Branched-chain amino acid leucine is one of the best proteins to add to your diet to help stimulate an anabolic state for optimal results in the gym. When combined with isoleucine and valine it forms a powerful trio of nutrients to increase muscle strength and size, fat loss and quicker recovery.
Leucine is one of nine essential amino acids required by the body to function optimally and must be supplied through dietary sources or supplementation. It is also one of the three branched-chain amino acids (BCAAs), which plays an integral role in muscle strength and growth, muscle repair and recovery and increasing energy. Along with the other BCAAs Isoleucine, and Valine, Leucine constitutes nearly 70% of all the amino acids in the body’s proteins.
It contributes to a number of key functions in the body for athletes including;
- Improved Muscle Growth
- Improved Muscle Repair and Recovery
- Fat Loss
History of Leucine
Leucine was one of the first amino acids to be discovered. It was first isolated in its impure form in cheese in 1818 by French chemist Joseph Louis Proust. A year later it was isolated in its crystalline form in muscle fibre, and given its name by French chemist Henri Braconnot. It wasn’t until the end of the 19th century that its chemical structure was established by laboratory synthesis.
The word Leucine comes from the Greek word ‘Leukos’, meaning ‘White’. This is due to that a substance from nature turning to a white crystalline state was considered breathtaking at the time.
Leucine is one of nine amino acids that is structurally a nonpolar amino acid.
All amino acids consist of a basic amino group (−NH2), an acidic carboxyl group (−COOH). What makes each amino acid different from each other is the chemical structure of the R group (side chain).
The R group of leucine is hydrophobic (“water fearing”).
What does Leucine do for your body?
As one of three branched chain amino acids (BCAAs) Leucine is effective at protein synthesis, which will help you increase muscle mass and help improve your body’s ability to recover from your workouts. I will dive into those benefits in the next section. What I want to show you in this section is that it also plays a number of other key roles that are important for the optimal functioning of your body.
Leucine plays an important role in regulating blood sugar levels. A leucine deficiency has been shown to induce symptoms similar to low blood sugar (hypoglycemia), which can cause symptoms such as headaches, dizziness, irritability and depression. 
Due to Leucine’s ability to be absorbed quickly by the body, studies have shown that leucine can be an effective nutrient for people who have Diabetes, high cholesterol and obesity. 
Is Leucine ketogenic or glucogenic?
Leucine along with lysine are the only two amino acids that are only ketogenic, which means they can be converted into acetyl-CoA, which is the precursor of ketone bodies.
Leucine is a great amino acid not just for muscle building, but for its fat loss benefits as well. For those who have tried different muscle building or fat burning supplements, should ensure that leucine is a part of that protocol. Here are three powerful benefits for any serious athlete as to why you need leucine.
Improved Muscle Growth
Leucine is considered to be the primary BCAA, with the most anabolic potential for muscle stimulation.
Scientists now know that it is the level of amino acids in the blood that directly boosts protein synthesis in muscles, which leads to increases in muscle strength and size.
What makes leucine so effective is its ability to activate the anabolic pathway called mTOR, which regulates protein synthesis in the human body. When leucine levels start to drop, mTOR deactivates. On the flip side, when leucine levels are increased, mTOR gets activated, and protein synthesis is increased, which in turn stimulates muscle growth.
Researchers at The University of Illinois have shown that protein synthesis is increased after exercise when using leucine. 
Furthermore, in a double-blind, placebo study, researchers found that leucine along with the other branched chained amino acids, isoleucine and valine is effective at improving lean tissue mass and functional performance in people aged 65-75. 
Improved Muscle Repair & Recovery
If you’re training at high intensity, then a good recovery is essential for you to get the best results from your training.
Leucine has been shown to be effective at decreasing delayed onset muscle soreness (DOMS) after intense workouts.
The muscle damage induced by eccentric training, for example, can decrease muscle glycogen levels for up to three days after the workout. While these levels are low, your strength and power levels are down, and your ability to perform high-quality training sessions is diminished.
However, researchers at The Institute for Innovation in Japan found that leucine-enriched essential amino acids induce an increase in the glycogen stored in the muscle up to seven days after exercise. This allows your body to recover quicker and allows you to perform more effectively in the gym quicker after your last workout. 
Studies have shown that leucine acts in a unique way: unlike other amino acids, it aids in burning fat by sparing the muscles and leaving them to assist in building and in increasing the muscle strength and size.
Researchers at The University of Tennessee found that participants taking a leucine supplement lost twice as much weight as those who were given a placebo. 
Furthermore, researchers at The North Carolina Central University found that leucine taken with the other branched chained amino acids (BCAAs), isoleucine and valine had a significant effect on adipose tissue (fat cells). 
Leucine side effects
Leucine side effects are only known with extremely high doses and can cause brain and liver damage. Due to its impact on the neurotransmitter Serotonin it can also affect mood and cognitive functioning
*Popularly Recommended Dosing Guidelines for Leucine
The recommended dosage of leucine for everyday people is 50 mg/kg. It is not recommended to exceed dosages of 500 mg/kg.
In general, single amino acid supplements aren’t recommended for people who consume enough protein-rich foods. Using branched chain amino acids (BCAAs) or Essential Amino Acids (EAA) supplements are a good source of the necessary proteins that will help you achieve optimal results in the gym. When looking to add a single amino acid supplement to your diet, it is recommended to consult with a doctor or healthcare provider first.
Which foods are high in Leucine?
Most foods contain some form of amino acids. Protein-rich animal foods typically contain complete proteins, so offer the body a wider variety of the essential amino acids. Plant-based foods on the other hand often contain incomplete proteins and only some of the essential amino acids.
Leucine is found primarily high in foods such as;
Taking in a wide variety of proteins, whether through the diet, supplementation or ideally through both can help to develop and maintain a healthy body. For any serious athlete consuming amino acids such as Leucine can enhance your ability to increase muscle strength and size, lose body fat, recover from injuries and workouts faster, as well as a host of other health benefits.
*Popularly Recommended Dosing Guidelines are based on study and manufacturer information and are for informational purposes only. Always consult a doctor and follow manufacturer recommendations when taking any supplement.
- D.C.CharltonMabry(Trainee (AT-416))abc1M.D.Angelo M.DiGeorgeabc2Ph.D.Victor H.Auerbachabc Leucine-induced hypoglycemia: II. Studies concerning other amino acids and leucine metabolites https://www.sciencedirect.com/science/article/pii/S0022347660800819 Accessed on 8 August 2018
- Yiying Zhang12, Kaiying Guo1, Robert E. LeBlanc1, Daniella Loh1, Gary J. Schwartz3 and Yi-Hao Yu4 Increasing Dietary Leucine Intake Reduces Diet-Induced Obesity and Improves Glucose and Cholesterol Metabolism in Mice via Multimechanisms http://diabetes.diabetesjournals.org/content/56/6/1647 Accessed on 8 August 2018
- Layne E. Norton Donald K. Layman Leucine Regulates Translation Initiation of Protein Synthesis in Skeletal Muscle after Exercise https://academic.oup.com/jn/article/136/2/533S/4664398 Accessed on 8 August 2018
- T Ispoglou, H White, T Preston, S McElhone, J McKenna & K Hind 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 https://www.nature.com/articles/ejcn201591 Accessed on 8 August 2018
- Hiroyuki Kato, Kyoko Miura, Suzuki, and Makoto Bannai Leucine-Enriched Essential Amino Acids Augment Muscle Glycogen Content in Rats Seven Days after Eccentric Contraction https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5691775/ Accessed on 8 August 2018
- Michael B Zemel1,2 and Antje Bruckbauer1 Effects of a leucine and pyridoxine-containing nutraceutical on body weight and composition in obese subjects https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3755702/ Accessed on 8 August 2018
- Abderrazak Kitsy , Skyla Carney , Juan C. Vivar, Megan S. Knight, Mildred A. Pointer, Judith K. Gwathmey, Sujoy Ghosh Effects of Leucine Supplementation and Serum Withdrawal on Branched-Chain Amino Acid Pathway Gene and Protein Expression in Mouse Adipocytes http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0102615 Accessed on 8 August 2018