What do they do?
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).1 BCAAs also help prevent muscle protein breakdown during exercise.2
Some research has shown that BCAA supplementation (typically 10-20 grams per day) does not result in meaningful changes in body composition,3 nor does it improve exercise performance4 5 6 7 8 or enhance the effects of physical training.9 10 However, BCAA supplementation may be useful in special situations, such as preventing muscle loss at high altitudes11 and prolonging endurance performance in the heat.12 Studies by one group of researchers suggest that BCAA supplementation may also improve exercise-induced declines in some aspects of mental functioning.13 14 15
BCAAs can active 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.16 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.17 Other studies have shown no benefit of BCAA supplementation for ALS or other neuromuscular diseases,18 19 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.20
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.21
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,22 23 24 but a reanalysis of these studies found an overall benefit for the symptoms of encephalopathy.25 Therapeutic effects of BCAAs have also been shown in children with liver failure26 and adults with cirrhosis of the liver.27 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.28
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.29 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.30 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.
Where are they found?
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.
Who is likely to be deficient of branched-chain amino acids?
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.
How much branched-chain amino acids is usually taken?
Most diets provide an adequate amount of BCAAs for most people, which is about 25–65 mg per 2.2 pounds of body weight.31 32 Athletes involved in intense training often take 5 grams of leucine, 4 grams of valine, and 2 grams of isoleucine per day to prevent muscle loss and increase muscle gain, though most research does not support this use of BCAAs.
Are there any side effects or interactions with branched-chain amino acids?
Side effects have not been reported with the use of BCAAs. Until more research is conducted, people with ALS should avoid taking supplemental BCAAs. In one study, supplementation with a large amount of BCAAs (60 grams) caused alterations in the blood levels of tryptophan, phenylalanine, and tyrosine.33 The changes in the blood levels of these amino acids could, in theory, cause depression in susceptible individuals. Until more is known, individuals with a history of depression should consult a doctor before supplementing with BCAAs. People with kidney or liver disease should not consume high amounts of amino acids without consulting their doctor.
At the time of writing, there were no well-known drug interactions with branched-chain amino acids.