Valine represents a branched-chain essential amino acid. In addition to body composition, it is also used for energy production in situations of special performance requirements. The need for valine is particularly high in competitive athletes.
What is valine?
Valine is a branched-chain amino acid that is essential for the body. Due to the branched hydrocarbon chain, it cannot be synthesized by the human organism. Along with the branched-chain amino acids leucine and isoleucine, which are also essential, it belongs to the BCAAs (Branched-Chain Amino Acids), the need for which increases sharply in stressful situations and at the highest levels of athletic performance. They promote muscle growth, inhibit muscle breakdown and, if required, also serve to generate energy. Valine is always found in the diet together with leucine and isoleucine. In a normal diet without additional exercise, however, their requirements should be covered by the diet. Valine consists of two optical enantiomers, L-valine and D-valine. In the body, only L-valine is ever involved in protein building. In further mention, therefore, we will always speak simply of valine when referring to L-valine. The term valine is derived from the Latin validus and means strong and healthy. The branched hydrocarbon chain of valine contains four carbon atoms. When the amino acid is broken down, propionyl-CoA is formed, which can be converted to glucose via succinyl-CoA.
Function, action, and roles
The main function of valine is to be available as a building block for protein synthesis. Muscle fibers in particular contain a lot of valine. However, within muscle cells there is a lot of free valine along with free isoleucine and leucine. These BCAAs are available as a reserve for muscle building and energy supply. Thus, these amino acids are used for energy production during increased athletic performance. If the BCAA concentration in the amino acid pool is too low, increased athletic performance will lead to muscle breakdown instead of muscle building, because the corresponding amino acids must be available quickly for energy production. Valine is not absorbed by the liver like other amino acids, but enters the muscle cells immediately. For energy production, valine must first be converted into glucose. This conversion takes place as part of the citric acid cycle via propionyl-CoA and succinyl-CoA. Succinyl-CoA in turn serves as an intermediate in various metabolic processes and can also be converted into glucose. Excess glucose is stored as glucogen in muscle cells and can be used as a reserve for energy production. Due to its hydrophobic nature, valine is also involved in building the secondary structure of proteins. Valine also serves as a starting material for the synthesis of pantothenic acid. This is synthesized from valine by intestinal bacteria and can be reabsorbed in the intestine for the body. With the help of pantothenic acid, valine also has a great influence on nerve functions. Valine also serves as a starting compound for the production of the neurotransmitter glutamate. Furthermore, valine also stimulates the release of insulin and thus ensures both the regulation of blood sugar levels and protein building. However, this effect is only developed together with the intake of the other amino acids. An isolated valine substitution even interferes with muscle building. Because of this building effect, valine, together with leucine and isoleucine, also supports the healing of injuries and wounds.
Formation, occurrence, properties, and optimal values
Valine is found in all protein-containing foods. This amino acid is particularly abundant in animal products such as beef, chicken breast, salmon, chicken eggs or cow’s milk. Walnuts, unshelled rice, dried peas or the whole grain flour of wheat and corn also contain a lot of valine. The daily requirement of valine for healthy adults is between 10 and 29 milligrams per kilogram of body weight. The average daily requirement is therefore about 1.6 grams. Athletes have an increased daily requirement and can take it additionally through protein powder. A preventive intake is not necessary.
Diseases and disorders
Although valine is one of the essential amino acids, deficiency of valine occurs very rarely. Most foods contain sufficient amounts of valine.However, a relative valine deficiency can result from an increased requirement, an unbalanced diet and energy-consuming diseases. In this case, this deficiency manifests itself in growth disorders, motor disorders, muscle breakdown, hypersensitivity to touch or cramps. In this case, a protein-rich diet guarantees an adequate supply of valine. Care should always be taken to ensure that valine and the other two BCAAs, leucine and isoleucine, are taken together with other amino acids. An isolated application of BCAAs can even lead to muscle breakdown. Much worse health problems, however, can result from degradation of valine. In so-called maple syrup disease, the breakdown of the branched-chain amino acids valine, isoleucine and leucine is disturbed. The cause is an autosomal recessive mutation that leads to a defect in the 2-keto acid dehydrogenase enzyme complex. This enzyme complex catalyzes the degradation of BCAAs. All three amino acids are excreted in the urine and cause a spicy odor reminiscent of maple syrup. The newborns quickly suffer from weakness in drinking, vomiting, coma, muscular hypertension and seizures in addition to this characteristic urine odor. Without treatment, death quickly results from ketoacidosis. Treatment consists of a lifelong low-protein diet. Another hereditary condition results in a secondary deficiency of several amino acids, including valine. This is Hartnup’s disease, which is characterized by a transport disorder of amino acids through the cell membrane. Pellagra-like symptoms develop because the production of niacin is impaired. Treatment involves substitution of the missing substances.
