Valine is the essential branched-chain amino acid that is critical for the muscle energy metabolism and for the neural function — it is one of the three branched-chain amino acids (leucine, isoleucine, valine), and it has a unique role as a both a gluconeogenic amino acid and a precursor of the neurotransmitter glutamate. The valine is metabolised in the skeletal muscle (where it is transaminated by the branched-chain aminotransferase to the alpha-ketoisovalerate, which is then oxidised by the branched-chain alpha-ketoacid dehydrogenase to the propionyl-CoA, which enters the gluconeogenic pathway or the TCA cycle). The valine is unique among the branched-chain amino acids because it is exclusively glucogenic (it is converted to the glucose and not to the ketone bodies), and it is therefore particularly important for the maintenance of the blood glucose levels during the exercise and during the fasting — when the glucose availability is limited and the muscle must rely on the gluconeogenesis from the amino acids for the energy. The valine is also a precursor of the glutamate — it is converted to the glutamate through the transamination pathway, and the glutamate is the primary excitatory neurotransmitter of the brain, the precursor of the GABA (the primary inhibitory neurotransmitter), and the key regulator of the nitrogen metabolism. Without adequate valine and branched-chain amino acid balance, the muscle energy is impaired, the blood glucose falls, and the neural function is compromised — the hallmark of the valine deficiency and of the branched-chain amino acid imbalance. The typical dietary valine intake from the protein-rich foods (meat, fish, poultry, eggs, dairy) is 0.5-2g daily, and the therapeutic doses for the muscle and neural support are 1-3g of the valine supplement daily — making it one of the most important branched-chain amino acids for the exercise performance, for the blood glucose regulation, and for the neural function.
Valine and the Muscle Energy
Valine supports the muscle energy metabolism through its role as a gluconeogenic precursor — during the exercise, when the blood glucose levels fall and the muscle glycogen is depleted, the valine (along with the other glucogenic amino acids) is taken up by the liver and converted to the glucose through the gluconeogenesis pathway. This glucose is then released into the bloodstream and taken up by the muscle, where it is used for the ATP production through the glycolysis and the oxidative phosphorylation. The valine also supports the muscle energy by providing the substrate for the TCA cycle — its oxidation produces the acetyl-CoA and the propionyl-CoA, which enter the TCA cycle and generate the ATP through the oxidative phosphorylation. This dual role of the valine as a gluconeogenic precursor and as a TCA cycle substrate makes it one of the most important amino acids for the muscle energy metabolism, particularly during the prolonged exercise and during the fasting. The valine also has a protein-sparing effect — by providing an alternative energy substrate for the muscle, it reduces the need for the muscle protein breakdown and thereby preserves the muscle mass during the exercise and during the caloric restriction.
The clinical importance of the valine for the muscle health is underscored by the observation that the branched-chain amino acid supplementation (including the valine) improves the exercise performance and reduces the muscle damage in athletes and in people with the muscle wasting. A study in 20 athletes found that the branched-chain amino acid supplementation (with a balanced ratio of leucine, isoleucine, and valine) at 5g daily during the training significantly reduced the muscle damage markers (by 30-40%, as measured by the creatine kinase and the lactate dehydrogenase), reduced the muscle soreness (by 20-30%), and improved the exercise performance (by 10-15%) — demonstrating the potent muscle-protective effect of the branched-chain amino acids in athletes.
Practical Application
For general valine supplementation for the muscle energy and for the neural support, the evidence-based approach is to supplement with 1-3g of L-valine daily (as the pure L-valine powder or capsule, taken in divided doses with the meals or before the exercise). The valine should be taken with the leucine and the isoleucine (which are the other branched-chain amino acids that work synergistically with the valine for the muscle protein synthesis, for the energy metabolism, and for the neural function). The valine is generally well-tolerated with no significant adverse effects at doses up to 6g daily, and it does not have any known drug interactions or contraindications — though people with the maple syrup urine disease should not use the valine supplementation. For comprehensive branched-chain amino acid and muscle support, valine pairs well with the leucine (which is the most potent activator of the mTOR pathway and which works synergistically with the valine for the muscle protein synthesis and for the energy metabolism), with the isoleucine (which is the third branched-chain amino acid and which has complementary metabolic effects), with the carbohydrates (which enhance the insulin secretion and which promote the amino acid uptake by the muscle), and with the exercise (which activates the mTOR pathway and which works synergistically with the valine for the muscle adaptation and for the metabolic health).
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