscle needs for fuel increase during intense exercise, BCAAs can directly target the working muscles to provide energy. Targeting specific muscles makes the BCAAs unique; all other amino acids have to undergo a multi stage transformation process in the liver before they can play a role in energy production.
Scientists have concluded that the special role BCAAs play in energy production may help athletes avoid fatigue during exercise. A second method in which BCAAs may sustain exercise is by acting on the brain and central nervous system to offset feelings of fatigue in athletes. Researchers theorize that BCAA supplementation leads to increased entry of BCAA into the brain and central nervous system resulting in a decreased entry of another amino acid, tryptophan. Tryptophan is a precursor to serotonin, a chemical messenger in the brain known to elevate mood and suppress appetite. Increased levels of tryptophan entry to the brain lead to sensations of drowsiness and lethargy. In fact, tryptophan supplements are often taken as a natural sleep aid. When there are greater BCAAs available in the blood, the entry of BCAAs to the brain is increased while tryptophan entry decreases-prolonging the time to fatigue during exercise.
BCAAs have also been proven to have an anabolic effect on protein metabolism in skeletal muscle by increasing the rate of protein synthesis and reducing protein breakdown. Evidence suggests that exercise may increase the BCAA requirement in skeletal muscle, and that a greater intake will help muscles recover after an intense workout. When using BCAA supplements before a workout session, muscle damage due to the degradation of protein during exercise is decreased. Post-exercise, the increased protein synthesis activated by BCAA supplementation may increase muscle gains during recovery and offset soreness. Research has found that BCAAs can decrease soreness and fatigue up to several days following an exhaustive lifting session.
BCAA supplementation has the potential to help athletes increase performance during training and aid in recovery. The benefits of greater energy levels and decreased fatigue can give athletes the opportunity to intensify their training. Higher intensity inevitably leads to better results in muscle size and strength gains. When higher intensity is combined with better muscle recovery from an increased rate of protein synthesis post-exercise, athletes will find the anabolic effects make BCAA supplementation a necessary addition to their workout regime.
- Blomstrand E, Ek S, Newsholme EA. Influence of ingesting a solution of branched-chain amino acids on plasma and muscle contractions of amino acids during prolonged submaximal exercise. Nutrition. 1996; 12: 485-490.
- Blomstrand E, Eliasson J, Karlsson HKR, Kohnke R. Branched-chain amino acids activate key enzymes in protein synthesis after physical exercise. Journal of Nutrition. 2006; 136: 269S-273S.
- Davis JM, Welsh RS, De Volve KL, Alderson NA. Effects of branched-chain amino acids and carbohydrates on fatigue during intermittent, high intensity running. Internation Journal of Sports Medicine. 1999; 20: 309-314.
- Garlick PJ, Grant I. Amino acid infusion increases the sensitivity of muscle protein synthesis in vivo to insulin. Biochemistry Journal. 1988; 254: 579-584.
- Karlsson HKR, Nilsson P, Nilsson J, Chibalin AV, Zierath JR, Blomstrand E. Branched-chain amino acids increase p70S6k phophorylation in human skeletal muscle after resistance exercise. American Journal of Physiology-Endocrinology and Metabolism. 2004; 287: 1-7.
- Kimball SR, Jefferson LS. Signaling pathways and molecular mechanisms through which branched-chain amino acids mediate translational control of protein synthesis. Journal of Nutrition. 2006; 136: 227-231.
- Kurpad AV, Regan MM, Raj T, Gnanou JV. Branched-chain amino acid requirements in healthy adult human subjects. Journal of Nutrition. 2006; 136: 256-263.
- Maclean DA, Graham TE, Saltin B. Branched-chain amino acids augment ammonia metabolism while attenuating protein breakdown during exercise. American Journal of Physiology. 1994; 267: E1010-E1022.
- Shimomura Y, Murakami T, Nakai N, Nagasaki M, Harris RA. Exercise promotes BCAA catabolism: Effects of BCAA supplementation on skeletal muscle during exercise. Journal of Nutrition. 2004; 134: 1583S-1587S.
- 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. Journal of Nutrition. 2006; 136: 529S-532S.