June 26, 2013

Protein, Amino Acids & BCAAs

Proteins are made up of amino acids, which contain carbon, hydrogen, oxygen and nitrogen. It is the nitrogen that distinguishes them from the composition of carbohydrates, fats and alcohol, which are made up of only carbon, hydrogen and oxygen.

20 AMINO ACIDS RUNDOWN | (1) Alanine  (2) Arginine  (3) Asparagine  (4) Aspartic Acid  (5) Cysteine  (6) Glutamic Acid  (7) Glutamine  (8) Glycine  (9) Histidine  (10) Isoleucine  (11) Leucine  (12) Lysine  (13) Methionine  (14) Phenylalanine  (15) Proline  (16) Serine  (17) Threonine  (18) Tryptophan  (19) Tyrosine  (20) Valine

Of the twenty amino acids needed by healthy adults, nine are considered indispensable because the body can't manufacture them and the remaining eleven are termed dispensable because they can be manufactured in the liver. Six of these eleven amino acids are referred to as conditionally indispensable because during periods of stress, the body can't manufacture a sufficient amount.

 Indispensable (9) | Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan & Valine
 Conditionally Indispensable (6) | Arginine, Cysteine, Glutamic Acid, Glycine, Proline & Tyrosine

Leucine, isoleucine and valine are the branched chain amino acids (BCAAs), so named because of their chemical structure. During prolonged endurance exercise when glycogen stores are low, skeletal muscle can metabolize these amino acids for energy. In addition to being used as an energy source, BCAAs compete with tryptophan, an amino acid associated with mental fatigue. BCAAs are also involved in the immune system. Athletes use BCAA supplements in an effort to reduce skeletal muscle damage and muscular fatigue. The usual recommended dose for supplemental BCAA is 5-20 grams/day in divided doses.

Six amino acids commonly broken down in muscle cells to yield energy include: branched chain amino acids (leucine, isoleucine and valine), aspartate, asparagine and glutamate. The breakdown of muscle or proteolysis, is stimulated by the stress hormone cortisol, which is secreted by the adrenal glands. When the body is stressed, one response is the oxidation of amino acids. Endurance exercise represents an acute (short-term) stress, so the use of amino acids for energy is not unexpected. Endurance exercise results in an increased oxidation of leucine. At the beginning of an endurance exercise task, there are usually sufficient carbohydrates stored as muscle glycogen, so little of the energy needed comes from amino acids initially. But as muscle glycogen store decline significantly, the skeletal muscle uses some amino acids, particularly leucine, for energy. Eighteen of the the twenty amino acids can be converted into glucose (only leucine and lysine cannot) and this takes place in the liver.