Branched-chain amino acids (BCAAs)

DEFINITION: Natural substance of the human body used as a supplement to treat specific health conditions.

PRINCIPAL PROPOSED USES: Amyotrophic lateral sclerosis (Lou Gehrig’s disease), loss of appetite (in persons with cancer)

OTHER PROPOSED USES: Muscular dystrophy, recovery from surgery, recovery from traumatic brain injury, severe liver disease such as cirrhosis, sports and fitness support, tardive dyskinesia, muscle growth and repair, diabetes management, obesity, neurological conditions

Overview

Branched-chain amino acids (BCAAs) are naturally occurring molecules (leucine, isoleucine, and valine) that the body uses to build proteins. The term “branched chain” refers to the molecular structure of these particular amino acids. Muscles have a particularly high content of BCAAs. For reasons that are not entirely clear, BCAA supplements may improve appetite in cancer patients and slow the progression of amyotrophic lateral sclerosis (ALS, or Lou Gehrig’s disease, a condition that leads to degeneration of nerves, atrophy of the muscles, and eventual death). BCAAs have also been proposed as a supplement to boost athletic performance. There have been many other proposed therapeutic uses for BCAAs.

Requirements and Sources

Dietary protein usually provides all the BCAAs needed. However, physical stress and injury can increase a person’s need for BCAAs to repair damage, so supplementation may be helpful.

BCAAs are present in all protein-containing foods, but the best sources are red meat and dairy products. Chicken, fish, and eggs are excellent sources as well. Whey protein and egg protein supplements are another way to ensure that a person is getting enough BCAAs. Supplements may contain all three BCAAs together or simply individual BCAAs.

Therapeutic Dosages

The typical dosage of BCAAs is 1 to 5 grams (g) daily.

Therapeutic Uses

Preliminary evidence suggests that BCAAs may improve appetite in people undergoing treatment for cancer. There is also some evidence that BCAA supplements may reduce symptoms of amyotrophic lateral sclerosis (ALS, or Lou Gehrig’s disease); however, not all studies have had positive results.

Preliminary evidence from a series of small studies suggests that BCAAs might decrease symptoms of tardive dyskinesia, a movement disorder caused by long-term usage of antipsychotic drugs. BCAAs have also shown a bit of promise for enhancing recovery from traumatic brain injury.

Because of how they are metabolized in the body, BCAAs might be helpful for individuals with severe liver disease (such as cirrhosis). BCAAs have also been tried for aiding muscle recovery after bed rest, such as following surgery.

Although there is little supportive evidence, on balance, existing research does not indicate that BCAAs are effective for enhancing sports performance. Some research hints that BCAAs might aid recovery from long-distance running and limit soreness. BCAAs have also failed to prove effective for muscular dystrophy.

Other therapeutic uses for BCAAS include managing diabetes, combating obesity, and managing the symptoms of neurological disorders. However, more studies are needed on these uses. 

Scientific Evidence

Appetite in cancer patients. A double-blind study tested BCAAs on twenty-eight people with cancer who had lost their appetites because of either the disease itself or its treatment. Appetite improved in 55 percent of those taking BCAAs (4.8 g daily) compared with only 16 percent of those taking a placebo.

Amyotrophic lateral sclerosis (Lou Gehrig’s disease). A small double-blind study found evidence that BCAAs might help protect muscle strength in people with Lou Gehrig’s disease. Eighteen individuals were given either BCAAs (taken four times daily between meals) or a placebo and followed for one year. The results showed that people taking BCAAs declined much more slowly than those receiving a placebo. In the placebo group, five of nine participants lost their ability to walk, two died, and another required a respirator. Only one of the nine participants receiving BCAAs became unable to walk during the study period. This study is too small to provide conclusive evidence, but it does suggest that BCAAs might be helpful for this disease. However, other studies found no effect, and one actually found a slight increase in deaths during the study period among those treated with BCAAs compared with those treated with a placebo.

Muscular dystrophy. One double-blind, placebo-controlled study found leucine (one of the amino acids in BCAAs) ineffective at the dose of 0.2 g per kilogram body weight (for example, 15 g daily for a 75-kilogram woman) in ninety-six individuals with muscular dystrophy. Over the course of one year, no differences were seen between the effects of leucine and a placebo.

Muscle Soreness. A 2023 study published in the Journal of the International Society of Sports Nutrition examined BCAA for muscle soreness and recovery after exercise and found no benefits over the placebo. 

Sports performance. A 2022 study published in the European Journal of Applied Physiology found that supplementation with BCAAs did not improve exercise performance or reduce muscle damage. However, double-blind, placebo-controlled studies performed on BCAAs in the 2020s did show benefits for liver conditions and tardive dyskinesia. Additionally, a 2025 study of young, active males found that BCAAs improved fat oxidation during constant load exercise and increased the participants' exercise efficiency in terms of time to exhaustion.

Safety Issues

BCAAs are believed to be safe; when taken in excess, they are simply converted into other amino acids. However, like other amino acids, BCAAs may interfere with medications for Parkinson’s disease. They may reduce the effectiveness of medications for Parkinson’s disease (such as levodopa).

Bibliography

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