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 terrible 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.



Dietary protein usually provides all the BCAAs you need. However, physical stress and injury can increase your 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 you're getting enough BCAAs. Supplements may contain all three BCAAs together or simply individual BCAAs.

Therapeutic Dosages

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

Therapeutic Uses

Preliminary evidence suggests that BCAAs may improve appetite in people undergoing treatment for cancer]]> . ]]>1]]> 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. ]]>2-5]]>

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. ]]>6,25-26]]> BCAAs have also shown a bit of promise for enhancing recovery from traumatic brain injury. ]]>29]]>

Because of how they are metabolized in the body, BCAAs might be helpful for individuals with severe liver disease (such as ]]>cirrhosis]]> ). ]]>7,30,33]]>

BCAAs have also been tried for aiding muscle recovery after bedrest, such as following ]]>surgery]]> . ]]>24]]>

Although there is a little supportive evidence, on balance, current research does not indicate that BCAAs are effective as a for ]]>enhancing sports performance]]> . ]]>8-15,27,31]]> One preliminary study hints that BCAAs might aid ]]>recovery]]> from long distance running. ]]>32]]>

BCAAs have also as yet failed to prove effective for muscular dystrophy. ]]>16]]>


What Is the Scientific Evidence for Branched Chain Amino Acids?

Appetite in Cancer Patients

A double-blind study tested BCAAs on 28 people with cancer who had lost their appetites]]> due to either the disease itself or its treatment. ]]>17]]> Appetite improved in 55% of those taking BCAAs (4.8 g daily) compared to only 16% of those who took 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]]> . ]]>18]]> Eighteen individuals were given either BCAAs (taken 4 times daily between meals) or placebo and followed for 1 year. The results showed that people taking BCAAs declined much more slowly than those receiving placebo. In the placebo group, 5 of 9 participants lost their ability to walk, 2 died, and another required a respirator. Only 1 of the 9 participants receiving BCAAs became unable to walk during the study period. This study is too small to give conclusive evidence, but it does suggest that BCAAs might be helpful for this disease.

However, other studies found no effect, ]]>19,20]]> and one actually found a slight increase in deaths during the study period among those treated with BCAAs compared to placebo. ]]>21]]>

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 96 individuals with muscular dystrophy. ]]>22]]> Over the course of 1 year, no differences were seen between the effects of leucine and placebo.


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]]> . ]]>23]]>


Interactions You Should Know About

  • If you are taking medication for Parkinson's disease (such as levodopa]]> ), BCAAs may reduce its effectiveness.