L-Leucine is one of the essential Amino Acids and one of three Branched Chained Amino Acids, along with Isoleucine & Valine. There are eight Essential Amino Acids in total, with the others being: L-Isoleucine, L-Lysine, L-Methionine, L-Phenylalaline, L-Threonine, L-Tryptophan and L-Valine. (L-Histidine and L-Arginine are often included as EAAs).1 They cannot be made by the body, thus must be derived from the diet. L-Leucine is found in nuts, brown rice and whole wheat bread, or supplements.2 There are three branched-chain amino acids (BCAAs) in the body, L-Isoleucine, L-Valine, and L-Leucine, and all of them help promote muscle recovery after exercise.
The body's protein structures are made up of about eight percent L-Leucine, which is the fourth most concentrated amino acid in muscle. L-Leucine is not only essential to your health, but is beneficial for bodybuilders. L-Leucine helps maintain muscle tissue through sustaining nitrogen balance, supplies energy to the body even when under the stress of training and preserves muscle glycogen used for muscle contraction. Leucine is essential for a muscle building environment and assists mental ability even when exercise becomes more intense. L-Leucine is the strongest of the BCAA's and if you do not have enough of it in proportion to other amino acids, your body cannot utilise what you ingest. An L-Leucine deficiency will mean that you cannot use protein that you consume, regardless of how much you have. So basically, without L-Leucine, your protein consumption is wasted! Without protein, muscle building cannot be sustained or occur.
This is a topic of conjecture. Some believe that to ensure optimum dietary absorption, you need two parts L-Leucine and two parts L-Valine for every one part L-Isoleucine, whilst others believe in a ratio of 1:1.8:1.2, which is their ratio in the muscle. Some companies will even offer the essential, a creation of a muscle building amino acids in supplement form in a ratio of 4:1:1 and 3:1:1. The latest research at the time of writing this article suggests either a ratio of 4:1:1 or 8:1:1, four parts Leucine or 8 parts Leucine, is the most beneficial for creation of a muscle building anabolic enviroment.
L-Leucine is an essential amino acid, hence it is required by everyone for basic health.
BCAAs consumed before, during or after training support muscle protein synthesis, decrease protein catabolism and are very important to the use and production of glucose for energy. Leucine enhances insulins anabolic response, and is believed to be the most important BCAA with respect to increasing protein synthesis and prevention of muscle catabolism.3
1 Essentials of Sports Nutrition and Supplements, p. 486
2 Macrobolic Nutrition, p. 33
3 Essentials of Sports Nutrition and Supplements, p. 474 and 498