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Leucine: the most important building block for your muscles

2019-09-26 by Peter Hespel & Martijn Redegeld

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Whoever wants to optimise their muscle building as much as possible will need to do more than just train hard and eat enough high-quality proteins. In addition to the total amount of proteins  and its distribution  throughout the day, the precise amino acid composition of a protein is also important. BCAAs (branched-chain amino acids) are often promoted as ‘super amino acids’. On the contrary, this is not true because leucine works in a unique fashion. This amino acid provides the most important stimulus needed for muscle building. It is why you must consume a sufficient amount of leucine to optimally stimulate muscle building.

Amino acids are nutrients needed for muscle tissue. In fact, the composition of a protein’s amino acid determines the quality of the protein. A protein is ‘high-quality’ when the amino acid composition stimulates a relatively large amount of muscle building. Research shows that the amount of leucine significantly determines the quality of a protein. The more leucine, the more muscle building. This explains why proteins from animal products, such as whey protein, that have a relatively large amount of leucine, stimulate muscle building and recovery better than proteins from vegetable sources, such as soya and quinoa (that have a relatively small amount of leucine). Food that is naturally rich in whey proteins, and thus leucine, include milk, cheese, cottage cheese, chicken, beef and tuna. Another option is to supplement your leucine intake by eating food naturally rich in protein.

To stimulate muscle building, you need to have a high-concentration of leucine in your blood. Research shows that this starts to happen when you consume at least 3 grams of leucine at each meal. Consuming the same amount of proteins with this minimal amount of leucine builds more muscle mass than when consuming the same amount of proteins with less leucine. Moreover, research shows that leucine partially offsets a deficiency in the total consumption of proteins and thus still provides a boost to muscle building when the amount of proteins in one meal is insufficient. For example, this can be really important for retaining muscle mass during periods of weight loss.

Leucine vs BCAAs

The consumption of branched-chain amino acids (BCAA) is very popular in strength sports. Taking BCAAs has been really hyped. Besides leucine, BCAAs include the amino acids valine and isoleucine. It was thought for a long time that the combination of these three amino acids was necessary to optimise muscle building. This led to the selling of these supplements becoming a million-dollar business. However, further research has shown that BCAAs absolutely do not optimise muscle building. On the contrary, there are even indications that muscle building is slowed by consuming an excessive amount of BCAAs.

At first glance, this seems contradictory because BCAA supplements contain leucine and thus should also increase the total amount consumed. However, recent research shows that muscle building with the same total amount of protein is greater than when only leucine is consumed compared to when leucine is consumed in combination with the other two BCAAs. This implies that the other two BCAAs most likely impede the absorption of leucine in the intestines. This is why the current recommendation is to not consume BCAAs. The single amino acid leucine is the only one worthwhile consuming as a supplement to stimulate muscle building and recovery.


The amino acid leucine plays a key role in further optimising muscle building and recovery. Leucine boosts the muscle building stimulus in muscles. This does not alter that fact that it is more important to consume the correct total amount of proteins   spread across four to five meals each day . In this case, leucine provides an additional stimulus. Furthermore, a leucine supplement can (partially) compensate for when the total consumption of proteins is sub-optimal. It is recommended that large amounts of BCAAs not be consumed because, at the least, this blocks the added value of leucine.


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