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Leucine is an amino acid that cannot be produced by the biochemistry of the human body, and is hence an essential part of our diets. It is one of twenty amino acids essential for the production of proteins of various types through what are known as messenger RNA molecules that take a template from the appropriate sections of our DNA.

It is used in supplement form by athletes and bodybuilders to increase the speed of the recovery of muscles from hard exercise without making any significant changes to the composition or appearance of the body.

It speeds up the generation of new muscle to replace old muscle that has been destroyed rather than significantly increase muscle mass as an anabolic steroid would. The term anabolic refers to the building of larger units from smaller ones, and specifically the building up of muscle protein from smaller amino acids. In this respect, leucine is an anabolic agent, though not used in the same way as anabolic steroids.

Leucine was first isolated from cheese in 1819, though in an impure state. It was finally isolated from muscle and wool in a pure crystalline form a year later and eventually synthesized in the laboratory in 1891, thus confirming its structure. It was only later that its full impact on the biochemistry of protein and muscle development was understood, or at least partially understood since even now all of the biochemical pathways have not been completely identified.

Physiologically, it is an essential part of the system that regulates the level of sugars in the blood, and also assists in the repair of muscle tissue, and its growth. Leucine is what is known as a branched chain amino acid (BCAA) that is not broken down by the enzymes in the liver in the same way as other amino acids. What this means is that among others, leucine can be transported by the circulation to peripheral parts of the body without first being destroyed.

During physical exercise, muscle tissue undergoes trauma and is broken down. The rate at which this muscle loss is replaced with new muscle determines the recovery rate after exercise. The soreness that people often feel after extreme exercise is an indication of this muscle trauma, and it can be helped by the use of antioxidants such as Vitamins C and E. However, while this can help to reduce the rate of muscle loss, it has only a relatively minor effect.

In addition to playing a part in regulating insulin and stabilizing blood glucose levels, leucine is also involved in controlling the rates at which protein is synthesized and the rate at which it breaks down. Muscle growth is a function of the difference in rates between protein generation and its destruction, and leucine is essential for the production of new proteins. The production of proteins is essential to muscle growth: in fact it is the only way for muscles to grow. Without leucine, your muscle mass cannot grow.

However, leucine does more than just promote muscle gain through the synthesis of new protein. It also helps to prevent muscle loss. Leucine slows down the rate of muscle loss to the extent that it generates protein faster than it is destroyed, and so has the net effect of speeding up the rate of muscular recovery. There are several such branched chain amino acids that are involved in the metabolism and biochemistry of protein and muscle synthesis, although leucine is the major one involved in recovery after exercise.

Leucine has benefits other than muscle growth and recovery, although it is for these reasons that it is used as a supplement by athletes and bodybuilders. It is important in the regulation of blood sugar levels. However, those suffering from glucose intolerance or insulin deficiency do not use leucine efficiently and would likely need a supplement. The recommended daily allowance is 16 mg per kilogram of body weight per day which equates to 1.2 grams a day for 75 Kg person (12 stones). However, it is more for a child, and a child over 10 needs 42 mg and an infant 128 mg.

Other than that, it is very rare for anyone to suffer from a deficiency of leucine since there is plenty in a normal diet. Leucine is contained in all protein-based foods including cheese, fish, meat, nuts, seeds, pulses, etc. vegans might need a supplement, and the main sign of a deficiency are symptoms of hypoglycemia: dizziness, headaches and tiredness.

If taken as a supplement, it must also be supplemented with 2 mg of the BCAAs isoleucine and valine for each mg of leucine since the branched chain amino acids work in combination with each other. Beware of supplements that have only leucine as the sole amino acid ingredient, since it will not be fully effective. Although there are no known toxic effects of an excess of supplementation, it can lead to pellagra which can be treated with niacin (nicotinic acid or vitamin B3).

The wound healing properties of leucine are associated with its protein biochemistry. The healing of wounds is a process that involves a number of steps, including the reconstruction of collagen fibers, and it is here that leucine becomes involved, organizing collagen fibrils that aid the healing process. Technically, it is the leucine rich proteoglycans that regulate collagen fibrillogenesis that is where leucine becomes involved in the wound healing biochemistry of the human body.

It is for its energy boosting properties; however, that leucine is mostly used as a supplement. It does not so much boost energy as increase the rate of muscular recovery after exercise, and so allow athletes to regain full strength much quicker after extreme exercise. It is popular among weightlifters but especially with athletes since explosive events, or those that involve rapid loss of muscle tissue such as sprinting, benefit from rapid restitution of lost muscle tissue, or the slowing down of tissue loss.

Leucine is a very useful and necessary amino acid in mammalian biochemistry and, like all the necessary amino acids, life could not exist without it even though the body cannot produce it for itself.