Branched-Chain Amino Acids | How Leucine Promotes Muscle Growth

  The Branched-Chain Amino Acids (BCAA’s) consist of three essential amino acids: Leucine, Isoleucine and Valine. Due to the unique nature of these amino acids researchers believe that the BCAA’S, especially leucine, may work to increase lean muscle tissue and promote recovery. For this reason BCAA supplementation is of particular interest to those looking to achieve their goals faster. The following mechanisms have been suggested to be enhanced as a result of BCAA supplementation:

? Prevention of tryptophan from crossing the blood-brain barrier and increasing central fatigue

? Regulation of muscle protein synthesis and increased muscle hypertrophy

? Greater post-exercise insulin response and nutrient shuttling

BCAA’s and Central Fatigue

When performing exercise the stress on the body causes significant hormonal alterations. Specifically, increased levels of the hormone adrenaline stimulate lipolysis (fat burning). The increased concentration of plasma free-fatty acids can displace the amino acid tryptophan from its protein carrier, albumin. With all those fatty acids binding to albumin, tryptophan is readily available for transport across the blood brain barrier where it leads to an increase in serotonin levels. Long story short; high levels of tryptophan and serotonin in the brain can be a bad thing and is thought to be a major contributor to central fatigue and feelings of lethargy when training.

But here’s where BCAA’s can help: It's thought that BCAA’s can compete with tryptophan for uptake into the brain, thereby diminishing central fatigue and improving exercise performance.

Crowe et al. (2006) performed an investigation to determine the effects of BCAA supplementation compared to a placebo on canoeists, with particular emphasis on central fatigue. Leucine was provided as a dietary supplement for six weeks, with the purpose to improve endurance performance by decreasing the plasma ratio of tryptophan to BCAA’s. The study showed that “Six weeks’ dietary leucine supplementation significantly improved endurance performance and upper body power”.  However, it was suggested that the ergogenic effect was not because of a reduction in central fatigue, but as a product of the canoeists experiencing reduced muscle damage during training as well as increased muscle protein synthesis.

The jury is still out on whether BCAA’s can help prevent central fatigue, however the results of this research and of others show promising affects in other areas.

BCAA’s and Muscle Growth

Translation initiation is the first step by which muscle protein synthesis occurs and hypertrophy takes place. The other two stages are referred to as chain elongation and termination. Without translation, there can't be protein synthesis or muscle growth.

Research by Norton & Layman (2006) have demonstrated that after exhaustive resistance training, the body is in a catabolic state until adequate nutrition is provided, in order to initiate the recovery phase. During this catabolic state, muscle protein synthesis becomes impaired at the cellular level due to the inhibition of specific translation initiation factors (eIF4G, eIF4E and rpS6). These factors are what turn on the process of translation and eventually, protein synthesis. These translation initiation factors are controlled by intracellular insulin signalling and leucine concentrations.

Remember: leucine is one of the BCAA’s. When leucine is ingested, tissue levels increase, and translation initiation is activated. Hence, supplementing with the BCAA leucine actually activates the beginning steps of muscle protein synthesis, leading to hypertrophy. Leucine's effect on protein synthesis is also synergistic with insulin, and most of us know how anabolic insulin can be.

BCAA’s and Insulin

In an investigation by Manninen (2006) involving the supplementation of a carbohydrate, hydrolysed protein and leucine mixture taken during exercise, it was demonstrated that the mixture lead to greater increases in skeletal muscle hypertrophy and strength versus a placebo supplement. In the study, a 221% greater insulin response was achieved when subjects ingested a high glycaemic carbohydrate with hydrolysed protein and leucine versus carbohydrate alone. When the subjects ingested carbohydrate alongside hydrolysed protein, but without leucine, only a 66% greater insulin response was observed versus carbohydrate alone. Therefore:

? Hydrolysed protein + Carbohydrate + Leucine, is more effective than

? Hydrolysed protein + Carbohydrate, which is more effective than

? Carbohydrate alone

In order for most amino acids to effectively stimulate insulin release, certain levels of blood glucose (2.5 - 5.0 mM) must be present. However the BCAA leucine is an exception, as it's the only amino acid capable of increasing circulating insulin levels regardless of blood glucose concentration. This insulin response will provide an environment that promotes tissue building, as opposed to tissue breakdown. By limiting protein breakdown, leucine may allow for a net increase in protein synthesis post-exercise, leading to greater muscle hypertrophy and strength.

A winning post-workout combination would therefore include some form of fast acting carbohydrate and protein, where the addition of leucine would maximise the anabolic power of your post-workout cocktail!

Considerations when Using BCAA’s

BCAA’s and leucine may be one of the most effective supplements on the market for increasing lean muscle mass. But here are the F-A-C-T-S that you may want to consider before supplementing with BCAA’s:

Using BCAA’s directly around the time of your workout has been considered a highly effective strategy. Aim to consume up to 15g spread throughout the course of your training session, beginning 30 minutes prior. Alternatively 5g doses can be taken up to 4 times spread throughout the day. This would assist the body from entering a catabolic state, and can even be used as a ‘bridge’ between meals. If using a leucine-only supplement then a similar dose can be effective, with a 5g dose mixed in your post-workout protein shake.

15g spread throughout your workout or 5g doses spread throughout the day, achieving 20g daily.

BCAA’s can be consumed by themselves and contain minimal calories.  This can make them particularly useful when on a dieting phase. Leucine is most effectively consumed post-workout alongside a mixture of fast acting carbohydrates and protein, particularly hydrolysed protein, to maximise the post-exercise insulin response referred to as ‘hyperinsulinemia’.

Types of BCAA

  BCAA’s can be found in powder or pill form. Both are as effective but which one you choose will depend on convenience, practicality and taste. When trying to find a good BCAA supplement look for a 2:1:1 ratio of leucine, isoleucine and valine.

When looking to supplement with leucine-alone, look for a powder with good mix ability, as adding it to your post-workout shake can sometimes give it a ‘frothy’ look.

Safety/Side-Effects

No serious side-effects have been reported from BCAA or leucine use. However excessive use of leucine can cause the body to enter a ketogenic state faster, similar to that of a low carbohydrate diet, and hence similar effects.

Take Home Message

  Hopefully you understand a little more about how BCAA's work and the effects Amino Acid Leucine has on the body!

Crowe, M., Bowden, B & Weatherson, J (2006) Effects of dietary leucine supplementation on exercise performance. Euro J. appl phys; Vol 97, no 6, p 664-672. Manninen, A. H (2006)

Hyperinsulinaemia, hyperaminoacidaemia and post-exercise muscle anabolism : The search for the optimal recovery drink : the search for the Br. J. Sports Med. 2006;40;900-905. Norton, L. E & Layman D. K (2006)

Branched-Chain Amino Acids in Exercise: Leucine Regulates Translation Initiation of Protein Synthesis in Skeletal Muscle after Exercise. J. Nutr; 136(2):533S-537S.

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