Valine is an aliphatic amino acid that is closely related to leucine and isoleucine both in structure and function. These amino acids are extremely hydrophobic and are almost always found in the interior of proteins. They are also seldom useful in routine biochemical reactions, but are relegated to the duty of determining the three-dimensional structure of proteins due to their hydrophobic nature. They are also essential amino acids and must be obtained in the diet. Important sources of valine include soy flour, cottage cheese, fish, meats, and vegetables. Valine is incorporated into proteins and enzymes at the molar rate of 6.9 percent when compared to the other amino acids.

The branched-chain amino acids (BCAAs) are leucine, isoleucine, and valine. BCAAs are considered essential amino acids, because human beings cannot survive unless these amino acids are present in the diet. BCAAs are needed for the maintenance of muscle tissue and appear to preserve muscle stores of glycogen (a storage form of carbohydrate that can be converted into energy). BCAAs also help prevent muscle protein breakdown during exercise.

Some research has shown that BCAA supplementation (typically 10–20 grams per day) does not result in meaningful changes in body composition, nor does it improve exercise performance or enhance the effects of physical training. However, BCAA supplementation may be useful in special situations, such as preventing muscle loss at high altitudes and prolonging endurance performance in the heat. Studies by one group of researchers suggest that BCAA supplementation may also improve exercise-induced declines in some aspects of mental functioning.

BCAAs can activate glutamate dehydrogenase—an enzyme that is deficient in amyotrophic lateral sclerosis (ALS), also called Lou Gehrig’s disease. In one double-blind trial, 26 grams per day of BCAA supplements helped those with ALS maintain muscle strength. However, a larger study was ended early when people using BCAAs not only failed to improve, but experienced higher death rates than the placebo group. Other studies have shown no benefit of BCAA supplementation for ALS or other neuromuscular diseases, though a small group of people suffering from diseases of the nervous system, collectively called spinocerebellar degeneration, did improve when given BCAAs in a preliminary study.

One study investigating the advantages of BCAA supplementation for people with diabetes undergoing an intense exercise program found no additional benefit of BCAAs on reducing abdominal fat or improving glucose metabolism.

Patients with liver diseases that lead to coma—called hepatic encephalopathy—have low concentrations of BCAAs and excess levels of certain other amino acids. Preliminary research suggested that people with this condition might be helped by BCAAs. Double-blind studies have produced somewhat inconsistent results, but a re-analysis of these studies found an overall benefit for the symptoms of encephalopathy. Therapeutic effects of BCAAs have also been shown in children with liver failure and adults with cirrhosis of the liver. Any treatment of people with liver failure requires the direction of a physician.

People with chronic kidney failure may also benefit from BCAA supplementation. A preliminary study found improved breathing and sleep quality in people given intravenous BCAAs during kidney dialysis. Phenylketonuria (PKU) is a genetic disease that causes abnormally high amounts of phenylalanine and its end products to accumulate in the blood, causing damage to the nervous system. A controlled trial demonstrated that regular use of BCAAs by adolescents and young adults with PKU, improved performance on some tests of mental functioning. This outcome makes sense because BCAAs may compete with phenylalanine, reducing its toxic effects. In tardive dyskinesia, phenylalanine levels have also been reported to be elevated. As a result, one group of researchers gave tardive dyskinesia patients BCAAs (from 150 mg per 2.2 pounds body weight, up to 209 mg per 2.2 pounds body weight) after breakfast, and one hour before lunch and dinner for two weeks. The BCAA mixture included equal parts valine and isoleucine plus 33% more leucine than either of the other two amino acids. Of nine patients so treated, six had at least a 58% decrease in symptoms, and all people in the study had a decrease of at least 38% in symptoms.

Only a person deficient in protein would become deficient in BCAAs, because most foods that are sources of protein, supply BCAAs. Few people in Western societies are protein deficient.

Side effects have not been reported with the use of BCAAs. Until more research is conducted, people with ALS should avoid taking supplemental BCAAs. At high intakes, BCAAs are simply converted into other amino acids, used as energy, or converted to fat for storage. However, people with kidney or liver disease should not consume high amounts of amino acids without consulting their doctor.

Dairy products and red meat contain the greatest amounts of BCAAs, although they are present in all protein-containing foods. Whey protein and egg protein supplements are other sources of BCAAs. BCAA supplements provide the amino acids leucine, isoleucine, and valine.