The best amino acid for muscle growth is leucine. Leucine is proven in numerous studies to be the best amino acid for building muscle. In addition to building muscle, leucine can speed up muscle recovery and repair post-workout. Leucine is an essential amino acid, which means it has to be obtained from the food and diet because the body cannot manufacture it. Leucine is also a branched-chain amino acid or BCAA. Branched-chain amino acids have an extensive library of clinical research showing their benefit to muscle growth and repair. Leucine is by far the most potent and anabolic of the branched-chain amino acids.
Is leucine the best amino acid for building muscle?
Numerous studies show that leucine is the best amino acid for muscle-building. It is such a potent anabolic agent that it can stimulate muscle growth without the need for working out or training.  Leucine is a potent mTOR stimulator, meaning when ingested in sufficient quantities, it will stimulate mTOR.  mTOR stands for mammalian target of rapamycin, and once it is activated, it will increase protein synthesis and, ultimately, muscle growth.
Not only can leucine stimulate muscle growth, but it can prevent the breakdown of skeletal muscle. When the body breaks down muscle, it is called catabolism. Leucine has proven anti-catabolic properties, which stop the body from breaking down skeletal muscle. 
leucine dosage for muscle building
The optimal leucine dosage for muscle growth is 4 grams per day, but doses of up to 20 grams per day are also effective.  When dosing leucine, it is essential to take it with high protein meals for maximum muscle-building effect. Adding 1 to 2 grams of leucine to each meal is the best way to ensure you are getting the maximum muscle-building benefit from leucine. The key to getting the leucine dosage right is to understand that you need enough leucine to trigger mTOR, but the threshold for triggering mTOR changes based on age, sex and activity level. Because of this, you have to adjust the leucine dosage based on these variables to achieve the best muscle-building effects.
The older you are, the less sensitive your mTOR is, and thus you need to ingest higher amounts of leucine to reach the threshold that will stimulate mTOR and ultimately turn on muscle building.  You can make mTOR more sensitive to leucine, and the most effective way is working out or training. Strenuous physical activity can lower the leucine threshold required to stimulate mTOR.
Food Sources of Leucine
Leucine can be found in generous quantities in certain founds, such as meats, fish, nuts and dairy. You can also supplement with leucine, but it is always beneficial to try and obtain the bulk of your leucine from food sources as food contains other healthy nutrients and compounds. Below is a table that shows the top 20 leucine-containing foods. The food sources of leucine are sorted by highest to lowest and display the leucine content in grams per 100-gram serving size.
|Food||Leucine content in grams per 100g serving|
Summary of the best amino acid for muscle growth
To sum up, leucine is by far the best amino acid for building muscle. It is backed up by an extensive collection of research proving its abilities to help muscle growth, muscle recovery and other performance benefits. It is easy to obtain from food sources in large quantities, so one does not have to supplement with it necessarily. However, if one does want to supplement with leucine, it is widely available in powder and pill form. It is relatively inexpensive and can be bought in bulk powder form to reduce the price even further. Leucine should be part of every athlete or bodybuilder’s supplement arsenal, either by itself or as part of another supplement like a BCAA supplement.
- Double-blind, placebo-controlled pilot trial of L-Leucine-enriched amino-acid mixtures on body composition and physical performance in men and women aged 65-75 years – PubMed (nih.gov)
- Leucine as a regulator of whole body and skeletal muscle protein metabolism in humans – PubMed (nih.gov)
- Rapamycin administration in humans blocks the contraction-induced increase in skeletal muscle protein synthesis – PubMed (nih.gov)
- Leucine stimulates translation initiation in skeletal muscle of postabsorptive rats via a rapamycin-sensitive pathway – PubMed (nih.gov)
- Amino acids and muscle loss with aging – PubMed (nih.gov)
- Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects | American Journal of Physiology-Endocrinology and Metabolism
- Stimulation of in vitro rat muscle protein synthesis by leucine decreases with age – PubMed (nih.gov)
- The actions of exogenous leucine on mTOR signalling and amino acid transporters in human myotubes (nih.gov)
The information presented within this article is in no way intended to be taken as medical advice. you should always talk with your doctor before taking or starting any supplement.