Branched Chain Amino Acids (BCAAs) 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 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.

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

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. ¹ 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 . ² 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, ³ and one actually found a slight increase in deaths during the study period among those treated with BCAAs compared to placebo. ⁴

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. ⁵ Over the course of 1 year, no differences were seen between the effects of leucine and placebo.

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